Feeding (kicking) the watchdog in Embedded C - Step-by-Step Execution

Concept Flow - Feeding (kicking) the watchdog

Start Program

↓

Initialize Watchdog

↓

Enter Main Loop

↓

Perform Tasks

↓

Feed (Kick) Watchdog

↓

Check Watchdog Timer

↓

Timer OK

↓

Continue

The program initializes the watchdog, then repeatedly performs tasks and feeds the watchdog to prevent system reset.

Execution Sample

Embedded C

void main() {
  WDT_Init();
  while(1) {
    DoTasks();
    WDT_Feed();
  }
}

This code initializes the watchdog timer and then continuously performs tasks and feeds the watchdog to avoid reset.

Execution Table

Step	Action	Watchdog Timer (ticks)	Condition	Result
1	Initialize watchdog	0	N/A	Watchdog timer started
2	Enter main loop	0	N/A	Loop begins
3	Perform tasks	5	Timer < timeout	Tasks done, timer running
4	Feed watchdog	0	Timer reset	Watchdog timer reset to 0
5	Perform tasks	5	Timer < timeout	Tasks done, timer running
6	Feed watchdog	0	Timer reset	Watchdog timer reset to 0
7	Perform tasks	5	Timer < timeout	Tasks done, timer running
8	Feed watchdog	0	Timer reset	Watchdog timer reset to 0
9	Perform tasks	5	Timer < timeout	Tasks done, timer running
10	Feed watchdog	0	Timer reset	Watchdog timer reset to 0
11	Watchdog timer expires	10	Timer >= timeout	System reset triggered

💡 System resets if watchdog timer reaches timeout without feeding.

Variable Tracker

Variable	Start	After Step 3	After Step 4	After Step 5	After Step 6	After Step 7	After Step 8	After Step 9	After Step 10	After Step 11
Watchdog Timer (ticks)	0	5	0	5	0	5	0	5	0	10

Key Moments - 3 Insights

Why does the watchdog timer reset to 0 after feeding?

Feeding the watchdog resets the timer to 0 to prevent system reset, as shown in steps 4, 6, 8, and 10 in the execution_table.

What happens if the watchdog is not fed before the timer reaches the timeout?

If the timer reaches the timeout value without feeding, the system triggers a reset, as shown in step 11 in the execution_table.

Why does the watchdog timer increase during task execution?

The timer counts up during task execution to measure elapsed time since last feeding, shown by the increase from 0 to 5 ticks in steps 3, 5, 7, and 9.

Visual Quiz - 3 Questions

Look at the execution_table, what is the watchdog timer value immediately after step 6?

A 10

B 5

C 0

D Undefined

💡 Hint

Check the 'Watchdog Timer (ticks)' column for step 6 in the execution_table.

At which step does the system reset occur according to the execution_table?

A Step 11

B Step 9

C Step 4

D Step 2

💡 Hint

Look for the row where 'Result' mentions 'System reset triggered' in the execution_table.

If the feeding step is skipped after step 3, what will happen to the watchdog timer at step 5?

A It resets to 0

B It increases beyond 5

C It remains at 5

D It decreases

💡 Hint

Refer to the variable_tracker to see how the timer increments when feeding is skipped.

Concept Snapshot

Feeding (kicking) the watchdog means resetting its timer regularly.
Syntax: call WDT_Feed() inside main loop.
If not fed before timeout, system resets.
Prevents system hang by ensuring code runs.
Feed watchdog after tasks to avoid reset.

Full Transcript

This example shows how an embedded program uses a watchdog timer to keep the system running safely. The watchdog timer counts up while the program runs tasks. The program must regularly feed or kick the watchdog to reset the timer to zero. If the watchdog timer reaches its timeout without being fed, it triggers a system reset to recover from possible errors. The execution table traces each step: initializing the watchdog, performing tasks, feeding the watchdog, and the timer values. Feeding the watchdog resets the timer to zero, preventing reset. If feeding is skipped, the timer continues to count up and eventually causes a reset. This mechanism helps embedded systems recover from software faults by restarting automatically.

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