BELK-AN-011: Using the external watchdog timer

Info Box Applies to BORA Application Notes Applies to BORA Xpress Application Notes Applies to BORA Lite Application Notes

This application note was validated against specific versions of the kit only. It may not work with other versions. Supported versions are listed in the History section.

History

ID#	Date	BELK version	Notes
18006	Jul 2023	BELK 4.1.4	First release

Introduction

BORA, BORA Xpress and BORA Lite SOMs have an onboard watchdog timer (MAX6373 device) usable as a system monitor to detect and - in case of stall condition - reset the main SoC.

This application note shows, for instance, how is configured by default the watchdog peripheral (aka WDT) and how to configure a generic Linux driver for managing the WDT.

Configuration

The default configuration is clearly explained in the SOM Hardware Manual and in the following wiki pages:

• watchdog in BORA
• watchdog in BORA Xpress
• watchdog in BORA Lite

Linux driver

It is possible to enable the gpio driver for using the gpio-watchdog driver: you have to enable the kernel driver CONFIG_GPIO_WATCHDOG=y and then configure the MIO 15 pin in the device tree, for example:

watchdog: watchdog {
       /* MAX6373 */
       compatible = "linux,wdt-gpio";
       gpios = <&gpio0 15 0>;
       hw_algo = "toggle";
       hw_margin_ms = <10000>;
       always-running;
};

&watchdog {
    status = "okay";
};

Using the WDT via sysfs

If it is required to manage directly the WDI pin at userspace, it is possible - for example - to manage the simply by activating it via sysfs interface:

root@bora:~# echo 921 > /sys/class/gpio/export
root@bora:~# echo out > /sys/class/gpio/gpio921/direction
root@bora:~# echo 1 > /sys/class/gpio/gpio921/value
…
root@bora:~# echo 0 > /sys/class/gpio/gpio921/value

In this example, it is worth remembering that the MIO pins (BANK 500) are available starting from gpio906 (corresponding to MIO00), so:

• PS_MIO15_500 → MIO 15 → 906+15 → 921

Kernel debug

It is possible to see the kernel recognizes the GPIO pin status via:

root@bora:~# cat /sys/kernel/debug/gpio
gpiochip0: GPIOs 906-1023, parent: platform/e000a000.gpio, zynq_gpio:
gpio-921 (                    |watchdog            ) out hi
root@bora:~#