The BCM2835 library allows access to the I/O pins of the Raspberry PI board.

bcm2835 by Mike McCauley

C library for Broadcom BCM 2835 as used in Raspberry Pi

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sudo wget http://www.airspayce.com/mikem/bcm2835/bcm2835-1.50.tar.gz
sudo tar zxvf bcm2835-1.50.tar.gz
cd bcm2835-1.50
sudo ./configure
sudo make
sudo make check
sudo make install