ALSA: doc: ReSTize OSS-Emulation document

A simple conversion from a text file.
Put to designs subdirectory.

Signed-off-by: Takashi Iwai <tiwai@suse.de>

2 files changed, 337 insertions, 0 deletions

diff --git a/Documentation/sound/designs/index.rst b/Documentation/sound/designs/index.rst
index dd4fcbc..5b3033c 100644
--- a/Documentation/sound/designs/index.rst
+++ b/Documentation/sound/designs/index.rst
@@ -7,3 +7,4 @@ Designs and Implementations
    channel-mapping-api
    procfile
    powersave
+   oss-emulation
diff --git a/Documentation/sound/designs/oss-emulation.rst b/Documentation/sound/designs/oss-emulation.rst
new file mode 100644
index 0000000..e8dcb96
--- /dev/null
+++ b/Documentation/sound/designs/oss-emulation.rst
@@ -0,0 +1,336 @@
+=============================
+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.d/alsa.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.