Appendix A Watchdog Timer; A.1 About Watchdog Timer; A.2 How To Use Watchdog Timer - AXIOMTEK PICO840 User Manual

A.1 About Watchdog Timer

Software stability is major issue in most application. Some embedded systems are not
watched by human for 24 hours. It is usually too slow to wait for someone to reboot when
computer hangs. The systems need to be able to reset automatically when things go wrong.
The watchdog timer gives us solution.
The watchdog timer is a counter that triggers a system reset when it counts down to zero from
a preset value. The software starts counter with an initial value and must reset it periodically. If
the counter ever reaches zero which means the software has crashed, the system will reboot.

A.2 How to Use Watchdog Timer

The I/O port base addresses of watchdog timer are 2E (hex) and 2F (hex). The 2E (hex) and
2F (hex) are address and data port respectively.
Assume that program A is put in a loop that must execute at least once every 10ms. Initialize
watchdog timer with a value bigger than 10ms. If the software has no problems; watchdog
timer will never expire because software will always restart the counter before it reaches zero.
Begin
Next
Enable and Initialize
Watchdog Timer
Next
Program "A"
Next
Disable Watchdog
Timer
Next
Watchdog Timer
PICO840/842 Pico-ITX Board
Appendix A
Watchdog Timer
Begin
Next
Enable and Initialize
Watchdog Timer
Next
Program "A"
Next
Reset Watchdog
Timer
Next
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