rtems_clock_tick execution time

Manuel Pedro Coutinho manuelpedrocoutinho at hotmail.com
Sun Jan 21 12:02:24 UTC 2007


I've been studying RTEMS, in particular the clock manager and I have a 
question relating to the amount of time that the rtems_clock_tick function 
takes.(I hope this question isn't already placed but I couldn't find it)

In the processor family (i386, SPARC, etc) RTEMS supplement manuals it is 
refered that this function takes at maximum a given time.

But when I see the code for this particular function, some questions arise 
in the _watchdog_tickle function... it does a do-while cicle for all nodes 
on the chain that migth have became "active" during that clock tick.

My question is: in the worst case scenario, all the application tasks can 
became active in a clock tick so, how can the complexity of this algorithm 
not be dependent on the number of application tasks (or another object)? And 
since the number of application tasks is variable, I think there is no way 
to say that this function takes a maximum of XXX useconds...

I don't claim to be right about this, it is just a question. I might have 
wrongly interpreted the code.
Anyway, I have thought about this and if I am right, I can't think of a 
solution to make the complexity object independent (if one makes this easier 
in this step, it makes it harder on another)

Hope I made myself understand (my english is rubish) ;)

Best regards
Manuel Coutinho

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