Pc 6408, C. watchdog timer – Acnodes PC 6408 User Manual

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PC 6408

8” Fanless Panel PC

C. WATCHDOG TIMER

NOTE:
The following discussion applies to DOS environment. Acnodes support is contacted or

the Acnodes website visited for specific drivers for more sophisticated operating sys-

tems, e.g., Windows and Linux.
The Watchdog Timer is provided to ensure that standalone systems can always recover from

catastrophic conditions that cause the CPU to crash. This condition may have occurred by

external EMIs or a software bug. When the CPU stops working correctly, Watchdog Timer

either performs a hardware reset (cold boot) or a Non-Maskable Interrupt (NMI) to bring the

system back to a known state.
A BIOS function call (INT 15H) is used to control the Watchdog Timer.

Call sub-function 2 to set the time-out period of Watchdog Timer first. If the time-out value is

not zero, the Watchdog Timer starts counting down. When the timer value reaches zero, the

system resets. To ensure that this reset condition does not occur, calling sub-function
2 must periodically refresh the Watchdog Timer. However, the watchdog timer is disabled if

the time-out value is set to zero.
A tolerance of at least 10% must be maintained to avoid unknown routines within the operat-

ing system (DOS), such as disk I/O that can be very time-consuming.

NOTE:
When exiting a program it is necessary to disable the Watchdog Timer, otherwise the

system resets.