Re: [linux-audio-dev] muse and /dev/rtc

Re: [linux-audio-dev] muse and /dev/rtc

[Lee Revell]

(added alsa-devel to cc)

On Mon, 2004-11-22 at 18:53 +0100, Alfons Adriaensen wrote:
> Which leads to the following question I've been asking myself for some time:
> 
> the ALSA sequencer API seems to allow *timestamped* events - you put such
> an event in a queue and it will appear at the other end at the right moment.
> If this is true, and if ALSA has an high precision timer available to
> implement it, why should apps like MusE bother to do the fine timing
> themselves ? 

Yes, my thoughts exactly.  You don't even have to use the ALSA sequencer
API, you can use the ALSA timer API directly.  You get multiple timer
sources (system, RTC, sound card).  It should also be more portable.
For example if your sound card's timer is supported by your ALSA driver
like emu10k1 and ymfpci then I think you can use this timer to give
better sync with the hardware.

ALSA devs, is this correct?

Lee



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Re: Re: [linux-audio-dev] muse and /dev/rtc

[Takashi Iwai]

At Mon, 22 Nov 2004 13:21:07 -0500,
Lee Revell wrote:
> 
> (added alsa-devel to cc)
> 
> On Mon, 2004-11-22 at 18:53 +0100, Alfons Adriaensen wrote:
> > Which leads to the following question I've been asking myself for some time:
> > 
> > the ALSA sequencer API seems to allow *timestamped* events - you put such
> > an event in a queue and it will appear at the other end at the right moment.
> > If this is true, and if ALSA has an high precision timer available to
> > implement it, why should apps like MusE bother to do the fine timing
> > themselves ? 
> 
> Yes, my thoughts exactly.  You don't even have to use the ALSA sequencer
> API, you can use the ALSA timer API directly.  You get multiple timer
> sources (system, RTC, sound card).  It should also be more portable.
> For example if your sound card's timer is supported by your ALSA driver
> like emu10k1 and ymfpci then I think you can use this timer to give
> better sync with the hardware.
> 
> ALSA devs, is this correct?

Yes, I agree that ALSA timer API would be useful for such a case.  The
app can reject to run or do some workaround if the queried timer 
resolution is worse than requirements.

Well, my guess for the next reaction is "the lack of documentation" ;)


Takashi


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Re: Re: [linux-audio-dev] muse and /dev/rtc

[Lee Revell]

On Mon, 2004-11-22 at 19:54 +0100, Takashi Iwai wrote:
> Yes, I agree that ALSA timer API would be useful for such a case.  The
> app can reject to run or do some workaround if the queried timer 
> resolution is worse than requirements.
> 
> Well, my guess for the next reaction is "the lack of documentation" ;)

I think the only issue is that adding timer support to a driver is not
documented.  I did not even know ALSA had a timer API until it was
pointed out to me on the list, as the driver guide was my main
reference.  Adding a chapter to the guide would ensure that new drivers
get timer support.


Lee




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Re: [linux-audio-dev] muse and /dev/rtc

[Fons Adriaensen]

On Mon, Nov 22, 2004 at 01:21:07PM -0500, Lee Revell wrote:

> Yes, my thoughts exactly.  You don't even have to use the ALSA sequencer
> API, you can use the ALSA timer API directly.  You get multiple timer
> sources (system, RTC, sound card).  It should also be more portable.

Yes, but using the sequencer's timing should require less process swaps.

-- 
FA







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