American Megatrends TPC6000-A2152 User Manual page 90

NOTE:
The following discussion applies to DOS environment. NODKA support is contacted or the
NODKA 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:
AL – 2:
BL:
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.
NOTE:
When exiting a program it is necessary to disable the Watchdog Timer, otherwise the system
resets.
Example program:
INITIAL TIMER PERIOD COUNTER
;
W_LOOP:
MOV AX, 6F02H ;
MOV BL, 30 ;
TPC6000‐A2152 User Manual
90
AH‐6FH Sub‐function
Sets the Watchdog Timer's period.
Time‐out value (Its unit‐second is dependent on the item
"Watchdog Timer unit select" in CMOS setup).
//setting the time‐out value
//time‐out value is 48 seconds