Watchdog reset recovery in Embedded C - Step-by-Step Execution

Concept Flow - Watchdog reset recovery

System starts

↓

Initialize watchdog

↓

Main loop starts

↓

Reset watchdog timer periodically?

No→Watchdog timeout

↓

System reset triggered

↓

Continue normal operation

↓

Loop repeats

The system initializes the watchdog timer and enters the main loop. It must reset the watchdog timer regularly to avoid a system reset. If it fails, the watchdog triggers a reset, and the system restarts.

Execution Sample

Embedded C

void main() {
  WDT_Init();
  while(1) {
    WDT_Reset();
    // normal tasks
  }
}

This code initializes the watchdog timer and resets it continuously inside the main loop to prevent system reset.

Execution Table

Step	Action	Watchdog Timer (ticks)	Condition	Result
1	System starts and initializes watchdog	0	N/A	Watchdog timer starts counting
2	Enter main loop	0	N/A	Ready to reset watchdog periodically
3	Reset watchdog timer	0	Timer reset	Watchdog timer cleared
4	Perform normal tasks	1	Timer < timeout	Continue loop
5	Reset watchdog timer again	0	Timer reset	Watchdog timer cleared
6	Perform normal tasks	1	Timer < timeout	Continue loop
7	Watchdog reset missed	5	Timer >= timeout	Watchdog triggers system reset
8	System resets	0	N/A	Restart from step 1

💡 Execution stops because watchdog timer reached timeout without reset, causing system reset.

Variable Tracker

Variable	Start	After Step 3	After Step 5	After Step 7	Final
Watchdog Timer (ticks)	0	0	0	5	0
System State	Start	Running	Running	Reset triggered	Restarted

Key Moments - 3 Insights

Why does the system reset if the watchdog timer is not reset in time?

Because the watchdog timer counts up and triggers a reset when it reaches the timeout value, as shown in execution_table row 7.

What happens to the watchdog timer when WDT_Reset() is called?

The watchdog timer is cleared to zero, preventing a reset, as seen in execution_table rows 3 and 5.

Why must WDT_Reset() be called regularly inside the main loop?

To keep the watchdog timer from reaching its timeout and causing a system reset, as shown by the repeated resets in the loop (rows 3 and 5).

Visual Quiz - 3 Questions

Look at the execution table, what is the watchdog timer value right after the first WDT_Reset() call?

A 5

B 1

C 0

D Not reset yet

💡 Hint

Check execution_table row 3 where WDT_Reset() is called and timer is cleared.

At which step does the watchdog timer reach the timeout and cause a system reset?

A Step 7

B Step 3

C Step 5

D Step 2

💡 Hint

Look at execution_table row 7 where timer >= timeout triggers reset.

If WDT_Reset() is never called, what will happen according to the execution flow?

A System continues normally

B System resets due to watchdog timeout

C Watchdog timer resets automatically

D Watchdog timer stops counting

💡 Hint

Refer to concept_flow and execution_table rows 6-8 showing reset triggered by timeout.

Concept Snapshot

Watchdog Reset Recovery:
- Initialize watchdog timer at system start
- Regularly call WDT_Reset() in main loop
- Watchdog timer counts up if not reset
- If timer reaches timeout, system resets
- Reset recovery starts system from beginning

Full Transcript

This example shows how a watchdog timer helps recover from system hangs by forcing a reset if the system fails to reset the timer regularly. The system initializes the watchdog, then enters a main loop where it resets the watchdog timer periodically. If the reset is missed, the watchdog timer reaches its timeout and triggers a system reset. This reset restarts the system, allowing recovery from faults. The execution table traces each step, showing the watchdog timer value and system state. Key moments clarify why resetting the watchdog is critical and what happens when it is missed. The quiz tests understanding of timer values and reset conditions.