samples: driver: watchdog: Sample fails on disco_l475_iot1

[hwilmers]

Describe the bug
The sample app samples/driver/watchdog fails at runtime, sending an error message.
Tested using Zephyr 2.5.0 on disco_l475_iot1.

To Reproduce
Steps to reproduce the behavior:

1. cd samples/driver/watchdog
2. west build -b disco_l475_iot1
3. west flash
4. See error

Expected behavior
The expected behaviour of the app is to repeat following sequence:

• initialise watchdog
• feed the watchdog a few times
• stop feeding, and wait for a watchdog reset

Impact
The watchdog is not functional.

Logs and console output
Console log:

*** Booting Zephyr OS build zephyr-v2.5.0 ***
Watchdog sample application
Attempting to test pre-reset callback
Watchdog install error

Environment (please complete the following information):

• OS: Linux
• Toolchain: zephyr 0.11.2
• Zephyr Release 2.5.0

[hwilmers]

Further debugging shows that wdt_install_timeout() returrns -EINVAL here, on line 112:

zephyr/samples/drivers/watchdog/src/main.c

Lines 112 to 120 in b9fdab4

	wdt_channel_id = wdt_install_timeout(wdt, &wdt_config);
	if (wdt_channel_id == -ENOTSUP) {
	/* IWDG driver for STM32 doesn't support callback */
	printk("Callback support rejected, continuing anyway\n");
	wdt_config.callback = NULL;
	wdt_channel_id = wdt_install_timeout(wdt, &wdt_config);
	}
	if (wdt_channel_id < 0) {
	printk("Watchdog install error\n");

[hwilmers]

In the driver, at the attempt of setting timeout to 100ms, here the calculated timeout is set to 26214us:

zephyr/drivers/watchdog/wdt_wwdg_stm32.c

Line 192 in b275fec

calculated_timeout = wwdg_stm32_get_timeout(dev, prescaler, counter);

Is this the max timeout achievable with this MCU? Or is there a calculation error somewhere?

[hwilmers]

When using the IWDG, the sample works with the timeout values used in the sample.

This opens up for two possible workarounds:

• remove the overlay file boards/disco_l475_iot1.overlay, so the default IWDG is used instead of WWDG
• if WWDG shall be used, set WDT_MAX_WINDOW to a value <= 26

[erwango]

@hwilmers Thanks for reporting. Actually the wwdg test should run with APB bu clock tunning: CONFIG_CLOCK_STM32_APB1_PRESCALER=16
Problem is that tunning is provided in sample.yaml file and then only applied when running twister.

I'll modify so this is available even when run with west.