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.