- A Watchdog timer is a software timer used to detect and recover from deadlock conditions.
- When a Watchdog timer triggers it interrupts the controller processor by initiating a controller reset.
Placating or resetting the watchdog device
- The interrupt service routine in the firmware must respond with an action to placate, or reset, the watchdog hardware within a short period of time.
- If not placated, the watchdog timer will force a hard reset (similar to sysReboot) of the controller.
- Upon reset, the firmware reports that the controller had been reset by the watchdog timer with the message:
WARNING: Restart by watchdog time
- The watchdog timer is enabled for Fibre Channel as there is no equivalent of a scsi-bus-reset.
- The watchdog timer will reset the controller if there is no fibre channel interrupt serviced for about 5-10 seconds.
- The array controller generates its own interrupts to cover timers when the host is inactive.
Benefits of a watchdog timer
- A watchdog timer protects the system from software hangs.
- It provides a means for errors to be detected and resolved automatically.
- When watchdog timer ticks down to 0, a system reset is triggered.
- Watchdog timers allow an automated means of recovering in the event the software becomes hung, so administrator intervention is not required.
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