Chaining The Isrs; Enabling The Watchdog Nmi - Intel NetStructure ZT 5504 Manual

System master processor board

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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:

#define 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.

}

To activate the NMI feature, enable it in the watchdog register

might look like the following:

#define WD_NMI_EN_BIT_SET 0x10

void EnableWatchdogNmi(void){

unsigned char WdValue;

WdValue = inb(WD_CSR_IO_ADDRESS);

WdValue |= WD_NMI_EN_BIT_SET;

outb(WD_CSR_IO_ADDRESS,WdValue);

}

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// Save the old vector.

(Port

79h). The code to do this

// Holds watchdog register values.

// Read the current contents of the

// watchdog register.

// Assert the enable bit in the

// local copy.

// Assert the enable in the watchdog

// register.

7. Watchdog Timer

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