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-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 ciruit 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
-