Watchdog Timer Calculator

Watchdog Timers prevent system lockups by resetting the MCU if the firmware fails to "kick" or reload the timer before it expires.

Formulas:

• IWDG Timeout: Timeout = (4 * 2^PR * RLR) / LSI_Clock
• WWDG Timeout: Timeout = (4096 * 2^WDGTB * (T - 63)) / PCLK1

Usage: Choose your watchdog type. Set the prescaler and reload values to find the exact timing constraints for refreshing your watchdog safely.

When you need it: Recovering an embedded system from firmware hangs — stuck loops, deadlocks, corrupted state — out in the field where nobody can press reset. The watchdog resets the MCU automatically unless your code "kicks" (reloads) it within the timeout window.

Worked example: STM32 IWDG with LSI ≈ 32 kHz, prescaler PR = 4 (÷64) and reload RLR = 1000 → Timeout = (4 × 2⁴ × 1000) / 32000 = 2.0 s. Kick it at least every ~1.5 s to leave margin against jitter.

Tips & gotchas:

• Set the timeout to roughly 1.5–2× your longest legitimate loop: too short causes false resets, too long slows recovery.
• Kick the watchdog from one place in your main loop — never scatter kicks across interrupts, or a hung main loop still gets refreshed and the watchdog is useless.
• STM32 IWDG runs off the independent LSI oscillator (survives a main-clock failure); WWDG runs off PCLK1 and adds a window — kicking too early also triggers a reset.
• The LSI frequency has a wide tolerance (≈ ±5–10%); design your kick interval with that margin in mind.