Re: Lowest latency: JACK, or ALSA directly?

[Takashi Iwai <tiwai@suse.de>]

At 17 Nov 2004 20:07:57 -0600,
Jack O'Quin wrote:
> 
> > Untested as usual :)
> 
> I'll try it here with my Delta-66.  
> 
> That won't test any of the strange cases where -nperiods=2 but the
> device actually requires a three-period buffer.  Which cards do you
> know of that are affected by this?

rme32, rme96 and korg1212 have the fixed buffer size.
ymfpci has 3 periods as minimum, too.


> > (BTW, the jack code is still based on the older ALSA API.
> >  Is this intentional?)
> 
> It was intentional last year so JACK would work with all ALSA
> versions.  A patch was recently submitted to use the newer interfaces.
> The consensus on jackit-devel was that it is time to do that now, but
> the patch has not yet been committed to CVS.
> 
> (Patch follows for your review...)
> > [2. text/x-patch; 2004-11-02.0.patch]...
> @@ -620,19 +621,15 @@
(snip)
> +		err = snd_pcm_hw_params_get_period_size (
> +			driver->playback_hw_params, &p_period_size, &dir);
> +		err = snd_pcm_hw_params_get_periods (
> +			driver->playback_hw_params, &p_nfragments, &dir);
> +		err = snd_pcm_hw_params_get_format (
> +			driver->playback_hw_params, &(driver->playback_sample_format));
> +		snd_pcm_access_t access ;

^^^ the variable declaration should be moved in the beginning of the
block.

Otherwise it looks fine.
You could check the return value of snd_pcm_hw_params_get_*, but it's
usually ok.


Takashi


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