blinkio is a c program to toggle a heartbeat output using the <time.h> library and <bcm2835.h> gpio library on a raspberry pi.
There is a fritzing project to capture the breadboard and schematic.
Example code comes from:
http://www.airspayce.com/mikem/bcm2835/blink_8c-example.html
http://www.raspberry-projects.com/pi/programming-in-c/timing/clock_gettime-for-acurate-timing