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Hardware Watchdog Timer Vs Software Watchdog Timer

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Full Member level 3
Oct 31, 2013
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I have a better idea about the hardware watchdog timer, but i don't know about the software watchdog timer? what is the importance and where it is useful?

I come across the web, but i didn't found the answer for it. Can any one help me

Thanks & Regards,

A wakeup H/W timer is often used to get out of sleep mode.

A timer is also used to count successful operations for over or under-runs over any significant time interval, and if error, check by NMI or hard reset routine.
This can be S/W or Hardware driven to check faults in other routines independent of S/W or H/W being used.

Simplest method is set count periodically then decrement on expected I/O but if reach zero then fault condition reached.
This requires tasks to be periodically pushed onto stack, not simply wait.

We used to call these Sanity or Watchdog Timers.

As per my knowledge I think it is implemented in software like as follows

Slave is programmed in such way that has to send some signal (either it can be high to low or low to high) for a pre-determined time (for example once in 10 seconds) to the master. If the master is programmed in such a way that if it doesn't receive the signal then it resets the slave. Same can be repeated in vice versa I guess.

The problem that I see using the software watchdog is in the case of failure occurrence on the code so that stops the timer operation. Most microcontrolers have watchdog enable configured at the fuse bits, turning difficult to disable it during normal operation.

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