WSB-9454 CPU Card
Page 190
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 been
caused by a software bug. When the CPU stops working correctly, hardware on the board
will perform a hardware reset (cold boot) to bring the system back to a known state.
A BIOS function call (INT 15H) is used to control the Watchdog Timer.
INT 15H:
AH – 6FH
Sub-function:
AL – 2 : Sets the Watchdog Timer’s time-out period.
BL : Time-out value (Its unit-second is dependent on the item “Watchdog
Timer unit select” in CMOS setup).
Table C-1: AH-6FH Sub-function
Sub-function 2 must be called to set the time-out period of Watchdog Timer first. If the
time-out value is not zero, the Watchdog Timer will start counting down. When the timer
value reaches zero, the system will reset. To ensure that this reset condition does not
occur, the Watchdog Timer must be periodically refreshed by calling sub-function 2. Note
that the Watchdog timer will be 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
operating system (DOS), such as disk I/O that can be very time-consuming.
NOTE:
For inquiries, refer to the original datasheets or contact the IEI
Customer Service Department.
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