1.27. Watchdog Support

1.27.1. Barebox Watchdog Functionality

In some cases we are not able to influence the hardware design anymore or while developing one needs to be able to feed the watchdog to disable it from within the bootloader. For these scenarios barebox provides the watchdog framework with the following functionality and at least CONFIG_WATCHDOG should be enabled.

1.27.1.1. Polling

Watchdog polling/feeding allows to feed the watchdog and keep it running on one side and to not reset the system on the other side. It is needed on hardware with short-time watchdogs. For example the Atheros ar9331 watchdog has a maximal timeout of 7 seconds, so it may reset even on netboot. Or it can be used on systems where the watchdog is already running and can’t be disabled, an example for that is the watchdog of the i.MX2 series. This functionally can be seen as a threat, since in error cases barebox will continue to feed the watchdog even if that is not desired. So, depending on your needs CONFIG_WATCHDOG_POLLER can be enabled or disabled at compile time. Even if barebox was built with watchdog polling support, it is not enabled by default. To start polling from command line run:

wdog0.autoping=1

NOTE Using this feature might have the effect that the watchdog is effectively disabled. In case barebox is stuck in a loop that includes feeding the watchdog, then the watchdog will never trigger. Only use this feature during development or when a bad watchdog design (Short watchdog timeout enabled as boot default) doesn’t give you another choice.

The poller interval is not configurable, but fixed at 500ms and the watchdog timeout is configured by default to the maximum of the supported values by hardware. To change the timeout used by the poller, run:

wdog0.timeout_cur=7

To read the current watchdog’s configuration, run:

devinfo wdog0

The output may look as follows where timeout_cur and timeout_max are measured in seconds:

barebox@DPTechnics DPT-Module:/ devinfo wdog0
Parameters:
  autoping: 1 (type: bool)
  timeout_cur: 7 (type: uint32)
  timeout_max: 10 (type: uint32)

Use barebox’ environment to persist these changes between reboots:

nv dev.wdog0.autoping=1
nv dev.wdog0.timeout_cur=7

1.27.1.2. Boot Watchdog Timeout

With this functionality barebox may start a watchdog or update the timeout of an already-running one, just before kicking the boot image. It can be configured temporarily via

global boot.watchdog_timeout=10

or persistently by

nv boot.watchdog_timeout=10

where the used value again is measured in seconds.

On a system with multiple watchdogs, the watchdog with the highest positive priority is the one affected by the boot.watchdog_timeout parameter. If multiple watchdogs share the same priority, only one will be started.