Window watchdog concept in Embedded C

Introduction

A window watchdog helps keep an embedded system safe by making sure the program is running correctly and on time.

When you want to reset the system if it gets stuck or runs too slow.

When you need to detect if a task is not completed within a certain time window.

When you want to improve system reliability by recovering from software errors automatically.

When you want to monitor critical parts of your embedded program to avoid freezes.

When you want to avoid system crashes caused by unexpected delays or infinite loops.

Syntax

Embedded C

/* Example pseudocode for Window Watchdog setup and refresh */
void WWDG_Init(void) {
    // Enable clock for WWDG
    // Set window value (time window)
    // Set counter value (timeout)
    // Enable WWDG
}

void WWDG_Refresh(void) {
    // Reload the counter within the allowed window
}

The window watchdog timer must be refreshed only during a specific time window.

Refreshing too early or too late causes a system reset.

Examples

This sets the allowed time window and starts the watchdog timer.

Embedded C

/* Initialize WWDG with window = 80, counter = 127 */
WWDG->CFR = 80;  // Set window value
WWDG->CR = 0x7F;  // Set counter and enable WWDG

Refreshing the counter resets the timer if done inside the window.

Embedded C

/* Refresh WWDG counter within window */
WWDG->CR = 0x7F;  // Reload counter to prevent reset

Sample Program

This program initializes the window watchdog and refreshes it three times during normal operation to prevent reset.

Embedded C

#include <stdint.h>
#include <stdio.h>

// Simulated registers for example
uint8_t WWDG_CFR = 0;
uint8_t WWDG_CR = 0;

void WWDG_Init(void) {
    WWDG_CFR = 80;  // Set window value
    WWDG_CR = 0x7F;  // Set counter and enable WWDG
    printf("WWDG initialized with window=80 and counter=127\n");
}

void WWDG_Refresh(void) {
    // Refresh counter within window
    WWDG_CR = 0x7F;
    printf("WWDG refreshed\n");
}

int main(void) {
    WWDG_Init();
    // Simulate normal operation
    for (int i = 0; i < 3; i++) {
        // Do some work
        printf("Working... iteration %d\n", i+1);
        // Refresh watchdog
        WWDG_Refresh();
    }
    return 0;
}

Important Notes

Always refresh the watchdog timer within the allowed window to avoid unwanted resets.

Window watchdogs are stricter than regular watchdogs because they check timing more precisely.

Use watchdogs to improve system safety in critical embedded applications.

Summary

A window watchdog timer helps detect software problems by requiring timely refreshes.

Refreshing too early or too late causes a system reset, helping catch errors.

It is useful to keep embedded systems running safely and reliably.