IWatchdog

Introduction

The IWatchdog library provides an interface to the independent watchdog (IWDG) of the STM32 microcontrollers. The IWDG generates a reset of the CPU when the software becomes stuck or unresponsive.

The IWDG contains a down-counter. When it reaches zero, the microcontroller is reset. In normal operation the software reloads the counter periodically to prevent the reset. If a software error keeps the CPU away from the reload for too long, the IWDG resets the CPU.

Usage

The library is delivered with the STM32 core. Include its header in the sketch:

#include <IWatchdog.h>

void setup() {
  // Reset the CPU if the watchdog is not reloaded within 4 seconds.
  IWatchdog.begin(4000000);
}

void loop() {
  // ... code executed in less than 2 seconds to keep 50% headroom ...
  IWatchdog.reload();
}

A default instance named IWatchdog is available. See the IWDG_Button example of the library.

Warning

Once started, the IWDG cannot be stopped. A debugging session can be reset by the watchdog while the CPU is halted. Also consider the watchdog when the CPU is put in a low power mode.

Timeout and window

Timeouts are in microseconds. Plan to reload the counter at least twice as often as the timeout: reload() is not expensive. A very large timeout leaves the system stuck for a long time before the reset.

The valid range depends on the LSI clock. With a 32 kHz LSI it goes from 125 µs to about 32.8 s, and the precision depends on the value:

Timeout range	Precision
125 µs - 512 ms	125 µs
513 ms - 1024 ms	250 µs
1025 ms - 2048 ms	500 µs
2049 ms - 4096 ms	1 ms
4097 ms - 8192 ms	2 ms
8193 ms - 16384 ms	4 ms
16385 ms - 32768 ms	8 ms

The optional window must be less than the timeout. When the window is enabled, the counter has to be reloaded inside the window, otherwise a reset is generated.

Note

The window feature is not available on all STM32 series.

API

Method	Description
`void begin(uint32_t timeout, uint32_t window = IWDG_TIMEOUT_MAX)`	Initializes and starts the IWDG. `timeout` and `window` are in microseconds. Returns without starting the IWDG if `timeout` is out of the valid range.
`void reload()`	Reloads the counter. Call it periodically once the IWDG is started.
`void set(uint32_t timeout, uint32_t window = IWDG_TIMEOUT_MAX)`	Sets the timeout and window values. Same parameters as `begin()`.
`void get(uint32_t timeout, uint32_t window = NULL)`	Gets the current timeout and window values, in microseconds.
`bool isEnabled()`	Returns `true` if the IWDG has been started.
`bool isReset(bool clear = false)`	Returns `true` if the last reset was caused by the IWDG. Clears the IWDG reset flag if `clear` is `true`.
`void clearReset()`	Clears the IWDG reset flag.

Constant	Description
`IWDG_TIMEOUT_MIN`	Minimal timeout in microseconds.
`IWDG_TIMEOUT_MAX`	Maximal timeout in microseconds.