WAFER-CV-D25501/N26001 3.5" SBCPage 117NOTE:The following discussion applies to DOS environment. Contact IEI supportor visit the IEI website for specific drivers for other operating systems.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 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.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 E-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. When 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.
