Feeding (kicking) the watchdog in Embedded C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of feeding (kicking) the watchdog in embedded systems?

Feeding the watchdog prevents the system from resetting by signaling that the program is running correctly and not stuck.

beginner

How often should the watchdog be fed?

The watchdog should be fed regularly within its timeout period to avoid system reset.

beginner

What happens if the watchdog is not fed in time?

If the watchdog is not fed before the timeout, it triggers a system reset to recover from potential software faults.

intermediate

Show a simple C code snippet to feed the watchdog.

Example:

void feed_watchdog() {
    WDT->CLEAR = 0xA5; // Write specific value to clear watchdog timer
}

beginner

Why is feeding the watchdog compared to 'kicking' it?

Because feeding the watchdog resets its timer, similar to kicking a dog to keep it active and prevent it from barking (resetting).

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

A Manage power consumption

B Increase system speed

C Store user data

D Reset the system if software hangs

The watchdog timer resets the system if the software stops responding.

What must a program do to prevent the watchdog from resetting the system?

A Feed (kick) the watchdog regularly

B Disable the watchdog permanently

C Increase the watchdog timeout to maximum

D Ignore the watchdog

Regular feeding tells the watchdog the system is running fine.

What happens if the watchdog is not fed in time?

A Watchdog disables itself

B System reset occurs

C System speed doubles

D Nothing happens

Failing to feed the watchdog causes a system reset to recover from faults.

Which of these is a common method to feed the watchdog in C code?

A Writing a specific value to a watchdog register

B Calling printf()

C Turning off interrupts

D Resetting the CPU manually

Feeding the watchdog usually involves writing a special value to its control register.

Why is the watchdog called a 'watchdog'?

A Because it stores data securely

B Because it barks when the system is slow

C Because it watches the system and resets it if it misbehaves

D Because it controls the clock speed

It monitors the system and resets it if the software stops responding.

Explain in your own words what feeding (kicking) the watchdog means and why it is important.

Think about how the watchdog timer works to keep the system safe.

Describe what could happen if an embedded program forgets to feed the watchdog on time.

Consider the watchdog as a safety guard for the system.

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