spi_butterfly - parport-to-butterfly adapter driver¶
This is a hardware and software project that includes building and usinga parallel port adapter cable, together with an “AVR Butterfly” to runfirmware for user interfacing and/or sensors. A Butterfly is a $US20battery powered card with an AVR microcontroller and lots of goodies:sensors, LCD, flash, toggle stick, and more. You can use AVR-GCC todevelop firmware for this, and flash it using this adapter cable.
You can make this adapter from an old printer cable and solder thingsdirectly to the Butterfly. Or (if you have the parts and skills) youcan come up with something fancier, providing ciruit protection to theButterfly and the printer port, or with a better power supply than twosignal pins from the printer port. Or for that matter, you can usesimilar cables to talk to many AVR boards, even a breadboard.
This is more powerful than “ISP programming” cables since it lets kernelSPI protocol drivers interact with the AVR, and could even let the AVRissue interrupts to them. Later, your protocol driver should workeasily with a “real SPI controller”, instead of this bitbanger.
The first cable connections will hook Linux up to one SPI bus, with theAVR and a DataFlash chip; and to the AVR reset line. This is all youneed to reflash the firmware, and the pins are the standard Atmel “ISP”connector pins (used also on non-Butterfly AVR boards). On the parportside this is like “sp12” programming cables.
Signal Butterfly Parport (DB-25) SCK J403.PB1/SCK pin 2/D0 RESET J403.nRST pin 3/D1 VCC J403.VCC_EXT pin 8/D6 MOSI J403.PB2/MOSI pin 9/D7 MISO J403.PB3/MISO pin 11/S7,nBUSY GND J403.GND pin 23/GND
Then to let Linux master that bus to talk to the DataFlash chip, you must(a) flash new firmware that disables SPI (set PRR.2, and disable pullupsby clearing PORTB.[0-3]); (b) configure the mtd_dataflash driver; and(c) cable in the chipselect.
Signal Butterfly Parport (DB-25) VCC J400.VCC_EXT pin 7/D5 SELECT J400.PB0/nSS pin 17/C3,nSELECT GND J400.GND pin 24/GND
Or you could flash firmware making the AVR into an SPI slave (keeping theDataFlash in reset) and tweak the spi_butterfly driver to make it bind tothe driver for your custom SPI-based protocol.
The “USI” controller, using J405, can also be used for a second SPI bus.That would let you talk to the AVR using custom SPI-with-USI firmware,while letting either Linux or the AVR use the DataFlash. There are plentyof spare parport pins to wire this one up, such as:
Signal Butterfly Parport (DB-25) SCK J403.PE4/USCK pin 5/D3 MOSI J403.PE5/DI pin 6/D4 MISO J403.PE6/DO pin 12/S5,nPAPEROUT GND J403.GND pin 22/GND IRQ J402.PF4 pin 10/S6,ACK GND J402.GND(P2) pin 25/GND