Slow event responses (~400ms)

rg rg at
Fri Jan 26 10:42:23 UTC 2007

Joel Sherrill wrote:
> rg wrote:
>> Remailed with an intelligent subject..
>> Hi
>> I have just started programming rtems.
>> And I see a slow response to events in the order
>> of 400ms or on my system 80 ticks
>> (50MHz Leon2 CPU) RTEMS 4.6
>> I need a event response time closer to 10 ms, or 2 ticks.
>> I am measuring the response time by setting an IO output
>> just after sending the event and clearing it after receiving it
>> in the receiving task..and then I measure on a oscillioscope....
>> (difficult to spell that one...)
>> Ive tested by sending the event from a ISR and also a task...
>> all tasks have the same priority and are preemptive, tested to have
>> the receiving task no preemptive..this gives slightly better results
>> otherwise the results are the same.
> This is the problem.  You have a lot of tasks at the same priority and 
> preemption
> really isn't going to be the factor.  Tasks are in a FIFO per priority 
> and every task
> ahead of the one receiving the event will have to run and give up the 
> CPU (block or
> yield) before the task receiving the event will run.
> If you made the task receiving the event higher priority than the 
> other tasks and
> those lower priority tasks were preemptive, the number would be MUCH 
> lower.
> Most of the time, the higher priority task would execute immediately 
> after the ISR
> exits.
> This is an application design/tuning issue which could occur on any 
> priority based
> operating system.
> --joel
>> mrr
>> _______________________________________________
>> rtems-users mailing list
>> rtems-users at
Ok I tested your suggestion and now its down to 22 us about ~18000
times faster...Im happy :)


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