Lanner electronic FW-7890 user manual Appendix B, Watchdog Timer

Appendix B

Watchdog Timer

Introduction

Most systems need to be self-reliant. It's not usually possible to wait for someone to reboot them if there are some component wrong. Some system designs, such as space probes, are simply not accessible to human operators. If the system ever hangs, such systems are permanently disabled. In other cases, the speed with which a human operator might reset the system would be too slow to meet the uptime requirements of the product.

A watchdog timer is a piece of hardware that can be used to automatically detect system anomalies and reset the processor if any occur. Generally speaking, a watchdog timer is based on a counter that counts down from some initial value to zero. The software selects the counter's initial value and periodically restarts it. If the counter ever reaches zero before the software restarts it, the software is presumed to be malfunctioning and the processor's reset signal is asserted. The processor will be restarted as if a human operator had cycled the power.

Notes : The watchdog function is design from the Intel 6300ESB. Lanner provide the sample code and Intel 6300ESB datasheet in the manual/driver CD. The path is under //WATCHDOG