RE: Under what circumstances will wdt fail

rajeev — Fri, 25 Jul 2025 16:19:14 GMT

Here are the key scenarios where a watchdog timer may not work as intended:

Disabled or Not Initialized: If the watchdog timer is not enabled in firmware/software, it won’t trigger a reset.
Incorrect Timeout Setting: If the timeout is too long, the system may hang indefinitely before the watchdog resets it.
Improper Feeding Mechanism: If the "kick" or "feed" signal is incorrectly implemented, the watchdog may reset the system unnecessarily or fail to detect a hang.

Infinite Loop with Watchdog Feed: If the system is stuck in a loop that still feeds the watchdog, it won’t trigger a reset.
High-Priority Interrupts Blocking Execution: If an ISR (Interrupt Service Routine) keeps feeding the watchdog while the main application is frozen, the watchdog won’t fire.
Race Conditions or Deadlocks: Some hangs may prevent the watchdog from being serviced but also avoid a timeout due to unexpected timing issues.

Faulty Watchdog Circuit: If the watchdog hardware itself is defective, it may not issue a reset.
Power Supply Issues: If voltage drops too low, the watchdog may not function correctly.
Clock Signal Failure: If the system clock (which drives the watchdog) fails, the timer may stop counting.

EMI (Electromagnetic Interference): Strong noise can disrupt the watchdog’s operation.
Radiation or Cosmic Rays (in space applications): Can cause bit flips in registers controlling the watchdog.

Manual Reset Disables Watchdog: Some systems allow a debugger or external command to disable the watchdog.
Brownout Reset Takes Priority: If the system resets due to power loss before the watchdog triggers, the watchdog may not act.

Multi-Core Systems: If one core hangs but others keep feeding the watchdog, the system may not reset.
RTOS Task Scheduling Issues: A high-priority task might keep running and feeding the watchdog while lower-priority tasks are deadlocked.