Appendix A: Programming Watchdog Timer - Lanner FW-7573 User Manual

Appendix A: Programming Watchdog Timer

A watchdog timer is a piece of hardware that can be used to automatically detect system anomalies and
reset the processor in case there are any problems. Generally speaking, a watchdog timer is based on a
counter that counts down from an initial value to zero. The software selects the counter's initial value and
periodically restarts it. Should the counter reach zero before the software restarts it, the software is
resumed to be malfunctioning and watchdog timer expired. One of two expected events could be selected
by software: One is processor reset (i.e., system reset), the other is Gen2 LAN bypass activated. In the first
case, the processor's reset signal is asserted. Thus, the processor will be restarted as if a human operator
had cycled the power. In the other case, LAN bypass is activated immediately through watchdog timer
circuits. Keep in mind that in the latest case, system is not reset, but Gen2 LAN bypass activated. See
Appendix. B to learn more how to configure the system to act like reset or LAN-bypass while watchdog
timer expired.
Reset
Watchdog Timer
Processor
Restart
Clock
To execute the sample code: enter the number of seconds to start the countdown before the system can be
reset. Press start to start the counter and stop to stop the counter.
wd_tst --swt xxx (Set Watchdog Timer 1-255 seconds)
wd_tst[*] --start (Start Watchdog Timer)
wd_tst --stop (Stop Watchdog Timer)
For sample Watchdog code, please download the ZIP file "FW 7573 7571 drivers" from
http://www.lannerinc.com/category/1197-network-appliances, and "Lanner Bypass Watchdog module-
user guide" from http://www.lannerinc.com/category/1202-network-appliances
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