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: AT91SAM9G20 Microcontroller Data Sheet
: http://www.atmel.com/dyn/products/product_card.asp?part_id=4337
: This data sheet provides reference information for the AT91SAM9G20 microcontroller, describing the functional blocks of the system-on-chip (SoC) device designed around the ARM926EJ-S processor. All MCU registers are described in the data sheet.

: at91lib Software Library
: http://www.atmel.com/dyn/products/tools_card.asp?tool_id=4343
: AT91 peripheral drivers and code examples. Shows which processor registers are commonly used with the microcontroller peripherals. Some of the logic can be used under Linux user space applications by invoking mmap() to map the peripheral base address to a virtual address.

: Writing device drivers in Linux: A brief tutorial
: http://www.scss.tcd.ie/~simonn/ON3/device_driver_tutorial.pdf
: This article by Xavier Calbet published on [http://www.freesoftwaremagazine.com Free Software Magazine] is a good introduction to Linux device drivers.