Re: emu10k1 latency / capture period

[Takashi Iwai <tiwai@suse.de>]

At Sun, 20 Jun 2004 00:06:23 -0400,
Lee Revell wrote:
> 
> [1  <text/plain (7bit)>]
> On Wed, 2004-06-16 at 16:14, Lee Revell wrote:
> > Hey,
> > 
> > I am having a problem with the emu10k1 driver where I am unable to set
> > the capture period lower than 512.  The result is that the lowest
> > achievable input to output latency is in the neighborhood of 40ms.
> > 
> 
> I think I may have solved this problem.  Here is a patch against
> alsa-driver-1.0.5a.
> 
> --- alsa-driver-1.0.5a/alsa-kernel/pci/emu10k1/emupcm.c.orig   
> 2004-06-19 23:21:09.000000000 -0400
> +++ alsa-driver-1.0.5a/alsa-kernel/pci/emu10k1/emupcm.c 2004-06-19
> 23:21:12.000000000 -0400
> @@ -932,7 +932,7 @@
>         spin_unlock_irqrestore(&emu->reg_lock, flags);
>         emu->capture_efx_interrupt = snd_emu10k1_pcm_efx_interrupt;
>         emu->pcm_capture_efx_substream = substream;
> -       snd_pcm_hw_constraint_list(runtime, 0,
> SNDRV_PCM_HW_PARAM_PERIOD_SIZE, &hw_constraints_capture_period_sizes);
> +       // snd_pcm_hw_constraint_list(runtime, 0,
> SNDRV_PCM_HW_PARAM_PERIOD_SIZE, &hw_constraints_capture_period_sizes);
>         return 0;
>  }
> 
> I do not think that the FX8010 capture device is constrained by the 
> period size limitations on the standard emu10k1 capture device.

Right, this constraint is invalid.
Thanks for pointint out.

> With this patch I can run JACK in capture only mode with the period size
> set as low as 128.  64 gives an error.  This is exactly the expected
> behavior: 128 frames is the lowest setting the kX ASIO driver allows.
> 
> Now, there is one more issue.  For some reason, in the emu10k1 driver, 
> different numbered devices are used for FXBus capture and playback -
> capture is hw:0,2 and playback is hw:0,3.  I don't think JACK supports 
> full duplex mode if the playback and capture devices are different.  
> It seems like these should be part of the same device anyway, they refer
> to the exact same registers.

Yes, it would make more sense.  I'll fix this, too.

Meanwhile, you can use asym plugin for this purpose, e.g. adding the
following to ~/.asoundrc:

	pcm.fx {
		type asym
		playback.pcm "hw:0,3"
		capture.pcm "hw:0,2"
	}

and use the PCM "fx" for jack.

> [2 fxbus_capture_fix.patch <text/x-patch (7bit)>]

What is this patch?


Takashi


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