Watchdog Nmi; Chaining The Isrs - Intel NetStructure ZT 5515 Product Specification

Watchdog Timer
8.2.2
8.2.2.1
44
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Watchdog NMI

When enabled, an NMI precedes a watchdog reset by 250 ms. The NMI generation feature gives an
application 250 ms to perform essential tasks before the hardware is reset. Before using watchdog
NMI, ensure the following:
•
The essential task code is included in an interrupt service routine (ISR).
•
The ISR is chained to the existing NMI ISR.
•
The watchdog NMI is enabled.

Chaining the ISRs

Save the original NMI ISR vector so that it can be invoked from the new watchdog NMI ISR. Alter
the interrupt vector table so that the NMI ISR vector is overwritten with a vector to the watchdog
ISR. C code to do this in DOS might look like the following:
#de
fine NMI_INTERRUPT_VECTOR_NUMBER 2
void interrupt far (*OldNmiIsr)();
void HookWatchdogIsr(void){
//
// To be absolutely certain the interrupt table is not accessed by an
// NMI (this is quite unlikely), the application could disable NMI in
// the chip set before installing the new vector.
//
.
.
.
//
// Install the new ISR.
//
oldNmiIsr = getvect(IsrVector);
setvect(NMI_INTERRUPT_VECTOR_NUMBER, WatchdogIsr);// Install the new.
}
®
TM
Intel NetStructure ZT 5515 Compute Processor Board Technical Product Specification
// Save the old vector.