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ICOP Embedded 386SX PC/104 AIO CPU Module User's Manual
2.4 Watchdog
Timer
The watchdog timer uses a 32.768 KHz frequency source with a 24-bit
counter. Its time range stretches from 30.5 ms to 512 sec. with a resolution
of 30.5 ms. When the watchdog times out a System RESET, NMI or IRQ
can be invoked. Watchdog timer control and the 24-bit counter itself occupy
6 consecutive 8-bit address locations.
When functioning properly the system resets the watchdog timer
periodically to prohibit that it times out. If the watchdog timer times out, it
will RESET the system, or generate and NMI or IRQ, depending on its
configuration.
Watchdog or System Timer
Another great application is to generate a periodic IRQ signal. Under DOS
environment, the 8254, system timer 0, will generate IRQ0 every 54.9 ms.
The watchdog is like system timer 0. It can be programmed to periodically
generate a configurable IRQ. It may be clear that the selected IRQ, will be
no longer available to the system.
Configuring the Watchdog Timer in the BIOS
The M6117D watchdog configuration register can be controlled by software
or can be setup in the BIOS. To do so go to BIOS Setup’s “Advanched
Chipset Setup”
Watchdog Function = Enable/Disable
Watchdog Signal = RESET, NMI or IRQ
3/4/5/6/7/9/10/11/12/14/15
Watchdog Timer = 1/2/4/8/16/32/64/128/256/512 Seconds
The BIOS setup only offers a limited amount of time-out values. More a
hiher resolution of timeout values refer to the next paragraph “Configuring
the Watchdog Timer by Software” Note that in case of using the BIOS
setup, the watchdog starts counting the moment it passes the BIOS setup.
This means that if you set the time-out period to 1 second, the system will
keep rebooting before being able to load operating system or software !
After you have finnished configuring you watchdog timer read “Timeout
Status & Reset - INDEX 3CH” on page 12 and look at the example on page
15 to find out how to priodically reseting the timeout status to prevent the
watchdog timer from invoking a RESET, NMI or IRQ.
