Spi bus

Use of SPI

Currently the main envisioned use of SPI is to program the AVR flash memory. Using the uisp program and robostix driver designed for interfacing Gumstix boards to Robostix boards, we should be able to program other AVR microcontrollers.

SPI in our application

The SPI port utilizes the MISO, MOSI, [NSSP]FRAME, [NSSP]CLK, gnd, and Vcc. The signals are available on the console-st and breakout gumstix boards at a ~3V level with a 276ns risetime. When the signals are used internally with the Robostix they are level shifted using "74LVC4245ATSSOP" chips. The AVR specification defines a low signal as -0.5V to 0.3Vcc, and a high signal as 0.7Vcc to Vcc+0.5V. In our case level shifting to Vcc (5v probably) should be sufficient.