Feeding (kicking) the watchdog in Embedded C - Mini Project: Build & Apply

Feeding (kicking) the watchdog

📖 Scenario: In embedded systems, a watchdog timer helps keep the system safe by resetting it if the program stops working properly. To prevent this reset, the program must regularly 'feed' or 'kick' the watchdog timer.Imagine you are programming a simple embedded device that needs to feed the watchdog every few seconds to keep running smoothly.

🎯 Goal: You will write a small embedded C program that sets up a watchdog timer and regularly feeds it inside a loop to prevent the system reset.

📋 What You'll Learn

Create a variable called watchdog_counter initialized to 0

Create a constant WATCHDOG_THRESHOLD set to 5

Use a while loop to simulate the program running

Inside the loop, increment watchdog_counter and feed the watchdog when it reaches the threshold

Print "Watchdog fed" each time the watchdog is fed

💡 Why This Matters

🌍 Real World

Watchdog timers are used in embedded devices like home appliances, cars, and medical devices to keep them running safely by resetting if the software hangs.

💼 Career

Understanding how to feed the watchdog is essential for embedded software engineers to ensure system reliability and prevent crashes.

1

Create the watchdog counter variable

Create an integer variable called watchdog_counter and set it to 0.

Embedded C

# Create an integer variable called watchdog_counter and set it to 0
# Your code here

Hint

Use int watchdog_counter = 0; to create the variable.

2

Define the watchdog threshold

Create a constant integer called WATCHDOG_THRESHOLD and set it to 5.

Embedded C

int watchdog_counter = 0;
// Define a constant WATCHDOG_THRESHOLD with value 5
# Your code here

Hint

Use const int WATCHDOG_THRESHOLD = 5; to define the threshold.

3

Implement the main loop and feeding logic

Write a while(1) loop. Inside it, increment watchdog_counter by 1. When watchdog_counter equals WATCHDOG_THRESHOLD, reset watchdog_counter to 0 and print "Watchdog fed".

Embedded C

int watchdog_counter = 0;
const int WATCHDOG_THRESHOLD = 5;

// Write a while(1) loop to increment watchdog_counter
// Feed the watchdog and reset counter when threshold is reached
# Your code here

Hint

Use while(1) for an infinite loop. Increment the counter and check if it reached the threshold to feed the watchdog.

4

Run the program and observe output

Run the program and observe that it prints "Watchdog fed" repeatedly every 5 increments.

Embedded C

#include 

int watchdog_counter = 0;
const int WATCHDOG_THRESHOLD = 5;

int main() {
    while(1) {
        watchdog_counter++;
        if (watchdog_counter == WATCHDOG_THRESHOLD) {
            watchdog_counter = 0;
            printf("Watchdog fed\n");
        }
    }
    return 0;
}

// Run the program and observe output

Hint

The program prints "Watchdog fed" every 5 increments. You may need to stop the infinite loop manually after seeing several lines.

Practice

1. What is the main purpose of feeding (kicking) the watchdog in embedded C systems?

easy

A. To start a new program execution

B. To increase the system clock speed

C. To save power by turning off peripherals

D. To reset the watchdog timer and prevent system reset

Solution

1. Step 1: Understand watchdog function

   The watchdog timer resets the system if it is not fed in time, preventing hangs.

2. Step 2: Purpose of feeding watchdog

   Feeding the watchdog resets its timer, showing the system is running fine.

3. Final Answer:

   To reset the watchdog timer and prevent system reset -> Option D

4. Quick Check:

   Feeding watchdog = reset timer [OK]

Hint: Feeding watchdog means resetting its timer regularly [OK]

Common Mistakes:

• Thinking feeding increases clock speed
• Confusing feeding with power saving
• Assuming feeding starts program execution

2. Which of the following is the correct syntax to feed (kick) the watchdog in embedded C if the function is named FeedWatchdog()?

easy

A. FeedWatchdog();

B. feed_watchdog();

C. FeedWatchdog;

D. FeedWatchdog[];

Solution

1. Step 1: Identify correct function call syntax

   In C, calling a function requires parentheses and a semicolon.

2. Step 2: Check each option

   FeedWatchdog(); uses correct capitalization and parentheses; others are incorrect syntax.

3. Final Answer:

   FeedWatchdog(); -> Option A

4. Quick Check:

   Function call syntax = functionName(); [OK]

Hint: Function calls need parentheses and semicolon [OK]

Common Mistakes:

• Omitting parentheses when calling function
• Using wrong capitalization
• Using brackets instead of parentheses

3. What will be the output of the following code snippet if the watchdog is not fed within 5 seconds?

void main() {
  init_watchdog(5); // 5 seconds timeout
  while(1) {
    // no FeedWatchdog() call here
  }
}

medium

A. System runs normally without reset

B. System resets after 5 seconds

C. Compilation error due to missing FeedWatchdog()

D. Watchdog timer disables automatically

Solution

1. Step 1: Understand watchdog timeout behavior

   If the watchdog is not fed within the timeout, it triggers a system reset.

2. Step 2: Analyze code behavior

   No FeedWatchdog() call means timer is not reset, so system resets after 5 seconds.

3. Final Answer:

   System resets after 5 seconds -> Option B

4. Quick Check:

   Not feeding watchdog = system reset [OK]

Hint: No feeding within timeout causes reset [OK]

Common Mistakes:

• Assuming system runs normally without feeding
• Expecting compilation error for missing feed
• Thinking watchdog disables automatically

4. Identify the error in this code snippet that feeds the watchdog incorrectly:

void main() {
  init_watchdog(10);
  while(1) {
    FeedWatchdog;
    delay(1000);
  }
}

medium

A. Missing parentheses in FeedWatchdog call

B. Incorrect delay function usage

C. Watchdog timeout too short

D. No error, code is correct

Solution

1. Step 1: Check FeedWatchdog usage

   FeedWatchdog is a function and must be called with parentheses.

2. Step 2: Analyze code snippet

   FeedWatchdog; is missing parentheses, so it does not call the function.

3. Final Answer:

   Missing parentheses in FeedWatchdog call -> Option A

4. Quick Check:

   Function call needs () [OK]

Hint: Always use () to call functions [OK]

Common Mistakes:

• Forgetting parentheses on function calls
• Assuming delay is incorrect without context
• Thinking timeout value causes error

5. You have a system with a watchdog timeout of 3 seconds. Your main loop takes 5 seconds to complete one iteration. How should you modify your code to prevent the watchdog from resetting the system?

hard

A. Remove the FeedWatchdog() calls entirely

B. Increase the watchdog timeout to 10 seconds

C. Call FeedWatchdog() multiple times inside the loop before 3 seconds pass

D. Call FeedWatchdog() only once after the loop finishes

Solution

1. Step 1: Understand watchdog timeout vs loop time

   The loop takes longer than the watchdog timeout, so feeding once per loop is too late.

2. Step 2: Feeding watchdog multiple times inside loop

   Calling FeedWatchdog() multiple times before 3 seconds resets timer and prevents reset.

3. Final Answer:

   Call FeedWatchdog() multiple times inside the loop before 3 seconds pass -> Option C

4. Quick Check:

   Feed watchdog before timeout expires [OK]

Hint: Feed watchdog often enough within timeout [OK]

Common Mistakes:

• Assuming increasing timeout is always possible
• Feeding watchdog only once after long loop
• Removing feeding calls thinking it helps