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Date: Mon, 14 May 2007 22:11:27 +0200
From: Jan Kiszka <jan.kiszka@domain.hid>
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Subject: Re: [Xenomai-help] rt_task_set_periodic and different time base
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To: Jeff Koftinoff <jeffk@domain.hid>
Cc: xenomai@xenomai.org

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Jeff Koftinoff wrote:
> Hi everyone.
>=20
> I am going to be running xenomai on custom hardware to process audio.  =
I=20
> want my processes to be scheduled via rt_task_set_periodic(), but I do =

> not want to specify time in jiffies or nanoseconds.
>=20
> I need to specify time in terms of audio sample interrupts which can be=
=20
> generated by an external signal and can be slightly variable via a VCXO=
=20
> for synchronization.
>=20
> The processes that I run must be synchronous to the audio, which is=20
> asynchronous to any other clock period/time in the system.
>=20
> Should I modify Xenomai to make my audio interrupt the source of the=20
> jiffies? What is recommended in this case?

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?

>=20
> My original thought was to use rt_intr_wait() in my user mode program=20
> 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 :)).

>=20
> But it would be ideal if rt_task_set_periodic() could just use the=20
> appropriate time source itself.

Why?

Jan


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