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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.
+
+
+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).
+
+        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
+
+The "USI" controller, using J405, can be used for a second SPI bus.  That
+would let you talk to the AVR over SPI, running firmware that makes it act
+as an SPI slave, 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
+