PCISA-MARK CPU CardNOTE:The following discussion applies to DOS environment.Contact IEI support or visit the IEI website for specific driversfor more sophisticated operating systems, e.g., Windows®and Linux.The Watchdog Timer is provided to ensure that standalone systems can always recoverfrom catastrophic conditions that cause the CPU to crash. This condition may haveoccurred by external EMI 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:INT 15H:AH – 6FH Sub-function:AL – 2: Sets the Watchdog Timer’s period.BL: Time-out value (Its unit-second is dependent on the item “WatchdogTimer unit select” in CMOS setup).Table B-1: AH-6FH Sub-functionCall sub-function 2 to set the time-out period of Watchdog Timer first. If the time-out valueis not zero, the Watchdog Timer starts counting down. While the timer value reaches zero,the system resets. To ensure that this reset condition does not occur, calling sub-function2 must periodically refresh the Watchdog Timer. However, the Watchdog timer is disabledif the time-out value is set to zero.A tolerance of at least 10% must be maintained to avoid unknown routines within theoperating system (DOS), such as disk I/O that can be very time-consuming.Page 192 IEI® Technology, Corp.
