Written by: Venelin Efremov and Frederic Pillon
- Arduino_Core_STM32 version > 1.3.0
Th IWatchdog library provides an interface to the independent watchdog module (IWDG) inside STM32 chips. The IWDG module is used in production systems to generate a reset signal to the CPU in case some catastrophic event causes the software to become "stuck" or unresponsive.
The IWDG module contains a count-down timer. The module would generate a reset condition when the timer reaches zero. In normal operation mode the software running on the CPU would reload the timer periodically to prevent the reset condition from happening. However if a software bug or other error causes the CPU to execute a different code path for too long, the reload would not happen and the IWDG module would reset the CPU.
The IWatchdog is a built-in library included with the STM32 core package. To add its functionality to your sketch
you will need to reference the library header file. It is done by adding: #include <IWatchdog.h>
#include <IWatchdog.h>
void setup() {
...
// Initialize the IWDG with 4 seconds timeout.
// This would cause a CPU reset if the IWDG timer
// is not reloaded in approximately 4 seconds.
IWatchdog.begin(4000000);
}
void loop() {
...your code here...
// make sure the code in this loop is executed in
// less than 2 seconds to leave 50% headroom for
// the timer reload.
IWatchdog.reload();
}
A default instance is available: IWatchdog
IWatchdogClass IWatchdog = IWatchdogClass();
- Minimal timeout in microseconds:
IWDG_TIMEOUT_MIN - Maximal timeout in microseconds:
IWDG_TIMEOUT_MAX
The begin() function would initialize the IWDG hardware block.
The timeout parameter is in microseconds and set the timer reset timeout.
When the timer reaches zero the hardware block would generate a reset signal
for the CPU.
When specifying timeout value plan to refresh the timer at least twice
as often. The reload() operation is not expensive.
The downside of selecting a very large timeout value is that your system may be left in a "stuck" state for too long, before the reset is generated.
Valid timeout values depends of the LSI clock. Typically, it is 32kH value are between 125µs and 32,768ms (~32.8 seconds). The precision depends of the timeout values:
| timeout value range | timeout value precision |
|---|---|
| 125µs - 512ms | 125µs |
| 513ms - 1024ms | 250µs |
| 1025ms - 2048ms | 500µs |
| 2049ms - 4096ms | 1ms |
| 4097ms - 8192ms | 2ms |
| 8193ms - 16384ms | 4ms |
| 16385ms - 32768ms | 8ms |
The optional window parameter is in microseconds and must be less than timeout.
If the window option is enabled, the counter must be refreshed inside the window;
otherwise, a system reset is generated.
Note: Window feature is not available for all STM32 series.
Calling the begin() method with value outside of the valid range
would return without initializing the watchdog timer.
WARNING: Once started the IWDG timer can not be stopped. If you are planning to debug the live system, the watchdog timer may cause the system to be reset while you are stopped in the debugger. Also consider the iwatchdog timer implications if you are designing a system which puts the CPU in sleep mode.
The reload() method reloads the counter value.
Once you have initialized the IWDG you HAVE to call reload()
periodically to prevent the CPU being reset.
The set() method allows to set the timeout and window values.
The timeout and optional window parameters are the same than begin() method.
The get() method allows to get the current timeout and window values
currently set.
The timeout and optional window pointers to get values are in microseconds.
The isEnabled() method returns status of the IWDG block. If enabled or not.
The isReset() method checks if the system has resumed from IWDG reset.
The optional clear parameter allow to clear IWDG reset flag if true. Default: false.
The clearReset() method clears IWDG reset flag.