Automatic Restarts

Meadow offers two systems to handle when your code doesn't behave as expected. If your application throws an unhandled exception, there is an automatic restart system for when your app doesn't recover from an error. If you have some code that might become unresponsive, there is a watchdog timer system to reset the device if some part of your code execution takes too long.

Application Error Restart

If your application fails with an unhandled exception, Meadow can offer to detect this and relaunch your application. You can enable this feature and set a custom delay before any restart by configuring the Lifecycle application settings.

These settings are added to a YAML or JSON configuration file. Learn more about configuring automatic restarts for your Meadow applications in application settings configuration.

Lifecycle:
    RestartOnAppFailure: true
    AppFailureRestartDelaySeconds: 15

Watchdog Timer

In addition to restarting when an unhandled exception occurs, you can also use the watchdog timer to restart the device if your application becomes unresponsive. This increases solution reliability by making sure that if the application code runs longer than expected, the device is rebooted and the application can start operating again.

To use the watchdog timer, first enable it, passing a countdown timeout TimeSpan which specifies how long you have to reset the countdown before the device is restarted.

Then, prior to the countdown elapsing, you must reset the countdown to prevent the device from restarting.

Enable the Watchdog Timer

Start by enabling the Meadow watchdog system.

// Enable the watchdog for 10 seconds.
Device.WatchdogEnable(TimeSpan.FromSeconds(10));
// Start the thread that resets the counter.
StartPettingWatchdog(TimeSpan.FromSeconds(9));

Reset the Timer

Then, later in your code, you need to reset the watchdog before the required interval to prevent the device from restarting.

void StartPettingWatchdog(TimeSpan pettingInterval)
{
    // Just for good measure, let's reset the watchdog to begin with.
    Device.WatchdogReset();
    // Start a thread that restarts it.
    Thread t = new Thread(() => {
        while (true) {
            Thread.Sleep(pettingInterval);
            Console.WriteLine("Petting watchdog.");
            Device.WatchdogReset();
        }
    });
    t.Start();
}

Use Watchdog Timer Outside App

The current Device property is available from within your App instance. If you want to use the watchdog system from outside your application class, you can find the current device from the Resolver class.

Resolver.Device.WatchdogEnable(TimeSpan.FromSeconds(10));

Watchdog Timer Considerations

There are several elements to consider when implementing the watchdog time for your app.

As described in the API auto-complete documentation, the watchdog timer duration cannot exceed 32,768 milliseconds. If you try to enable the timer for longer than that, you will cause an ArgumentOutOfRangeException.
If the watchdog timer system is enabled at any point, it cannot be disabled without resetting the Meadow board. This is a constraint of the underlying STM32's watchdog system, exposed for use by Meadow.
When sleeping your Meadow in combination with the watchdog timer, sleep durations should not exceed the watchdog duration you choose. If you sleep longer than the watchdog timer duration, the watchdog system will trigger before Meadow can resume from sleep. To work around the watchdog timer while sleeping for long periods of time, you would need to wake prior to the watchdog timer elapsing, potentially many times, to reset the watchdog before returning to sleep.

Application Error Restart​

Watchdog Timer​

Enable the Watchdog Timer​

Reset the Timer​

Use Watchdog Timer Outside App​