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#! | 68 lines | 55 code | 13 blank | 0 comment | 0 complexity | 3ef825da35f6becd5dbae1fba51f7a39 MD5 | raw file
Possible License(s): GPL-2.0, LGPL-2.0, AGPL-1.0
 1spi_butterfly - parport-to-butterfly adapter driver
 4This is a hardware and software project that includes building and using
 5a parallel port adapter cable, together with an "AVR Butterfly" to run
 6firmware for user interfacing and/or sensors.  A Butterfly is a $US20
 7battery powered card with an AVR microcontroller and lots of goodies:
 8sensors, LCD, flash, toggle stick, and more.  You can use AVR-GCC to
 9develop firmware for this, and flash it using this adapter cable.
11You can make this adapter from an old printer cable and solder things
12directly to the Butterfly.  Or (if you have the parts and skills) you
13can come up with something fancier, providing ciruit protection to the
14Butterfly and the printer port, or with a better power supply than two
15signal pins from the printer port.  Or for that matter, you can use
16similar cables to talk to many AVR boards, even a breadboard.
18This is more powerful than "ISP programming" cables since it lets kernel
19SPI protocol drivers interact with the AVR, and could even let the AVR
20issue interrupts to them.  Later, your protocol driver should work
21easily with a "real SPI controller", instead of this bitbanger.
24The first cable connections will hook Linux up to one SPI bus, with the
25AVR and a DataFlash chip; and to the AVR reset line.  This is all you
26need to reflash the firmware, and the pins are the standard Atmel "ISP"
27connector pins (used also on non-Butterfly AVR boards).  On the parport
28side this is like "sp12" programming cables.
30	Signal	  Butterfly	  Parport (DB-25)
31	------	  ---------	  ---------------
32	SCK	= J403.PB1/SCK	= pin 2/D0
33	RESET	= J403.nRST	= pin 3/D1
34	VCC	= J403.VCC_EXT	= pin 8/D6
35	MOSI	= J403.PB2/MOSI	= pin 9/D7
36	MISO	= J403.PB3/MISO	= pin 11/S7,nBUSY
37	GND	= J403.GND	= pin 23/GND
39Then to let Linux master that bus to talk to the DataFlash chip, you must
40(a) flash new firmware that disables SPI (set PRR.2, and disable pullups
41by clearing PORTB.[0-3]); (b) configure the mtd_dataflash driver; and
42(c) cable in the chipselect.
44	Signal	  Butterfly	  Parport (DB-25)
45	------	  ---------	  ---------------
46	VCC	= J400.VCC_EXT	= pin 7/D5
47	SELECT	= J400.PB0/nSS	= pin 17/C3,nSELECT
48	GND	= J400.GND	= pin 24/GND
50Or you could flash firmware making the AVR into an SPI slave (keeping the
51DataFlash in reset) and tweak the spi_butterfly driver to make it bind to
52the driver for your custom SPI-based protocol.
54The "USI" controller, using J405, can also be used for a second SPI bus.
55That would let you talk to the AVR using custom SPI-with-USI firmware,
56while letting either Linux or the AVR use the DataFlash.  There are plenty
57of spare parport pins to wire this one up, such as:
59	Signal	  Butterfly	  Parport (DB-25)
60	------	  ---------	  ---------------
61	SCK	= J403.PE4/USCK	= pin 5/D3
62	MOSI	= J403.PE5/DI	= pin 6/D4
63	MISO	= J403.PE6/DO	= pin 12/S5,nPAPEROUT
64	GND	= J403.GND	= pin 22/GND
66	IRQ	= J402.PF4	= pin 10/S6,ACK
67	GND	= J402.GND(P2)	= pin 25/GND