Method for Using a Pseudo Watchdog Timer to Extend the Watchdog Time-out Interval
Original Publication Date: 2005-Sep-20
Included in the Prior Art Database: 2005-Sep-20
In real time systems it can become necessary to tie up the processor for longer than the hardware watch dog timer allows. By combining a hardware watchdog with a software interrupt driven extension the limitations of a hardware can be overcome.
Method for Using a Pseudo Watchdog Timer to Extend the Watchdog Time -out Interval
Watchdog timers are used to recover from fatal processor errors that are usually caused by firmware design problems. The common design for a watchdog timer is a countdown timer, where a count that reaches zero results in a processor interrupt. The firmware periodically resets the counter to keep if from counting down to zero. If the firmware doesn't reset the counter in time, the interrupt will occur. The watchdog interrupt usually performs some kind of recovery that often results in a processor reset.
Many processors have built-in watchdog timers and their counters are usually driven off the processor clock. The maximum period that one can set for a watchdog timer may be relatively short. For example, some watchdog timers may be limited to a maximum period of hundreds of milliseconds. Some applications may require a longer interval. For example, a design may require a watchdog timer with a maximum interval of seconds or minutes.
What is needed, is a method of extending the period or interval of a watchdog timer without additional hardware. One solution to this problem is to use another timer interrupt. The second timer interrupt may be used to extend the length of the watchdog interval.
The watchdog timer would be set to some arbitrary value, such as it's maximum value. A timer interrupt would reset the watchdog timer at some regular interval, such as every millisecond. The timer...