Feeding (kicking) the watchdog in Embedded C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to feed the watchdog by writing the correct function call.

Embedded C

void main() {
    // Feed the watchdog
    [1]();
}

Drag options to blanks, or click blank then click option'

Astop_watchdog

Bstart_watchdog

Ckick_watchdog

Dinit_watchdog

Attempts:

3 left

💡 Hint

Common Mistakes

Using start_watchdog() instead of feeding function.

Using stop_watchdog() which disables the watchdog.

Using init_watchdog() which only initializes but does not feed.

The function kick_watchdog() is used to feed or reset the watchdog timer to prevent system reset.

2fill in blank

medium

Complete the code to initialize the watchdog with a timeout value of 1000 milliseconds.

Embedded C

void setup() {
    watchdog_init([1]);
}

Drag options to blanks, or click blank then click option'

A1000

B500

C2000

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 disables the watchdog timer.

Using 500 or 2000 sets incorrect timeout values.

The watchdog is initialized with a timeout of 1000 milliseconds to reset the system if not fed within this time.

3fill in blank

hard

Fix the error in the watchdog feeding code by completing the missing function call.

Embedded C

int main() {
    while(1) {
        // Feed the watchdog
        [1]();
        delay_ms(500);
    }
    return 0;
}

Drag options to blanks, or click blank then click option'

Ainit_watchdog

Bkick_watchdog

Cwatchdog_stop

Dwatchdog_start

Attempts:

3 left

💡 Hint

Common Mistakes

Using watchdog_start() which only starts but does not feed.

Using watchdog_stop() which disables the watchdog.

Using init_watchdog() which initializes but does not feed.

The correct function to feed the watchdog repeatedly is kick_watchdog(). This prevents the system from resetting.

4fill in blank

hard

Fill both blanks to create a dictionary that maps watchdog states to their descriptions.

Embedded C

const char* watchdog_states[] = {"[1]", "[2]"};

Drag options to blanks, or click blank then click option'

AACTIVE

BINACTIVE

CSTARTED

DSTOPPED

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'STARTED' and 'STOPPED' which are less common terms.

Mixing up the order of states.

The watchdog states are commonly represented as "ACTIVE" and "INACTIVE" to indicate if it is running or stopped.

5fill in blank

hard

Fill all three blanks to complete the watchdog feeding function with proper checks.

Embedded C

void feed_watchdog() {
    if (watchdog_[1]()) {
        [2]_watchdog();
    } else {
        watchdog_[3]();
    }
}

Drag options to blanks, or click blank then click option'

Ais_running

Bkick

Cstart

Dstop

Attempts:

3 left

💡 Hint

Common Mistakes

Using stop instead of start in the else branch.

Using start instead of kick to feed the watchdog.

Checking wrong status function.

This function checks if the watchdog is running using is_running(). If yes, it feeds the watchdog with kick_watchdog(). Otherwise, it starts the watchdog with start_watchdog().

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