Lanner LEC-7900 User Manual download pdf (Page 27)

Appendix A. Watchdog Timer

Introduction

Most systems need to be self-reliant. If an error should occur it is typically not possible to

wait for the system to be rebooted manually. In some cases, such as apace probes, the system

is simply disabled. In other cases, the speed at which a human operator would reset the

system would be too slow to meet the uptime requirements of the product.

A watchdog timer is a piece of hardware that can be used to automatically detect system

anomalies and reset the processor if the case any problems are found. Generally speaking, a

watchdog timer is based on a counter that counts down from an initial value to zero. The

software selects the counter's initial value and periodically restarts it. Should the counter

reach zero before the software restarts it, the software is presumed to be malfunctioning and

the processor's reset signal is asserted. Thus, the processor will be restarted as if a human

operator had cycled the power

Watch Dog Sample code:

// Watchdog control utility for LEB-7900

#include <stdio.h>

#include <string.h>

#include <dos.h>

#include <stdlib.h>

#include <inlines/pc.h>

#define INDEX_PORT 0x2e

#define DATA_PORT 0x2f

#define CR20_REG 0x20 //This register indicate the device's ID

#define W83627UHG_ID 0xA2

void help()

{

printf("Lanner Electronics Inc. 2009-05-22\n");

printf("Watchdog timer control V1.0 for LEB-7900\n\n");

printf("wdbp.exe -wr xxx (1-255 sec)(Watchdog Control - SYSTEM RESET)\n");

printf("\n");

}

int main(int argc, char *argv[])

{

int temp9 = 0;

int time;

if( argc < 2 )

{

help();

return -1;

}

//;********** Detect SIO ******************

Enter_Configuation();

if(detect_sio())

{

printf("It's not correct SuperIO, program terminated!!!\n");

temp9 = read_w83627UHG_reg(0, CR20_REG);

printf("Rx20 = %02X\n", temp9);

return -1;

}

Exit_Configuation();

Init_WDTO_GPIO_Interface();

//;********************* Setting Watchdog timer for System Reset

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Lanner LEC-7900 User Manual Page 27

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