Setting up watchdog_set_period to max value causes reboot

Question

I don't much about how watchdog timer works in embedded environment and I am facing issue related to watchdog timer

Maximum time out value defined in one of the macro is 55 and when we try to set up this value from watchdog_set_period function ,our board is getting reboot

#define Max_time_out 55

watchdog_set_period(int period) // Set watchdogs timeout counter

where period = 55

Now is it something expected or how what is the reason for reboot

We are writing this period value to some driver which we are accessing through file descriptor.

Answer 1

The link states this description on watchdog timers.

A watchdog timer is a piece of hardware that can be used to automatically detect software anomalies and reset the processor if any occur. Generally speaking, a watchdog timer is based on a counter that counts down from some initial value to zero. The embedded software selects the counter's initial value and periodically restarts it. If the counter ever reaches zero before the software restarts it, the software is presumed to be malfunctioning and the processor's reset signal is asserted. The processor (and the embedded software it's running) will be restarted as if a human operator had cycled the power.

You haven't posted the code so we can't judge what exactly is the problem. If you have written the code check if your code is causing any problems which is causing the watch dog timer to reset.

Answer 2

A watchdog timer is a special kind of timer usually found on embedded systems that is used to detect when the running software/firmware is hung up on some task. The watchdog timer is basically a countdown timer that counts from some initial value down to zero. When zero is reached, the watchdog timer understands that the system is hung up and resets it.

Therefore, the running software must periodically update the watchdog timer(in a infinite while loop) with a new value to stop it from reaching zero and causing a reset. When the running software is locked up doing a certain task and cannot update(refresh fails) the watchdog timer, the timer will eventually reach zero and a reset/reboot will occur.

So in summary, if you enable watchdog timer then you need to periodically refresh watchdog timer. Otherwise the board reboots when the watchdog timer expires.