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diff --git a/Documentation/spi/butterfly.rst b/Documentation/spi/butterfly.rst new file mode 100644 index 000000000000..56088fb090c7 --- /dev/null +++ b/Documentation/spi/butterfly.rst @@ -0,0 +1,74 @@ +=================================================== +spi_butterfly - parport-to-butterfly adapter driver +=================================================== + +This is a hardware and software project that includes building and using +a parallel port adapter cable, together with an "AVR Butterfly" to run +firmware for user interfacing and/or sensors. A Butterfly is a $US20 +battery powered card with an AVR microcontroller and lots of goodies: +sensors, LCD, flash, toggle stick, and more. You can use AVR-GCC to +develop firmware for this, and flash it using this adapter cable. + +You can make this adapter from an old printer cable and solder things +directly to the Butterfly. Or (if you have the parts and skills) you +can come up with something fancier, providing circuit protection to the +Butterfly and the printer port, or with a better power supply than two +signal pins from the printer port. Or for that matter, you can use +similar cables to talk to many AVR boards, even a breadboard. + +This is more powerful than "ISP programming" cables since it lets kernel +SPI protocol drivers interact with the AVR, and could even let the AVR +issue interrupts to them. Later, your protocol driver should work +easily with a "real SPI controller", instead of this bitbanger. + + +The first cable connections will hook Linux up to one SPI bus, with the +AVR and a DataFlash chip; and to the AVR reset line. This is all you +need to reflash the firmware, and the pins are the standard Atmel "ISP" +connector pins (used also on non-Butterfly AVR boards). On the parport +side 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 pullups +by 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 the +DataFlash in reset) and tweak the spi_butterfly driver to make it bind to +the 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 plenty +of 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 + ====== ============= =================== |