[En-Nut-Discussion] Thread priority

[Henrik Maier]

Petting a watchdog in an timer ISR defeats the purpose (assuming your 
purpose is to detect software defects not only hardware defects). It is 
very likely that your timer ISR is still executed even your main 
application has fully crashed.

Some thought has to be spend on implementing a sensible watchdog 
supervision in a multi-threaded application and there is no general 
answer as it depends how your worker threads are executed. That can be 
event driven, cyclically or something else.

In a concept I have implemented in several designs I supervise all 
threads from a low priority master thread. If that master thread sees 
one worker thread not meeting it's performing criteria, then we stop 
petting the watchdog. The performance criteria depends on what the 
thread is doing and is in most cases simply monitoring a cycle counter.

Is also have event-blocking threads (TCP read/accept etc) time-out so 
they can report to the monitoring thread that they are still alive.

At the end of the day each thread is a self contained execution 
environment which needs to be monitored. Each single thread can lock-up 
in a way that the other thread still executes and this should be taken 
into account in a watchdog concept.


Henrik
http://www.proconx.com

Alexander Baranov wrote:
> Really I don't rely upon threads and use timer interrupt for that.
> Alexnder.