Rockwell Automation 6182 Industrial Computer for the Windows CE Operating System - Manual (Page 115)

Watchdog Timer
This chapter describes how to use the RAC6182 watchdog timer to
automatically reset the RAC6182 Computer in case of system lockup.
The RAC6182 Industrial Computer has a built-in hardware timer that can
be used to detect if the computer's processor locks up. To accomplish
this, a software application is setup to restart the watchdog timer at
regular intervals. If the system locks up, the application cannot restart
the external watchdog timer, and the timer circuitry enters time-out mode
and automatically resets the RAC6182 Industrial Computer.
Simple Watchdog Implementation
The RAC6182 watchdog timer system software is a simple watchdog
implementation, protecting against a catastrophic system lockup.
The RAC6182 watchdog timer application runs as a normal priority task
in Windows CE. This application will continue to run in the background
and restart the watchdog timer unless:
• The operating system itself locks up
• A higher priority task locks up (by entering infinite loop or having a
memory error)
With a simple implementation, it is possible for an application with a low
priority to lock up, or for two applications to reach deadlock without the
watchdog timer being reset.
Watchdog Control for Critical Applications
A critical control application or multitasking application may need to
control the RAC6182 watchdog timer circuitry directly, to protect against
system lockup. Software designers can utilize the watchdog API in their
applications to restart the watchdog timer, instead of using the watchdog
timer system software application.
If you integrate watchdog functionality in your application, do not enable
the watchdog timer system software application provided with the
RAC6182. Otherwise, the system software application may continue to
restart the timer when your application is locked up.
Note also, that a watchdog timer only provides protection against system
lockups. You may also need to consider other types of protection, such
as a checksum, when designing critical applications.
Chapter
12
Chapter Objective
Watchdog Functionality