# SPDX-License-Identifier: GPL-2.0+## (C) Copyright 2000 - 2013# Wolfgang Denk, DENX Software Engineering, wd@denx.de.Summary:========This directory contains the source code for U-Boot, a boot loader forEmbedded boards based on PowerPC, ARM, MIPS and several otherprocessors, which can be installed in a boot ROM and used toinitialize and test the hardware or to download and run applicationcode.The development of U-Boot is closely related to Linux: some parts ofthe source code originate in the Linux source tree, we have someheader files in common, and special provision has been made tosupport booting of Linux images.Some attention has been paid to make this software easilyconfigurable and extendable. For instance, all monitor commands areimplemented with the same call interface, so that it's very easy toadd new commands. Also, instead of permanently adding rarely usedcode (for instance hardware test utilities) to the monitor, you canload and run it dynamically.Status:=======In general, all boards for which a configuration option exists in theMakefile have been tested to some extent and can be considered"working". In fact, many of them are used in production systems.In case of problems see the CHANGELOG file to find out who contributedthe specific port. In addition, there are various MAINTAINERS filesscattered throughout the U-Boot source identifying the people orcompanies responsible for various boards and subsystems.Note: As of August, 2010, there is no longer a CHANGELOG file in theactual U-Boot source tree; however, it can be created dynamicallyfrom the Git log using:make CHANGELOGWhere to get help:==================In case you have questions about, problems with or contributions forU-Boot, you should send a message to the U-Boot mailing list at<u-boot@lists.denx.de>. There is also an archive of previous trafficon the mailing list - please search the archive before asking FAQ's.Please seehttps://lists.denx.de/pipermail/u-boot andhttps://marc.info/?l=u-bootWhere to get source code:=========================The U-Boot source code is maintained in the Git repository athttps://source.denx.de/u-boot/u-boot.git ; you can browse it online athttps://source.denx.de/u-boot/u-bootThe "Tags" links on this page allow you to download tarballs ofany version you might be interested in. Official releases are alsoavailable from the DENX file server through HTTPS or FTP.https://ftp.denx.de/pub/u-boot/ftp://ftp.denx.de/pub/u-boot/Where we come from:===================- start from 8xxrom sources- create PPCBoot project (https://sourceforge.net/projects/ppcboot)- clean up code- make it easier to add custom boards- make it possible to add other [PowerPC] CPUs- extend functions, especially:  * Provide extended interface to Linux boot loader  * S-Record download  * network boot  * ATA disk / SCSI ... boot- create ARMBoot project (https://sourceforge.net/projects/armboot)- add other CPU families (starting with ARM)- create U-Boot project (https://sourceforge.net/projects/u-boot)- current project page: seehttps://www.denx.de/wiki/U-BootNames and Spelling:===================The "official" name of this project is "Das U-Boot". The spelling"U-Boot" shall be used in all written text (documentation, commentsin source files etc.). Example:This is the README file for the U-Boot project.File names etc. shall be based on the string "u-boot". Examples:include/asm-ppc/u-boot.h#include <asm/u-boot.h>Variable names, preprocessor constants etc. shall be either based onthe string "u_boot" or on "U_BOOT". Example:U_BOOT_VERSIONu_boot_logoIH_OS_U_BOOTu_boot_hush_startVersioning:===========Starting with the release in October 2008, the names of the releaseswere changed from numerical release numbers without deeper meaninginto a time stamp based numbering. Regular releases are identified bynames consisting of the calendar year and month of the release date.Additional fields (if present) indicate release candidates or bug fixreleases in "stable" maintenance trees.Examples:U-Boot v2009.11    - Release November 2009U-Boot v2009.11.1   - Release 1 in version November 2009 stable treeU-Boot v2010.09-rc1 - Release candidate 1 for September 2010 releaseDirectory Hierarchy:====================/archArchitecture-specific files  /arcFiles generic to ARC architecture  /armFiles generic to ARM architecture  /m68kFiles generic to m68k architecture  /microblazeFiles generic to microblaze architecture  /mipsFiles generic to MIPS architecture  /nds32Files generic to NDS32 architecture  /nios2Files generic to Altera NIOS2 architecture  /powerpcFiles generic to PowerPC architecture  /riscvFiles generic to RISC-V architecture  /sandboxFiles generic to HW-independent "sandbox"  /shFiles generic to SH architecture  /x86Files generic to x86 architecture  /xtensaFiles generic to Xtensa architecture/apiMachine/arch-independent API for external apps/boardBoard-dependent files/cmdU-Boot commands functions/commonMisc architecture-independent functions/configsBoard default configuration files/diskCode for disk drive partition handling/docDocumentation (a mix of ReST and READMEs)/driversDevice drivers/dtsMakefile for building internal U-Boot fdt./envEnvironment support/examplesExample code for standalone applications, etc./fsFilesystem code (cramfs, ext2, jffs2, etc.)/includeHeader Files/libLibrary routines generic to all architectures/LicensesVarious license files/netNetworking code/postPower On Self Test/scriptsVarious build scripts and Makefiles/testVarious unit test files/toolsTools to build and sign FIT images, etc.Software Configuration:=======================Configuration is usually done using C preprocessor defines; therationale behind that is to avoid dead code whenever possible.There are two classes of configuration variables:* Configuration _OPTIONS_:  These are selectable by the user and have names beginning with  "CONFIG_".* Configuration _SETTINGS_:  These depend on the hardware etc. and should not be meddled with if  you don't know what you're doing; they have names beginning with  "CONFIG_SYS_".Previously, all configuration was done by hand, which involved creatingsymbolic links and editing configuration files manually. More recently,U-Boot has added the Kbuild infrastructure used by the Linux kernel,allowing you to use the "make menuconfig" command to configure yourbuild.Selection of Processor Architecture and Board Type:---------------------------------------------------For all supported boards there are ready-to-use defaultconfigurations available; just type "make <board_name>_defconfig".Example: For a TQM823L module type:cd u-bootmake TQM823L_defconfigNote: If you're looking for the default configuration file for a boardyou're sure used to be there but is now missing, check the filedoc/README.scrapyard for a list of no longer supported boards.Sandbox Environment:--------------------U-Boot can be built natively to run on a Linux host using the 'sandbox'board. This allows feature development which is not board- or architecture-specific to be undertaken on a native platform. The sandbox is also used torun some of U-Boot's tests.See doc/arch/sandbox.rst for more details.Board Initialisation Flow:--------------------------This is the intended start-up flow for boards. This should apply for bothSPL and U-Boot proper (i.e. they both follow the same rules).Note: "SPL" stands for "Secondary Program Loader," which is explained inmore detail later in this file.At present, SPL mostly uses a separate code path, but the function namesand roles of each function are the same. Some boards or architecturesmay not conform to this.  At least most ARM boards which useCONFIG_SPL_FRAMEWORK conform to this.Execution typically starts with an architecture-specific (and possiblyCPU-specific) start.S file, such as:- arch/arm/cpu/armv7/start.S- arch/powerpc/cpu/mpc83xx/start.S- arch/mips/cpu/start.Sand so on. From there, three functions are called; the purpose andlimitations of each of these functions are described below.lowlevel_init():- purpose: essential init to permit execution to reach board_init_f()- no global_data or BSS- there is no stack (ARMv7 may have one but it will soon be removed)- must not set up SDRAM or use console- must only do the bare minimum to allow execution to continue toboard_init_f()- this is almost never needed- return normally from this functionboard_init_f():- purpose: set up the machine ready for running board_init_r():i.e. SDRAM and serial UART- global_data is available- stack is in SRAM- BSS is not available, so you cannot use global/static variables,only stack variables and global_dataNon-SPL-specific notes:- dram_init() is called to set up DRAM. If already done in SPL thiscan do nothingSPL-specific notes:- you can override the entire board_init_f() function with your ownversion as needed.- preloader_console_init() can be called here in extremis- should set up SDRAM, and anything needed to make the UART work- there is no need to clear BSS, it will be done by crt0.S- for specific scenarios on certain architectures an early BSS *can*  be made available (via CONFIG_SPL_EARLY_BSS by moving the clearing  of BSS prior to entering board_init_f()) but doing so is discouraged.  Instead it is strongly recommended to architect any code changes  or additions such to not depend on the availability of BSS during  board_init_f() as indicated in other sections of this README to  maintain compatibility and consistency across the entire code base.- must return normally from this function (don't call board_init_r()directly)Here the BSS is cleared. For SPL, if CONFIG_SPL_STACK_R is defined, then atthis point the stack and global_data are relocated to belowCONFIG_SPL_STACK_R_ADDR. For non-SPL, U-Boot is relocated to run at the top ofmemory.board_init_r():- purpose: main execution, common code- global_data is available- SDRAM is available- BSS is available, all static/global variables can be used- execution eventually continues to main_loop()Non-SPL-specific notes:- U-Boot is relocated to the top of memory and is now running fromthere.SPL-specific notes:- stack is optionally in SDRAM, if CONFIG_SPL_STACK_R is defined andCONFIG_SPL_STACK_R_ADDR points into SDRAM- preloader_console_init() can be called here - typically this isdone by selecting CONFIG_SPL_BOARD_INIT and then supplying aspl_board_init() function containing this call- loads U-Boot or (in falcon mode) LinuxConfiguration Options:----------------------Configuration depends on the combination of board and CPU type; allsuch information is kept in a configuration file"include/configs/<board_name>.h".Example: For a TQM823L module, all configuration settings are in"include/configs/TQM823L.h".Many of the options are named exactly as the corresponding Linuxkernel configuration options. The intention is to make it easier tobuild a config tool - later.- ARM Platform Bus Type(CCI):CoreLink Cache Coherent Interconnect (CCI) is ARM BUS whichprovides full cache coherency between two clusters of multi-coreCPUs and I/O coherency for devices and I/O mastersCONFIG_SYS_FSL_HAS_CCI400Defined For SoC that has cache coherent interconnectCCN-400CONFIG_SYS_FSL_HAS_CCN504Defined for SoC that has cache coherent interconnect CCN-504The following options need to be configured:- CPU Type:Define exactly one, e.g. CONFIG_MPC85XX.- Board Type:Define exactly one, e.g. CONFIG_MPC8540ADS.- 85xx CPU Options:CONFIG_SYS_PPC64Specifies that the core is a 64-bit PowerPC implementation (implementsthe "64" category of the Power ISA). This is necessary for ePAPRcompliance, among other possible reasons.CONFIG_SYS_FSL_TBCLK_DIVDefines the core time base clock divider ratio compared to thesystem clock.  On most PQ3 devices this is 8, on newer QorIQdevices it can be 16 or 32.  The ratio varies from SoC to Soc.CONFIG_SYS_FSL_PCIE_COMPATDefines the string to utilize when trying to match PCIe devicetree nodes for the given platform.CONFIG_SYS_FSL_ERRATUM_A004510Enables a workaround for erratum A004510.  If set,then CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV andCONFIG_SYS_FSL_CORENET_SNOOPVEC_COREONLY must be set.CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REVCONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV2 (optional)Defines one or two SoC revisions (low 8 bits of SVR)for which the A004510 workaround should be applied.The rest of SVR is either not relevant to the decisionof whether the erratum is present (e.g. p2040 versusp2041) or is implied by the build target, which controlswhether CONFIG_SYS_FSL_ERRATUM_A004510 is set.See Freescale App Note 4493 for more information aboutthis erratum.CONFIG_A003399_NOR_WORKAROUNDEnables a workaround for IFC erratum A003399. It is onlyrequired during NOR boot.CONFIG_A008044_WORKAROUNDEnables a workaround for T1040/T1042 erratum A008044. It is onlyrequired during NAND boot and valid for Rev 1.0 SoC revisionCONFIG_SYS_FSL_CORENET_SNOOPVEC_COREONLYThis is the value to write into CCSR offset 0x18600according to the A004510 workaround.CONFIG_SYS_FSL_DSP_DDR_ADDRThis value denotes start offset of DDR memory which isconnected exclusively to the DSP cores.CONFIG_SYS_FSL_DSP_M2_RAM_ADDRThis value denotes start offset of M2 memorywhich is directly connected to the DSP core.CONFIG_SYS_FSL_DSP_M3_RAM_ADDRThis value denotes start offset of M3 memory which is directlyconnected to the DSP core.CONFIG_SYS_FSL_DSP_CCSRBAR_DEFAULTThis value denotes start offset of DSP CCSR space.CONFIG_SYS_FSL_SINGLE_SOURCE_CLKSingle Source Clock is clocking mode present in some of FSL SoC's.In this mode, a single differential clock is used to supplyclocks to the sysclock, ddrclock and usbclock.CONFIG_SYS_CPC_REINIT_FThis CONFIG is defined when the CPC is configured as SRAM at thetime of U-Boot entry and is required to be re-initialized.CONFIG_DEEP_SLEEPIndicates this SoC supports deep sleep feature. If deep sleep issupported, core will start to execute uboot when wakes up.- Generic CPU options:CONFIG_SYS_BIG_ENDIAN, CONFIG_SYS_LITTLE_ENDIANDefines the endianess of the CPU. Implementation of thosevalues is arch specific.CONFIG_SYS_FSL_DDRFreescale DDR driver in use. This type of DDR controller isfound in mpc83xx, mpc85xx as well as some ARM core SoCs.CONFIG_SYS_FSL_DDR_ADDRFreescale DDR memory-mapped register base.CONFIG_SYS_FSL_DDR_EMUSpecify emulator support for DDR. Some DDR features such asdeskew training are not available.CONFIG_SYS_FSL_DDRC_GEN1Freescale DDR1 controller.CONFIG_SYS_FSL_DDRC_GEN2Freescale DDR2 controller.CONFIG_SYS_FSL_DDRC_GEN3Freescale DDR3 controller.CONFIG_SYS_FSL_DDRC_GEN4Freescale DDR4 controller.CONFIG_SYS_FSL_DDRC_ARM_GEN3Freescale DDR3 controller for ARM-based SoCs.CONFIG_SYS_FSL_DDR1Board config to use DDR1. It can be enabled for SoCs withFreescale DDR1 or DDR2 controllers, depending on the boardimplemetation.CONFIG_SYS_FSL_DDR2Board config to use DDR2. It can be enabled for SoCs withFreescale DDR2 or DDR3 controllers, depending on the boardimplementation.CONFIG_SYS_FSL_DDR3Board config to use DDR3. It can be enabled for SoCs withFreescale DDR3 or DDR3L controllers.CONFIG_SYS_FSL_DDR3LBoard config to use DDR3L. It can be enabled for SoCs withDDR3L controllers.CONFIG_SYS_FSL_IFC_BEDefines the IFC controller register space as Big EndianCONFIG_SYS_FSL_IFC_LEDefines the IFC controller register space as Little EndianCONFIG_SYS_FSL_IFC_CLK_DIVDefines divider of platform clock(clock input to IFC controller).CONFIG_SYS_FSL_LBC_CLK_DIVDefines divider of platform clock(clock input to eLBC controller).CONFIG_SYS_FSL_DDR_BEDefines the DDR controller register space as Big EndianCONFIG_SYS_FSL_DDR_LEDefines the DDR controller register space as Little EndianCONFIG_SYS_FSL_DDR_SDRAM_BASE_PHYPhysical address from the view of DDR controllers. It is thesame as CONFIG_SYS_DDR_SDRAM_BASE for  all Power SoCs. Butit could be different for ARM SoCs.CONFIG_SYS_FSL_DDR_INTLV_256BDDR controller interleaving on 256-byte. This is a specialinterleaving mode, handled by Dickens for Freescale layerscapeSoCs with ARM core.CONFIG_SYS_FSL_DDR_MAIN_NUM_CTRLSNumber of controllers used as main memory.CONFIG_SYS_FSL_OTHER_DDR_NUM_CTRLSNumber of controllers used for other than main memory.CONFIG_SYS_FSL_HAS_DP_DDRDefines the SoC has DP-DDR used for DPAA.CONFIG_SYS_FSL_SEC_BEDefines the SEC controller register space as Big EndianCONFIG_SYS_FSL_SEC_LEDefines the SEC controller register space as Little Endian- MIPS CPU options:CONFIG_SYS_INIT_SP_OFFSETOffset relative to CONFIG_SYS_SDRAM_BASE for initial stackpointer. This is needed for the temporary stack beforerelocation.CONFIG_XWAY_SWAP_BYTESEnable compilation of tools/xway-swap-bytes needed for LantiqXWAY SoCs for booting from NOR flash. The U-Boot image needs tobe swapped if a flash programmer is used.- ARM options:CONFIG_SYS_EXCEPTION_VECTORS_HIGHSelect high exception vectors of the ARM core, e.g., do notclear the V bit of the c1 register of CP15.COUNTER_FREQUENCYGeneric timer clock source frequency.COUNTER_FREQUENCY_REALGeneric timer clock source frequency if the real clock isdifferent from COUNTER_FREQUENCY, and can only be determinedat run time.- Tegra SoC options:CONFIG_TEGRA_SUPPORT_NON_SECURESupport executing U-Boot in non-secure (NS) mode. Certainimpossible actions will be skipped if the CPU is in NS mode,such as ARM architectural timer initialization.- Linux Kernel Interface:CONFIG_MEMSIZE_IN_BYTES[relevant for MIPS only]When transferring memsize parameter to Linux, some versionsexpect it to be in bytes, others in MB.Define CONFIG_MEMSIZE_IN_BYTES to make it in bytes.CONFIG_OF_LIBFDTNew kernel versions are expecting firmware settings to bepassed using flattened device trees (based on open firmwareconcepts).CONFIG_OF_LIBFDT * New libfdt-based support * Adds the "fdt" command * The bootm command automatically updates the fdtOF_TBCLK - The timebase frequency.boards with QUICC Engines require OF_QE to set UCC MACaddressesCONFIG_OF_BOARD_SETUPBoard code has addition modification that it wants to maketo the flat device tree before handing it off to the kernelCONFIG_OF_SYSTEM_SETUPOther code has addition modification that it wants to maketo the flat device tree before handing it off to the kernel.This causes ft_system_setup() to be called before bootingthe kernel.CONFIG_OF_IDE_FIXUPU-Boot can detect if an IDE device is present or not.If not, and this new config option is activated, U-Bootremoves the ATA node from the DTS before booting Linux,so the Linux IDE driver does not probe the device andcrash. This is needed for buggy hardware (uc101) whereno pull down resistor is connected to the signal IDE5V_DD7.- vxWorks boot parameters:bootvx constructs a valid bootline using the followingenvironments variables: bootdev, bootfile, ipaddr, netmask,serverip, gatewayip, hostname, othbootargs.It loads the vxWorks image pointed bootfile.Note: If a "bootargs" environment is defined, it will overridethe defaults discussed just above.- Cache Configuration:CONFIG_SYS_L2CACHE_OFF- Do not enable L2 cache in U-Boot- Cache Configuration for ARM:CONFIG_SYS_L2_PL310 - Enable support for ARM PL310 L2 cache      controllerCONFIG_SYS_PL310_BASE - Physical base address of PL310controller register space- Serial Ports:CONFIG_PL011_SERIALDefine this if you want support for Amba PrimeCell PL011 UARTs.CONFIG_PL011_CLOCKIf you have Amba PrimeCell PL011 UARTs, set this variable tothe clock speed of the UARTs.CONFIG_PL01x_PORTSIf you have Amba PrimeCell PL010 or PL011 UARTs on your board,define this to a list of base addresses for each (supported)port. See e.g. include/configs/versatile.hCONFIG_SERIAL_HW_FLOW_CONTROLDefine this variable to enable hw flow control in serial driver.Current user of this option is drivers/serial/nsl16550.c driver- Autoboot Command:CONFIG_BOOTCOMMANDOnly needed when CONFIG_BOOTDELAY is enabled;define a command string that is automatically executedwhen no character is read on the console interfacewithin "Boot Delay" after reset.CONFIG_RAMBOOT and CONFIG_NFSBOOTThe value of these goes into the environment as"ramboot" and "nfsboot" respectively, and can be usedas a convenience, when switching between booting fromRAM and NFS.- Serial Download Echo Mode:CONFIG_LOADS_ECHOIf defined to 1, all characters received during aserial download (using the "loads" command) areechoed back. This might be needed by some terminalemulations (like "cu"), but may as well just taketime on others. This setting #define's the initialvalue of the "loads_echo" environment variable.- Removal of commandsIf no commands are needed to boot, you can disableCONFIG_CMDLINE to remove them. In this case, the command linewill not be available, and when U-Boot wants to execute theboot command (on start-up) it will call board_run_command()instead. This can reduce image size significantly for verysimple boot procedures.- Regular expression support:CONFIG_REGEXIf this variable is defined, U-Boot is linked againstthe SLRE (Super Light Regular Expression) library,which adds regex support to some commands, as forexample "env grep" and "setexpr".- Device tree:CONFIG_OF_CONTROLIf this variable is defined, U-Boot will use a device treeto configure its devices, instead of relying on staticallycompiled #defines in the board file. This option isexperimental and only available on a few boards. The devicetree is available in the global data as gd->fdt_blob.U-Boot needs to get its device tree from somewhere. This canbe done using one of the three options below:CONFIG_OF_EMBEDIf this variable is defined, U-Boot will embed a device treebinary in its image. This device tree file should be in theboard directory and called <soc>-<board>.dts. The binary fileis then picked up in board_init_f() and made available throughthe global data structure as gd->fdt_blob.CONFIG_OF_SEPARATEIf this variable is defined, U-Boot will build a device treebinary. It will be called u-boot.dtb. Architecture-specificcode will locate it at run-time. Generally this works by:cat u-boot.bin u-boot.dtb >image.binand in fact, U-Boot does this for you, creating a file calledu-boot-dtb.bin which is useful in the common case. You canstill use the individual files if you need something moreexotic.CONFIG_OF_BOARDIf this variable is defined, U-Boot will use the device treeprovided by the board at runtime instead of embedding one withthe image. Only boards defining board_fdt_blob_setup() supportthis option (see include/fdtdec.h file).- Watchdog:CONFIG_WATCHDOGIf this variable is defined, it enables watchdogsupport for the SoC. There must be support in the SoCspecific code for a watchdog. For the 8xxCPUs, the SIU Watchdog feature is enabled in the SYPCRregister.  When supported for a specific SoC isavailable, then no further board specific code shouldbe needed to use it.CONFIG_HW_WATCHDOGWhen using a watchdog circuitry external to the usedSoC, then define this variable and provide boardspecific code for the "hw_watchdog_reset" function.CONFIG_SYS_WATCHDOG_FREQSome platforms automatically call WATCHDOG_RESET()from the timer interrupt handler everyCONFIG_SYS_WATCHDOG_FREQ interrupts. If not set by theboard configuration file, a default of CONFIG_SYS_HZ/2(i.e. 500) is used. Setting CONFIG_SYS_WATCHDOG_FREQto 0 disables calling WATCHDOG_RESET() from the timerinterrupt.- Real-Time Clock:When CONFIG_CMD_DATE is selected, the type of the RTChas to be selected, too. Define exactly one of thefollowing options:CONFIG_RTC_PCF8563- use Philips PCF8563 RTCCONFIG_RTC_MC13XXX- use MC13783 or MC13892 RTCCONFIG_RTC_MC146818- use MC146818 RTCCONFIG_RTC_DS1307- use Maxim, Inc. DS1307 RTCCONFIG_RTC_DS1337- use Maxim, Inc. DS1337 RTCCONFIG_RTC_DS1338- use Maxim, Inc. DS1338 RTCCONFIG_RTC_DS1339- use Maxim, Inc. DS1339 RTCCONFIG_RTC_DS164x- use Dallas DS164x RTCCONFIG_RTC_ISL1208- use Intersil ISL1208 RTCCONFIG_RTC_MAX6900- use Maxim, Inc. MAX6900 RTCCONFIG_RTC_DS1337_NOOSC- Turn off the OSC output for DS1337CONFIG_SYS_RV3029_TCR- enable trickle charger on  RV3029 RTC.Note that if the RTC uses I2C, then the I2C interfacemust also be configured. See I2C Support, below.- GPIO Support:CONFIG_PCA953X- use NXP's PCA953X series I2C GPIOThe CONFIG_SYS_I2C_PCA953X_WIDTH option specifies a list ofchip-ngpio pairs that tell the PCA953X driver the number ofpins supported by a particular chip.Note that if the GPIO device uses I2C, then the I2C interfacemust also be configured. See I2C Support, below.- I/O tracing:When CONFIG_IO_TRACE is selected, U-Boot intercepts all I/Oaccesses and can checksum them or write a list of them outto memory. See the 'iotrace' command for details. This isuseful for testing device drivers since it can confirm thatthe driver behaves the same way before and after a codechange. Currently this is supported on sandbox and arm. Toadd support for your architecture, add '#include <iotrace.h>'to the bottom of arch/<arch>/include/asm/io.h and test.Example output from the 'iotrace stats' command is below.Note that if the trace buffer is exhausted, the checksum willstill continue to operate.iotrace is enabledStart:  10000000(buffer start address)Size:   00010000(buffer size)Offset: 00000120(current buffer offset)Output: 10000120(start + offset)Count:  00000018(number of trace records)CRC32:  9526fb66(CRC32 of all trace records)- Timestamp Support:When CONFIG_TIMESTAMP is selected, the timestamp(date and time) of an image is printed by imagecommands like bootm or iminfo. This option isautomatically enabled when you select CONFIG_CMD_DATE .- Partition Labels (disklabels) Supported:Zero or more of the following:CONFIG_MAC_PARTITION   Apple's MacOS partition table.CONFIG_ISO_PARTITION   ISO partition table, used on CDROM etc.CONFIG_EFI_PARTITION   GPT partition table, common when EFI is the       bootloader.  Note 2TB partition limit; see       disk/part_efi.cCONFIG_SCSI) you must configure support for atleast one non-MTD partition type as well.- IDE Reset method:CONFIG_IDE_RESET_ROUTINE - this is defined in severalboard configurations files but used nowhere!CONFIG_IDE_RESET - is this is defined, IDE Reset willbe performed by calling the functionide_set_reset(int reset)which has to be defined in a board specific file- ATAPI Support:CONFIG_ATAPISet this to enable ATAPI support.- LBA48 SupportCONFIG_LBA48Set this to enable support for disks larger than 137GBAlso look at CONFIG_SYS_64BIT_LBA.Whithout these , LBA48 support uses 32bit variables and will 'only'support disks up to 2.1TB.CONFIG_SYS_64BIT_LBA:When enabled, makes the IDE subsystem use 64bit sector addresses.Default is 32bit.- SCSI Support:CONFIG_SYS_SCSI_MAX_LUN [8], CONFIG_SYS_SCSI_MAX_SCSI_ID [7] andCONFIG_SYS_SCSI_MAX_DEVICE [CONFIG_SYS_SCSI_MAX_SCSI_ID *CONFIG_SYS_SCSI_MAX_LUN] can be adjusted to define themaximum numbers of LUNs, SCSI ID's and targetdevices.The environment variable 'scsidevs' is set to the number ofSCSI devices found during the last scan.- NETWORK Support (PCI):CONFIG_E1000Support for Intel 8254x/8257x gigabit chips.CONFIG_E1000_SPIUtility code for direct access to the SPI bus on Intel 8257x.This does not do anything useful unless you set at least oneof CONFIG_CMD_E1000 or CONFIG_E1000_SPI_GENERIC.CONFIG_E1000_SPI_GENERICAllow generic access to the SPI bus on the Intel 8257x, forexample with the "sspi" command.CONFIG_NATSEMISupport for National dp83815 chips.CONFIG_NS8382XSupport for National dp8382[01] gigabit chips.- NETWORK Support (other):CONFIG_CALXEDA_XGMACSupport for the Calxeda XGMAC deviceCONFIG_LAN91C96Support for SMSC's LAN91C96 chips.CONFIG_LAN91C96_USE_32_BITDefine this to enable 32 bit addressingCONFIG_SMC91111Support for SMSC's LAN91C111 chipCONFIG_SMC91111_BASEDefine this to hold the physical addressof the device (I/O space)CONFIG_SMC_USE_32_BITDefine this if data bus is 32 bitsCONFIG_SMC_USE_IOFUNCSDefine this to use i/o functions instead of macros(some hardware wont work with macros)CONFIG_SYS_DAVINCI_EMAC_PHY_COUNTDefine this if you have more then 3 PHYs.CONFIG_FTGMAC100Support for Faraday's FTGMAC100 Gigabit SoC EthernetCONFIG_FTGMAC100_EGIGADefine this to use GE link update with gigabit PHY.Define this if FTGMAC100 is connected to gigabit PHY.If your system has 10/100 PHY only, it might not occurwrong behavior. Because PHY usually return timeout oruseless data when polling gigabit status and gigabitcontrol registers. This behavior won't affect thecorrectnessof 10/100 link speed update.CONFIG_SH_ETHERSupport for Renesas on-chip Ethernet controllerCONFIG_SH_ETHER_USE_PORTDefine the number of ports to be usedCONFIG_SH_ETHER_PHY_ADDRDefine the ETH PHY's addressCONFIG_SH_ETHER_CACHE_WRITEBACKIf this option is set, the driver enables cache flush.- TPM Support:CONFIG_TPMSupport TPM devices.CONFIG_TPM_TIS_INFINEONSupport for Infineon i2c bus TPM devices. Only one deviceper system is supported at this time.CONFIG_TPM_TIS_I2C_BURST_LIMITATIONDefine the burst count bytes upper limitCONFIG_TPM_ST33ZP24Support for STMicroelectronics TPM devices. Requires DM_TPM support.CONFIG_TPM_ST33ZP24_I2CSupport for STMicroelectronics ST33ZP24 I2C devices.Requires TPM_ST33ZP24 and I2C.CONFIG_TPM_ST33ZP24_SPISupport for STMicroelectronics ST33ZP24 SPI devices.Requires TPM_ST33ZP24 and SPI.CONFIG_TPM_ATMEL_TWISupport for Atmel TWI TPM device. Requires I2C support.CONFIG_TPM_TIS_LPCSupport for generic parallel port TPM devices. Only one deviceper system is supported at this time.CONFIG_TPM_TIS_BASE_ADDRESSBase address where the generic TPM device is mappedto. Contemporary x86 systems usually map it at0xfed40000.CONFIG_TPMDefine this to enable the TPM support library which providesfunctional interfaces to some TPM commands.Requires support for a TPM device.CONFIG_TPM_AUTH_SESSIONSDefine this to enable authorized functions in the TPM library.Requires CONFIG_TPM and CONFIG_SHA1.- USB Support:At the moment only the UHCI host controller issupported (PIP405, MIP405); defineCONFIG_USB_UHCI to enable it.define CONFIG_USB_KEYBOARD to enable the USB Keyboardand define CONFIG_USB_STORAGE to enable the USBstorage devices.Note:Supported are USB Keyboards and USB Floppy drives(TEAC FD-05PUB).CONFIG_USB_EHCI_TXFIFO_THRESH enables setting of thetxfilltuning field in the EHCI controller on reset.CONFIG_USB_DWC2_REG_ADDR the physical CPU address of the DWC2HW module registers.- USB Device:Define the below if you wish to use the USB console.Once firmware is rebuilt from a serial console issue thecommand "setenv stdin usbtty; setenv stdout usbtty" andattach your USB cable. The Unix command "dmesg" should printit has found a new device. The environment variable usbttycan be set to gserial or cdc_acm to enable your device toappear to a USB host as a Linux gserial device or aCommon Device Class Abstract Control Model serial device.If you select usbtty = gserial you should be able to enumeratea Linux host by# modprobe usbserial vendor=0xVendorID product=0xProductIDelse if using cdc_acm, simply setting the environmentvariable usbtty to be cdc_acm should suffice. The followingmight be defined in YourBoardName.hCONFIG_USB_DEVICEDefine this to build a UDC deviceCONFIG_USB_TTYDefine this to have a tty type of device available totalk to the UDC deviceCONFIG_USBD_HSDefine this to enable the high speed support for usbdevice and usbtty. If this feature is enabled, a routineint is_usbd_high_speed(void)also needs to be defined by the driver to dynamically pollwhether the enumeration has succeded at high speed or fullspeed.CONFIG_SYS_CONSOLE_IS_IN_ENVDefine this if you want stdin, stdout &/or stderr tobe set to usbtty.If you have a USB-IF assigned VendorID then you may wish todefine your own vendor specific values either in BoardName.hor directly in usbd_vendor_info.h. If you don't defineCONFIG_USBD_MANUFACTURER, CONFIG_USBD_PRODUCT_NAME,CONFIG_USBD_VENDORID and CONFIG_USBD_PRODUCTID, then U-Bootshould pretend to be a Linux device to it's target host.CONFIG_USBD_MANUFACTURERDefine this string as the name of your company for- CONFIG_USBD_MANUFACTURER "my company"CONFIG_USBD_PRODUCT_NAMEDefine this string as the name of your product- CONFIG_USBD_PRODUCT_NAME "acme usb device"CONFIG_USBD_VENDORIDDefine this as your assigned Vendor ID from the USBImplementors Forum. This *must* be a genuine Vendor IDto avoid polluting the USB namespace.- CONFIG_USBD_VENDORID 0xFFFFCONFIG_USBD_PRODUCTIDDefine this as the unique Product IDfor your device- CONFIG_USBD_PRODUCTID 0xFFFF- ULPI Layer Support:The ULPI (UTMI Low Pin (count) Interface) PHYs are supported viathe generic ULPI layer. The generic layer accesses the ULPI PHYvia the platform viewport, so you need both the genric layer andthe viewport enabled. Currently only Chipidea/ARC basedviewport is supported.To enable the ULPI layer support, define CONFIG_USB_ULPI andCONFIG_USB_ULPI_VIEWPORT in your board configuration file.If your ULPI phy needs a different reference clock than thestandard 24 MHz then you have to define CONFIG_ULPI_REF_CLK tothe appropriate value in Hz.- MMC Support:The MMC controller on the Intel PXA is supported. Toenable this define CONFIG_MMC. The MMC can beaccessed from the boot prompt by mapping the deviceto physical memory similar to flash. Command line isenabled with CONFIG_CMD_MMC. The MMC driver also works withthe FAT fs. This is enabled with CONFIG_CMD_FAT.CONFIG_SH_MMCIFSupport for Renesas on-chip MMCIF controllerCONFIG_SH_MMCIF_ADDRDefine the base address of MMCIF registersCONFIG_SH_MMCIF_CLKDefine the clock frequency for MMCIF- USB Device Firmware Update (DFU) class support:CONFIG_DFU_OVER_USBThis enables the USB portion of the DFU USB classCONFIG_DFU_NANDThis enables support for exposing NAND devices via DFU.CONFIG_DFU_RAMThis enables support for exposing RAM via DFU.Note: DFU spec refer to non-volatile memory usage, butallow usages beyond the scope of spec - here RAM usage,one that would help mostly the developer.CONFIG_SYS_DFU_DATA_BUF_SIZEDfu transfer uses a buffer before writing data to theraw storage device. Make the size (in bytes) of this bufferconfigurable. The size of this buffer is also configurablethrough the "dfu_bufsiz" environment variable.CONFIG_SYS_DFU_MAX_FILE_SIZEWhen updating files rather than the raw storage device,we use a static buffer to copy the file into and then writethe buffer once we've been given the whole file.  Definethis to the maximum filesize (in bytes) for the buffer.Default is 4 MiB if undefined.DFU_DEFAULT_POLL_TIMEOUTPoll timeout [ms], is the timeout a device can send to thehost. The host must wait for this timeout before sendinga subsequent DFU_GET_STATUS request to the device.DFU_MANIFEST_POLL_TIMEOUTPoll timeout [ms], which the device sends to the host whenentering dfuMANIFEST state. Host waits this timeout, beforesending again an USB request to the device.- Journaling Flash filesystem support:CONFIG_JFFS2_NANDDefine these for a default partition on a NAND deviceCONFIG_SYS_JFFS2_FIRST_SECTOR,CONFIG_SYS_JFFS2_FIRST_BANK, CONFIG_SYS_JFFS2_NUM_BANKSDefine these for a default partition on a NOR device- Keyboard Support:See Kconfig help for available keyboard drivers.CONFIG_KEYBOARDDefine this to enable a custom keyboard support.This simply calls drv_keyboard_init() which must bedefined in your board-specific files. This option is deprecatedand is only used by novena. For new boards, use driver modelinstead.- Video support:CONFIG_FSL_DIU_FBEnable the Freescale DIU video driver.Reference boards forSOCs that have a DIU should define this macro to enable DIUsupport, and should also define these other macros:CONFIG_SYS_DIU_ADDRCONFIG_VIDEOCONFIG_CFB_CONSOLECONFIG_VIDEO_SW_CURSORCONFIG_VGA_AS_SINGLE_DEVICECONFIG_VIDEO_LOGOCONFIG_VIDEO_BMP_LOGOThe DIU driver will look for the 'video-mode' environmentvariable, and if defined, enable the DIU as a console duringboot.  See the documentation file doc/README.video for adescription of this variable.- LCD Support:CONFIG_LCDDefine this to enable LCD support (for output to LCDdisplay); also select one of the supported displaysby defining one of these:CONFIG_ATMEL_LCD:HITACHI TX09D70VM1CCA, 3.5", 240x320.CONFIG_NEC_NL6448AC33:NEC NL6448AC33-18. Active, color, single scan.CONFIG_NEC_NL6448BC20NEC NL6448BC20-08. 6.5", 640x480.Active, color, single scan.CONFIG_NEC_NL6448BC33_54NEC NL6448BC33-54. 10.4", 640x480.Active, color, single scan.CONFIG_SHARP_16x9Sharp 320x240. Active, color, single scan.It isn't 16x9, and I am not sure what it is.CONFIG_SHARP_LQ64D341Sharp LQ64D341 display, 640x480.Active, color, single scan.CONFIG_HLD1045HLD1045 display, 640x480.Active, color, single scan.CONFIG_OPTREX_BWOptrex CBL50840-2 NF-FW 99 22 M5orHitachi LMG6912RPFC-00TorHitachi SP14Q002320x240. Black & white.CONFIG_LCD_ALIGNMENTNormally the LCD is page-aligned (typically 4KB). If this isdefined then the LCD will be aligned to this value instead.For ARM it is sometimes useful to use MMU_SECTION_SIZEhere, since it is cheaper to change data cache settings ona per-section basis.CONFIG_LCD_ROTATIONSometimes, for example if the display is mounted in portraitmode or even if it's mounted landscape but rotated by 180degree,we need to rotate our content of the display relative to theframebuffer, so that user can read the messages which areprinted out.Once CONFIG_LCD_ROTATION is defined, the lcd_console will beinitialized with a given rotation from "vl_rot" out of"vidinfo_t" which is provided by the board specific code.The value for vl_rot is coded as following (matching tofbcon=rotate:<n> linux-kernel commandline):0 = no rotation respectively 0 degree1 = 90 degree rotation2 = 180 degree rotation3 = 270 degree rotationIf CONFIG_LCD_ROTATION is not defined, the console will beinitialized with 0degree rotation.CONFIG_LCD_BMP_RLE8Support drawing of RLE8-compressed bitmaps on the LCD.CONFIG_I2C_EDIDEnables an 'i2c edid' command which can read EDIDinformation over I2C from an attached LCD display.- MII/PHY support:CONFIG_PHY_CLOCK_FREQ (ppc4xx)The clock frequency of the MII busCONFIG_PHY_RESET_DELAYSome PHY like Intel LXT971A need extra delay afterreset before any MII register access is possible.For such PHY, set this option to the usec delayrequired. (minimum 300usec for LXT971A)CONFIG_PHY_CMD_DELAY (ppc4xx)Some PHY like Intel LXT971A need extra delay aftercommand issued before MII status register can be read- IP address:CONFIG_IPADDRDefine a default value for the IP address to use forthe default Ethernet interface, in case this is notdetermined through e.g. bootp.(Environment variable "ipaddr")- Server IP address:CONFIG_SERVERIPDefines a default value for the IP address of a TFTPserver to contact when using the "tftboot" command.(Environment variable "serverip")CONFIG_KEEP_SERVERADDRKeeps the server's MAC address, in the env 'serveraddr'for passing to bootargs (like Linux's netconsole option)- Gateway IP address:CONFIG_GATEWAYIPDefines a default value for the IP address of thedefault router where packets to other networks aresent to.(Environment variable "gatewayip")- Subnet mask:CONFIG_NETMASKDefines a default value for the subnet mask (orrouting prefix) which is used to determine if an IPaddress belongs to the local subnet or needs to beforwarded through a router.(Environment variable "netmask")- BOOTP Recovery Mode:CONFIG_BOOTP_RANDOM_DELAYIf you have many targets in a network that try toboot using BOOTP, you may want to avoid that allsystems send out BOOTP requests at precisely the samemoment (which would happen for instance at recoveryfrom a power failure, when all systems will try toboot, thus flooding the BOOTP server. DefiningCONFIG_BOOTP_RANDOM_DELAY causes a random delay to beinserted before sending out BOOTP requests. Thefollowing delays are inserted then:1st BOOTP request:delay 0 ... 1 sec2nd BOOTP request:delay 0 ... 2 sec3rd BOOTP request:delay 0 ... 4 sec4th and followingBOOTP requests:delay 0 ... 8 secCONFIG_BOOTP_ID_CACHE_SIZEBOOTP packets are uniquely identified using a 32-bit ID. Theserver will copy the ID from client requests to responses andU-Boot will use this to determine if it is the destination ofan incoming response. Some servers will check that addressesaren't in use before handing them out (usually using an ARPping) and therefore take up to a few hundred milliseconds torespond. Network congestion may also influence the time ittakes for a response to make it back to the client. If thattime is too long, U-Boot will retransmit requests. In orderto allow earlier responses to still be accepted after theseretransmissions, U-Boot's BOOTP client keeps a small cache ofIDs. The CONFIG_BOOTP_ID_CACHE_SIZE controls the size of thiscache. The default is to keep IDs for up to four outstandingrequests. Increasing this will allow U-Boot to accept offersfrom a BOOTP client in networks with unusually high latency.- DHCP Advanced Options:You can fine tune the DHCP functionality by definingCONFIG_BOOTP_* symbols:CONFIG_BOOTP_NISDOMAINCONFIG_BOOTP_BOOTFILESIZECONFIG_BOOTP_NTPSERVERCONFIG_BOOTP_TIMEOFFSETCONFIG_BOOTP_VENDOREXCONFIG_BOOTP_MAY_FAILCONFIG_BOOTP_SERVERIP - TFTP server will be the serveripenvironment variable, not the BOOTP server.CONFIG_BOOTP_MAY_FAIL - If the DHCP server is not foundafter the configured retry count, the call will failinstead of starting over.  This can be used to fail overto Link-local IP address configuration if the DHCP serveris not available.CONFIG_BOOTP_DHCP_REQUEST_DELAYA 32bit value in microseconds for a delay betweenreceiving a "DHCP Offer" and sending the "DHCP Request".This fixes a problem with certain DHCP servers that don'trespond 100% of the time to a "DHCP request". E.g. On anAT91RM9200 processor running at 180MHz, this delay neededto be *at least* 15,000 usec before a Windows Server 2003DHCP server would reply 100% of the time. I recommend atleast 50,000 usec to be safe. The alternative is to hopethat one of the retries will be successful but note thatthe DHCP timeout and retry process takes a longer thanthis delay. - Link-local IP address negotiation:Negotiate with other link-local clients on the local networkfor an address that doesn't require explicit configuration.This is especially useful if a DHCP server cannot be guaranteedto exist in all environments that the device must operate.See doc/README.link-local for more information. - MAC address from environment variablesFDT_SEQ_MACADDR_FROM_ENVFix-up device tree with MAC addresses fetched sequentially fromenvironment variables. This config work on assumption thatnon-usable ethernet node of device-tree are either not presentor their status has been marked as "disabled". - CDP Options:CONFIG_CDP_DEVICE_IDThe device id used in CDP trigger frames.CONFIG_CDP_DEVICE_ID_PREFIXA two character string which is prefixed to the MAC addressof the device.CONFIG_CDP_PORT_IDA printf format string which contains the ascii name ofthe port. Normally is set to "eth%d" which setseth0 for the first Ethernet, eth1 for the second etc.CONFIG_CDP_CAPABILITIESA 32bit integer which indicates the device capabilities;0x00000010 for a normal host which does not forwards.CONFIG_CDP_VERSIONAn ascii string containing the version of the software.CONFIG_CDP_PLATFORMAn ascii string containing the name of the platform.CONFIG_CDP_TRIGGERA 32bit integer sent on the trigger.CONFIG_CDP_POWER_CONSUMPTIONA 16bit integer containing the power consumption of thedevice in .1 of milliwatts.CONFIG_CDP_APPLIANCE_VLAN_TYPEA byte containing the id of the VLAN.- Status LED:CONFIG_LED_STATUSSeveral configurations allow to display the currentstatus using a LED. For instance, the LED will blinkfast while running U-Boot code, stop blinking assoon as a reply to a BOOTP request was received, andstart blinking slow once the Linux kernel is running(supported by a status LED driver in the Linuxkernel). Defining CONFIG_LED_STATUS enables thisfeature in U-Boot.Additional options:CONFIG_LED_STATUS_GPIOThe status LED can be connected to a GPIO pin.In such cases, the gpio_led driver can be used as astatus LED backend implementation. Define CONFIG_LED_STATUS_GPIOto include the gpio_led driver in the U-Boot binary.CONFIG_GPIO_LED_INVERTED_TABLESome GPIO connected LEDs may have inverted polarity in whichcase the GPIO high value corresponds to LED off state andGPIO low value corresponds to LED on state.In such cases CONFIG_GPIO_LED_INVERTED_TABLE may be definedwith a list of GPIO LEDs that have inverted polarity.- I2C Support:CONFIG_SYS_NUM_I2C_BUSESHold the number of i2c buses you want to use.CONFIG_SYS_I2C_DIRECT_BUSdefine this, if you don't use i2c muxes on your hardware.if CONFIG_SYS_I2C_MAX_HOPS is not defined or == 0 you canomit this define.CONFIG_SYS_I2C_MAX_HOPSdefine how many muxes are maximal consecutively connectedon one i2c bus. If you not use i2c muxes, omit thisdefine.CONFIG_SYS_I2C_BUSEShold a list of buses you want to use, only used ifCONFIG_SYS_I2C_DIRECT_BUS is not defined, for examplea board with CONFIG_SYS_I2C_MAX_HOPS = 1 andCONFIG_SYS_NUM_I2C_BUSES = 9: CONFIG_SYS_I2C_BUSES{{0, {I2C_NULL_HOP}}, \{0, {{I2C_MUX_PCA9547, 0x70, 1}}}, \{0, {{I2C_MUX_PCA9547, 0x70, 2}}}, \{0, {{I2C_MUX_PCA9547, 0x70, 3}}}, \{0, {{I2C_MUX_PCA9547, 0x70, 4}}}, \{0, {{I2C_MUX_PCA9547, 0x70, 5}}}, \{1, {I2C_NULL_HOP}}, \{1, {{I2C_MUX_PCA9544, 0x72, 1}}}, \{1, {{I2C_MUX_PCA9544, 0x72, 2}}}, \}which definesbus 0 on adapter 0 without a muxbus 1 on adapter 0 with a PCA9547 on address 0x70 port 1bus 2 on adapter 0 with a PCA9547 on address 0x70 port 2bus 3 on adapter 0 with a PCA9547 on address 0x70 port 3bus 4 on adapter 0 with a PCA9547 on address 0x70 port 4bus 5 on adapter 0 with a PCA9547 on address 0x70 port 5bus 6 on adapter 1 without a muxbus 7 on adapter 1 with a PCA9544 on address 0x72 port 1bus 8 on adapter 1 with a PCA9544 on address 0x72 port 2If you do not have i2c muxes on your board, omit this define.- Legacy I2C Support:If you use the software i2c interface (CONFIG_SYS_I2C_SOFT)then the following macros need to be defined (examples arefrom include/configs/lwmon.h):I2C_INIT(Optional). Any commands necessary to enable the I2Ccontroller or configure ports.eg: #define I2C_INIT (immr->im_cpm.cp_pbdir |=PB_SCL)I2C_ACTIVEThe code necessary to make the I2C data line active(driven).  If the data line is open collector, thisdefine can be null.eg: #define I2C_ACTIVE (immr->im_cpm.cp_pbdir |=  PB_SDA)I2C_TRISTATEThe code necessary to make the I2C data line tri-stated(inactive).  If the data line is open collector, thisdefine can be null.eg: #define I2C_TRISTATE (immr->im_cpm.cp_pbdir &= ~PB_SDA)I2C_READCode that returns true if the I2C data line is high,false if it is low.eg: #define I2C_READ ((immr->im_cpm.cp_pbdat & PB_SDA) != 0)I2C_SDA(bit)If <bit> is true, sets the I2C data line high. If itis false, it clears it (low).eg: #define I2C_SDA(bit) \if(bit) immr->im_cpm.cp_pbdat |=  PB_SDA; \elseimmr->im_cpm.cp_pbdat &= ~PB_SDAI2C_SCL(bit)If <bit> is true, sets the I2C clock line high. If itis false, it clears it (low).eg: #define I2C_SCL(bit) \if(bit) immr->im_cpm.cp_pbdat |=  PB_SCL; \elseimmr->im_cpm.cp_pbdat &= ~PB_SCLI2C_DELAYThis delay is invoked four times per clock cycle so thiscontrols the rate of data transfer.  The data rate thusis 1 / (I2C_DELAY * 4). Often defined to be somethinglike:#define I2C_DELAY  udelay(2)CONFIG_SOFT_I2C_GPIO_SCL / CONFIG_SOFT_I2C_GPIO_SDAIf your arch supports the generic GPIO framework (asm/gpio.h),then you may alternatively define the two GPIOs that are to beused as SCL / SDA.  Any of the previous I2C_xxx macros willhave GPIO-based defaults assigned to them as appropriate.You should define these to the GPIO value as given directly tothe generic GPIO functions.CONFIG_SYS_I2C_INIT_BOARDWhen a board is reset during an i2c bus transferchips might think that the current transfer is stillin progress. On some boards it is possible to accessthe i2c SCLK line directly, either by using theprocessor pin as a GPIO or by having a second pinconnected to the bus. If this option is defined acustom i2c_init_board() routine in boards/xxx/board.cis run early in the boot sequence.CONFIG_I2C_MULTI_BUSThis option allows the use of multiple I2C buses, each of whichmust have a controller. At any point in time, only one bus isactive. To switch to a different bus, use the 'i2c dev' command.Note that bus numbering is zero-based.CONFIG_SYS_I2C_NOPROBESThis option specifies a list of I2C devices that will be skippedwhen the 'i2c probe' command is issued. If CONFIG_I2C_MULTI_BUSis set, specify a list of bus-device pairs.  Otherwise, specifya 1D array of device addressese.g.#undefCONFIG_I2C_MULTI_BUS#define CONFIG_SYS_I2C_NOPROBES {0x50,0x68}will skip addresses 0x50 and 0x68 on a board with one I2C bus#define CONFIG_I2C_MULTI_BUS#define CONFIG_SYS_I2C_NOPROBES{{0,0x50},{0,0x68},{1,0x54}}will skip addresses 0x50 and 0x68 on bus 0 and address 0x54 on bus 1CONFIG_SYS_SPD_BUS_NUMIf defined, then this indicates the I2C bus number for DDR SPD.If not defined, then U-Boot assumes that SPD is on I2C bus 0.CONFIG_SYS_RTC_BUS_NUMIf defined, then this indicates the I2C bus number for the RTC.If not defined, then U-Boot assumes that RTC is on I2C bus 0.CONFIG_SOFT_I2C_READ_REPEATED_STARTdefining this will force the i2c_read() function inthe soft_i2c driver to perform an I2C repeated startbetween writing the address pointer and reading thedata.  If this define is omitted the default behaviourof doing a stop-start sequence will be used.  Most I2Cdevices can use either method, but some require one orthe other.- SPI Support:CONFIG_SPIEnables SPI driver (so far only tested withSPI EEPROM, also an instance works with Crystal A/D andD/As on the SACSng board)CONFIG_SOFT_SPIEnables a software (bit-bang) SPI driver rather thanusing hardware support. This is a general purposedriver that only requires three general I/O port pins(two outputs, one input) to function. If this isdefined, the board configuration must define severalSPI configuration items (port pins to use, etc). Foran example, see include/configs/sacsng.h.CONFIG_SYS_SPI_MXC_WAITTimeout for waiting until spi transfer completed.default: (CONFIG_SYS_HZ/100)     /* 10 ms */- FPGA Support: CONFIG_FPGAEnables FPGA subsystem.CONFIG_FPGA_<vendor>Enables support for specific chip vendors.(ALTERA, XILINX)CONFIG_FPGA_<family>Enables support for FPGA family.(SPARTAN2, SPARTAN3, VIRTEX2, CYCLONE2, ACEX1K, ACEX)CONFIG_FPGA_COUNTSpecify the number of FPGA devices to support.CONFIG_SYS_FPGA_PROG_FEEDBACKEnable printing of hash marks during FPGA configuration.CONFIG_SYS_FPGA_CHECK_BUSYEnable checks on FPGA configuration interface busystatus by the configuration function. This optionwill require a board or device specific function tobe written.CONFIG_FPGA_DELAYIf defined, a function that provides delays in the FPGAconfiguration driver.CONFIG_SYS_FPGA_CHECK_CTRLCAllow Control-C to interrupt FPGA configurationCONFIG_SYS_FPGA_CHECK_ERRORCheck for configuration errors during FPGA bitfileloading. For example, abort during Virtex IIconfiguration if the INIT_B line goes low (whichindicated a CRC error).CONFIG_SYS_FPGA_WAIT_INITMaximum time to wait for the INIT_B line to de-assertafter PROB_B has been de-asserted during a Virtex IIFPGA configuration sequence. The default time is 500ms.CONFIG_SYS_FPGA_WAIT_BUSYMaximum time to wait for BUSY to de-assert duringVirtex II FPGA configuration. The default is 5 ms.CONFIG_SYS_FPGA_WAIT_CONFIGTime to wait after FPGA configuration. The default is200 ms.- Configuration Management:CONFIG_IDENT_STRINGIf defined, this string will be added to the U-Bootversion information (U_BOOT_VERSION)- Vendor Parameter Protection:U-Boot considers the values of the environmentvariables "serial#" (Board Serial Number) and"ethaddr" (Ethernet Address) to be parameters thatare set once by the board vendor / manufacturer, andprotects these variables from casual modification bythe user. Once set, these variables are read-only,and write or delete attempts are rejected. You canchange this behaviour:If CONFIG_ENV_OVERWRITE is #defined in your configfile, the write protection for vendor parameters iscompletely disabled. Anybody can change or deletethese parameters.Alternatively, if you define _both_ an ethaddr in thedefault env _and_ CONFIG_OVERWRITE_ETHADDR_ONCE, a defaultEthernet address is installed in the environment,which can be changed exactly ONCE by the user. [Theserial# is unaffected by this, i. e. it remainsread-only.]The same can be accomplished in a more flexible wayfor any variable by configuring the type of accessto allow for those variables in the ".flags" variableor define CONFIG_ENV_FLAGS_LIST_STATIC.- Protected RAM:CONFIG_PRAMDefine this variable to enable the reservation of"protected RAM", i. e. RAM which is not overwrittenby U-Boot. Define CONFIG_PRAM to hold the number ofkB you want to reserve for pRAM. You can overwritethis default value by defining an environmentvariable "pram" to the number of kB you want toreserve. Note that the board info structure willstill show the full amount of RAM. If pRAM isreserved, a new environment variable "mem" willautomatically be defined to hold the amount ofremaining RAM in a form that can be passed as bootargument to Linux, for instance like that:setenv bootargs ... mem=\${mem}saveenvThis way you can tell Linux not to use this memory,either, which results in a memory region that willnot be affected by reboots.*WARNING* If your board configuration uses automaticdetection of the RAM size, you must make sure thatthis memory test is non-destructive. So far, thefollowing board configurations are known to be"pRAM-clean":IVMS8, IVML24, SPD8xx,HERMES, IP860, RPXlite, LWMON,FLAGADM- Access to physical memory region (> 4GB)Some basic support is provided for operations on memory notnormally accessible to U-Boot - e.g. some architecturessupport access to more than 4GB of memory on 32-bitmachines using physical address extension or similar.Define CONFIG_PHYSMEM to access this basic support, whichcurrently only supports clearing the memory.- Error Recovery:CONFIG_NET_RETRY_COUNTThis variable defines the number of retries fornetwork operations like ARP, RARP, TFTP, or BOOTPbefore giving up the operation. If not defined, adefault value of 5 is used.CONFIG_ARP_TIMEOUTTimeout waiting for an ARP reply in milliseconds.CONFIG_NFS_TIMEOUTTimeout in milliseconds used in NFS protocol.If you encounter "ERROR: Cannot umount" in nfs command,try longer timeout such as#define CONFIG_NFS_TIMEOUT 10000ULNote:In the current implementation, the local variablesspace and global environment variables space areseparated. Local variables are those you define bysimply typing `name=value'. To access a localvariable later on, you have write `$name' or`${name}'; to execute the contents of a variabledirectly type `$name' at the command prompt.Global environment variables are those you usesetenv/printenv to work with. To run a command storedin such a variable, you need to use the run command,and you must not use the '$' sign to access them.To store commands and special characters in avariable, please use double quotation markssurrounding the whole text of the variable, insteadof the backslashes before semicolons and specialsymbols.- Command Line Editing and History:CONFIG_CMDLINE_PS_SUPPORTEnable support for changing the command prompt stringat run-time. Only static string is supported so far.The string is obtained from environment variables PS1and PS2.- Default Environment:CONFIG_EXTRA_ENV_SETTINGSDefine this to contain any number of null terminatedstrings (variable = value pairs) that will be part ofthe default environment compiled into the boot image.For example, place something like this in yourboard's config file:#define CONFIG_EXTRA_ENV_SETTINGS \"myvar1=value1\0" \"myvar2=value2\0"Warning: This method is based on knowledge about theinternal format how the environment is stored by theU-Boot code. This is NOT an official, exportedinterface! Although it is unlikely that this formatwill change soon, there is no guarantee either.You better know what you are doing here.Note: overly (ab)use of the default environment isdiscouraged. Make sure to check other ways to presetthe environment like the "source" command or theboot command first.CONFIG_DELAY_ENVIRONMENTNormally the environment is loaded when the board isinitialised so that it is available to U-Boot. This inhibitsthat so that the environment is not available untilexplicitly loaded later by U-Boot code. With CONFIG_OF_CONTROLthis is instead controlled by the value of/config/load-environment.- TFTP Fixed UDP Port:CONFIG_TFTP_PORTIf this is defined, the environment variable tftpsrcpis used to supply the TFTP UDP source port value.If tftpsrcp isn't defined, the normal pseudo-random portnumber generator is used.Also, the environment variable tftpdstp is used to supplythe TFTP UDP destination port value.  If tftpdstp isn'tdefined, the normal port 69 is used.The purpose for tftpsrcp is to allow a TFTP server toblindly start the TFTP transfer using the pre-configuredtarget IP address and UDP port. This has the effect of"punching through" the (Windows XP) firewall, allowingthe remainder of the TFTP transfer to proceed normally.A better solution is to properly configure the firewall,but sometimes that is not allowed.CONFIG_STANDALONE_LOAD_ADDRThis option defines a board specific value for theaddress where standalone program gets loaded, thusoverwriting the architecture dependent defaultsettings.- Frame Buffer Address:CONFIG_FB_ADDRDefine CONFIG_FB_ADDR if you want to use specificaddress for frame buffer.  This is typically the casewhen using a graphics controller has separate videomemory.  U-Boot will then place the frame buffer atthe given address instead of dynamically reserving itin system RAM by calling lcd_setmem(), which grabsthe memory for the frame buffer depending on theconfigured panel size.Please see board_init_f function.- Automatic software updates via TFTP serverCONFIG_UPDATE_TFTPCONFIG_UPDATE_TFTP_CNT_MAXCONFIG_UPDATE_TFTP_MSEC_MAXThese options enable and control the auto-update feature;for a more detailed description refer to doc/README.update.- MTD Support (mtdparts command, UBI support)CONFIG_MTD_UBI_WL_THRESHOLDThis parameter defines the maximum difference between the highesterase counter value and the lowest erase counter value of eraseblocksof UBI devices. When this threshold is exceeded, UBI starts performingwear leveling by means of moving data from eraseblock with low erasecounter to eraseblocks with high erase counter.The default value should be OK for SLC NAND flashes, NOR flashes andother flashes which have eraseblock life-cycle 100000 or more.However, in case of MLC NAND flashes which typically have eraseblocklife-cycle less than 10000, the threshold should be lessened (e.g.,to 128 or 256, although it does not have to be power of 2).default: 4096CONFIG_MTD_UBI_BEB_LIMITThis option specifies the maximum bad physical eraseblocks UBIexpects on the MTD device (per 1024 eraseblocks). If theunderlying flash does not admit of bad eraseblocks (e.g. NORflash), this value is ignored.NAND datasheets often specify the minimum and maximum NVM(Number of Valid Blocks) for the flashes' endurance lifetime.The maximum expected bad eraseblocks per 1024 eraseblocksthen can be calculated as "1024 * (1 - MinNVB / MaxNVB)",which gives 20 for most NANDs (MaxNVB is basically the totalcount of eraseblocks on the chip).To put it differently, if this value is 20, UBI will try toreserve about 1.9% of physical eraseblocks for bad blockshandling. And that will be 1.9% of eraseblocks on the entireNAND chip, not just the MTD partition UBI attaches. This meansthat if you have, say, a NAND flash chip admits maximum 40 baderaseblocks, and it is split on two MTD partitions of the samesize, UBI will reserve 40 eraseblocks when attaching apartition.default: 20CONFIG_MTD_UBI_FASTMAPFastmap is a mechanism which allows attaching an UBI devicein nearly constant time. Instead of scanning the whole MTD device itonly has to locate a checkpoint (called fastmap) on the device.The on-flash fastmap contains all information needed to attachthe device. Using fastmap makes only sense on large devices whereattaching by scanning takes long. UBI will not automatically installa fastmap on old images, but you can set the UBI parameterCONFIG_MTD_UBI_FASTMAP_AUTOCONVERT to 1 if you want so. Please notethat fastmap-enabled images are still usable with UBI implementationswithoutfastmap support. On typical flash devices the whole fastmapfits into one PEB. UBI will reserve PEBs to hold two fastmaps.CONFIG_MTD_UBI_FASTMAP_AUTOCONVERTSet this parameter to enable fastmap automatically on imageswithout a fastmap.default: 0CONFIG_MTD_UBI_FM_DEBUGEnable UBI fastmap debugdefault: 0- SPL frameworkCONFIG_SPLEnable building of SPL globally.CONFIG_SPL_LDSCRIPTLDSCRIPT for linking the SPL binary.CONFIG_SPL_MAX_FOOTPRINTMaximum size in memory allocated to the SPL, BSS included.When defined, the linker checks that the actual memoryused by SPL from _start to __bss_end does not exceed it.CONFIG_SPL_MAX_FOOTPRINT and CONFIG_SPL_BSS_MAX_SIZEmust not be both defined at the same time.CONFIG_SPL_MAX_SIZEMaximum size of the SPL image (text, data, rodata, andlinker lists sections), BSS excluded.When defined, the linker checks that the actual size doesnot exceed it.CONFIG_SPL_RELOC_TEXT_BASEAddress to relocate to.  If unspecified, this is equal toCONFIG_SPL_TEXT_BASE (i.e. no relocation is done).CONFIG_SPL_BSS_START_ADDRLink address for the BSS within the SPL binary.CONFIG_SPL_BSS_MAX_SIZEMaximum size in memory allocated to the SPL BSS.When defined, the linker checks that the actual memory usedby SPL from __bss_start to __bss_end does not exceed it.CONFIG_SPL_MAX_FOOTPRINT and CONFIG_SPL_BSS_MAX_SIZEmust not be both defined at the same time.CONFIG_SPL_STACKAdress of the start of the stack SPL will useCONFIG_SPL_PANIC_ON_RAW_IMAGEWhen defined, SPL will panic() if the image it hasloaded does not have a signature.Defining this is useful when code which loads imagesin SPL cannot guarantee that absolutely all read errorswill be caught.An example is the LPC32XX MLC NAND driver, which willconsider that a completely unreadable NAND block is bad,and thus should be skipped silently.CONFIG_SPL_RELOC_STACKAdress of the start of the stack SPL will use afterrelocation.  If unspecified, this is equal toCONFIG_SPL_STACK.CONFIG_SYS_SPL_MALLOC_STARTStarting address of the malloc pool used in SPL.When this option is set the full malloc is used in SPL andit is set up by spl_init() and before that, the simple malloc()can be used if CONFIG_SYS_MALLOC_F is defined.CONFIG_SYS_SPL_MALLOC_SIZEThe size of the malloc pool used in SPL.CONFIG_SPL_OS_BOOTEnable booting directly to an OS from SPL.See also: doc/README.falconCONFIG_SPL_DISPLAY_PRINTFor ARM, enable an optional function to print more informationabout the running system.CONFIG_SPL_INIT_MINIMALArch init code should be built for a very small imageCONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_PARTITIONPartition on the MMC to load U-Boot from when the MMC is beingused in raw modeCONFIG_SYS_MMCSD_RAW_MODE_KERNEL_SECTORSector to load kernel uImage from when MMC is beingused in raw mode (for Falcon mode)CONFIG_SYS_MMCSD_RAW_MODE_ARGS_SECTOR,CONFIG_SYS_MMCSD_RAW_MODE_ARGS_SECTORSSector and number of sectors to load kernel argumentparameters from when MMC is being used in raw mode(for falcon mode)CONFIG_SPL_FS_LOAD_PAYLOAD_NAMEFilename to read to load U-Boot when reading from filesystemCONFIG_SPL_FS_LOAD_KERNEL_NAMEFilename to read to load kernel uImage when readingfrom filesystem (for Falcon mode)CONFIG_SPL_FS_LOAD_ARGS_NAMEFilename to read to load kernel argument parameterswhen reading from filesystem (for Falcon mode)CONFIG_SPL_MPC83XX_WAIT_FOR_NANDSet this for NAND SPL on PPC mpc83xx targets, so thatstart.S waits for the rest of the SPL to load beforecontinuing (the hardware starts execution after justloading the first page rather than the full 4K).CONFIG_SPL_SKIP_RELOCATEAvoid SPL relocationCONFIG_SPL_NAND_IDENTSPL uses the chip ID list to identify the NAND flash.Requires CONFIG_SPL_NAND_BASE.CONFIG_SPL_UBISupport for a lightweight UBI (fastmap) scanner andloaderCONFIG_SPL_NAND_RAW_ONLYSupport to boot only raw u-boot.bin images. Use this onlyif you need to save space.CONFIG_SPL_COMMON_INIT_DDRSet for common ddr init with serial presence detect inSPL binary.CONFIG_SYS_NAND_5_ADDR_CYCLE, CONFIG_SYS_NAND_PAGE_COUNT,CONFIG_SYS_NAND_PAGE_SIZE, CONFIG_SYS_NAND_OOBSIZE,CONFIG_SYS_NAND_BLOCK_SIZE, CONFIG_SYS_NAND_BAD_BLOCK_POS,CONFIG_SYS_NAND_ECCPOS, CONFIG_SYS_NAND_ECCSIZE,CONFIG_SYS_NAND_ECCBYTESDefines the size and behavior of the NAND that SPL usesto read U-BootCONFIG_SYS_NAND_U_BOOT_DSTLocation in memory to load U-Boot toCONFIG_SYS_NAND_U_BOOT_SIZESize of image to loadCONFIG_SYS_NAND_U_BOOT_STARTEntry point in loaded image to jump toCONFIG_SYS_NAND_HW_ECC_OOBFIRSTDefine this if you need to first read the OOB and then thedata. This is used, for example, on davinci platforms.CONFIG_SPL_RAM_DEVICESupport for running image already present in ram, in SPL binaryCONFIG_SPL_PAD_TOImage offset to which the SPL should be padded before appendingthe SPL payload. By default, this is defined asCONFIG_SPL_MAX_SIZE, or 0 if CONFIG_SPL_MAX_SIZE is undefined.CONFIG_SPL_PAD_TO must be either 0, meaning to append the SPLpayload without any padding, or >= CONFIG_SPL_MAX_SIZE.CONFIG_SPL_TARGETFinal target image containing SPL and payload.  Some SPLsuse an arch-specific makefile fragment instead, forexample if more than one image needs to be produced.CONFIG_SPL_FIT_PRINTPrinting information about a FIT image adds quite a bit ofcode to SPL. So this is normally disabled in SPL. Use thisoption to re-enable it. This will affect the output of thebootm command when booting a FIT image.- TPL frameworkCONFIG_TPLEnable building of TPL globally.CONFIG_TPL_PAD_TOImage offset to which the TPL should be padded before appendingthe TPL payload. By default, this is defined asCONFIG_SPL_MAX_SIZE, or 0 if CONFIG_SPL_MAX_SIZE is undefined.CONFIG_SPL_PAD_TO must be either 0, meaning to append the SPLpayload without any padding, or >= CONFIG_SPL_MAX_SIZE.- Interrupt support (PPC):There are common interrupt_init() and timer_interrupt()for all PPC archs. interrupt_init() calls interrupt_init_cpu()for CPU specific initialization. interrupt_init_cpu()should set decrementer_count to appropriate value. IfCPU resets decrementer automatically after interrupt(ppc4xx) it should set decrementer_count to zero.timer_interrupt() calls timer_interrupt_cpu() for CPUspecific handling. If board has watchdog / status_led/ other_activity_monitor it works automatically fromgeneral timer_interrupt().Board initialization settings:------------------------------During Initialization u-boot calls a number of board specific functionsto allow the preparation of board specific prerequisites, e.g. pin setupbefore drivers are initialized. To enable these callbacks thefollowing configuration macros have to be defined. Currently this isarchitecture specific, so please check arch/your_architecture/lib/board.ctypically in board_init_f() and board_init_r().- CONFIG_BOARD_EARLY_INIT_F: Call board_early_init_f()- CONFIG_BOARD_EARLY_INIT_R: Call board_early_init_r()- CONFIG_BOARD_LATE_INIT: Call board_late_init()- CONFIG_BOARD_POSTCLK_INIT: Call board_postclk_init()Configuration Settings:------------------------ MEM_SUPPORT_64BIT_DATA: Defined automatically if compiled as 64-bit.Optionally it can be defined to support 64-bit memory commands.- CONFIG_SYS_LONGHELP: Defined when you want long help messages included;undefine this when you're short of memory.- CONFIG_SYS_HELP_CMD_WIDTH: Defined when you want to override the defaultwidth of the commands listed in the 'help' command output.- CONFIG_SYS_PROMPT:This is what U-Boot prints on the console toprompt for user input.- CONFIG_SYS_CBSIZE:Buffer size for input from the Console- CONFIG_SYS_PBSIZE:Buffer size for Console output- CONFIG_SYS_MAXARGS:max. Number of arguments accepted for monitor commands- CONFIG_SYS_BARGSIZE: Buffer size for Boot Arguments which are passed tothe application (usually a Linux kernel) when it isbooted- CONFIG_SYS_BAUDRATE_TABLE:List of legal baudrate settings for this board.- CONFIG_SYS_MEM_RESERVE_SECUREOnly implemented for ARMv8 for now.If defined, the size of CONFIG_SYS_MEM_RESERVE_SECURE memoryis substracted from total RAM and won't be reported to OS.This memory can be used as secure memory. A variablegd->arch.secure_ram is used to track the location. In systemsthe RAM base is not zero, or RAM is divided into banks,this variable needs to be recalcuated to get the address.- CONFIG_SYS_MEM_TOP_HIDE:If CONFIG_SYS_MEM_TOP_HIDE is defined in the board config header,this specified memory area will get subtracted from the top(end) of RAM and won't get "touched" at all by U-Boot. Byfixing up gd->ram_size the Linux kernel should gets passedthe now "corrected" memory size and won't touch it either.This should work for arch/ppc and arch/powerpc. Only Linuxboard ports in arch/powerpc with bootwrapper support thatrecalculate the memory size from the SDRAM controller setupwill have to get fixed in Linux additionally.This option can be used as a workaround for the 440EPx/GRxCHIP 11 errata where the last 256 bytes in SDRAM shouldn'tbe touched.WARNING: Please make sure that this value is a multiple ofthe Linux page size (normally 4k). If this is not the case,then the end address of the Linux memory will be located at anon page size aligned address and this could cause majorproblems.- CONFIG_SYS_LOADS_BAUD_CHANGE:Enable temporary baudrate change while serial download- CONFIG_SYS_SDRAM_BASE:Physical start address of SDRAM. _Must_ be 0 here.- CONFIG_SYS_FLASH_BASE:Physical start address of Flash memory.- CONFIG_SYS_MONITOR_BASE:Physical start address of boot monitor code (set bymake config files to be same as the text base address(CONFIG_SYS_TEXT_BASE) used when linking) - same asCONFIG_SYS_FLASH_BASE when booting from flash.- CONFIG_SYS_MONITOR_LEN:Size of memory reserved for monitor code, used todetermine _at_compile_time_ (!) if the environment isembedded within the U-Boot image, or in a separateflash sector.- CONFIG_SYS_MALLOC_LEN:Size of DRAM reserved for malloc() use.- CONFIG_SYS_MALLOC_F_LENSize of the malloc() pool for use before relocation. Ifthis is defined, then a very simple malloc() implementationwill become available before relocation. The address is justbelow the global data, and the stack is moved down to makespace.This feature allocates regions with increasing addresseswithin the region. calloc() is supported, but realloc()is not available. free() is supported but does nothing.The memory will be freed (or in fact just forgotten) whenU-Boot relocates itself.- CONFIG_SYS_MALLOC_SIMPLEProvides a simple and small malloc() and calloc() for thoseboards which do not use the full malloc in SPL (which isenabled with CONFIG_SYS_SPL_MALLOC_START).- CONFIG_SYS_NONCACHED_MEMORY:Size of non-cached memory area. This area of memory will betypically located right below the malloc() area and mappeduncached in the MMU. This is useful for drivers that wouldotherwise require a lot of explicit cache maintenance. Forsome drivers it's also impossible to properly maintain thecache. For example if the regions that need to be flushedare not a multiple of the cache-line size, *and* paddingcannot be allocated between the regions to align them (i.e.if the HW requires a contiguous array of regions, and thesize of each region is not cache-aligned), then a flush ofone region may result in overwriting data that hardware haswritten to another region in the same cache-line. This canhappen for example in network drivers where descriptors forbuffers are typically smaller than the CPU cache-line (e.g.16 bytes vs. 32 or 64 bytes).Non-cached memory is only supported on 32-bit ARM at present.- CONFIG_SYS_BOOTM_LEN:Normally compressed uImages are limited to anuncompressed size of 8 MBytes. If this is not enough,you can define CONFIG_SYS_BOOTM_LEN in your board config fileto adjust this setting to your needs.- CONFIG_SYS_BOOTMAPSZ:Maximum size of memory mapped by the startup code ofthe Linux kernel; all data that must be processed bythe Linux kernel (bd_info, boot arguments, FDT blob ifused) must be put below this limit, unless "bootm_low"environment variable is defined and non-zero. In such caseall data for the Linux kernel must be between "bootm_low"and "bootm_low" + CONFIG_SYS_BOOTMAPSZ. The environmentvariable "bootm_mapsize" will override the value ofCONFIG_SYS_BOOTMAPSZ.  If CONFIG_SYS_BOOTMAPSZ is undefined,then the value in "bootm_size" will be used instead.- CONFIG_SYS_BOOT_RAMDISK_HIGH:Enable initrd_high functionality.  If defined then theinitrd_high feature is enabled and the bootm ramdisk subcommandis enabled.- CONFIG_SYS_BOOT_GET_CMDLINE:Enables allocating and saving kernel cmdline in space between"bootm_low" and "bootm_low" + BOOTMAPSZ.- CONFIG_SYS_BOOT_GET_KBD:Enables allocating and saving a kernel copy of the bd_info inspace between "bootm_low" and "bootm_low" + BOOTMAPSZ.- CONFIG_SYS_MAX_FLASH_BANKS:Max number of Flash memory banks- CONFIG_SYS_MAX_FLASH_SECT:Max number of sectors on a Flash chip- CONFIG_SYS_FLASH_ERASE_TOUT:Timeout for Flash erase operations (in ms)- CONFIG_SYS_FLASH_WRITE_TOUT:Timeout for Flash write operations (in ms)- CONFIG_SYS_FLASH_LOCK_TOUTTimeout for Flash set sector lock bit operation (in ms)- CONFIG_SYS_FLASH_UNLOCK_TOUTTimeout for Flash clear lock bits operation (in ms)- CONFIG_SYS_FLASH_PROTECTIONIf defined, hardware flash sectors protection is usedinstead of U-Boot software protection.- CONFIG_SYS_DIRECT_FLASH_TFTP:Enable TFTP transfers directly to flash memory;without this option such a download has to beperformed in two steps: (1) download to RAM, and (2)copy from RAM to flash.The two-step approach is usually more reliable, sinceyou can check if the download worked before you erasethe flash, but in some situations (when system RAM istoo limited to allow for a temporary copy of thedownloaded image) this option may be very useful.- CONFIG_SYS_FLASH_CFI:Define if the flash driver uses extra elements in thecommon flash structure for storing flash geometry.- CONFIG_FLASH_CFI_DRIVERThis option also enables the building of the cfi_flash driverin the drivers directory- CONFIG_FLASH_CFI_MTDThis option enables the building of the cfi_mtd driverin the drivers directory. The driver exports CFI flashto the MTD layer.- CONFIG_SYS_FLASH_USE_BUFFER_WRITEUse buffered writes to flash.- CONFIG_FLASH_SPANSION_S29WS_Ns29ws-n MirrorBit flash has non-standard addresses for bufferedwrite commands.- CONFIG_SYS_FLASH_QUIET_TESTIf this option is defined, the common CFI flash doesn'tprint it's warning upon not recognized FLASH banks. Thisis useful, if some of the configured banks are onlyoptionally available.- CONFIG_FLASH_SHOW_PROGRESSIf defined (must be an integer), print out countdowndigits and dots.  Recommended value: 45 (9..1) for 80column displays, 15 (3..1) for 40 column displays.- CONFIG_FLASH_VERIFYIf defined, the content of the flash (destination) is comparedagainst the source after the write operation. An error messagewill be printed when the contents are not identical.Please note that this option is useless in nearly all cases,since such flash programming errors usually are detected earlierwhile unprotecting/erasing/programming. Please only enablethis option if you really know what you are doing.- CONFIG_SYS_RX_ETH_BUFFER:Defines the number of Ethernet receive buffers. On someEthernet controllers it is recommended to set this valueto 8 or even higher (EEPRO100 or 405 EMAC), since allbuffers can be full shortly after enabling the interfaceon high Ethernet traffic.Defaults to 4 if not defined.- CONFIG_ENV_MAX_ENTRIESMaximum number of entries in the hash table that is usedinternally to store the environment settings. The defaultsetting is supposed to be generous and should work in mostcases. This setting can be used to tune behaviour; seelib/hashtable.c for details.- CONFIG_ENV_FLAGS_LIST_DEFAULT- CONFIG_ENV_FLAGS_LIST_STATICEnable validation of the values given to environment variables whencalling env set.  Variables can be restricted to only decimal,hexadecimal, or boolean.  If CONFIG_CMD_NET is also defined,the variables can also be restricted to IP address or MAC address.The format of the list is:type_attribute = [s|d|x|b|i|m]access_attribute = [a|r|o|c]attributes = type_attribute[access_attribute]entry = variable_name[:attributes]list = entry[,list]The type attributes are:s - String (default)d - Decimalx - Hexadecimalb - Boolean ([1yYtT|0nNfF])i - IP addressm - MAC addressThe access attributes are:a - Any (default)r - Read-onlyo - Write-oncec - Change-default- CONFIG_ENV_FLAGS_LIST_DEFAULTDefine this to a list (string) to define the ".flags"environment variable in the default or embedded environment.- CONFIG_ENV_FLAGS_LIST_STATICDefine this to a list (string) to define validation thatshould be done if an entry is not found in the ".flags"environment variable.  To override a setting in the staticlist, simply add an entry for the same variable name to the".flags" variable.If CONFIG_REGEX is defined, the variable_name above is evaluated as aregular expression. This allows multiple variables to define the sameflags without explicitly listing them for each variable.The following definitions that deal with the placement and managementof environment data (variable area); in general, we support thefollowing configurations:- CONFIG_BUILD_ENVCRC:Builds up envcrc with the target environment so that external utilsmay easily extract it and embed it in final U-Boot images.BE CAREFUL! The first access to the environment happens quite earlyin U-Boot initialization (when we try to get the setting of for theconsole baudrate). You *MUST* have mapped your NVRAM area then, orU-Boot will hang.Please note that even with NVRAM we still use a copy of theenvironment in RAM: we could work on NVRAM directly, but we want tokeep settings there always unmodified except somebody uses "saveenv"to save the current settings.BE CAREFUL! For some special cases, the local device can not use"saveenv" command. For example, the local device will get theenvironment stored in a remote NOR flash by SRIO or PCIE link,but it can not erase, write this NOR flash by SRIO or PCIE interface.- CONFIG_NAND_ENV_DSTDefines address in RAM to which the nand_spl code should copy theenvironment. If redundant environment is used, it will be copied toCONFIG_NAND_ENV_DST + CONFIG_ENV_SIZE.Please note that the environment is read-only until the monitorhas been relocated to RAM and a RAM copy of the environment has beencreated; also, when using EEPROM you will have to use env_get_f()until then to read environment variables.The environment is protected by a CRC32 checksum. Before the monitoris relocated into RAM, as a result of a bad CRC you will be workingwith the compiled-in default environment - *silently*!!! [This isnecessary, because the first environment variable we need is the"baudrate" setting for the console - if we have a bad CRC, we don'thave any device yet where we could complain.]Note: once the monitor has been relocated, then it will complain ifthe default environment is used; a new CRC is computed as soon as youuse the "saveenv" command to store a valid environment.- CONFIG_SYS_FAULT_ECHO_LINK_DOWN:Echo the inverted Ethernet link state to the fault LED.Note: If this option is active, then CONFIG_SYS_FAULT_MII_ADDR      also needs to be defined.- CONFIG_SYS_FAULT_MII_ADDR:MII address of the PHY to check for the Ethernet link state.- CONFIG_NS16550_MIN_FUNCTIONS:Define this if you desire to only have use of the NS16550_initand NS16550_putc functions for the serial driver located atdrivers/serial/ns16550.c.  This option is useful for savingspace for already greatly restricted images, including but notlimited to NAND_SPL configurations.- CONFIG_DISPLAY_BOARDINFODisplay information about the board that U-Boot is running onwhen U-Boot starts up. The board function checkboard() is calledto do this.- CONFIG_DISPLAY_BOARDINFO_LATESimilar to the previous option, but display this informationlater, once stdio is running and output goes to the LCD, ifpresent.- CONFIG_BOARD_SIZE_LIMIT:Maximum size of the U-Boot image. When defined, thebuild system checks that the actual size does notexceed it.Low Level (hardware related) configuration options:---------------------------------------------------- CONFIG_SYS_CACHELINE_SIZE:Cache Line Size of the CPU.- CONFIG_SYS_CCSRBAR_DEFAULT:Default (power-on reset) physical address of CCSR on FreescalePowerPC SOCs.- CONFIG_SYS_CCSRBAR:Virtual address of CCSR.  On a 32-bit build, this is typicallythe same value as CONFIG_SYS_CCSRBAR_DEFAULT.- CONFIG_SYS_CCSRBAR_PHYS:Physical address of CCSR.  CCSR can be relocated to a newphysical address, if desired.  In this case, this macro shouldbe set to that address. Otherwise, it should be set to thesame value as CONFIG_SYS_CCSRBAR_DEFAULT.  For example, CCSRis typically relocated on 36-bit builds.  It is recommendedthat this macro be defined via the _HIGH and _LOW macros:#define CONFIG_SYS_CCSRBAR_PHYS ((CONFIG_SYS_CCSRBAR_PHYS_HIGH* 1ull) << 32 | CONFIG_SYS_CCSRBAR_PHYS_LOW)- CONFIG_SYS_CCSRBAR_PHYS_HIGH:Bits 33-36 of CONFIG_SYS_CCSRBAR_PHYS.This value is typicallyeither 0 (32-bit build) or 0xF (36-bit build).This macro isused in assembly code, so it must not contain typecasts orinteger size suffixes (e.g. "ULL").- CONFIG_SYS_CCSRBAR_PHYS_LOW:Lower 32-bits of CONFIG_SYS_CCSRBAR_PHYS.  This macro isused in assembly code, so it must not contain typecasts orinteger size suffixes (e.g. "ULL").- CONFIG_SYS_CCSR_DO_NOT_RELOCATE:If this macro is defined, then CONFIG_SYS_CCSRBAR_PHYS will beforced to a value that ensures that CCSR is not relocated.- CONFIG_IDE_AHB:Most IDE controllers were designed to be connected with PCIinterface. Only few of them were designed for AHB interface.When software is doing ATA command and data transfer toIDE devices through IDE-AHB controller, some additionalregisters accessing to these kind of IDE-AHB controlleris required.- CONFIG_SYS_IMMR:Physical address of the Internal Memory.DO NOT CHANGE unless you know exactly what you'redoing! (11-4) [MPC8xx systems only]- CONFIG_SYS_INIT_RAM_ADDR:Start address of memory area that can be used forinitial data and stack; please note that this must bewritable memory that is working WITHOUT specialinitialization, i. e. you CANNOT use normal RAM whichwill become available only after programming thememory controller and running certain initializationsequences.U-Boot uses the following memory types:- MPC8xx: IMMR (internal memory of the CPU)- CONFIG_SYS_GBL_DATA_OFFSET:Offset of the initial data structure in the memoryarea defined by CONFIG_SYS_INIT_RAM_ADDR. UsuallyCONFIG_SYS_GBL_DATA_OFFSET is chosen such that the initialdata is located at the end of the available space(sometimes written as (CONFIG_SYS_INIT_RAM_SIZE -GENERATED_GBL_DATA_SIZE), and the initial stack is justbelow that area (growing from (CONFIG_SYS_INIT_RAM_ADDR +CONFIG_SYS_GBL_DATA_OFFSET) downward.Note:On the MPC824X (or other systems that use the datacache for initial memory) the address chosen forCONFIG_SYS_INIT_RAM_ADDR is basically arbitrary - it mustpoint to an otherwise UNUSED address space betweenthe top of RAM and the start of the PCI space.- CONFIG_SYS_SCCR:System Clock and reset Control Register (15-27)- CONFIG_SYS_OR_TIMING_SDRAM:SDRAM timing- CONFIG_SYS_MAMR_PTA:periodic timer for refresh- FLASH_BASE0_PRELIM, FLASH_BASE1_PRELIM, CONFIG_SYS_REMAP_OR_AM,  CONFIG_SYS_PRELIM_OR_AM, CONFIG_SYS_OR_TIMING_FLASH, CONFIG_SYS_OR0_REMAP,  CONFIG_SYS_OR0_PRELIM, CONFIG_SYS_BR0_PRELIM, CONFIG_SYS_OR1_REMAP, CONFIG_SYS_OR1_PRELIM,  CONFIG_SYS_BR1_PRELIM:Memory Controller Definitions: BR0/1 and OR0/1 (FLASH)- SDRAM_BASE2_PRELIM, SDRAM_BASE3_PRELIM, SDRAM_MAX_SIZE,  CONFIG_SYS_OR_TIMING_SDRAM, CONFIG_SYS_OR2_PRELIM, CONFIG_SYS_BR2_PRELIM,  CONFIG_SYS_OR3_PRELIM, CONFIG_SYS_BR3_PRELIM:Memory Controller Definitions: BR2/3 and OR2/3 (SDRAM)- CONFIG_SYS_SRIO:Chip has SRIO or not- CONFIG_SRIO1:Board has SRIO 1 port available- CONFIG_SRIO2:Board has SRIO 2 port available- CONFIG_SRIO_PCIE_BOOT_MASTERBoard can support master function for Boot from SRIO and PCIE- CONFIG_SYS_SRIOn_MEM_VIRT:Virtual Address of SRIO port 'n' memory region- CONFIG_SYS_SRIOn_MEM_PHYxS:Physical Address of SRIO port 'n' memory region- CONFIG_SYS_SRIOn_MEM_SIZE:Size of SRIO port 'n' memory region- CONFIG_SYS_NAND_BUSWIDTH_16BITDefined to tell the NAND controller that the NAND chip is usinga 16 bit bus.Not all NAND drivers use this symbol.Example of drivers that use it:- drivers/mtd/nand/raw/ndfc.c- drivers/mtd/nand/raw/mxc_nand.c- CONFIG_SYS_NDFC_EBC0_CFGSets the EBC0_CFG register for the NDFC. If not defineda default value will be used.- CONFIG_SPD_EEPROMGet DDR timing information from an I2C EEPROM. Commonwith pluggable memory modules such as SODIMMs  SPD_EEPROM_ADDRESSI2C address of the SPD EEPROM- CONFIG_SYS_SPD_BUS_NUMIf SPD EEPROM is on an I2C bus other than the firstone, specify here. Note that the value must resolveto something your driver can deal with.- CONFIG_SYS_DDR_RAW_TIMINGGet DDR timing information from other than SPD. Common withsoldered DDR chips onboard without SPD. DDR raw timingparameters are extracted from datasheet and hard-coded intoheader files or board specific files.- CONFIG_FSL_DDR_INTERACTIVEEnable interactive DDR debugging. See doc/README.fsl-ddr.- CONFIG_FSL_DDR_SYNC_REFRESHEnable sync of refresh for multiple controllers.- CONFIG_FSL_DDR_BISTEnable built-in memory test for Freescale DDR controllers.- CONFIG_SYS_83XX_DDR_USES_CS0Only for 83xx systems. If specified, then DDR shouldbe configured using CS0 and CS1 instead of CS2 and CS3.- CONFIG_RMIIEnable RMII mode for all FECs.Note that this is a global option, we can'thave one FEC in standard MII mode and another in RMII mode.- CONFIG_CRC32_VERIFYAdd a verify option to the crc32 command.The syntax is:=> crc32 -v <address> <count> <crc32>Where address/count indicate a memory areaand crc32 is the correct crc32 which thearea should have.- CONFIG_LOOPWAdd the "loopw" memory command. This only takes effect ifthe memory commands are activated globally (CONFIG_CMD_MEMORY).- CONFIG_CMD_MX_CYCLICAdd the "mdc" and "mwc" memory commands. These are cyclic"md/mw" commands.Examples:=> mdc.b 10 4 500This command will print 4 bytes (10,11,12,13) each 500 ms.=> mwc.l 100 12345678 10This command will write 12345678 to address 100 all 10 ms.This only takes effect if the memory commands are activatedglobally (CONFIG_CMD_MEMORY).- CONFIG_SPL_BUILDSet when the currently-running compilation is for an artifactthat will end up in the SPL (as opposed to the TPL or U-Bootproper). Code that needs stage-specific behavior should checkthis.- CONFIG_TPL_BUILDSet when the currently-running compilation is for an artifactthat will end up in the TPL (as opposed to the SPL or U-Bootproper). Code that needs stage-specific behavior should checkthis.- CONFIG_SYS_MPC85XX_NO_RESETVECOnly for 85xx systems. If this variable is specified, the section.resetvec is not kept and the section .bootpg is placed in theprevious 4k of the .text section.- CONFIG_ARCH_MAP_SYSMEMGenerally U-Boot (and in particular the md command) useseffective address. It is therefore not necessary to regardU-Boot address as virtual addresses that need to be translatedto physical addresses. However, sandbox requires this, sinceit maintains its own little RAM buffer which contains alladdressable memory. This option causes some memory accessesto be mapped through map_sysmem() / unmap_sysmem().- CONFIG_X86_RESET_VECTORIf defined, the x86 reset vector code is included. This is notneeded when U-Boot is running from Coreboot.- CONFIG_SYS_NAND_NO_SUBPAGE_WRITEOption to disable subpage write in NAND driverdriver that uses this:drivers/mtd/nand/raw/davinci_nand.cFreescale QE/FMAN Firmware Support:-----------------------------------The Freescale QUICCEngine (QE) and Frame Manager (FMAN) both support theloading of "firmware", which is encoded in the QE firmware binary format.This firmware often needs to be loaded during U-Boot booting, so macrosare used to identify the storage device (NOR flash, SPI, etc) and the addresswithin that device.- CONFIG_SYS_FMAN_FW_ADDRThe address in the storage device where the FMAN microcode is located.  Themeaning of this address depends on which CONFIG_SYS_QE_FMAN_FW_IN_xxx macrois also specified.- CONFIG_SYS_QE_FW_ADDRThe address in the storage device where the QE microcode is located.  Themeaning of this address depends on which CONFIG_SYS_QE_FMAN_FW_IN_xxx macrois also specified.- CONFIG_SYS_QE_FMAN_FW_LENGTHThe maximum possible size of the firmware.  The firmware binary formathas a field that specifies the actual size of the firmware, but itmight not be possible to read any part of the firmware unless somelocal storage is allocated to hold the entire firmware first.- CONFIG_SYS_QE_FMAN_FW_IN_NORSpecifies that QE/FMAN firmware is located in NOR flash, mapped asnormal addressable memory via the LBC.  CONFIG_SYS_FMAN_FW_ADDR is thevirtual address in NOR flash.- CONFIG_SYS_QE_FMAN_FW_IN_NANDSpecifies that QE/FMAN firmware is located in NAND flash.CONFIG_SYS_FMAN_FW_ADDR is the offset within NAND flash.- CONFIG_SYS_QE_FMAN_FW_IN_MMCSpecifies that QE/FMAN firmware is located on the primary SD/MMCdevice.  CONFIG_SYS_FMAN_FW_ADDR is the byte offset on that device.- CONFIG_SYS_QE_FMAN_FW_IN_REMOTESpecifies that QE/FMAN firmware is located in the remote (master)memory space.CONFIG_SYS_FMAN_FW_ADDR is a virtual address whichcan be mapped from slave TLB->slave LAW->slave SRIO or PCIE outboundwindow->master inbound window->master LAW->the ucode address inmaster's memory space.Freescale Layerscape Management Complex Firmware Support:---------------------------------------------------------The Freescale Layerscape Management Complex (MC) supports the loading of"firmware".This firmware often needs to be loaded during U-Boot booting, so macrosare used to identify the storage device (NOR flash, SPI, etc) and the addresswithin that device.- CONFIG_FSL_MC_ENETEnable the MC driver for Layerscape SoCs.Freescale Layerscape Debug Server Support:-------------------------------------------The Freescale Layerscape Debug Server Support supports the loading of"Debug Server firmware" and triggering SP boot-rom.This firmware often needs to be loaded during U-Boot booting.- CONFIG_SYS_MC_RSV_MEM_ALIGNDefine alignment of reserved memory MC requiresReproducible builds-------------------In order to achieve reproducible builds, timestamps used in the U-Boot buildprocess have to be set to a fixed value.This is done using the SOURCE_DATE_EPOCH environment variable.SOURCE_DATE_EPOCH is to be set on the build host's shell, not as a configurationoption for U-Boot or an environment variable in U-Boot.SOURCE_DATE_EPOCH should be set to a number of seconds since the epoch, in UTC.Building the Software:======================Building U-Boot has been tested in several native build environmentsand in many different cross environments. Of course we cannot supportall possibly existing versions of cross development tools in all(potentially obsolete) versions. In case of tool chain problems werecommend to use the ELDK (seehttps://www.denx.de/wiki/DULG/ELDK)which is extensively used to build and test U-Boot.If you are not using a native environment, it is assumed that youhave GNU cross compiling tools available in your path. In this case,you must set the environment variable CROSS_COMPILE in your shell.Note that no changes to the Makefile or any other source files arenecessary. For example using the ELDK on a 4xx CPU, please enter:$ CROSS_COMPILE=ppc_4xx-$ export CROSS_COMPILEU-Boot is intended to be simple to build. After installing thesources you must configure U-Boot for one specific board type. Thisis done by typing:make NAME_defconfigwhere "NAME_defconfig" is the name of one of the existing configu-rations; see configs/*_defconfig for supported names.Note: for some boards special configuration names may exist; check if      additional information is available from the board vendor; for      instance, the TQM823L systems are available without (standard)      or with LCD support. You can select such additional "features"      when choosing the configuration, i. e.      make TQM823L_defconfig- will configure for a plain TQM823L, i. e. no LCD support      make TQM823L_LCD_defconfig- will configure for a TQM823L with U-Boot console on LCD      etc.Finally, type "make all", and you should get some working U-Bootimages ready for download to / installation on your system:- "u-boot.bin" is a raw binary image- "u-boot" is an image in ELF binary format- "u-boot.srec" is in Motorola S-Record formatBy default the build is performed locally and the objects are savedin the source directory. One of the two methods can be used to changethis behavior and build U-Boot to some external directory:1. Add O= to the make command line invocations:make O=/tmp/build distcleanmake O=/tmp/build NAME_defconfigmake O=/tmp/build all2. Set environment variable KBUILD_OUTPUT to point to the desired location:export KBUILD_OUTPUT=/tmp/buildmake distcleanmake NAME_defconfigmake allNote that the command line "O=" setting overrides the KBUILD_OUTPUT environmentvariable.User specific CPPFLAGS, AFLAGS and CFLAGS can be passed to the compiler bysetting the according environment variables KCPPFLAGS, KAFLAGS and KCFLAGS.For example to treat all compiler warnings as errors:make KCFLAGS=-WerrorPlease be aware that the Makefiles assume you are using GNU make, sofor instance on NetBSD you might need to use "gmake" instead ofnative "make".If the system board that you have is not listed, then you will needto port U-Boot to your hardware platform. To do this, follow thesesteps:1.  Create a new directory to hold your board specific code. Add any    files you need. In your board directory, you will need at least    the "Makefile" and a "<board>.c".2.  Create a new configuration file "include/configs/<board>.h" for    your board.3.  If you're porting U-Boot to a new CPU, then also create a new    directory to hold your CPU specific code. Add any files you need.4.  Run "make <board>_defconfig" with your new name.5.  Type "make", and you should get a working "u-boot.srec" file    to be installed on your target system.6.  Debug and solve any problems that might arise.    [Of course, this last step is much harder than it sounds.]Testing of U-Boot Modifications, Ports to New Hardware, etc.:==============================================================If you have modified U-Boot sources (for instance added a new boardor support for new devices, a new CPU, etc.) you are expected toprovide feedback to the other developers. The feedback normally takesthe form of a "patch", i.e. a context diff against a certain (latestofficial or latest in the git repository) version of U-Boot sources.But before you submit such a patch, please verify that your modifi-cation did not break existing code. At least make sure that *ALL* ofthe supported boards compile WITHOUT ANY compiler warnings. To do so,just run the buildman script (tools/buildman/buildman), which willconfigure and build U-Boot for ALL supported system. Be warned, thiswill take a while. Please see the buildman README, or run 'buildman -H'for documentation.See also "U-Boot Porting Guide" below.Monitor Commands - Overview:============================go- start application at address 'addr'run- run commands in an environment variablebootm- boot application image from memorybootp- boot image via network using BootP/TFTP protocolbootz   - boot zImage from memorytftpboot- boot image via network using TFTP protocol       and env variables "ipaddr" and "serverip"       (and eventually "gatewayip")tftpput - upload a file via network using TFTP protocolrarpboot- boot image via network using RARP/TFTP protocoldiskboot- boot from IDE devicebootd   - boot default, i.e., run 'bootcmd'loads- load S-Record file over serial lineloadb- load binary file over serial line (kermit mode)md- memory displaymm- memory modify (auto-incrementing)nm- memory modify (constant address)mw- memory write (fill)ms- memory searchcp- memory copycmp- memory comparecrc32- checksum calculationi2c- I2C sub-systemsspi- SPI utility commandsbase- print or set address offsetprintenv- print environment variablespwm- control pwm channelssetenv- set environment variablessaveenv - save environment variables to persistent storageprotect - enable or disable FLASH write protectionerase- erase FLASH memoryflinfo- print FLASH memory informationnand- NAND memory operations (see doc/README.nand)bdinfo- print Board Info structureiminfo- print header information for application imageconinfo - print console devices and informationside- IDE sub-systemloop- infinite loop on address rangeloopw- infinite write loop on address rangemtest- simple RAM testicache- enable or disable instruction cachedcache- enable or disable data cachereset- Perform RESET of the CPUecho- echo args to consoleversion - print monitor versionhelp- print online help?- alias for 'help'Monitor Commands - Detailed Description:========================================TODO.For now: just type "help <command>".Environment Variables:======================U-Boot supports user configuration using Environment Variables whichcan be made persistent by saving to Flash memory.Environment Variables are set using "setenv", printed using"printenv", and saved to Flash using "saveenv". Using "setenv"without a value can be used to delete a variable from theenvironment. As long as you don't save the environment you areworking with an in-memory copy. In case the Flash area containing theenvironment is erased by accident, a default environment is provided.Some configuration options can be set using Environment Variables.List of environment variables (most likely not complete):  baudrate- see CONFIG_BAUDRATE  bootdelay- see CONFIG_BOOTDELAY  bootcmd- see CONFIG_BOOTCOMMAND  bootargs- Boot arguments when booting an RTOS image  bootfile- Name of the image to load with TFTP  bootm_low- Memory range available for image processing in the bootm  command can be restricted. This variable is given as  a hexadecimal number and defines lowest address allowed  for use by the bootm command. See also "bootm_size"  environment variable. Address defined by "bootm_low" is  also the base of the initial memory mapping for the Linux  kernel -- see the description of CONFIG_SYS_BOOTMAPSZ and  bootm_mapsize.  bootm_mapsize - Size of the initial memory mapping for the Linux kernel.  This variable is given as a hexadecimal number and it  defines the size of the memory region starting at base  address bootm_low that is accessible by the Linux kernel  during early boot.  If unset, CONFIG_SYS_BOOTMAPSZ is used  as the default value if it is defined, and bootm_size is  used otherwise.  bootm_size- Memory range available for image processing in the bootm  command can be restricted. This variable is given as  a hexadecimal number and defines the size of the region  allowed for use by the bootm command. See also "bootm_low"  environment variable.  bootstopkeysha256, bootdelaykey, bootstopkey- See README.autoboot  updatefile- Location of the software update file on a TFTP server, used  by the automatic software update feature. Please refer to  documentation in doc/README.update for more details.  autoload- if set to "no" (any string beginning with 'n'),  "bootp" will just load perform a lookup of the  configuration from the BOOTP server, but not try to  load any image using TFTP  autostart- if set to "yes", an image loaded using the "bootp",  "rarpboot", "tftpboot" or "diskboot" commands will  be automatically started (by internally calling  "bootm")  If set to "no", a standalone image passed to the  "bootm" command will be copied to the load address  (and eventually uncompressed), but NOT be started.  This can be used to load and uncompress arbitrary  data.  fdt_high- if set this restricts the maximum address that the  flattened device tree will be copied into upon boot.  For example, if you have a system with 1 GB memory  at physical address 0x10000000, while Linux kernel  only recognizes the first 704 MB as low memory, you  may need to set fdt_high as 0x3C000000 to have the  device tree blob be copied to the maximum address  of the 704 MB low memory, so that Linux kernel can  access it during the boot procedure.  If this is set to the special value 0xFFFFFFFF then  the fdt will not be copied at all on boot.  For this  to work it must reside in writable memory, have  sufficient padding on the end of it for u-boot to  add the information it needs into it, and the memory  must be accessible by the kernel.  fdtcontroladdr- if set this is the address of the control flattened  device tree used by U-Boot when CONFIG_OF_CONTROL is  defined.  i2cfast- (PPC405GP|PPC405EP only)  if set to 'y' configures Linux I2C driver for fast  mode (400kHZ). This environment variable is used in  initialization code. So, for changes to be effective  it must be saved and board must be reset.  initrd_high- restrict positioning of initrd images:  If this variable is not set, initrd images will be  copied to the highest possible address in RAM; this  is usually what you want since it allows for  maximum initrd size. If for some reason you want to  make sure that the initrd image is loaded below the  CONFIG_SYS_BOOTMAPSZ limit, you can set this environment  variable to a value of "no" or "off" or "0".  Alternatively, you can set it to a maximum upper  address to use (U-Boot will still check that it  does not overwrite the U-Boot stack and data).  For instance, when you have a system with 16 MB  RAM, and want to reserve 4 MB from use by Linux,  you can do this by adding "mem=12M" to the value of  the "bootargs" variable. However, now you must make  sure that the initrd image is placed in the first  12 MB as well - this can be done with  setenv initrd_high 00c00000  If you set initrd_high to 0xFFFFFFFF, this is an  indication to U-Boot that all addresses are legal  for the Linux kernel, including addresses in flash  memory. In this case U-Boot will NOT COPY the  ramdisk at all. This may be useful to reduce the  boot time on your system, but requires that this  feature is supported by your Linux kernel.  ipaddr- IP address; needed for tftpboot command  loadaddr- Default load address for commands like "bootp",  "rarpboot", "tftpboot", "loadb" or "diskboot"  loads_echo- see CONFIG_LOADS_ECHO  serverip- TFTP server IP address; needed for tftpboot command  bootretry- see CONFIG_BOOT_RETRY_TIME  bootdelaykey- see CONFIG_AUTOBOOT_DELAY_STR  bootstopkey- see CONFIG_AUTOBOOT_STOP_STR  ethprime- controls which interface is used first.  ethact- controls which interface is currently active.  For example you can do the following  => setenv ethact FEC  => ping 192.168.0.1 # traffic sent on FEC  => setenv ethact SCC  => ping 10.0.0.1 # traffic sent on SCC  ethrotate- When set to "no" U-Boot does not go through all  available network interfaces.  It just stays at the currently selected interface.  netretry- When set to "no" each network operation will  either succeed or fail without retrying.  When set to "once" the network operation will  fail when all the available network interfaces  are tried once without success.  Useful on scripts which control the retry operation  themselves.  npe_ucode- set load address for the NPE microcode  silent_linux  - If set then Linux will be told to boot silently, by  changing the console to be empty. If "yes" it will be  made silent. If "no" it will not be made silent. If  unset, then it will be made silent if the U-Boot console  is silent.  tftpsrcp- If this is set, the value is used for TFTP's  UDP source port.  tftpdstp- If this is set, the value is used for TFTP's UDP  destination port instead of the Well Know Port 69.  tftpblocksize - Block size to use for TFTP transfers; if not set,  we use the TFTP server's default block size  tftptimeout- Retransmission timeout for TFTP packets (in milli-  seconds, minimum value is 1000 = 1 second). Defines  when a packet is considered to be lost so it has to  be retransmitted. The default is 5000 = 5 seconds.  Lowering this value may make downloads succeed  faster in networks with high packet loss rates or  with unreliable TFTP servers.  tftptimeoutcountmax- maximum count of TFTP timeouts (no  unit, minimum value = 0). Defines how many timeouts  can happen during a single file transfer before that  transfer is aborted. The default is 10, and 0 means  'no timeouts allowed'. Increasing this value may help  downloads succeed with high packet loss rates, or with  unreliable TFTP servers or client hardware.  tftpwindowsize- if this is set, the value is used for TFTP's  window size as described by RFC 7440.  This means the count of blocks we can receive before  sending ack to server.  vlan- When set to a value < 4095 the traffic over  Ethernet is encapsulated/received over 802.1q  VLAN tagged frames.  bootpretryperiod- Period during which BOOTP/DHCP sends retries.  Unsigned value, in milliseconds. If not set, the period will  be either the default (28000), or a value based on  CONFIG_NET_RETRY_COUNT, if defined. This value has  precedence over the valu based on CONFIG_NET_RETRY_COUNT.  memmatches- Number of matches found by the last 'ms' command, in hex  memaddr- Address of the last match found by the 'ms' command, in hex,  or 0 if none  mempos- Index position of the last match found by the 'ms' command,  in units of the size (.b, .w, .l) of the search  zbootbase- (x86 only) Base address of the bzImage 'setup' block  zbootaddr- (x86 only) Address of the loaded bzImage, typically  BZIMAGE_LOAD_ADDR which is 0x100000The following image location variables contain the location of imagesused in booting. The "Image" column gives the role of the image and isnot an environment variable name. The other columns are environmentvariable names. "File Name" gives the name of the file on a TFTPserver, "RAM Address" gives the location in RAM the image will beloaded to, and "Flash Location" gives the image's address in NORflash or offset in NAND flash.*Note* - these variables don't have to be defined for all boards, someboards currently use other variables for these purposes, and someboards use these variables for other purposes.Image    File Name     RAM Address       Flash Location-----    ---------     -----------       --------------u-boot    u-boot     u-boot_addr_r     u-boot_addrLinux kernel    bootfile     kernel_addr_r     kernel_addrdevice tree blob    fdtfile     fdt_addr_r       fdt_addrramdisk    ramdiskfile     ramdisk_addr_r    ramdisk_addrThe following environment variables may be used and automaticallyupdated by the network boot commands ("bootp" and "rarpboot"),depending the information provided by your boot server:  bootfile- see above  dnsip- IP address of your Domain Name Server  dnsip2- IP address of your secondary Domain Name Server  gatewayip- IP address of the Gateway (Router) to use  hostname- Target hostname  ipaddr- see above  netmask- Subnet Mask  rootpath- Pathname of the root filesystem on the NFS server  serverip- see aboveThere are two special Environment Variables:  serial#- contains hardware identification information such  as type string and/or serial number  ethaddr- Ethernet addressThese variables can be set only once (usually during manufacturing ofthe board). U-Boot refuses to delete or overwrite these variablesonce they have been set once.Further special Environment Variables:  ver- Contains the U-Boot version string as printed  with the "version" command. This variable is  readonly (see CONFIG_VERSION_VARIABLE).Please note that changes to some configuration parameters may takeonly effect after the next boot (yes, that's just like Windoze :-).Callback functions for environment variables:---------------------------------------------For some environment variables, the behavior of u-boot needs to changewhen their values are changed.  This functionality allows functions tobe associated with arbitrary variables.  On creation, overwrite, ordeletion, the callback will provide the opportunity for some sideeffect to happen or for the change to be rejected.The callbacks are named and associated with a function using theU_BOOT_ENV_CALLBACK macro in your board or driver code.These callbacks are associated with variables in one of two ways.  Thestatic list can be added to by defining CONFIG_ENV_CALLBACK_LIST_STATICin the board configuration to a string that defines a list ofassociations.  The list must be in the following format:entry = variable_name[:callback_name]list = entry[,list]If the callback name is not specified, then the callback is deleted.Spaces are also allowed anywhere in the list.Callbacks can also be associated by defining the ".callbacks" variablewith the same list format above.  Any association in ".callbacks" willoverride any association in the static list. You can defineCONFIG_ENV_CALLBACK_LIST_DEFAULT to a list (string) to define the".callbacks" environment variable in the default or embedded environment.If CONFIG_REGEX is defined, the variable_name above is evaluated as aregular expression. This allows multiple variables to be connected tothe same callback without explicitly listing them all out.The signature of the callback functions is:    int callback(const char *name, const char *value, enum env_op op, int flags)* name - changed environment variable* value - new value of the environment variable* op - operation (create, overwrite, or delete)* flags - attributes of the environment variable change, see flags H_* in  include/search.hThe return value is 0 if the variable change is accepted and 1 otherwise.Note for Redundant Ethernet Interfaces:=======================================Some boards come with redundant Ethernet interfaces; U-Boot supportssuch configurations and is capable of automatic selection of a"working" interface when needed. MAC assignment works as follows:Network interfaces are numbered eth0, eth1, eth2, ... CorrespondingMAC addresses can be stored in the environment as "ethaddr" (=>eth0),"eth1addr" (=>eth1), "eth2addr", ...If the network interface stores some valid MAC address (for instancein SROM), this is used as default address if there is NO correspon-ding setting in the environment; if the corresponding environmentvariable is set, this overrides the settings in the card; that means:o If the SROM has a valid MAC address, and there is no address in the  environment, the SROM's address is used.o If there is no valid address in the SROM, and a definition in the  environment exists, then the value from the environment variable is  used.o If both the SROM and the environment contain a MAC address, and  both addresses are the same, this MAC address is used.o If both the SROM and the environment contain a MAC address, and the  addresses differ, the value from the environment is used and a  warning is printed.o If neither SROM nor the environment contain a MAC address, an error  is raised. If CONFIG_NET_RANDOM_ETHADDR is defined, then in this case  a random, locally-assigned MAC is used.If Ethernet drivers implement the 'write_hwaddr' function, valid MAC addresseswill be programmed into hardware as part of the initialization process. Thismay be skipped by setting the appropriate 'ethmacskip' environment variable.The naming convention is as follows:"ethmacskip" (=>eth0), "eth1macskip" (=>eth1) etc.Image Formats:==============U-Boot is capable of booting (and performing other auxiliary operations on)images in two formats:New uImage format (FIT)-----------------------Flexible and powerful format based on Flattened Image Tree -- FIT (similarto Flattened Device Tree). It allows the use of images with multiplecomponents (several kernels, ramdisks, etc.), with contents protected bySHA1, MD5 or CRC32. More details are found in the doc/uImage.FIT directory.Old uImage format-----------------Old image format is based on binary files which can be basically anything,preceded by a special header; see the definitions in include/image.h fordetails; basically, the header defines the following image properties:* Target Operating System (Provisions for OpenBSD, NetBSD, FreeBSD,  4.4BSD, Linux, SVR4, Esix, Solaris, Irix, SCO, Dell, NCR, VxWorks,  LynxOS, pSOS, QNX, RTEMS, INTEGRITY;  Currently supported: Linux, NetBSD, VxWorks, QNX, RTEMS, LynxOS,  INTEGRITY).* Target CPU Architecture (Provisions for Alpha, ARM, Intel x86,  IA64, MIPS, NDS32, Nios II, PowerPC, IBM S390, SuperH, Sparc, Sparc 64 Bit;  Currently supported: ARM, Intel x86, MIPS, NDS32, Nios II, PowerPC).* Compression Type (uncompressed, gzip, bzip2)* Load Address* Entry Point* Image Name* Image TimestampThe header is marked by a special Magic Number, and both the headerand the data portions of the image are secured against corruption byCRC32 checksums.Linux Support:==============Although U-Boot should support any OS or standalone applicationeasily, the main focus has always been on Linux during the design ofU-Boot.U-Boot includes many features that so far have been part of somespecial "boot loader" code within the Linux kernel. Also, any"initrd" images to be used are no longer part of one big Linux image;instead, kernel and "initrd" are separate images. This implementationserves several purposes:- the same features can be used for other OS or standalone  applications (for instance: using compressed images to reduce the  Flash memory footprint)- it becomes much easier to port new Linux kernel versions because  lots of low-level, hardware dependent stuff are done by U-Boot- the same Linux kernel image can now be used with different "initrd"  images; of course this also means that different kernel images can  be run with the same "initrd". This makes testing easier (you don't  have to build a new "zImage.initrd" Linux image when you just  change a file in your "initrd"). Also, a field-upgrade of the  software is easier now.Linux HOWTO:============Porting Linux to U-Boot based systems:---------------------------------------U-Boot cannot save you from doing all the necessary modifications toconfigure the Linux device drivers for use with your target hardware(no, we don't intend to provide a full virtual machine interface toLinux :-).But now you can ignore ALL boot loader code (in arch/powerpc/mbxboot).Just make sure your machine specific header file (for instanceinclude/asm-ppc/tqm8xx.h) includes the same definition of the BoardInformation structure as we define in include/asm-<arch>/u-boot.h,and make sure that your definition of IMAP_ADDR uses the same valueas your U-Boot configuration in CONFIG_SYS_IMMR.Note that U-Boot now has a driver model, a unified model for drivers.If you are adding a new driver, plumb it into driver model. If thereis no uclass available, you are encouraged to create one. Seedoc/driver-model.Configuring the Linux kernel:-----------------------------No specific requirements for U-Boot. Make sure you have some rootdevice (initial ramdisk, NFS) for your target system.Building a Linux Image:-----------------------With U-Boot, "normal" build targets like "zImage" or "bzImage" arenot used. If you use recent kernel source, a new build target"uImage" will exist which automatically builds an image usable byU-Boot. Most older kernels also have support for a "pImage" target,which was introduced for our predecessor project PPCBoot and uses a100% compatible format.Example:make TQM850L_defconfigmake oldconfigmake depmake uImageThe "uImage" build target uses a special tool (in 'tools/mkimage') toencapsulate a compressed Linux kernel image with header information,CRC32 checksum etc. for use with U-Boot. This is what we are doing:* build a standard "vmlinux" kernel image (in ELF binary format):* convert the kernel into a raw binary image:${CROSS_COMPILE}-objcopy -O binary \ -R .note -R .comment \ -S vmlinux linux.bin* compress the binary image:gzip -9 linux.bin* package compressed binary image for U-Boot:mkimage -A ppc -O linux -T kernel -C gzip \-a 0 -e 0 -n "Linux Kernel Image" \-d linux.bin.gz uImageThe "mkimage" tool can also be used to create ramdisk images for usewith U-Boot, either separated from the Linux kernel image, orcombined into one file. "mkimage" encapsulates the images with a 64byte header containing information about target architecture,operating system, image type, compression method, entry points, timestamp, CRC32 checksums, etc."mkimage" can be called in two ways: to verify existing images andprint the header information, or to build new images.In the first form (with "-l" option) mkimage lists the informationcontained in the header of an existing U-Boot image; this includeschecksum verification:tools/mkimage -l image  -l ==> list image header informationThe second form (with "-d" option) is used to build a U-Boot imagefrom a "data file" which is used as image payload:tools/mkimage -A arch -O os -T type -C comp -a addr -e ep \      -n name -d data_file image  -A ==> set architecture to 'arch'  -O ==> set operating system to 'os'  -T ==> set image type to 'type'  -C ==> set compression type 'comp'  -a ==> set load address to 'addr' (hex)  -e ==> set entry point to 'ep' (hex)  -n ==> set image name to 'name'  -d ==> use image data from 'datafile'Right now, all Linux kernels for PowerPC systems use the same loadaddress (0x00000000), but the entry point address depends on thekernel version:- 2.2.x kernels have the entry point at 0x0000000C,- 2.3.x and later kernels have the entry point at 0x00000000.So a typical call to build a U-Boot image would read:-> tools/mkimage -n '2.4.4 kernel for TQM850L' \> -A ppc -O linux -T kernel -C gzip -a 0 -e 0 \> -d /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux.gz \> examples/uImage.TQM850LImage Name:   2.4.4 kernel for TQM850LCreated:      Wed Jul 19 02:34:59 2000Image Type:   PowerPC Linux Kernel Image (gzip compressed)Data Size:    335725 Bytes = 327.86 kB = 0.32 MBLoad Address: 0x00000000Entry Point:  0x00000000To verify the contents of the image (or check for corruption):-> tools/mkimage -l examples/uImage.TQM850LImage Name:   2.4.4 kernel for TQM850LCreated:      Wed Jul 19 02:34:59 2000Image Type:   PowerPC Linux Kernel Image (gzip compressed)Data Size:    335725 Bytes = 327.86 kB = 0.32 MBLoad Address: 0x00000000Entry Point:  0x00000000NOTE: for embedded systems where boot time is critical you can tradespeed for memory and install an UNCOMPRESSED image instead: thisneeds more space in Flash, but boots much faster since it does notneed to be uncompressed:-> gunzip /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux.gz-> tools/mkimage -n '2.4.4 kernel for TQM850L' \> -A ppc -O linux -T kernel -C none -a 0 -e 0 \> -d /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux \> examples/uImage.TQM850L-uncompressedImage Name:   2.4.4 kernel for TQM850LCreated:      Wed Jul 19 02:34:59 2000Image Type:   PowerPC Linux Kernel Image (uncompressed)Data Size:    792160 Bytes = 773.59 kB = 0.76 MBLoad Address: 0x00000000Entry Point:  0x00000000Similar you can build U-Boot images from a 'ramdisk.image.gz' filewhen your kernel is intended to use an initial ramdisk:-> tools/mkimage -n 'Simple Ramdisk Image' \> -A ppc -O linux -T ramdisk -C gzip \> -d /LinuxPPC/images/SIMPLE-ramdisk.image.gz examples/simple-initrdImage Name:   Simple Ramdisk ImageCreated:      Wed Jan 12 14:01:50 2000Image Type:   PowerPC Linux RAMDisk Image (gzip compressed)Data Size:    566530 Bytes = 553.25 kB = 0.54 MBLoad Address: 0x00000000Entry Point:  0x00000000The "dumpimage" tool can be used to disassemble or list the contents of imagesbuilt by mkimage. See dumpimage's help output (-h) for details.Installing a Linux Image:-------------------------To downloading a U-Boot image over the serial (console) interface,you must convert the image to S-Record format:objcopy -I binary -O srec examples/image examples/image.srecThe 'objcopy' does not understand the information in the U-Bootimage header, so the resulting S-Record file will be relative toaddress 0x00000000. To load it to a given address, you need tospecify the target address as 'offset' parameter with the 'loads'command.Example: install the image to address 0x40100000 (which on theTQM8xxL is in the first Flash bank):=> erase 40100000 401FFFFF.......... doneErased 8 sectors=> loads 40100000## Ready for S-Record download ...~>examples/image.srec1 2 3 4 5 6 7 8 9 10 11 12 13 ......15989 15990 15991 15992[file transfer complete][connected]## Start Addr = 0x00000000You can check the success of the download using the 'iminfo' command;this includes a checksum verification so you can be sure no datacorruption happened:=> imi 40100000## Checking Image at 40100000 ...   Image Name: 2.2.13 for initrd on TQM850L   Image Type: PowerPC Linux Kernel Image (gzip compressed)   Data Size: 335725 Bytes = 327 kB = 0 MB   Load Address: 00000000   Entry Point: 0000000c   Verifying Checksum ... OKBoot Linux:-----------The "bootm" command is used to boot an application that is stored inmemory (RAM or Flash). In case of a Linux kernel image, the contentsof the "bootargs" environment variable is passed to the kernel asparameters. You can check and modify this variable using the"printenv" and "setenv" commands:=> printenv bootargsbootargs=root=/dev/ram=> setenv bootargs root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2=> printenv bootargsbootargs=root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2=> bootm 40020000## Booting Linux kernel at 40020000 ...   Image Name: 2.2.13 for NFS on TQM850L   Image Type: PowerPC Linux Kernel Image (gzip compressed)   Data Size: 381681 Bytes = 372 kB = 0 MB   Load Address: 00000000   Entry Point: 0000000c   Verifying Checksum ... OK   Uncompressing Kernel Image ... OKLinux version 2.2.13 (wd@denx.local.net) (gcc version 2.95.2 19991024 (release)) #1 Wed Jul 19 02:35:17 MEST 2000Boot arguments: root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2time_init: decrementer frequency = 187500000/60Calibrating delay loop... 49.77 BogoMIPSMemory: 15208k available (700k kernel code, 444k data, 32k init) [c0000000,c1000000]...If you want to boot a Linux kernel with initial RAM disk, you passthe memory addresses of both the kernel and the initrd image (PPBCOOTformat!) to the "bootm" command:=> imi 40100000 40200000## Checking Image at 40100000 ...   Image Name: 2.2.13 for initrd on TQM850L   Image Type: PowerPC Linux Kernel Image (gzip compressed)   Data Size: 335725 Bytes = 327 kB = 0 MB   Load Address: 00000000   Entry Point: 0000000c   Verifying Checksum ... OK## Checking Image at 40200000 ...   Image Name: Simple Ramdisk Image   Image Type: PowerPC Linux RAMDisk Image (gzip compressed)   Data Size: 566530 Bytes = 553 kB = 0 MB   Load Address: 00000000   Entry Point: 00000000   Verifying Checksum ... OK=> bootm 40100000 40200000## Booting Linux kernel at 40100000 ...   Image Name: 2.2.13 for initrd on TQM850L   Image Type: PowerPC Linux Kernel Image (gzip compressed)   Data Size: 335725 Bytes = 327 kB = 0 MB   Load Address: 00000000   Entry Point: 0000000c   Verifying Checksum ... OK   Uncompressing Kernel Image ... OK## Loading RAMDisk Image at 40200000 ...   Image Name: Simple Ramdisk Image   Image Type: PowerPC Linux RAMDisk Image (gzip compressed)   Data Size: 566530 Bytes = 553 kB = 0 MB   Load Address: 00000000   Entry Point: 00000000   Verifying Checksum ... OK   Loading Ramdisk ... OKLinux version 2.2.13 (wd@denx.local.net) (gcc version 2.95.2 19991024 (release)) #1 Wed Jul 19 02:32:08 MEST 2000Boot arguments: root=/dev/ramtime_init: decrementer frequency = 187500000/60Calibrating delay loop... 49.77 BogoMIPS...RAMDISK: Compressed image found at block 0VFS: Mounted root (ext2 filesystem).bash#Boot Linux and pass a flat device tree:-----------First, U-Boot must be compiled with the appropriate defines. See the sectiontitled "Linux Kernel Interface" above for a more in depth explanation. Thefollowing is an example of how to start a kernel and pass an updatedflat device tree:=> print oftaddroftaddr=0x300000=> print oftoft=oftrees/mpc8540ads.dtb=> tftp $oftaddr $oftSpeed: 1000, full duplexUsing TSEC0 deviceTFTP from server 192.168.1.1; our IP address is 192.168.1.101Filename 'oftrees/mpc8540ads.dtb'.Load address: 0x300000Loading: #doneBytes transferred = 4106 (100a hex)=> tftp $loadaddr $bootfileSpeed: 1000, full duplexUsing TSEC0 deviceTFTP from server 192.168.1.1; our IP address is 192.168.1.2Filename 'uImage'.Load address: 0x200000Loading:############doneBytes transferred = 1029407 (fb51f hex)=> print loadaddrloadaddr=200000=> print oftaddroftaddr=0x300000=> bootm $loadaddr - $oftaddr## Booting image at 00200000 ...   Image Name: Linux-2.6.17-dirty   Image Type: PowerPC Linux Kernel Image (gzip compressed)   Data Size: 1029343 Bytes = 1005.2 kB   Load Address: 00000000   Entry Point: 00000000   Verifying Checksum ... OK   Uncompressing Kernel Image ... OKBooting using flat device tree at 0x300000Using MPC85xx ADS machine descriptionMemory CAM mapping: CAM0=256Mb, CAM1=256Mb, CAM2=0Mb residual: 0Mb[snip]More About U-Boot Image Types:------------------------------U-Boot supports the following image types:   "Standalone Programs" are directly runnable in the environmentprovided by U-Boot; it is expected that (if they behavewell) you can continue to work in U-Boot after return fromthe Standalone Program.   "OS Kernel Images" are usually images of some Embedded OS whichwill take over control completely. Usually these programswill install their own set of exception handlers, devicedrivers, set up the MMU, etc. - this means, that you cannotexpect to re-enter U-Boot except by resetting the CPU.   "RAMDisk Images" are more or less just data blocks, and theirparameters (address, size) are passed to an OS kernel that isbeing started.   "Multi-File Images" contain several images, typically an OS(Linux) kernel image and one or more data images likeRAMDisks. This construct is useful for instance when you wantto boot over the network using BOOTP etc., where the bootserver provides just a single image file, but you want to getfor instance an OS kernel and a RAMDisk image."Multi-File Images" start with a list of image sizes, eachimage size (in bytes) specified by an "uint32_t" in networkbyte order. This list is terminated by an "(uint32_t)0".Immediately after the terminating 0 follow the images, one byone, all aligned on "uint32_t" boundaries (size rounded up toa multiple of 4 bytes).   "Firmware Images" are binary images containing firmware (likeU-Boot or FPGA images) which usually will be programmed toflash memory.   "Script files" are command sequences that will be executed byU-Boot's command interpreter; this feature is especiallyuseful when you configure U-Boot to use a real shell (hush)as command interpreter.Booting the Linux zImage:-------------------------On some platforms, it's possible to boot Linux zImage. This is doneusing the "bootz" command. The syntax of "bootz" command is the sameas the syntax of "bootm" command.Note, defining the CONFIG_SUPPORT_RAW_INITRD allows user to supplykernel with raw initrd images. The syntax is slightly different, theaddress of the initrd must be augmented by it's size, in the followingformat: "<initrd addres>:<initrd size>".Standalone HOWTO:=================One of the features of U-Boot is that you can dynamically load andrun "standalone" applications, which can use some resources ofU-Boot like console I/O functions or interrupt services.Two simple examples are included with the sources:"Hello World" Demo:-------------------'examples/hello_world.c' contains a small "Hello World" Demoapplication; it is automatically compiled when you build U-Boot.It's configured to run at address 0x00040004, so you can play with itlike that:=> loads## Ready for S-Record download ...~>examples/hello_world.srec1 2 3 4 5 6 7 8 9 10 11 ...[file transfer complete][connected]## Start Addr = 0x00040004=> go 40004 Hello World! This is a test.## Starting application at 0x00040004 ...Hello Worldargc = 7argv[0] = "40004"argv[1] = "Hello"argv[2] = "World!"argv[3] = "This"argv[4] = "is"argv[5] = "a"argv[6] = "test."argv[7] = "<NULL>"Hit any key to exit ...## Application terminated, rc = 0x0Another example, which demonstrates how to register a CPM interrupthandler with the U-Boot code, can be found in 'examples/timer.c'.Here, a CPM timer is set up to generate an interrupt every second.The interrupt service routine is trivial, just printing a '.'character, but this is just a demo program. The application can becontrolled by the following keys:? - print current values og the CPM Timer registersb - enable interrupts and start timere - stop timer and disable interruptsq - quit application=> loads## Ready for S-Record download ...~>examples/timer.srec1 2 3 4 5 6 7 8 9 10 11 ...[file transfer complete][connected]## Start Addr = 0x00040004=> go 40004## Starting application at 0x00040004 ...TIMERS=0xfff00980Using timer 1  tgcr @ 0xfff00980, tmr @ 0xfff00990, trr @ 0xfff00994, tcr @ 0xfff00998, tcn @ 0xfff0099c, ter @ 0xfff009b0Hit 'b':[q, b, e, ?] Set interval 1000000 usEnabling timerHit '?':[q, b, e, ?] ........tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0xef6, ter=0x0Hit '?':[q, b, e, ?] .tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x2ad4, ter=0x0Hit '?':[q, b, e, ?] .tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x1efc, ter=0x0Hit '?':[q, b, e, ?] .tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x169d, ter=0x0Hit 'e':[q, b, e, ?] ...Stopping timerHit 'q':[q, b, e, ?] ## Application terminated, rc = 0x0Minicom warning:================Over time, many people have reported problems when trying to use the"minicom" terminal emulation program for serial download. I (wd)consider minicom to be broken, and recommend not to use it. UnderUnix, I recommend to use C-Kermit for general purpose use (andespecially for kermit binary protocol download ("loadb" command), anduse "cu" for S-Record download ("loads" command).  Seehttps://www.denx.de/wiki/view/DULG/SystemSetup#Section_4.3.for help with kermit.Nevertheless, if you absolutely want to use it try adding thisconfiguration to your "File transfer protocols" section:   Name   ProgramName U/D FullScr IO-Red. MultiX  kermit  /usr/bin/kermit -i -l %l -s Y    U   Y   N  NY  kermit  /usr/bin/kermit -i -l %l -r N    D   Y   N  NNetBSD Notes:=============Starting at version 0.9.2, U-Boot supports NetBSD both as host(build U-Boot) and target system (boots NetBSD/mpc8xx).Building requires a cross environment; it is known to work onNetBSD/i386 with the cross-powerpc-netbsd-1.3 package (you will alsoneed gmake since the Makefiles are not compatible with BSD make).Note that the cross-powerpc package does not install include files;attempting to build U-Boot will fail because <machine/ansi.h> ismissing.  This file has to be installed and patched manually:# cd /usr/pkg/cross/powerpc-netbsd/include# mkdir powerpc# ln -s powerpc machine# cp /usr/src/sys/arch/powerpc/include/ansi.h powerpc/ansi.h# ${EDIT} powerpc/ansi.h## must remove __va_list, _BSD_VA_LISTNative builds *don't* work due to incompatibilities between nativeand U-Boot include files.Booting assumes that (the first part of) the image booted is astage-2 loader which in turn loads and then invokes the kernelproper. Loader sources will eventually appear in the NetBSD sourcetree (probably in sys/arc/mpc8xx/stand/u-boot_stage2/); in themeantime, see ftp://ftp.denx.de/pub/u-boot/ppcboot_stage2.tar.gzImplementation Internals:=========================The following is not intended to be a complete description of everyimplementation detail. However, it should help to understand theinner workings of U-Boot and make it easier to port it to customhardware.Initial Stack, Global Data:---------------------------The implementation of U-Boot is complicated by the fact that U-Bootstarts running out of ROM (flash memory), usually without access tosystem RAM (because the memory controller is not initialized yet).This means that we don't have writable Data or BSS segments, and BSSis not initialized as zero. To be able to get a C environment workingat all, we have to allocate at least a minimal stack. Implementationoptions for this are defined and restricted by the CPU used: Some CPUmodels provide on-chip memory (like the IMMR area on MPC8xx andMPC826x processors), on others (parts of) the data cache can belocked as (mis-) used as memory, etc.Chris Hallinan posted a good summary of these issues to theU-Boot mailing list:Subject: RE: [U-Boot-Users] RE: More On Memory Bank x (nothingness)?From: "Chris Hallinan" <clh@net1plus.com>Date: Mon, 10 Feb 2003 16:43:46 -0500 (22:43 MET)...Correct me if I'm wrong, folks, but the way I understand itis this: Using DCACHE as initial RAM for Stack, etc, does notrequire any physical RAM backing up the cache. The clevernessis that the cache is being used as a temporary supply ofnecessary storage before the SDRAM controller is setup. It'sbeyond the scope of this list to explain the details, but youcan see how this works by studying the cache architecture andoperation in the architecture and processor-specific manuals.OCM is On Chip Memory, which I believe the 405GP has 4K. Itis another option for the system designer to use as aninitial stack/RAM area prior to SDRAM being available. Eitheroption should work for you. Using CS 4 should be fine if yourboard designers haven't used it for something that wouldcause you grief during the initial boot! It is frequently notused.CONFIG_SYS_INIT_RAM_ADDR should be somewhere that won't interferewith your processor/board/system design. The default valueyou will find in any recent u-boot distribution inwalnut.h should work for you. I'd set it to a value largerthan your SDRAM module. If you have a 64MB SDRAM module, setit above 400_0000. Just make sure your board has no resourcesthat are supposed to respond to that address! That code instart.S has been around a while and should work as is whenyou get the config right.-Chris HallinanDS4.COM, Inc.It is essential to remember this, since it has some impact on the Ccode for the initialization procedures:* Initialized global data (data segment) is read-only. Do not attempt  to write it.* Do not use any uninitialized global data (or implicitly initialized  as zero data - BSS segment) at all - this is undefined, initiali-  zation is performed later (when relocating to RAM).* Stack space is very limited. Avoid big data buffers or things like  that.Having only the stack as writable memory limits means we cannot usenormal global data to share information between the code. But itturned out that the implementation of U-Boot can be greatlysimplified by making a global data structure (gd_t) available to allfunctions. We could pass a pointer to this data as argument to _all_functions, but this would bloat the code. Instead we use a feature ofthe GCC compiler (Global Register Variables) to share the data: weplace a pointer (gd) to the global data into a register which wereserve for this purpose.When choosing a register for such a purpose we are restricted by therelevant  (E)ABI  specifications for the current architecture, and byGCC's implementation.For PowerPC, the following registers have specific use:R1:stack pointerR2:reserved for system useR3-R4:parameter passing and return valuesR5-R10: parameter passingR13:small data area pointerR30:GOT pointerR31:frame pointer(U-Boot also uses R12 as internal GOT pointer. r12is a volatile register so r12 needs to be reset whengoing back and forth between asm and C)    ==> U-Boot will use R2 to hold a pointer to the global data    Note: on PPC, we could use a static initializer (since the    address of the global data structure is known at compile time),    but it turned out that reserving a register results in somewhat    smaller code - although the code savings are not that big (on    average for all boards 752 bytes for the whole U-Boot image,    624 text + 127 data).On ARM, the following registers are used:R0:function argument word/integer resultR1-R3:function argument wordR9:platform specificR10:stack limit (used only if stack checking is enabled)R11:argument (frame) pointerR12:temporary workspaceR13:stack pointerR14:link registerR15:program counter    ==> U-Boot will use R9 to hold a pointer to the global data    Note: on ARM, only R_ARM_RELATIVE relocations are supported.On Nios II, the ABI is documented here:https://www.altera.com/literature/hb/nios2/n2cpu_nii51016.pdf    ==> U-Boot will use gp to hold a pointer to the global data    Note: on Nios II, we give "-G0" option to gcc and don't use gp    to access small data sections, so gp is free.On NDS32, the following registers are used:R0-R1:argument/returnR2-R5:argumentR15:temporary register for assemblerR16:trampoline registerR28:frame pointer (FP)R29:global pointer (GP)R30:link register (LP)R31:stack pointer (SP)PC:program counter (PC)    ==> U-Boot will use R10 to hold a pointer to the global dataNOTE: DECLARE_GLOBAL_DATA_PTR must be used with file-global scope,or current versions of GCC may "optimize" the code too much.On RISC-V, the following registers are used:x0: hard-wired zero (zero)x1: return address (ra)x2:stack pointer (sp)x3:global pointer (gp)x4:thread pointer (tp)x5:link register (t0)x8:frame pointer (fp)x10-x11:arguments/return values (a0-1)x12-x17:arguments (a2-7)x28-31: temporaries (t3-6)pc:program counter (pc)    ==> U-Boot will use gp to hold a pointer to the global dataMemory Management:------------------U-Boot runs in system state and uses physical addresses, i.e. theMMU is not used either for address mapping nor for memory protection.The available memory is mapped to fixed addresses using the memorycontroller. In this process, a contiguous block is formed for eachmemory type (Flash, SDRAM, SRAM), even when it consists of severalphysical memory banks.U-Boot is installed in the first 128 kB of the first Flash bank (onTQM8xxL modules this is the range 0x40000000 ... 0x4001FFFF). Afterbooting and sizing and initializing DRAM, the code relocates itselfto the upper end of DRAM. Immediately below the U-Boot code somememory is reserved for use by malloc() [see CONFIG_SYS_MALLOC_LENconfiguration setting]. Below that, a structure with global BoardInfo data is placed, followed by the stack (growing downward).Additionally, some exception handler code is copied to the low 8 kBof DRAM (0x00000000 ... 0x00001FFF).So a typical memory configuration with 16 MB of DRAM could look likethis:0x0000 0000Exception Vector code      :0x0000 1FFF0x0000 2000Free for Application Use      :      :      :      :0x00FB FF20Monitor Stack (Growing downward)0x00FB FFACBoard Info Data and permanent copy of global data0x00FC 0000Malloc Arena      :0x00FD FFFF0x00FE 0000RAM Copy of Monitor Code...eventually: LCD or video framebuffer...eventually: pRAM (Protected RAM - unchanged by reset)0x00FF FFFF[End of RAM]System Initialization:----------------------In the reset configuration, U-Boot starts at the reset entry point(on most PowerPC systems at address 0x00000100). Because of the resetconfiguration for CS0# this is a mirror of the on board Flash memory.To be able to re-map memory U-Boot then jumps to its link address.To be able to implement the initialization code in C, a (small!)initial stack is set up in the internal Dual Ported RAM (in case CPUswhich provide such a feature like), or in a locked part of the datacache. After that, U-Boot initializes the CPU core, the caches andthe SIU.Next, all (potentially) available memory banks are mapped using apreliminary mapping. For example, we put them on 512 MB boundaries(multiples of 0x20000000: SDRAM on 0x00000000 and 0x20000000, Flashon 0x40000000 and 0x60000000, SRAM on 0x80000000). Then UPM A isprogrammed for SDRAM access. Using the temporary configuration, asimple memory test is run that determines the size of the SDRAMbanks.When there is more than one SDRAM bank, and the banks are ofdifferent size, the largest is mapped first. For equal size, the firstbank (CS2#) is mapped first. The first mapping is always for address0x00000000, with any additional banks following immediately to createcontiguous memory starting from 0.Then, the monitor installs itself at the upper end of the SDRAM areaand allocates memory for use by malloc() and for the global BoardInfo data; also, the exception vector code is copied to the low RAMpages, and the final stack is set up.Only after this relocation will you have a "normal" C environment;until that you are restricted in several ways, mostly because you arerunning from ROM, and because the code will have to be relocated to anew address in RAM.U-Boot Porting Guide:----------------------[Based on messages by Jerry Van Baren in the U-Boot-Users mailinglist, October 2002]int main(int argc, char *argv[]){sighandler_t no_more_time;signal(SIGALRM, no_more_time);alarm(PROJECT_DEADLINE - toSec (3 * WEEK));if (available_money > available_manpower) {Pay consultant to port U-Boot;return 0;}Download latest U-Boot source;Subscribe to u-boot mailing list;if (clueless)email("Hi, I am new to U-Boot, how do I get started?");while (learning) {Read the README file in the top level directory;Readhttps://www.denx.de/wiki/bin/view/DULG/Manual;Read applicable doc/README.*;Read the source, Luke;/* find . -name "*.[chS]" | xargs grep -i <keyword> */}if (available_money > toLocalCurrency ($2500))Buy a BDI3000;elseAdd a lot of aggravation and time;if (a similar board exists) {/* hopefully... */cp -a board/<similar> board/<myboard>cp include/configs/<similar>.h include/configs/<myboard>.h} else {Create your own board support subdirectory;Create your own board include/configs/<myboard>.h file;}Edit new board/<myboard> filesEdit new include/configs/<myboard>.hwhile (!accepted) {while (!running) {do {Add / modify source code;} until (compiles);Debug;if (clueless)email("Hi, I am having problems...");}Send patch file to the U-Boot email list;if (reasonable critiques)Incorporate improvements from email list code review;elseDefend code as written;}return 0;}void no_more_time (int sig){      hire_a_guru();}Coding Standards:-----------------All contributions to U-Boot should conform to the Linux kernelcoding style; see the kernel coding style guide athttps://www.kernel.org/doc/html/latest/process/coding-style.html, and thescript "scripts/Lindent" in your Linux kernel source directory.Source files originating from a different project (for example theMTD subsystem) are generally exempt from these guidelines and are notreformatted to ease subsequent migration to newer versions of thosesources.Please note that U-Boot is implemented in C (and to some small parts inAssembler); no C++ is used, so please do not use C++ style comments (//)in your code.Please also stick to the following formatting rules:- remove any trailing white space- use TAB characters for indentation and vertical alignment, not spaces- make sure NOT to use DOS '\r\n' line feeds- do not add more than 2 consecutive empty lines to source files- do not add trailing empty lines to source filesSubmissions which do not conform to the standards may be returnedwith a request to reformat the changes.Submitting Patches:-------------------Since the number of patches for U-Boot is growing, we need toestablish some rules. Submissions which do not conform to these rulesmay be rejected, even when they contain important and valuable stuff.Please seehttps://www.denx.de/wiki/U-Boot/Patches for details.Patches shall be sent to the u-boot mailing list <u-boot@lists.denx.de>;seehttps://lists.denx.de/listinfo/u-bootWhen you send a patch, please include the following information withit:* For bug fixes: a description of the bug and how your patch fixes  this bug. Please try to include a way of demonstrating that the  patch actually fixes something.* For new features: a description of the feature and your  implementation.* For major contributions, add a MAINTAINERS file with your  information and associated file and directory references.* When you add support for a new board, don't forget to add a  maintainer e-mail address to the boards.cfg file, too.* If your patch adds new configuration options, don't forget to  document these in the README file.* The patch itself. If you are using git (which is *strongly*  recommended) you can easily generate the patch using the  "git format-patch". If you then use "git send-email" to send it to  the U-Boot mailing list, you will avoid most of the common problems  with some other mail clients.  If you cannot use git, use "diff -purN OLD NEW". If your version of  diff does not support these options, then get the latest version of  GNU diff.  The current directory when running this command shall be the parent  directory of the U-Boot source tree (i. e. please make sure that  your patch includes sufficient directory information for the  affected files).  We prefer patches as plain text. MIME attachments are discouraged,  and compressed attachments must not be used.* If one logical set of modifications affects or creates several  files, all these changes shall be submitted in a SINGLE patch file.* Changesets that contain different, unrelated modifications shall be  submitted as SEPARATE patches, one patch per changeset.Notes:* Before sending the patch, run the buildman script on your patched  source tree and make sure that no errors or warnings are reported  for any of the boards.* Keep your modifications to the necessary minimum: A patch  containing several unrelated changes or arbitrary reformats will be  returned with a request to re-formatting / split it.* If you modify existing code, make sure that your new code does not  add to the memory footprint of the code ;-) Small is beautiful!  When adding new features, these should compile conditionally only  (using #ifdef), and the resulting code with the new feature  disabled must not need more memory than the old code without your  modification.* Remember that there is a size limit of 100 kB per message on the  u-boot mailing list. Bigger patches will be moderated. If they are  reasonable and not too big, they will be acknowledged. But patches  bigger than the size limit should be avoided.