See the top level README for information on where to find the
schematic and programmers reference manual for the ARM processor
on the raspberry pi.  Also find information on how to load and run
these programs.

See the top level README for information on how to connect the raspi
uart to your host computer.

This example is using the raspberry pi as an AVR ISP.

The AVR board used initially is the Sparkfun pro micro 8Mhz/3.3v

http://www.sparkfun.com/products/10999

From an AVR document the chips with this serial isp are either byte
mode or page mode.  This chip atmega32u4 is page mode so you load a
temporary buffer with 64 instructions, then send one command to program
that buffer into a page of flash.

The serial protocol is quite trivial so writing code to use it or modify
this program is simple.

At this time the code only supports one page/buffer, 64 instructions.

At this time not worrying about exact timing, it works with count to
N loops.

Raspberry pi interesting pins

//GPIO7  SPI0_CE1_N  P1-26
//GPIO8  SPI0_CE0_N  P1-24
//GPIO9  SPI0_MISO   P1-21
//GPIO10 SPI0_MOSI   P1-19
//GPIO11 SPI0_SCLK   P1-23
//alt function 0 for all of the above

//P1 1  +3V3
//P1 25  GND
//p1 26  GPIO_CE1

Pro micro to raspi

(GND)              P1-25 GND
(RST)              P1-26 CE1_N
(VCC)              P1-1  +3V3
(15) SCK  JP6-9    P1-23 SCLK
(14) MISO JP6-10   P1-21 MISO
(16) MOSI JP6-11   P1-19 MOSI

The ATmega32U4 breakout board has a cluster of 6 pins (an AVR ISP header)
with all 6 labelled, you connect the raspberry pi signals (right side
of table above) to those six pins, nothing else.  That breakout board
does not have an led at least not in the same place so you would have
to add one or use a scope or meter to see the I/O pin toggle after
programming.

The AVR doesnt use the chip select for communication, so I support CS0
but didnt wire it.  The AVR is strange in that way, it does need the
chip held in reset so I abused CS1 (CE1_N) and mucked with its
non-asserted state as if it were a gpio pin to assert and deassert reset
on the AVR.  Normal spi stuff derived from this example should use CE0_N
(CS0).

The avr samples use the avra assembler apt-get install avra