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 MP25 has:
-
Three watchdogs available on the STM32MP25 system-on-chip
Features
The features of the STM32MP25 watchdog include:
-
Device tree-configurable timeout, in seconds
-
Option to disable the watchdog timer count during low power modes
-
Inability to stop watchdog once started
OP-TEE configuration
To prevent the non-secure world from making unwanted accesses to the watchdog timer that might cause a system reset, the watchdog iwdg1
is enabled and managed by the secure world (OP-TEE) by default.
&etzpc {
st,decprot = <
[...]
DECPROT(STM32MP1_ETZPC_IWDG1_ID, DECPROT_S_RW, DECPROT_UNLOCK)
[...]
>;
};
&iwdg1 {
timeout-sec = <32>;
status = "okay";
};
Kernel configuration
The non-secure world can access the secure watchdog through the kernel configuration option ARM Secure Monitor Call based watchdog support (CONFIG_ARM_SMC_WATCHDOG
).
The configuration option STM Independent Watchdog (CONFIG_STM32_WATCHDOG
) enables the driver for direct access to the SoC watchdogs from the non-secure world.
These options are enabled as built-in on the ConnectCore MP25 Development Kit kernel configuration file.
Kernel driver
File | Description |
---|---|
ARM Secure Monitor Call driver |
|
STM32MP watchdog driver |
Device tree bindings and customization
The ARM Secure Monitor Call device tree binding for the secure watchdog is located at Documentation/devicetree/bindings/watchdog/arm-smc-wdt.yaml
.
The watchdog device tree binding is documented at Documentation/devicetree/bindings/watchdog/st,stm32-iwdg.yaml
.
The ConnectCore MP25 configures the ARM SMC access to the secure watchdog:
/* Secure watchdog running in OP-TEE */
&arm_wdt {
timeout-sec = <32>;
status = "okay";
};
Using the watchdog
The watchdog is accessible via the file descriptor /dev/watchdog0
.
For information about the watchdog API, see the Linux kernel documentation at Documentation/watchdog/watchdog-api.rst
.
Sample application
An example application called apix-watchdog-example
is included in the dey-examples-digiapix recipe (part of dey-examples package) of the meta-digi layer.
This application uses the Digi APIx library to enable a watchdog device on the ConnectCore MP25.
Go to GitHub to see the application instructions and source code.
See Watchdog API for more information about the watchdog APIx.