See the top level README for information on where to find documentation for the raspberry pi and the ARM processor inside. Also find information on how to load and run these programs. This example is for the older pi boards, see other directories for other flavors of raspberry pi. So when surfing through the linux source for the raspberry pi I found some watchdog timer registers that dont appear to be in the datasheet. So I played with the registers a bit and it appears that from reset and/or using the settings as configured in this code, the watchdog timer is a divide by 4000 of the system timer, so 250,000,000/4000 = 62500 Hz. Based on assumptions from the linux code the biggest timer is 0xFFFFF which is 16.8 seconds. If you do not reprogram the timer and let it run out, then it resets the chip, down to re-reading the sd card and bringing the ARM up using kernel.img. This example simply uses the watchdog timer to time the led state changes. Because it reprograms the watchdog timer with a new time the timer does not timeout and reset the chip. Comment out or remove the break in the loop and it will timeout and reset the chip.