Watchdog

The watchdog timer, set to specific time intervals, handles gross system misbehavior. The watchdog timer can be enabled or disabled depending on the operating condition. Once the watchdog timer is activated, it must be serviced by software on a periodic basis. If servicing does not take place in time, the watchdog times out and issues a system reset.

The ConnectCore 6 system-on-module has:

Two watchdogs available on the i.MX6 system-on-chip
One watchdog available on the DA9063 PMIC

The Board Support Package (BSP) only supports the i.MX6 watchdogs.

Features

The features of the i.MX6 watchdog include:

Configurable timeout counter between 0.5s and 128s
Time resolution of 0.5s
Option to disable the watchdog timer count during low power mode
Assertion of WDOG_RESET_B_DEB reset signal on timeout
Inability to stop watchdog once started

Kernel configuration

You can manage the i.MX6 watchdog driver support through the kernel configuration option IMX2+ Watchdog (CONFIG_IMX2_WDT), which is enabled as built-in on the default ConnectCore 6 SBC kernel configuration file.

Platform driver mapping

The watchdog driver for the i.MX6 is located at drivers/watchdog/imx2_wdt.c.

Device tree bindings and customization

The watchdog device tree binding is documented at Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.txt.

The i.MX6 watchdog timers are defined in the common i.MX6 device tree file:

Common i.MX6 device tree

wdog1: wdog@020bc000 {
        compatible = "fsl,imx6q-wdt", "fsl,imx21-wdt";
        reg = <0x020bc000 0x4000>;
        interrupts = <0 80 IRQ_TYPE_LEVEL_HIGH>;
        clocks = <&clks IMX6QDL_CLK_DUMMY>;
};
wdog2: wdog@020c0000 {
        compatible = "fsl,imx6q-wdt", "fsl,imx21-wdt";
        reg = <0x020c0000 0x4000>;
        interrupts = <0 81 IRQ_TYPE_LEVEL_HIGH>;
        clocks = <&clks IMX6QDL_CLK_DUMMY>;
        status = "disabled";
};

The ConnectCore 6 system-on-module uses watchdog 1 (WDOG1) on the i.MX6 CPU to reset the system.

ConnectCore 6 SBC device tree

&gpc {
        fsl,cpu_pupscr_sw2iso = <0xf>;
        fsl,cpu_pupscr_sw = <0xf>;
        fsl,cpu_pdnscr_iso2sw = <0x1>;
        fsl,cpu_pdnscr_iso = <0x1>;
        fsl,ldo-bypass = <0>; /* No ldo-bypass */
        fsl,wdog-reset = <1>; /* watchdog select of reset source */
        pu-supply = <&reg_pu>;
};

Watchdog user space usage

Linux creates a device node /dev/watchdog that you can use to manage the watchdog timer.

For information about the watchdog API, refer to the Linux kernel documentation: Documentation/watchdog/watchdog-api.txt.

Watchdog test application

You can install the package dey-examples-watchdog, which includes the test application watchdog_test.

The watchdog_test application allows you to specify the watchdog timeout value and the test time. The application refreshes the watchdog timer every second during the test time. After the test time is over, the application no longer refreshes the watchdog. The driver resets the system when the configured timeout period ends without the watchdog being refreshed.

Syntax

To display the application syntax, run:

watchdog_test -h

Example

Run the test for 10 seconds, setting the watchdog timeout to two seconds:

watchdog_test -n 10 -t 2

In this example:

The watchdog timeout is set to two seconds
The watchdog timer is enabled
The application refreshes the watchdog timeout count every second for 10 seconds
After 10 seconds, the application quits and stops refreshing the watchdog
The driver resets the system two seconds after the application has stopped refreshing the watchdog