1 =============================
2 Notes on Kernel OSS-Emulation
3 =============================
4
5 Jan. 22, 2004 Takashi Iwai <tiwai@suse.de>
6
7
8 Modules
9 =======
10
11 ALSA provides a powerful OSS emulation on the
12 The OSS emulation for PCM, mixer and sequencer
13 as add-on kernel modules, snd-pcm-oss, snd-mix
14 When you need to access the OSS PCM, mixer or
15 corresponding module has to be loaded.
16
17 These modules are loaded automatically when th
18 is called. The alias is defined ``sound-servi
19 the card number and the minor unit number. Us
20 define these aliases by yourself.
21
22 Only necessary step for auto-loading of OSS mo
23 card alias in ``/etc/modprobe.d/alsa.conf``, s
24
25 alias sound-slot-0 snd-emu10k1
26
27 As the second card, define ``sound-slot-1`` as
28 Note that you can't use the aliased name as th
29 ``alias sound-slot-0 snd-card-0`` doesn't work
30 modutils).
31
32 The currently available OSS configuration is s
33 /proc/asound/oss/sndstat. This shows in the s
34 /dev/sndstat, which is available on the commer
35 On ALSA, you can symlink /dev/sndstat to this
36
37 Please note that the devices listed in this pr
38 after the corresponding OSS-emulation module i
39 even if "NOT ENABLED IN CONFIG" is shown in it
40
41
42 Device Mapping
43 ==============
44
45 ALSA supports the following OSS device files:
46 ::
47
48 PCM:
49 /dev/dspX
50 /dev/adspX
51
52 Mixer:
53 /dev/mixerX
54
55 MIDI:
56 /dev/midi0X
57 /dev/amidi0X
58
59 Sequencer:
60 /dev/sequencer
61 /dev/sequencer2 (aka /dev/musi
62
63 where X is the card number from 0 to 7.
64
65 (NOTE: Some distributions have the device file
66 /dev/midi1. They are NOT for OSS but for tclm
67 a totally different thing.)
68
69 Unlike the real OSS, ALSA cannot use the devic
70 assigned ones. For example, the first card ca
71 /dev/dsp2, but only /dev/dsp0 and /dev/adsp0.
72
73 As seen above, PCM and MIDI may have two devic
74 PCM device (``hw:0,0`` in ALSA) is mapped to /
75 device (``hw:0,1``) to /dev/adsp (if available
76 /dev/amidi, respectively.
77
78 You can change this device mapping via the mod
79 snd-pcm-oss and snd-rawmidi. In the case of P
80 options are available for snd-pcm-oss:
81
82 dsp_map
83 PCM device number assigned to /dev/dsp
84 (default = 0)
85 adsp_map
86 PCM device number assigned to /dev/ads
87 (default = 1)
88
89 For example, to map the third PCM device (``hw
90 define like this:
91 ::
92
93 options snd-pcm-oss adsp_map=2
94
95 The options take arrays. For configuring the
96 two entries separated by comma. For example,
97 device on the second card to /dev/adsp1, defin
98 ::
99
100 options snd-pcm-oss adsp_map=0,2
101
102 To change the mapping of MIDI devices, the fol
103 available for snd-rawmidi:
104
105 midi_map
106 MIDI device number assigned to /dev/mi
107 (default = 0)
108 amidi_map
109 MIDI device number assigned to /dev/am
110 (default = 1)
111
112 For example, to assign the third MIDI device o
113 /dev/midi00, define as follows:
114 ::
115
116 options snd-rawmidi midi_map=2
117
118
119 PCM Mode
120 ========
121
122 As default, ALSA emulates the OSS PCM with so-
123 i.e. tries to convert the sample format, rate
124 automatically when the card doesn't support it
125 This will lead to some problems for some appli
126 wine, especially if they use the card only in
127
128 In such a case, you can change the behavior of
129 writing a command to the proc file. There is
130 stream, ``/proc/asound/cardX/pcmY[cp]/oss``, w
131 (zero-based), Y the PCM device number (zero-ba
132 playback and ``c`` for capture, respectively.
133 exists only after snd-pcm-oss module is loaded
134
135 The command sequence has the following syntax:
136 ::
137
138 app_name fragments fragment_size [opti
139
140 ``app_name`` is the name of application with (
141 path.
142 ``fragments`` specifies the number of fragment
143 number is given.
144 ``fragment_size`` is the size of fragment in b
145 ``options`` is the optional parameters. The f
146 available:
147
148 disable
149 the application tries to open a pcm de
150 this channel but does not want to use
151 direct
152 don't use plugins
153 block
154 force block open mode
155 non-block
156 force non-block open mode
157 partial-frag
158 write also partial fragments (affects
159 no-silence
160 do not fill silence ahead to avoid cli
161
162 The ``disable`` option is useful when one stre
163 capture) is not handled correctly by the appli
164 hardware itself does support both directions.
165 The ``direct`` option is used, as mentioned ab
166 conversion and useful for MMAP-applications.
167 For example, to playback the first PCM device
168 quake, send a command via echo like the follow
169 ::
170
171 % echo "quake 0 0 direct" > /proc/asou
172
173 While quake wants only playback, you may appen
174 to notify driver that only this direction is a
175 ::
176
177 % echo "quake 0 0 disable" > /proc/aso
178
179 The permission of proc files depend on the mod
180 As default it's set as root, so you'll likely
181 sending the command above.
182
183 The block and non-block options are used to ch
184 opening the device file.
185
186 As default, ALSA behaves as original OSS drive
187 the file when it's busy. The -EBUSY error is r
188
189 This blocking behavior can be changed globally
190 module option of snd-pcm-oss. For using the b
191 for OSS devices, define like the following:
192 ::
193
194 options snd-pcm-oss nonblock_open=0
195
196 The ``partial-frag`` and ``no-silence`` comman
197 Both commands are for optimization use only.
198 specifies to invoke the write transfer only wh
199 filled. The latter stops writing the silence
200 automatically. Both are disabled as default.
201
202 You can check the currently defined configurat
203 file. The read image can be sent to the proc
204 can save the current configuration
205 ::
206
207 % cat /proc/asound/card0/pcm0p/oss > /
208
209 and restore it like
210 ::
211
212 % cat /somewhere/oss-cfg > /proc/asoun
213
214 Also, for clearing all the current configurati
215 as below:
216 ::
217
218 % echo "erase" > /proc/asound/card0/pc
219
220
221 Mixer Elements
222 ==============
223
224 Since ALSA has completely different mixer inte
225 OSS mixer is relatively complicated. ALSA bui
226 from several different ALSA (mixer) controls b
227 string. For example, the volume element SOUND
228 from "PCM Playback Volume" and "PCM Playback S
229 playback direction and from "PCM Capture Volum
230 Switch" for the capture directory (if exists).
231 OSS is changed, all the volume and switch cont
232 automatically.
233
234 As default, ALSA uses the following control fo
235
236 ==================== =====================
237 OSS volume ALSA control
238 ==================== =====================
239 SOUND_MIXER_VOLUME Master
240 SOUND_MIXER_BASS Tone Control - Bass
241 SOUND_MIXER_TREBLE Tone Control - Treble
242 SOUND_MIXER_SYNTH Synth
243 SOUND_MIXER_PCM PCM
244 SOUND_MIXER_SPEAKER PC Speaker
245 SOUND_MIXER_LINE Line
246 SOUND_MIXER_MIC Mic
247 SOUND_MIXER_CD CD
248 SOUND_MIXER_IMIX Monitor Mix
249 SOUND_MIXER_ALTPCM PCM
250 SOUND_MIXER_RECLEV (not assigned)
251 SOUND_MIXER_IGAIN Capture
252 SOUND_MIXER_OGAIN Playback
253 SOUND_MIXER_LINE1 Aux
254 SOUND_MIXER_LINE2 Aux
255 SOUND_MIXER_LINE3 Aux
256 SOUND_MIXER_DIGITAL1 Digital
257 SOUND_MIXER_DIGITAL2 Digital
258 SOUND_MIXER_DIGITAL3 Digital
259 SOUND_MIXER_PHONEIN Phone
260 SOUND_MIXER_PHONEOUT Phone
261 SOUND_MIXER_VIDEO Video
262 SOUND_MIXER_RADIO Radio
263 SOUND_MIXER_MONITOR Monitor
264 ==================== =====================
265
266 The second column is the base-string of the co
267 control. In fact, the controls with ``XXX [Pl
268 [Volume|Switch]`` will be checked in addition.
269
270 The current assignment of these mixer elements
271 file, /proc/asound/cardX/oss_mixer, which will
272 ::
273
274 VOLUME "Master" 0
275 BASS "" 0
276 TREBLE "" 0
277 SYNTH "" 0
278 PCM "PCM" 0
279 ...
280
281 where the first column is the OSS volume eleme
282 the base-string of the corresponding ALSA cont
283 control index. When the string is empty, it m
284 corresponding OSS control is not available.
285
286 For changing the assignment, you can write the
287 proc file. For example, to map "Wave Playback
288 send the command like the following:
289 ::
290
291 % echo 'VOLUME "Wave Playback" 0' > /p
292
293 The command is exactly as same as listed in th
294 change one or more elements, one volume per li
295 example, both "Wave Playback Volume" and "Wave
296 be affected when PCM volume is changed.
297
298 Like the case of PCM proc file, the permission
299 the module options of snd. you'll likely need
300 sending the command above.
301
302 As well as in the case of PCM proc file, you c
303 current mixer configuration by reading and wri
304 image.
305
306
307 Duplex Streams
308 ==============
309
310 Note that when attempting to use a single devi
311 capture, the OSS API provides no way to set th
312 number of channels different in each direction
313 ::
314
315 io_handle = open("device", O_RDWR)
316
317 will only function correctly if the values are
318
319 To use different values in the two directions,
320 ::
321
322 input_handle = open("device", O_RDONLY
323 output_handle = open("device", O_WRONL
324
325 and set the values for the corresponding handl
326
327
328 Unsupported Features
329 ====================
330
331 MMAP on ICE1712 driver
332 ----------------------
333 ICE1712 supports only the unconventional forma
334 10-channels 24bit (packed in 32bit) format. T
335 the buffer as the conventional (mono or 2-chan
336 on OSS.
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.