W1: Dallas’ 1-wire bus

Author:

David Fries

W1 API internal to the kernel

include/linux/w1.h

W1 kernel API functions.

structw1_reg_num

broken out slave device id

Definition:

struct w1_reg_num {#if defined(__LITTLE_ENDIAN_BITFIELD);    __u64 family:8, id:48, crc:8;#elif defined(__BIG_ENDIAN_BITFIELD);    __u64 crc:8, id:48, family:8;#else;#error "Please fix <asm/byteorder.h>";#endif;};

Members

family

identifies the type of device

id

along with family is the unique device id

crc

checksum of the other bytes

crc

checksum of the other bytes

id

along with family is the unique device id

family

identifies the type of device

structw1_slave

holds a single slave device on the bus

Definition:

struct w1_slave {    struct module           *owner;    unsigned char           name[W1_MAXNAMELEN];    struct list_head        w1_slave_entry;    struct w1_reg_num       reg_num;    atomic_t refcnt;    int ttl;    unsigned long           flags;    struct w1_master        *master;    struct w1_family        *family;    void *family_data;    struct device           dev;    struct device           *hwmon;};

Members

owner

Points to the one wire “wire” kernel module.

name

Device id is ascii.

w1_slave_entry

data for the linked list

reg_num

the slave id in binary

refcnt

reference count, delete when 0

ttl

decrement per search this slave isn’t found, deatch at 0

flags

bit flags for W1_SLAVE_ACTIVE W1_SLAVE_DETACH

master

bus which this slave is on

family

module for device family type

family_data

pointer for use by the family module

dev

kernel device identifier

hwmon

pointer to hwmon device

structw1_bus_master

operations available on a bus master

Definition:

struct w1_bus_master {    void *data;    u8 (*read_bit)(void *);    void (*write_bit)(void *, u8);    u8 (*touch_bit)(void *, u8);    u8 (*read_byte)(void *);    void (*write_byte)(void *, u8);    u8 (*read_block)(void *, u8 *, int);    void (*write_block)(void *, const u8 *, int);    u8 (*triplet)(void *, u8);    u8 (*reset_bus)(void *);    u8 (*set_pullup)(void *, int);    void (*search)(void *, struct w1_master *, u8, w1_slave_found_callback);    char *dev_id;};

Members

data

the first parameter in all the functions below

read_bit

Sample the line levelreturn the level read (0 or 1)

write_bit

Sets the line level

touch_bit

the lowest-level function for devices that really support the1-wire protocol.touch_bit(0) = write-0 cycletouch_bit(1) = write-1 / read cyclereturn the bit read (0 or 1)

read_byte

Reads a byte. Same as 8 touch_bit(1) calls.return the byte read

write_byte

Writes a byte. Same as 8 touch_bit(x) calls.

read_block

Same as a series ofread_byte() callsreturn the number of bytes read

write_block

Same as a series ofwrite_byte() calls

triplet

Combines two reads and a smart write for ROM searchesreturn bit0=Id bit1=comp_id bit2=dir_taken

reset_bus

long write-0 with a read for the presence pulse detectionreturn -1=Error, 0=Device present, 1=No device present

set_pullup

Put out a strong pull-up pulse of the specified duration.return -1=Error, 0=completed

search

Really nice hardware can handle the different types of ROM searchw1_master* is passed to the slave found callback.u8 is search_type, W1_SEARCH or W1_ALARM_SEARCH

dev_id

Optional device id string, which w1 slaves could use forcreating names, which then give a connection to the w1 master

Note

read_bit and write_bit are very low level functions and should onlybe used with hardware that doesn’t really support 1-wire operations,like a parallel/serial port.Either define read_bit and write_bit OR define, at minimum, touch_bit andreset_bus.

enumw1_master_flags

bitfields used in w1_master.flags

Constants

W1_ABORT_SEARCH

abort searching early on shutdown

W1_WARN_MAX_COUNT

limit warning when the maximum count is reached

structw1_master

one per bus master

Definition:

struct w1_master {    struct list_head        w1_master_entry;    struct module           *owner;    unsigned char           name[W1_MAXNAMELEN];    struct mutex            list_mutex;    struct list_head        slist;    struct list_head        async_list;    int max_slave_count, slave_count;    unsigned long           attempts;    int slave_ttl;    int initialized;    u32 id;    int search_count;    u64 search_id;    atomic_t refcnt;    void *priv;    int enable_pullup;    int pullup_duration;    long flags;    struct task_struct      *thread;    struct mutex            mutex;    struct mutex            bus_mutex;    struct device_driver    *driver;    struct device           dev;    struct w1_bus_master    *bus_master;    u32 seq;};

Members

w1_master_entry

master linked list

owner

module owner

name

dynamically allocate bus name

list_mutex

protect slist and async_list

slist

linked list of slaves

async_list

linked list of netlink commands to execute

max_slave_count

maximum number of slaves to search for at a time

slave_count

current number of slaves known

attempts

number of searches ran

slave_ttl

number of searches before a slave is timed out

initialized

prevent init/removal race conditions

id

w1 bus number

search_count

number of automatic searches to run, -1 unlimited

search_id

allows continuing a search

refcnt

reference count

priv

private data storage

enable_pullup

allows a strong pullup

pullup_duration

time for the next strong pullup

flags

one of w1_master_flags

thread

thread for bus search and netlink commands

mutex

protect most of w1_master

bus_mutex

pretect concurrent bus access

driver

sysfs driver

dev

sysfs device

bus_master

io operations available

seq

sequence number used for netlink broadcasts

structw1_family_ops

operations for a family type

Definition:

struct w1_family_ops {    int (*add_slave)(struct w1_slave *sl);    void (*remove_slave)(struct w1_slave *sl);    const struct attribute_group **groups;    const struct hwmon_chip_info *chip_info;};

Members

add_slave

add_slave

remove_slave

remove_slave

groups

sysfs group

chip_info

pointer tostructhwmon_chip_info

structw1_family

reference counted family structure.

Definition:

struct w1_family {    struct list_head        family_entry;    u8 fid;    const struct w1_family_ops *fops;    const struct of_device_id *of_match_table;    atomic_t refcnt;};

Members

family_entry

family linked list

fid

8 bit family identifier

fops

operations for this family

of_match_table

open firmware match table

refcnt

reference counter

module_w1_family

module_w1_family(__w1_family)

Helper macro for registering a 1-Wire families

Parameters

__w1_family

w1_family struct

Description

Helper macro for 1-Wire families which do not do anything special in moduleinit/exit. This eliminates a lot of boilerplate. Each module may onlyuse this macro once, and calling it replacesmodule_init() andmodule_exit()

drivers/w1/w1.c

W1 core functions.

voidw1_search(structw1_master*dev,u8search_type,w1_slave_found_callbackcb)

Performs a ROM Search & registers any devices found.

Parameters

structw1_master*dev

The master device to search

u8search_type

W1_SEARCH to search all devices, or W1_ALARM_SEARCHto return only devices in the alarmed state

w1_slave_found_callbackcb

Function to call when a device is found

Description

The 1-wire search is a simple binary tree search.For each bit of the address, we read two bits and write one bit.The bit written will put to sleep all devies that don’t match that bit.When the two reads differ, the direction choice is obvious.When both bits are 0, we must choose a path to take.When we can scan all 64 bits without having to choose a path, we are done.

See “Application note 187 1-wire search algorithm” at www.maxim-ic.com

intw1_process_callbacks(structw1_master*dev)

execute each dev->async_list callback entry

Parameters

structw1_master*dev

w1_master device

Description

The w1 master list_mutex must be held.

Return

1 if there were commands to executed 0 otherwise

drivers/w1/w1_family.c

Allows registering device family operations.

intw1_register_family(structw1_family*newf)

register a device family driver

Parameters

structw1_family*newf

family to register

voidw1_unregister_family(structw1_family*fent)

unregister a device family driver

Parameters

structw1_family*fent

family to unregister

drivers/w1/w1_internal.h

W1 internal initialization for master devices.

structw1_async_cmd

execute callback from the w1_process kthread

Definition:

struct w1_async_cmd {    struct list_head        async_entry;    void (*cb)(struct w1_master *dev, struct w1_async_cmd *async_cmd);};

Members

async_entry

link entry

cb

callback function, must list_del and destroy this list beforereturning

Description

When inserted into the w1_master async_list, w1_process will executethe callback. Embed this into the structure with the command details.

drivers/w1/w1_int.c

W1 internal initialization for master devices.

intw1_add_master_device(structw1_bus_master*master)

registers a new master device

Parameters

structw1_bus_master*master

master bus device to register

voidw1_remove_master_device(structw1_bus_master*bm)

unregister a master device

Parameters

structw1_bus_master*bm

master bus device to remove

drivers/w1/w1_netlink.h

W1 external netlink API structures and commands.

enumw1_cn_msg_flags

bitfield flags forstructcn_msg.flags

Constants

W1_CN_BUNDLE

Request bundling replies into fewer messagse. Be preparedto handle multiplestructcn_msg,structw1_netlink_msg, andstructw1_netlink_cmd in one packet.

enumw1_netlink_message_types

message type

Constants

W1_SLAVE_ADD

notification that a slave device was added

W1_SLAVE_REMOVE

notification that a slave device was removed

W1_MASTER_ADD

notification that a new bus master was added

W1_MASTER_REMOVE

notification that a bus masterwas removed

W1_MASTER_CMD

initiate operations on a specific master

W1_SLAVE_CMD

sends reset, selects the slave, then does a read/write/touchoperation

W1_LIST_MASTERS

used to determine the bus master identifiers

structw1_netlink_msg

holds w1 message type, id, and result

Definition:

struct w1_netlink_msg {    __u8 type;    __u8 status;    __u16 len;    union {        __u8 id[8];        struct w1_mst {            __u32 id;            __u32 res;        } mst;    } id;    __u8 data[];};

Members

type

one ofenumw1_netlink_message_types

status

kernel feedback for success 0 or errno failure value

len

length of data following w1_netlink_msg

id

unionholding bus master id (msg.id) and slave device id (id[8]).

id.id

Slave ID (8 bytes)

id.mst

bus master identification

id.mst.id

bus master ID

id.mst.res

bus master reserved

data

start address of any following data

Description

The base message structure for w1 messages over netlink.The netlink connector data sequence is,structnlmsghdr,structcn_msg,then one or morestructw1_netlink_msg (each with optional data).

enumw1_commands

commands available for master or slave operations

Constants

W1_CMD_READ

read len bytes

W1_CMD_WRITE

write len bytes

W1_CMD_SEARCH

initiate a standard search, returns only the slavedevices found during that search

W1_CMD_ALARM_SEARCH

search for devices that are currently alarming

W1_CMD_TOUCH

Touches a series of bytes.

W1_CMD_RESET

sends a bus reset on the given master

W1_CMD_SLAVE_ADD

adds a slave to the given master,8 byte slave id at data[0]

W1_CMD_SLAVE_REMOVE

removes a slave to the given master,8 byte slave id at data[0]

W1_CMD_LIST_SLAVES

list of slaves registered on this master

W1_CMD_MAX

number of available commands

structw1_netlink_cmd

holds the command and data

Definition:

struct w1_netlink_cmd {    __u8 cmd;    __u8 res;    __u16 len;    __u8 data[];};

Members

cmd

one ofenumw1_commands

res

reserved

len

length of data following w1_netlink_cmd

data

start address of any following data

Description

One or morestructw1_netlink_cmd is placed starting at w1_netlink_msg.dataeach with optional data.

drivers/w1/w1_io.c

W1 input/output.

u8w1_touch_bit(structw1_master*dev,intbit)

Generates a write-0 or write-1 cycle and samples the level.

Parameters

structw1_master*dev

the master device

intbit

0 - write a 0, 1 - write a 0 read the level

voidw1_write_8(structw1_master*dev,u8byte)

Writes 8 bits.

Parameters

structw1_master*dev

the master device

u8byte

the byte to write

u8w1_triplet(structw1_master*dev,intbdir)

  • Does a triplet - used for searching ROM addresses.

Parameters

structw1_master*dev

the master device

intbdir

the bit to write if both id_bit and comp_bit are 0

Description

Return bits:

bit 0 = id_bitbit 1 = comp_bitbit 2 = dir_taken

If both bits 0 & 1 are set, the search should be restarted.

Return

bit fields - see above

u8w1_read_8(structw1_master*dev)

Reads 8 bits.

Parameters

structw1_master*dev

the master device

Return

the byte read

voidw1_write_block(structw1_master*dev,constu8*buf,intlen)

Writes a series of bytes.

Parameters

structw1_master*dev

the master device

constu8*buf

pointer to the data to write

intlen

the number of bytes to write

voidw1_touch_block(structw1_master*dev,u8*buf,intlen)

Touches a series of bytes.

Parameters

structw1_master*dev

the master device

u8*buf

pointer to the data to write

intlen

the number of bytes to write

u8w1_read_block(structw1_master*dev,u8*buf,intlen)

Reads a series of bytes.

Parameters

structw1_master*dev

the master device

u8*buf

pointer to the buffer to fill

intlen

the number of bytes to read

Return

the number of bytes read

intw1_reset_bus(structw1_master*dev)

Issues a reset bus sequence.

Parameters

structw1_master*dev

the master device

Return

0=Device present, 1=No device present or error

intw1_reset_select_slave(structw1_slave*sl)

reset and select a slave

Parameters

structw1_slave*sl

the slave to select

Description

Resets the bus and then selects the slave by sending either a skip romor a rom match. A skip rom is issued if there is only one deviceregistered on the bus.The w1 master lock must be held.

Return

0=success, anything else=error

intw1_reset_resume_command(structw1_master*dev)

resume instead of another match ROM

Parameters

structw1_master*dev

the master device

Description

When the workflow with a slave amongst many requires severalsuccessive commands a reset between each, this function is similarto doing a reset then a match ROM for the last matched ROM. Theadvantage being that the matched ROM step is skipped in favor of theresume command. The slave must support the command of course.

If the bus has only one slave, traditionnaly the match ROM is skippedand a “SKIP ROM” is done for efficiency. On multi-slave busses, thisdoesn’t work of course, but the resume command is the next best thing.

The w1 master lock must be held.

voidw1_next_pullup(structw1_master*dev,intdelay)

register for a strong pullup

Parameters

structw1_master*dev

the master device

intdelay

time in milliseconds

Description

Put out a strong pull-up of the specified duration after the next writeoperation. Not all hardware supports strong pullups. Hardware thatdoesn’t support strong pullups will sleep for the given time after thewrite operation without a strong pullup. This is a one shot request forthe next write, specifying zero will clear a previous request.The w1 master lock must be held.

Return

0=success, anything else=error

voidw1_write_bit(structw1_master*dev,intbit)

Generates a write-0 or write-1 cycle.

Parameters

structw1_master*dev

the master device

intbit

bit to write

Description

Only call if dev->bus_master->touch_bit is NULL

voidw1_pre_write(structw1_master*dev)

pre-write operations

Parameters

structw1_master*dev

the master device

Description

Pre-write operation, currently only supporting strong pullups.Program the hardware for a strong pullup, if one has been requested andthe hardware supports it.

voidw1_post_write(structw1_master*dev)

post-write options

Parameters

structw1_master*dev

the master device

Description

Post-write operation, currently only supporting strong pullups.If a strong pullup was requested, clear it if the hardware supportsthem, or execute the delay otherwise, in either case clear the request.

u8w1_read_bit(structw1_master*dev)

Generates a write-1 cycle and samples the level.

Parameters

structw1_master*dev

the master device

Description

Only call if dev->bus_master->touch_bit is NULL