Watchdogs

Question 1

What is the job of a Watchdogs

Answer 1

Watchdogs monitor embedded systems to ensure they operate continuously

Question 2

How does a Watchdog work (bite & kick)

Answer 2

The watchdog takes the form of a hardware counter with its own clock/ timer
When the timer runs out it sends a hardware reset
When the software is operating normally it restarts the timer before it runs out

Question 3

What is one easy method of triggering the watchdog from inside of software

Answer 3

Enter an endless while loop, this will stop the CPU from executing any future bad decisions

Question 4

What are some software faults which a watchdog can pick up on

Answer 4

Endless loops
Interrupt floods
Deadlocks from multitasking

Question 5

What is one unintended problem which can arise with watchdogs

Answer 5

Watchdogs can end up disabling a system entirely and entering an endless loop of rebooting

Question 6

As well as fault recovery, what are some other uses of watchdogs

Answer 6

Low power oscillator to wake up from sleep
Clean software resets, for example when you need to do a firmware update

Question 7

What is the job of a monitor task

Answer 7

Monitor tasks are used when multi-tasking, they use a set of global flags to monitor all other tasks and only restart the watchdog when all tasks have reported success

Monitor tasks must be the only ones to kick the watchdog