The Serial Peripheral Interface (SPI)
http://avrbeginners.net/architecture/spi/spi.html
The SPI (Serial Peripheral Interface) is a peripheral used to communicate between the AVR and other devices, like others AVRs, external EEPROMs, DACs, ADCs, etc. With this interface, you have one Master device which initiates and controls the communication, and one or more slaves who receive and transmit to the Master.
Brian's Life: Getting SPI working on the Raspberry Pi
http://www.brianhensley.net/2012/07/getting-spi-working-on-raspberry-pi.html
This post is the 'how to' on getting your SPI signals outputting from your Raspberry Pi.
SPI Command-line Utility for Raspberry Pi | iP Solutions
http://ipsolutionscorp.com/raspberry-pi-spi-utility/
iP Solutions has created a Serial Peripheral Interface (SPI) command-line utility for the Raspberry Pi (www.raspberrypi.org) platform. The utility, spincl, is licensed under Open Source GNU GPLv3 and is being offered by iP Solutions as a free download with source included.
SPI Command-line Utility for Raspberry Pi | iP Solutions
http://ipsolutionscorp.com/raspberry-pi-spi-utility
iP Solutions has created a Serial Peripheral Interface (SPI) command-line utility for the Raspberry Pi (www.raspberrypi.org) platform. The utility, spincl, is licensed under Open Source GNU GPLv3 and is being offered by iP Solutions as a free download with source included.