Re: [LAU] Ardour session with plain ALSA, without JACK

On 02/20/2016 03:46 AM, Markus Seeber wrote:
> On 02/19/2016 11:46 PM, Robin Gareus wrote:
> [...]
>
>>
>>> Usually I use 48KHz p256 n2:
>>> [rocketmouse@email-addr-hidden ~]$ jackd -dalsa -dhw:0 -r48000 -p256 -n2
>>> jackdmp 1.9.10
>>> Copyright 2001-2005 Paul Davis and others.
>>> Copyright 2004-2014 Grame.
>>> jackdmp comes with ABSOLUTELY NO WARRANTY
>>> This is free software, and you are welcome to redistribute it
>>> under certain conditions; see the file COPYING for details
>>> no message buffer overruns
>>> no message buffer overruns
>>> no message buffer overruns
>>> JACK server starting in realtime mode with priority 10
>>> self-connect-mode is "Don't restrict self connect requests"
>>> audio_reservation_init
>>> Acquire audio card Audio0
>>> creating alsa driver ... hw:0|hw:0|256|2|48000|0|0|nomon|swmeter|-|32bit
>>> configuring for 48000Hz, period = 256 frames (5.3 ms), buffer = 2 periods
>>> ALSA: final selected sample format for capture: 32bit integer little-endian
>>> ALSA: use 64 periods for capture
>>> ALSA: final selected sample format for playback: 32bit integer little-endian
>>> ALSA: use 64 periods for playback
>>
>> and 64.
>>
>> I dimly recall seeing some message on LAU fly by about some RME devices
>> requiring 16K buffers.
>>
>> If you have such a kernel/card, Ardour/ALSA won't currently support it
>> directly, sorry.
>>
>
> That is correct, the AIO, same as the RayDAT has a fixed buffer of 16K.
> This means that regardless of the requested number of periods and frame
> size, it will always report a buffer size of 16K and a number of periods
> equal to buffersize divided by framesize.

Thanks for confirmation.

> Never the less, if requested 2
> periods with framesize of 64 samples, the card will still work correctly
> and have a latency that corresponds to 2 frames of 64 samples.

What is the case for exposing those this to userland?

I ask for two, I get behavior of two, but when checking the parameters
the value is 16. That sounds like a bug to me.

Did anyone flag this up at ALSA-dev, or report a bug?

> As said before, there are applications that make (most likely too many)
> assumptions about these numbers and therefor break with these cards.

Ardour is not as forgiving as JACK. if a call to a snd_pcm_hw_params_*
fails or if the requested value does not match the one reported by the
card, it constitutes hard failure.

best,
robin
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Received on Sat Feb 20 12:15:03 2016