General

A system can become unresponsive for many unforeseen reasons in the field. The "Platform Watchdog" feature of OpenSync provides a proxy between a HW watchdog timer (WDT) and OpenSync (OS). It provides a Watchdog Proxy Daemon (WPD) with the purpose of stimulating the hardware Watchdog Timer (WDT) while ensuring that the upper layers (OS) remain sufficiently responsive. In case of system anomalies, if the WPD fails to refresh and the hardware Watchdog Timer (WDT) expires, the WDT chip intervenes by resetting the system. Upper layer (OS) is responsible for providing the daemon with information affirming that everything is functioning correctly, prompting the daemon to continue refreshing the WDT.

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Command line interface

WPD is implemented as an executable binary located at /usr/opensync/bin/wpd, providing the following interface:

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Typically, WPD operates as a daemon in non-autonomous mode, meaning that it requires regular stimulation every few seconds (e.g., every 5 seconds). Stimulation is carried out by executing the commandwpd --ping .
The --set-auto option is employed to run the daemon in autonomous mode, reserved for specific system operation modes (e.g., manufacturing), where the application is not running, and WPD does not require external stimulation as it automatically refreshes the hardware Watchdog Timer (WDT).

Initialization script

By default, WPD supports a SysV SystemV init script, which is provided in file /etc/init.d/wpd and is universally applicable to both OpenWrt-based systems and other SysV SystemV systems. However, SystemD is currently not supported.

Signal handling

Internal signals:
SIGUSR1 - wpd set mode to autonomous
SIGUSR2 - wpd set mode to non-autonomous
SIGHUP - wpd to ping WD when in non-autonomous mode
SIGINT - kill wpd

Northbound API

NoneIf executed as --daemon, it will write it's own PID number to /var/run/wpd.pid, fork(), and run according to non-autonomous mode, waiting for signals to change mode of operation or to ping the watchdog.

If executed to change mode of operation or to ping the WDT, it will send a signal to the process with the PID from the PID file.

Northbound API

No northbound API.

Southbound API

Connection Manager CM in OpenSync calls function

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bool

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target_device_wdt_ping(void)

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which is provided in core and its purpose is to inform WPD that system is functioning correctly. If this function is not called every few seconds, the watchdog timer (WDT) will expire, triggering a hardware reset.

Requirements

WPD requires:

• HW WDT chip

• Kernel support for WDT providing a /dev/watchdog device to userspace

• The watchdog device /dev/watchdog should be closed before starting WPD, allowing WPD to open the watchdog device by itself.

• All default Linux watchdog daemons using /dev/watchdog, such as wdctl, should be stopped and are mutually exclusive with WPD.