Gen2: fixes the issue that the cellular modem is reset unexpectedly.

[XuGuohui]

Problem

If the WLAN_WD expires during device is connecting to the cellular tower followed by user requests to cancel the on-going cellular operation, the modem might be reset still.

Solution

Clear the WLAN_WD on user request to cancel the on-going cellular operation.

Steps to Test

N/A

Example App

SYSTEM_THREAD(ENABLED);
SYSTEM_MODE(SEMI_AUTOMATIC);

SerialLogHandler logHandler(115200, LOG_LEVEL_ALL);

bool shutoff = false;
system_tick_t last_sync = 0;

// handler for mode button being clicked to trigger
// connect/disconnect
void mode_clicked(system_event_t event, int param)
{
    shutoff = !shutoff;
    Log.info("mode button clicked");
}

// background thread to call blocking API
// this appears to allow the idle task in during the `Cellular.off` sequence
// and trigger the WLAN watchdog
void background_thread_func()
{
    while(true)
    {
        last_sync = Particle.timeSyncedLast();
        delay(1);
    }
}

void setup()
{
    auto background_thread = new Thread("sysapp_background", background_thread_func);
    (void) background_thread;

    System.on(button_click, mode_clicked);

    Particle.connect();
}

void loop()
{
    static bool last_shutoff = shutoff;

    if(last_shutoff != shutoff)
    {
        last_shutoff = shutoff;

        if(shutoff)
        {
            Log.info("disconnect");
            Cellular.off();
            Log.info("post disconnect");
        }
        else
        {
            Log.info("connecting again");
            Particle.connect();
        }
    }
}

References

N/A

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Completeness

• User is totes amazing for contributing!
• Contributor has signed CLA (Info here)
• Problem and Solution clearly stated
• Run unit/integration/application tests on device
• Added documentation
• Added to CHANGELOG.md after merging (add links to docs and issues)

[avtolstoy]

Let's add an automated test to wiring/no_fixture for this. Some examples on how to force a specific system thread behavior can be found in THREAD_07_particle_process_behavior_when_threading_enabled.

[XuGuohui]

Let's add an automated test to wiring/no_fixture for this. Some examples on how to force a specific system thread behavior can be found in THREAD_07_particle_process_behavior_when_threading_enabled.

I don’t think a no_fixture test can verify this. As we need to enforce a blocking connection attempt, which can be produced by detaching the antenna or put the device in a bad cellular environment.