Chapter 14: Watchdog timer and hardware reset
Description
The watchdog timer is a fail-safe against program crashes or processor lockups. It
has a programmable timeout period, ranging from 2.0 milliseconds to 2 minutes
(see next section). The watchdog timer can be enabled or disabled in Setup. INT17
software calls, a built–in function on the XE–800 SBC, can also be used to enable
and set the timeout, extend the timeout, strobe, and disable the watchdog timer
from your application. If the timer expires, it performs a hardware reset.
Timeout period (ranges)
Although the timeout periods are listed as 2.0 milliseconds to 2 minutes, the actual
timeouts are ranges of
±
50% of the listed values. Therefore, for a selected timeout
period of 2 minutes, the timeout could expire in as little as one minute or as long as
three minutes. To ensure that the watchdog does not reset the system accidentally,
always strobe the watchdog at a rate of at least twice the selected timeout period.
Booting, power down, and strobing the watchdog timer
When the watchdog is enabled in Setup, it sets the timeout period for two minutes.
The BIOS will strobe the watchdog during the boot process and once more just
before booting is finished. The user’s application must then begin strobing. The
watchdog will continue until it is disabled or power down occurs.
If the watchdog is enabled in Setup and your operating system cannot load up
before the timer expires, your system could reset. Also, if you do not disable the
watchdog and your strobing application ends before power down you could again
reset. If these watchdog situations should occur, remove the “S” jumper W1[1
−
2]
and reboot. This causes the XE–800 SBC to boot using Setup defaults (watchdog
disabled). Enter Setup, then change and save the watchdog settings in Setup.
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