Watchdog timer
Field devices hang: a sensor stops answering, a network call never returns. A watchdog is a hardware timer the program must reset regularly; if it ever runs out, the chip reboots itself and the device recovers on its own.
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How it works
loop() calls esp_task_wdt_reset() every 500 ms, well inside the 3 s timeout. Press the button and the sketch gets stuck in a loop that never resets it. 3 s later the task watchdog fires and the ESP32 reboots (reset reason TG0WDT_SYS_RESET), then carries on normally.
Pick a timeout longer than the slowest legitimate operation (a Wi-Fi connect can take several seconds) but short enough to recover quickly.
Try it on the bench
- Click the Hang button once. The serial output stops, then about 3 s later the chip reboots and recovers.
- Edit the sketch to remove esp_task_wdt_reset(): it now reboots every 3 s even without a hang.
Parts on the bench
- Bench power supply
- ESP32 DevKit
- USB charger / port
- Push button
In the course
Zen’s Electronics Design Mastery, module “Microcontrollers & Embedded”.