IEI Technology IOWA-8522, User Manual

Page: 218 / 244

IOWA-8522 Motherboard
Page 198
NOTE
:
The following discussion applies to DOS environment. IEI support is
contacted or the IEI website visited for specific drivers for more sophisticated
operating systems, 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.
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 “Watchdog
Timer unit select” in CMOS setup).
Table C-1: AH-6FH Sub-function
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
operating system (DOS), such as disk I/O that can be very time-consuming.