1===================================================
2spi_butterfly - parport-to-butterfly adapter driver
3===================================================
4
5This is a hardware and software project that includes building and using
6a parallel port adapter cable, together with an "AVR Butterfly" to run
7firmware for user interfacing and/or sensors.  A Butterfly is a $US20
8battery powered card with an AVR microcontroller and lots of goodies:
9sensors, LCD, flash, toggle stick, and more.  You can use AVR-GCC to
10develop firmware for this, and flash it using this adapter cable.
11
12You can make this adapter from an old printer cable and solder things
13directly to the Butterfly.  Or (if you have the parts and skills) you
14can come up with something fancier, providing circuit protection to the
15Butterfly and the printer port, or with a better power supply than two
16signal pins from the printer port.  Or for that matter, you can use
17similar cables to talk to many AVR boards, even a breadboard.
18
19This is more powerful than "ISP programming" cables since it lets kernel
20SPI protocol drivers interact with the AVR, and could even let the AVR
21issue interrupts to them.  Later, your protocol driver should work
22easily with a "real SPI controller", instead of this bitbanger.
23
24
25The first cable connections will hook Linux up to one SPI bus, with the
26AVR and a DataFlash chip; and to the AVR reset line.  This is all you
27need to reflash the firmware, and the pins are the standard Atmel "ISP"
28connector pins (used also on non-Butterfly AVR boards).  On the parport
29side this is like "sp12" programming cables.
30
31	======	  =============	  ===================
32	Signal	  Butterfly	  Parport (DB-25)
33	======	  =============	  ===================
34	SCK	  J403.PB1/SCK	  pin 2/D0
35	RESET	  J403.nRST	  pin 3/D1
36	VCC	  J403.VCC_EXT	  pin 8/D6
37	MOSI	  J403.PB2/MOSI	  pin 9/D7
38	MISO	  J403.PB3/MISO	  pin 11/S7,nBUSY
39	GND	  J403.GND	  pin 23/GND
40	======	  =============	  ===================
41
42Then to let Linux master that bus to talk to the DataFlash chip, you must
43(a) flash new firmware that disables SPI (set PRR.2, and disable pullups
44by clearing PORTB.[0-3]); (b) configure the mtd_dataflash driver; and
45(c) cable in the chipselect.
46
47	======	  ============	  ===================
48	Signal	  Butterfly	  Parport (DB-25)
49	======	  ============	  ===================
50	VCC	  J400.VCC_EXT	  pin 7/D5
51	SELECT	  J400.PB0/nSS	  pin 17/C3,nSELECT
52	GND	  J400.GND	  pin 24/GND
53	======	  ============	  ===================
54
55Or you could flash firmware making the AVR into an SPI slave (keeping the
56DataFlash in reset) and tweak the spi_butterfly driver to make it bind to
57the driver for your custom SPI-based protocol.
58
59The "USI" controller, using J405, can also be used for a second SPI bus.
60That would let you talk to the AVR using custom SPI-with-USI firmware,
61while letting either Linux or the AVR use the DataFlash.  There are plenty
62of spare parport pins to wire this one up, such as:
63
64	======	  =============	  ===================
65	Signal	  Butterfly	  Parport (DB-25)
66	======	  =============	  ===================
67	SCK	  J403.PE4/USCK	  pin 5/D3
68	MOSI	  J403.PE5/DI	  pin 6/D4
69	MISO	  J403.PE6/DO	  pin 12/S5,nPAPEROUT
70	GND	  J403.GND	  pin 22/GND
71
72	IRQ	  J402.PF4	  pin 10/S6,ACK
73	GND	  J402.GND(P2)	  pin 25/GND
74	======	  =============	  ===================
75