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CPEx GX-333-X CyberResearch
®
CPU Cards
72 ©Copyright 2007 CyberResearch, Inc.
NOTE:
The following discussion applies to DOS environment. It is recommended you
contact CYBERRESEARCH support or visit our website 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 EMI or a software bug. When the CPU stops working correctly, Watchdog Timer will
either perform 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: Set the Watchdog Timer’s period
BL : Time-out value(Its unit--second is dependent on the
item “Watchdog Timer unit select” in CMOS setup).
You have to 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 will start counting down. While the timer value reaches
zero, the system will reset. To ensure that this reset condition does not occur, calling sub-function
2 must periodically refresh the Watchdog Timer. However, the Watchdog timer will be disabled if
you set the time-out value to be 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.