Documentation/spi/butterfly.rst

2 spi_butterfly - parport-to-butterfly adapter driver
9 sensors, LCD, flash, toggle stick, and more.  You can use AVR-GCC to
16 signal pins from the printer port.  Or for that matter, you can use
27 need to reflash the firmware, and the pins are the standard Atmel "ISP"
28 connector pins (used also on non-Butterfly AVR boards).  On the parport
32 	Signal	  Butterfly	  Parport (DB-25)
38 	MISO	  J403.PB3/MISO	  pin 11/S7,nBUSY
44 by clearing PORTB.[0-3]); (b) configure the mtd_dataflash driver; and
48 	Signal	  Butterfly	  Parport (DB-25)
57 the driver for your custom SPI-based protocol.
60 That would let you talk to the AVR using custom SPI-with-USI firmware,
62 of spare parport pins to wire this one up, such as:
65 	Signal	  Butterfly	  Parport (DB-25)
69 	MISO	  J403.PE6/DO	  pin 12/S5,nPAPEROUT