0001 ===================================================
0002 spi_butterfly - parport-to-butterfly adapter driver
0003 ===================================================
0004
0005 This is a hardware and software project that includes building and using
0006 a parallel port adapter cable, together with an "AVR Butterfly" to run
0007 firmware for user interfacing and/or sensors. A Butterfly is a $US20
0008 battery powered card with an AVR microcontroller and lots of goodies:
0009 sensors, LCD, flash, toggle stick, and more. You can use AVR-GCC to
0010 develop firmware for this, and flash it using this adapter cable.
0011
0012 You can make this adapter from an old printer cable and solder things
0013 directly to the Butterfly. Or (if you have the parts and skills) you
0014 can come up with something fancier, providing circuit protection to the
0015 Butterfly and the printer port, or with a better power supply than two
0016 signal pins from the printer port. Or for that matter, you can use
0017 similar cables to talk to many AVR boards, even a breadboard.
0018
0019 This is more powerful than "ISP programming" cables since it lets kernel
0020 SPI protocol drivers interact with the AVR, and could even let the AVR
0021 issue interrupts to them. Later, your protocol driver should work
0022 easily with a "real SPI controller", instead of this bitbanger.
0023
0024
0025 The first cable connections will hook Linux up to one SPI bus, with the
0026 AVR and a DataFlash chip; and to the AVR reset line. This is all you
0027 need to reflash the firmware, and the pins are the standard Atmel "ISP"
0028 connector pins (used also on non-Butterfly AVR boards). On the parport
0029 side this is like "sp12" programming cables.
0030
0031 ====== ============= ===================
0032 Signal Butterfly Parport (DB-25)
0033 ====== ============= ===================
0034 SCK J403.PB1/SCK pin 2/D0
0035 RESET J403.nRST pin 3/D1
0036 VCC J403.VCC_EXT pin 8/D6
0037 MOSI J403.PB2/MOSI pin 9/D7
0038 MISO J403.PB3/MISO pin 11/S7,nBUSY
0039 GND J403.GND pin 23/GND
0040 ====== ============= ===================
0041
0042 Then to let Linux master that bus to talk to the DataFlash chip, you must
0043 (a) flash new firmware that disables SPI (set PRR.2, and disable pullups
0044 by clearing PORTB.[0-3]); (b) configure the mtd_dataflash driver; and
0045 (c) cable in the chipselect.
0046
0047 ====== ============ ===================
0048 Signal Butterfly Parport (DB-25)
0049 ====== ============ ===================
0050 VCC J400.VCC_EXT pin 7/D5
0051 SELECT J400.PB0/nSS pin 17/C3,nSELECT
0052 GND J400.GND pin 24/GND
0053 ====== ============ ===================
0054
0055 Or you could flash firmware making the AVR into an SPI slave (keeping the
0056 DataFlash in reset) and tweak the spi_butterfly driver to make it bind to
0057 the driver for your custom SPI-based protocol.
0058
0059 The "USI" controller, using J405, can also be used for a second SPI bus.
0060 That would let you talk to the AVR using custom SPI-with-USI firmware,
0061 while letting either Linux or the AVR use the DataFlash. There are plenty
0062 of spare parport pins to wire this one up, such as:
0063
0064 ====== ============= ===================
0065 Signal Butterfly Parport (DB-25)
0066 ====== ============= ===================
0067 SCK J403.PE4/USCK pin 5/D3
0068 MOSI J403.PE5/DI pin 6/D4
0069 MISO J403.PE6/DO pin 12/S5,nPAPEROUT
0070 GND J403.GND pin 22/GND
0071
0072 IRQ J402.PF4 pin 10/S6,ACK
0073 GND J402.GND(P2) pin 25/GND
0074 ====== ============= ===================
