RE: when performing FOTA, should we disable the watchdog timer?

Susheel Nuguru — Mon, 11 Nov 2024 07:58:45 GMT

Some FOTA applications do disable watchdog, but it is an architectural choice that you can make. A code snippet on how to do it can be as below. Please use this as a reference only as I have not tested this to work.

#include <zephyr.h>
#include <drivers/watchdog.h>

#define WDT_TIMEOUT_MS 10000  // Watchdog timeout in milliseconds (adjust as needed)
#define WDT_DEVICE_NAME DT_LABEL(DT_NODELABEL(wdt0))

static const struct device *wdt_dev;
static int wdt_channel_id = -1;

// Set up the watchdog timer to ensure system stability by resetting on timeouts
void watchdog_init(void) {
    // Get the watchdog device
    wdt_dev = device_get_binding(WDT_DEVICE_NAME);
    if (!wdt_dev) {
        printk("Error: Cannot find watchdog device\n");
        return;
    }

    // Configure the watchdog timer with the specified timeout and reset behavior
    struct wdt_timeout_cfg wdt_config = {
        .window = { .min = 0, .max = K_MSEC(WDT_TIMEOUT_MS) },
        .callback = NULL,  // We’re not using a callback for simplicity
        .flags = WDT_FLAG_RESET_SOC  // Trigger a full system reset on timeout
    };

    // Install the watchdog timeout with the configuration above
    wdt_channel_id = wdt_install_timeout(wdt_dev, &wdt_config);
    if (wdt_channel_id < 0) {
        printk("Error: Failed to install watchdog timeout\n");
        return;
    }

    // Start the watchdog timer
    int err = wdt_setup(wdt_dev, 0);
    if (err) {
        printk("Error: Failed to set up watchdog\n");
        return;
    }

    printk("Watchdog initialized with %d ms timeout\n", WDT_TIMEOUT_MS);
}

// Function to enable the watchdog, which starts the countdown
void watchdog_enable(void) {
    if (wdt_channel_id >= 0) {
        wdt_feed(wdt_dev, wdt_channel_id);  // Feed the watchdog to start it
        printk("Watchdog enabled\n");
    } else {
        printk("Error: Watchdog channel not initialized\n");
    }
}

// Function to disable the watchdog, typically before long operations like FOTA
void watchdog_disable(void) {
    if (wdt_channel_id >= 0) {
        int err = wdt_disable(wdt_dev);  // Disables the watchdog, if supported by your SDK
        if (err == 0) {
            printk("Watchdog disabled\n");
        } else {
            printk("Error: Unable to disable watchdog\n");
        }
    } else {
        printk("Error: Watchdog channel not initialized\n");
    }
}

// Call this function right before starting a FOTA update to avoid unexpected resets
void prepare_for_fota(void) {
    watchdog_disable();  // Temporarily turn off watchdog for the update
    // Any other FOTA preparation steps can go here
}

// Call this function after FOTA completes to re-enable the watchdog
void post_fota_cleanup(void) {
    // Any necessary cleanup steps after FOTA can go here
    watchdog_enable();  // Re-enable the watchdog to restore normal operation
}

// Function to regularly feed the watchdog to prevent unwanted resets
void watchdog_feed_periodic(void) {
    if (wdt_channel_id >= 0) {
        wdt_feed(wdt_dev, wdt_channel_id);  // Reset the watchdog timer countdown
    }
}