Re: [Xenomai-help] rt_task_set_periodic and different time base

[Jan Kiszka <jan.kiszka@domain.hid>]

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Jeff Koftinoff wrote:
> Jan Kiszka wrote:
>>
>> There exists some vague ideas to provide an infrastructure with Xenomai
>> that allows to smoothly synchronise its local clock on whatever external
>> (jittery) source, but note that "vague" above.
>>
>> Moreover, I don't think you actually want this for your scenario. You
>> may rather look for a hard sync on each audio tick, no?
>>
>>   
> correct, a hard sync on each audio tick is what I want. 166 +- 20
> Microseconds.
> 
>>> My original thought was to use rt_intr_wait() in my user mode program
>>> and do the scheduling of sub-tasks myself.
>>>     
>>
>> Sounds what you need (or directly derive an RTDM device with appropriate
>> interface for your audio-hw :)).
>>
>>   
> 90% of my CPU time needs to be spent processing audio and the control
> for this audio, at the highest priority above linux, and running in C++
> in userspace (really!)... There is no 'audio driver' involved, really,
> as the whole point of the hardware is to process live audio in real time
> from audio in to audio out with very low latency in usermode.

I see.

>>> But it would be ideal if rt_task_set_periodic() could just use the
>>> appropriate time source itself.
>>>     
>>
>> Why?
>>
>>   
> Because I have many layers of audio processing procedures that need to
> be scheduled at different periodic intervals, with different priorities.
> lower level audio processing procedures run every 166 microseconds and
> have highest priority, and interrupt higher level lower rate (5.3
> ms,10.66 ms and 32 ms) control processing procedures.

So they are all multiples of the base period? Why not let the high-rate
tasks wake the low-rate ones when time has come, e.g. via semaphores?

> I have non-xenomai usermode code right now that can use a recursive
> signal handler to manually schedule these 'layers' of processing tasks. 
> But then I'm just duplicating the rt_task_set_periodic() capability that
> is already there in xenomai.
> 
> I just want the Xenomai task scheduler to be controlled directly by the
> audio tick interrupt.... Is that a problem to enable?

You may hack this into the code, but I would rather suggest to design
this at application level in order to remain portable across Xenomai
releases. Only if you find relevant performance deficits (but I do not
see any yet), you may consider special solutions (in that case, please
come back with the issue, maybe we can find a generic way that helps
others as well).

Jan


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