306 lines
10 KiB
Plaintext
306 lines
10 KiB
Plaintext
|
NOTES ON KERNEL OSS-EMULATION
|
||
|
|
=============================
|
||
|
|
|
||
|
|
Jan. 22, 2004 Takashi Iwai <tiwai@suse.de>
|
||
|
|
|
||
|
|
|
||
|
|
Modules
|
||
|
|
=======
|
||
|
|
|
||
|
|
ALSA provides a powerful OSS emulation on the kernel.
|
||
|
|
The OSS emulation for PCM, mixer and sequencer devices is implemented
|
||
|
|
as add-on kernel modules, snd-pcm-oss, snd-mixer-oss and snd-seq-oss.
|
||
|
|
When you need to access the OSS PCM, mixer or sequencer devices, the
|
||
|
|
corresponding module has to be loaded.
|
||
|
|
|
||
|
|
These modules are loaded automatically when the corresponding service
|
||
|
|
is called. The alias is defined sound-service-x-y, where x and y are
|
||
|
|
the card number and the minor unit number. Usually you don't have to
|
||
|
|
define these aliases by yourself.
|
||
|
|
|
||
|
|
Only necessary step for auto-loading of OSS modules is to define the
|
||
|
|
card alias in /etc/modprobe.conf, such as
|
||
|
|
|
||
|
|
alias sound-slot-0 snd-emu10k1
|
||
|
|
|
||
|
|
As the second card, define sound-slot-1 as well.
|
||
|
|
Note that you can't use the aliased name as the target name (i.e.
|
||
|
|
"alias sound-slot-0 snd-card-0" doesn't work any more like the old
|
||
|
|
modutils).
|
||
|
|
|
||
|
|
The currently available OSS configuration is shown in
|
||
|
|
/proc/asound/oss/sndstat. This shows in the same syntax of
|
||
|
|
/dev/sndstat, which is available on the commercial OSS driver.
|
||
|
|
On ALSA, you can symlink /dev/sndstat to this proc file.
|
||
|
|
|
||
|
|
Please note that the devices listed in this proc file appear only
|
||
|
|
after the corresponding OSS-emulation module is loaded. Don't worry
|
||
|
|
even if "NOT ENABLED IN CONFIG" is shown in it.
|
||
|
|
|
||
|
|
|
||
|
|
Device Mapping
|
||
|
|
==============
|
||
|
|
|
||
|
|
ALSA supports the following OSS device files:
|
||
|
|
|
||
|
|
PCM:
|
||
|
|
/dev/dspX
|
||
|
|
/dev/adspX
|
||
|
|
|
||
|
|
Mixer:
|
||
|
|
/dev/mixerX
|
||
|
|
|
||
|
|
MIDI:
|
||
|
|
/dev/midi0X
|
||
|
|
/dev/amidi0X
|
||
|
|
|
||
|
|
Sequencer:
|
||
|
|
/dev/sequencer
|
||
|
|
/dev/sequencer2 (aka /dev/music)
|
||
|
|
|
||
|
|
where X is the card number from 0 to 7.
|
||
|
|
|
||
|
|
(NOTE: Some distributions have the device files like /dev/midi0 and
|
||
|
|
/dev/midi1. They are NOT for OSS but for tclmidi, which is
|
||
|
|
a totally different thing.)
|
||
|
|
|
||
|
|
Unlike the real OSS, ALSA cannot use the device files more than the
|
||
|
|
assigned ones. For example, the first card cannot use /dev/dsp1 or
|
||
|
|
/dev/dsp2, but only /dev/dsp0 and /dev/adsp0.
|
||
|
|
|
||
|
|
As seen above, PCM and MIDI may have two devices. Usually, the first
|
||
|
|
PCM device (hw:0,0 in ALSA) is mapped to /dev/dsp and the secondary
|
||
|
|
device (hw:0,1) to /dev/adsp (if available). For MIDI, /dev/midi and
|
||
|
|
/dev/amidi, respectively.
|
||
|
|
|
||
|
|
You can change this device mapping via the module options of
|
||
|
|
snd-pcm-oss and snd-rawmidi. In the case of PCM, the following
|
||
|
|
options are available for snd-pcm-oss:
|
||
|
|
|
||
|
|
dsp_map PCM device number assigned to /dev/dspX
|
||
|
|
(default = 0)
|
||
|
|
adsp_map PCM device number assigned to /dev/adspX
|
||
|
|
(default = 1)
|
||
|
|
|
||
|
|
For example, to map the third PCM device (hw:0,2) to /dev/adsp0,
|
||
|
|
define like this:
|
||
|
|
|
||
|
|
options snd-pcm-oss adsp_map=2
|
||
|
|
|
||
|
|
The options take arrays. For configuring the second card, specify
|
||
|
|
two entries separated by comma. For example, to map the third PCM
|
||
|
|
device on the second card to /dev/adsp1, define like below:
|
||
|
|
|
||
|
|
options snd-pcm-oss adsp_map=0,2
|
||
|
|
|
||
|
|
To change the mapping of MIDI devices, the following options are
|
||
|
|
available for snd-rawmidi:
|
||
|
|
|
||
|
|
midi_map MIDI device number assigned to /dev/midi0X
|
||
|
|
(default = 0)
|
||
|
|
amidi_map MIDI device number assigned to /dev/amidi0X
|
||
|
|
(default = 1)
|
||
|
|
|
||
|
|
For example, to assign the third MIDI device on the first card to
|
||
|
|
/dev/midi00, define as follows:
|
||
|
|
|
||
|
|
options snd-rawmidi midi_map=2
|
||
|
|
|
||
|
|
|
||
|
|
PCM Mode
|
||
|
|
========
|
||
|
|
|
||
|
|
As default, ALSA emulates the OSS PCM with so-called plugin layer,
|
||
|
|
i.e. tries to convert the sample format, rate or channels
|
||
|
|
automatically when the card doesn't support it natively.
|
||
|
|
This will lead to some problems for some applications like quake or
|
||
|
|
wine, especially if they use the card only in the MMAP mode.
|
||
|
|
|
||
|
|
In such a case, you can change the behavior of PCM per application by
|
||
|
|
writing a command to the proc file. There is a proc file for each PCM
|
||
|
|
stream, /proc/asound/cardX/pcmY[cp]/oss, where X is the card number
|
||
|
|
(zero-based), Y the PCM device number (zero-based), and 'p' is for
|
||
|
|
playback and 'c' for capture, respectively. Note that this proc file
|
||
|
|
exists only after snd-pcm-oss module is loaded.
|
||
|
|
|
||
|
|
The command sequence has the following syntax:
|
||
|
|
|
||
|
|
app_name fragments fragment_size [options]
|
||
|
|
|
||
|
|
app_name is the name of application with (higher priority) or without
|
||
|
|
path.
|
||
|
|
fragments specifies the number of fragments or zero if no specific
|
||
|
|
number is given.
|
||
|
|
fragment_size is the size of fragment in bytes or zero if not given.
|
||
|
|
options is the optional parameters. The following options are
|
||
|
|
available:
|
||
|
|
|
||
|
|
disable the application tries to open a pcm device for
|
||
|
|
this channel but does not want to use it.
|
||
|
|
direct don't use plugins
|
||
|
|
block force block open mode
|
||
|
|
non-block force non-block open mode
|
||
|
|
partial-frag write also partial fragments (affects playback only)
|
||
|
|
no-silence do not fill silence ahead to avoid clicks
|
||
|
|
|
||
|
|
The disable option is useful when one stream direction (playback or
|
||
|
|
capture) is not handled correctly by the application although the
|
||
|
|
hardware itself does support both directions.
|
||
|
|
The direct option is used, as mentioned above, to bypass the automatic
|
||
|
|
conversion and useful for MMAP-applications.
|
||
|
|
For example, to playback the first PCM device without plugins for
|
||
|
|
quake, send a command via echo like the following:
|
||
|
|
|
||
|
|
% echo "quake 0 0 direct" > /proc/asound/card0/pcm0p/oss
|
||
|
|
|
||
|
|
While quake wants only playback, you may append the second command
|
||
|
|
to notify driver that only this direction is about to be allocated:
|
||
|
|
|
||
|
|
% echo "quake 0 0 disable" > /proc/asound/card0/pcm0c/oss
|
||
|
|
|
||
|
|
The permission of proc files depend on the module options of snd.
|
||
|
|
As default it's set as root, so you'll likely need to be superuser for
|
||
|
|
sending the command above.
|
||
|
|
|
||
|
|
The block and non-block options are used to change the behavior of
|
||
|
|
opening the device file.
|
||
|
|
|
||
|
|
As default, ALSA behaves as original OSS drivers, i.e. does not block
|
||
|
|
the file when it's busy. The -EBUSY error is returned in this case.
|
||
|
|
|
||
|
|
This blocking behavior can be changed globally via nonblock_open
|
||
|
|
module option of snd-pcm-oss. For using the blocking mode as default
|
||
|
|
for OSS devices, define like the following:
|
||
|
|
|
||
|
|
options snd-pcm-oss nonblock_open=0
|
||
|
|
|
||
|
|
The partial-frag and no-silence commands have been added recently.
|
||
|
|
Both commands are for optimization use only. The former command
|
||
|
|
specifies to invoke the write transfer only when the whole fragment is
|
||
|
|
filled. The latter stops writing the silence data ahead
|
||
|
|
automatically. Both are disabled as default.
|
||
|
|
|
||
|
|
You can check the currently defined configuration by reading the proc
|
||
|
|
file. The read image can be sent to the proc file again, hence you
|
||
|
|
can save the current configuration
|
||
|
|
|
||
|
|
% cat /proc/asound/card0/pcm0p/oss > /somewhere/oss-cfg
|
||
|
|
|
||
|
|
and restore it like
|
||
|
|
|
||
|
|
% cat /somewhere/oss-cfg > /proc/asound/card0/pcm0p/oss
|
||
|
|
|
||
|
|
Also, for clearing all the current configuration, send "erase" command
|
||
|
|
as below:
|
||
|
|
|
||
|
|
% echo "erase" > /proc/asound/card0/pcm0p/oss
|
||
|
|
|
||
|
|
|
||
|
|
Mixer Elements
|
||
|
|
==============
|
||
|
|
|
||
|
|
Since ALSA has completely different mixer interface, the emulation of
|
||
|
|
OSS mixer is relatively complicated. ALSA builds up a mixer element
|
||
|
|
from several different ALSA (mixer) controls based on the name
|
||
|
|
string. For example, the volume element SOUND_MIXER_PCM is composed
|
||
|
|
from "PCM Playback Volume" and "PCM Playback Switch" controls for the
|
||
|
|
playback direction and from "PCM Capture Volume" and "PCM Capture
|
||
|
|
Switch" for the capture directory (if exists). When the PCM volume of
|
||
|
|
OSS is changed, all the volume and switch controls above are adjusted
|
||
|
|
automatically.
|
||
|
|
|
||
|
|
As default, ALSA uses the following control for OSS volumes:
|
||
|
|
|
||
|
|
OSS volume ALSA control Index
|
||
|
|
-----------------------------------------------------
|
||
|
|
SOUND_MIXER_VOLUME Master 0
|
||
|
|
SOUND_MIXER_BASS Tone Control - Bass 0
|
||
|
|
SOUND_MIXER_TREBLE Tone Control - Treble 0
|
||
|
|
SOUND_MIXER_SYNTH Synth 0
|
||
|
|
SOUND_MIXER_PCM PCM 0
|
||
|
|
SOUND_MIXER_SPEAKER PC Speaker 0
|
||
|
|
SOUND_MIXER_LINE Line 0
|
||
|
|
SOUND_MIXER_MIC Mic 0
|
||
|
|
SOUND_MIXER_CD CD 0
|
||
|
|
SOUND_MIXER_IMIX Monitor Mix 0
|
||
|
|
SOUND_MIXER_ALTPCM PCM 1
|
||
|
|
SOUND_MIXER_RECLEV (not assigned)
|
||
|
|
SOUND_MIXER_IGAIN Capture 0
|
||
|
|
SOUND_MIXER_OGAIN Playback 0
|
||
|
|
SOUND_MIXER_LINE1 Aux 0
|
||
|
|
SOUND_MIXER_LINE2 Aux 1
|
||
|
|
SOUND_MIXER_LINE3 Aux 2
|
||
|
|
SOUND_MIXER_DIGITAL1 Digital 0
|
||
|
|
SOUND_MIXER_DIGITAL2 Digital 1
|
||
|
|
SOUND_MIXER_DIGITAL3 Digital 2
|
||
|
|
SOUND_MIXER_PHONEIN Phone 0
|
||
|
|
SOUND_MIXER_PHONEOUT Phone 1
|
||
|
|
SOUND_MIXER_VIDEO Video 0
|
||
|
|
SOUND_MIXER_RADIO Radio 0
|
||
|
|
SOUND_MIXER_MONITOR Monitor 0
|
||
|
|
|
||
|
|
The second column is the base-string of the corresponding ALSA
|
||
|
|
control. In fact, the controls with "XXX [Playback|Capture]
|
||
|
|
[Volume|Switch]" will be checked in addition.
|
||
|
|
|
||
|
|
The current assignment of these mixer elements is listed in the proc
|
||
|
|
file, /proc/asound/cardX/oss_mixer, which will be like the following
|
||
|
|
|
||
|
|
VOLUME "Master" 0
|
||
|
|
BASS "" 0
|
||
|
|
TREBLE "" 0
|
||
|
|
SYNTH "" 0
|
||
|
|
PCM "PCM" 0
|
||
|
|
...
|
||
|
|
|
||
|
|
where the first column is the OSS volume element, the second column
|
||
|
|
the base-string of the corresponding ALSA control, and the third the
|
||
|
|
control index. When the string is empty, it means that the
|
||
|
|
corresponding OSS control is not available.
|
||
|
|
|
||
|
|
For changing the assignment, you can write the configuration to this
|
||
|
|
proc file. For example, to map "Wave Playback" to the PCM volume,
|
||
|
|
send the command like the following:
|
||
|
|
|
||
|
|
% echo 'VOLUME "Wave Playback" 0' > /proc/asound/card0/oss_mixer
|
||
|
|
|
||
|
|
The command is exactly as same as listed in the proc file. You can
|
||
|
|
change one or more elements, one volume per line. In the last
|
||
|
|
example, both "Wave Playback Volume" and "Wave Playback Switch" will
|
||
|
|
be affected when PCM volume is changed.
|
||
|
|
|
||
|
|
Like the case of PCM proc file, the permission of proc files depend on
|
||
|
|
the module options of snd. you'll likely need to be superuser for
|
||
|
|
sending the command above.
|
||
|
|
|
||
|
|
As well as in the case of PCM proc file, you can save and restore the
|
||
|
|
current mixer configuration by reading and writing the whole file
|
||
|
|
image.
|
||
|
|
|
||
|
|
|
||
|
|
Duplex Streams
|
||
|
|
==============
|
||
|
|
|
||
|
|
Note that when attempting to use a single device file for playback and
|
||
|
|
capture, the OSS API provides no way to set the format, sample rate or
|
||
|
|
number of channels different in each direction. Thus
|
||
|
|
io_handle = open("device", O_RDWR)
|
||
|
|
will only function correctly if the values are the same in each direction.
|
||
|
|
|
||
|
|
To use different values in the two directions, use both
|
||
|
|
input_handle = open("device", O_RDONLY)
|
||
|
|
output_handle = open("device", O_WRONLY)
|
||
|
|
and set the values for the corresponding handle.
|
||
|
|
|
||
|
|
|
||
|
|
Unsupported Features
|
||
|
|
====================
|
||
|
|
|
||
|
|
MMAP on ICE1712 driver
|
||
|
|
----------------------
|
||
|
|
ICE1712 supports only the unconventional format, interleaved
|
||
|
|
10-channels 24bit (packed in 32bit) format. Therefore you cannot mmap
|
||
|
|
the buffer as the conventional (mono or 2-channels, 8 or 16bit) format
|
||
|
|
on OSS.
|
||
|
|
|