Watchdog timer operation in Embedded C - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Watchdog Timer Reset Behavior

What will be the output of the following embedded C code snippet simulating a watchdog timer reset?

Embedded C

#include <stdio.h>
#include <stdbool.h>

bool watchdog_reset = false;

void watchdog_feed() {
    watchdog_reset = true;
}

void watchdog_check() {
    if (!watchdog_reset) {
        printf("System Reset by Watchdog\n");
    } else {
        printf("System Running Normally\n");
    }
}

int main() {
    watchdog_reset = true;
    watchdog_feed();
    watchdog_check();
    watchdog_reset = false;
    watchdog_check();
    return 0;
}

A

System Running Normally
System Reset by Watchdog

B

System Reset by Watchdog
System Reset by Watchdog

C

System Running Normally
System Running Normally

D

System Reset by Watchdog
System Running Normally

💡 Hint

Watchdog resets the system if it is not fed (reset) in time.

The first watchdog_check() call happens after watchdog_feed(), so the system is running normally. The second call happens after watchdog_reset is set to false, so the watchdog triggers a reset message.

🧠 Conceptual

intermediate

Purpose of a Watchdog Timer

What is the main purpose of a watchdog timer in embedded systems?

A To manage power consumption by shutting down peripherals

B To increase the processing speed of the CPU

C To store data persistently during power loss

D To monitor system health and reset the system if it becomes unresponsive

💡 Hint

Think about what happens when a system freezes or crashes.

A watchdog timer helps recover the system from hangs by resetting it if the software fails to reset the timer periodically.

🔧 Debug

advanced

Identify the Bug in Watchdog Feeding Code

What is the bug in the following watchdog feeding code snippet?

Embedded C

void feed_watchdog() {
    // Missing watchdog reset sequence
    // supposed to reset the watchdog timer here
}

int main() {
    while(1) {
        feed_watchdog();
        // Other tasks
    }
    return 0;
}

A The while loop will never execute

B The watchdog timer is never reset, causing system reset

C The function feed_watchdog() causes a memory leak

D The program will compile but never start

💡 Hint

Feeding the watchdog means resetting its timer to prevent reset.

The function feed_watchdog() is empty and does not reset the watchdog timer, so the watchdog will eventually reset the system.

📝 Syntax

advanced

Correct Watchdog Timer Initialization Syntax

Which option correctly initializes a watchdog timer with a timeout of 2 seconds in embedded C?

A WDT_Init(2000);

B WDT_Init(2000ms);

C WDT_Init(2);

D WDT_Init("2s");

💡 Hint

Timeouts are usually given in milliseconds as integers.

The function expects an integer value representing milliseconds. Option A passes 2000 (2 seconds) correctly.

🚀 Application

expert

Watchdog Timer Use Case Scenario

In an embedded system controlling a robotic arm, the watchdog timer is set to 1 second. The main control loop takes 1.5 seconds to complete one cycle. What will happen and why?

A The watchdog will extend its timeout automatically to 2 seconds

B The system will run normally because the watchdog timer is disabled during the control loop

C The watchdog will reset the system because the control loop exceeds the watchdog timeout

D The system will ignore the watchdog timer because the control loop is critical

💡 Hint

Watchdog timers reset the system if not fed before timeout.

Since the control loop takes longer than the watchdog timeout and the watchdog is not fed in time, the system will reset.