[alsa-devel] About impacts to user-land

[Takashi Sakamoto]

In this message, let me describe impacts to user-land by adding the drivers.

(I'm sorry but I re-post because previous post is not archived.)

[Supported devices]
Currently snd-fireworks, snd-bebob and snd-oxfw totally supports 65 devices.
But there are some models detected as the same device, there are some
models whici is based on Fireworks/BeBoB/OXFW but its IDs are unknown.
So they can totally supports 80-90 models.


[The number of PCM channels is different depending on models and
sampling rates]
There are some models detected as the same device but the number of
channels is different. (i.e. Mackie Onyx-i series)
There are some models in which the number of channels are different at
each sampling rate. (i.e. M-Audio Firewire 410)
There are many variations for PCM channels/rates.

In this reason, I cannot write ALSA Configuration with 'route' plugin
for 'front' or 'surround'.
The 'route' plugin needs fixed value for the number of channels but I
have no will to write Configurations for each devices.
(Maybe 100 or more files I have to write...)

If ALSA applications don't resolve channel mismatch in application side,
use 'plughw' device WITHOUT 'SND_PCM_NO_AUTO_CHANNELS' flag for
snd_pcm_open().

But PulseAudio has an issue. See:
http://lists.freedesktop.org/archives/pulseaudio-discuss/2014-January/019685.html


[Conflict against user-land driver]
The supported devices can transmit one AMDTP stream and receive one
AMDTP stream.
Then there is a conflict between kernel-land drivers and user-land drivers.

The supported devices manage their connection by Plug Register,
according to IEC 61883-1.
The drivers can know whether the device is used or not by reading this
register.

This mechanism is already implemented in kernel-land driver. So
kernel-land driver never interrupt user-land driver.

Currently I suggest a patch for this to FFADO project. See:
http://sourceforge.net/mailarchive/message.php?msg_id=31856195


[Both of PCM/MIDI functionality can starts streaming]
An AMDTP can transfer PCM samples and MIDI messages as its data channel,
according to IEC 61883-6 (in detail, MMA/AMEI RP-027).
This means that both of PCM/MIDI stream can be joined into the same
AMDTP stream.
So both of PCM/MIDI functionality can start AMDTP stream.
Then users can't simultaneously use ALSA's MIDI functionality and
user-land driver.


Regards

Takashi Sakamoto
o-takashi at sakamocchi.jp