Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 1 | ============================= |
| 2 | Notes on Kernel OSS-Emulation |
| 3 | ============================= |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 4 | |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 5 | Jan. 22, 2004 Takashi Iwai <tiwai@suse.de> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 6 | |
| 7 | |
| 8 | Modules |
| 9 | ======= |
| 10 | |
| 11 | ALSA provides a powerful OSS emulation on the kernel. |
| 12 | The OSS emulation for PCM, mixer and sequencer devices is implemented |
| 13 | as add-on kernel modules, snd-pcm-oss, snd-mixer-oss and snd-seq-oss. |
| 14 | When you need to access the OSS PCM, mixer or sequencer devices, the |
| 15 | corresponding module has to be loaded. |
| 16 | |
| 17 | These modules are loaded automatically when the corresponding service |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 18 | is called. The alias is defined ``sound-service-x-y``, where x and y are |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 19 | the card number and the minor unit number. Usually you don't have to |
| 20 | define these aliases by yourself. |
| 21 | |
| 22 | Only necessary step for auto-loading of OSS modules is to define the |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 23 | card alias in ``/etc/modprobe.d/alsa.conf``, such as:: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 24 | |
| 25 | alias sound-slot-0 snd-emu10k1 |
| 26 | |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 27 | As the second card, define ``sound-slot-1`` as well. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 28 | Note that you can't use the aliased name as the target name (i.e. |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 29 | ``alias sound-slot-0 snd-card-0`` doesn't work any more like the old |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 30 | modutils). |
| 31 | |
| 32 | The currently available OSS configuration is shown in |
| 33 | /proc/asound/oss/sndstat. This shows in the same syntax of |
| 34 | /dev/sndstat, which is available on the commercial OSS driver. |
| 35 | On ALSA, you can symlink /dev/sndstat to this proc file. |
| 36 | |
| 37 | Please note that the devices listed in this proc file appear only |
| 38 | after the corresponding OSS-emulation module is loaded. Don't worry |
| 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: |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 46 | :: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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/music) |
| 62 | |
| 63 | where X is the card number from 0 to 7. |
| 64 | |
| 65 | (NOTE: Some distributions have the device files like /dev/midi0 and |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 66 | /dev/midi1. They are NOT for OSS but for tclmidi, which is |
| 67 | a totally different thing.) |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 68 | |
| 69 | Unlike the real OSS, ALSA cannot use the device files more than the |
| 70 | assigned ones. For example, the first card cannot use /dev/dsp1 or |
| 71 | /dev/dsp2, but only /dev/dsp0 and /dev/adsp0. |
| 72 | |
| 73 | As seen above, PCM and MIDI may have two devices. Usually, the first |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 74 | PCM device (``hw:0,0`` in ALSA) is mapped to /dev/dsp and the secondary |
| 75 | device (``hw:0,1``) to /dev/adsp (if available). For MIDI, /dev/midi and |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 76 | /dev/amidi, respectively. |
| 77 | |
| 78 | You can change this device mapping via the module options of |
| 79 | snd-pcm-oss and snd-rawmidi. In the case of PCM, the following |
| 80 | options are available for snd-pcm-oss: |
| 81 | |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 82 | dsp_map |
| 83 | PCM device number assigned to /dev/dspX |
| 84 | (default = 0) |
| 85 | adsp_map |
| 86 | PCM device number assigned to /dev/adspX |
| 87 | (default = 1) |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 88 | |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 89 | For example, to map the third PCM device (``hw:0,2``) to /dev/adsp0, |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 90 | define like this: |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 91 | :: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 92 | |
| 93 | options snd-pcm-oss adsp_map=2 |
| 94 | |
| 95 | The options take arrays. For configuring the second card, specify |
| 96 | two entries separated by comma. For example, to map the third PCM |
| 97 | device on the second card to /dev/adsp1, define like below: |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 98 | :: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 99 | |
| 100 | options snd-pcm-oss adsp_map=0,2 |
| 101 | |
| 102 | To change the mapping of MIDI devices, the following options are |
| 103 | available for snd-rawmidi: |
| 104 | |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 105 | midi_map |
| 106 | MIDI device number assigned to /dev/midi0X |
| 107 | (default = 0) |
| 108 | amidi_map |
| 109 | MIDI device number assigned to /dev/amidi0X |
| 110 | (default = 1) |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 111 | |
| 112 | For example, to assign the third MIDI device on the first card to |
| 113 | /dev/midi00, define as follows: |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 114 | :: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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-called plugin layer, |
| 123 | i.e. tries to convert the sample format, rate or channels |
| 124 | automatically when the card doesn't support it natively. |
| 125 | This will lead to some problems for some applications like quake or |
| 126 | wine, especially if they use the card only in the MMAP mode. |
| 127 | |
| 128 | In such a case, you can change the behavior of PCM per application by |
| 129 | writing a command to the proc file. There is a proc file for each PCM |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 130 | stream, ``/proc/asound/cardX/pcmY[cp]/oss``, where X is the card number |
| 131 | (zero-based), Y the PCM device number (zero-based), and ``p`` is for |
| 132 | playback and ``c`` for capture, respectively. Note that this proc file |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 133 | exists only after snd-pcm-oss module is loaded. |
| 134 | |
| 135 | The command sequence has the following syntax: |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 136 | :: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 137 | |
| 138 | app_name fragments fragment_size [options] |
| 139 | |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 140 | ``app_name`` is the name of application with (higher priority) or without |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 141 | path. |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 142 | ``fragments`` specifies the number of fragments or zero if no specific |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 143 | number is given. |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 144 | ``fragment_size`` is the size of fragment in bytes or zero if not given. |
| 145 | ``options`` is the optional parameters. The following options are |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 146 | available: |
| 147 | |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 148 | disable |
| 149 | the application tries to open a pcm device for |
| 150 | this channel but does not want to use it. |
| 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 playback only) |
| 159 | no-silence |
| 160 | do not fill silence ahead to avoid clicks |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 161 | |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 162 | The ``disable`` option is useful when one stream direction (playback or |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 163 | capture) is not handled correctly by the application although the |
| 164 | hardware itself does support both directions. |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 165 | The ``direct`` option is used, as mentioned above, to bypass the automatic |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 166 | conversion and useful for MMAP-applications. |
| 167 | For example, to playback the first PCM device without plugins for |
| 168 | quake, send a command via echo like the following: |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 169 | :: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 170 | |
| 171 | % echo "quake 0 0 direct" > /proc/asound/card0/pcm0p/oss |
| 172 | |
| 173 | While quake wants only playback, you may append the second command |
| 174 | to notify driver that only this direction is about to be allocated: |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 175 | :: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 176 | |
| 177 | % echo "quake 0 0 disable" > /proc/asound/card0/pcm0c/oss |
| 178 | |
| 179 | The permission of proc files depend on the module options of snd. |
| 180 | As default it's set as root, so you'll likely need to be superuser for |
| 181 | sending the command above. |
| 182 | |
| 183 | The block and non-block options are used to change the behavior of |
| 184 | opening the device file. |
| 185 | |
| 186 | As default, ALSA behaves as original OSS drivers, i.e. does not block |
| 187 | the file when it's busy. The -EBUSY error is returned in this case. |
| 188 | |
| 189 | This blocking behavior can be changed globally via nonblock_open |
| 190 | module option of snd-pcm-oss. For using the blocking mode as default |
| 191 | for OSS devices, define like the following: |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 192 | :: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 193 | |
| 194 | options snd-pcm-oss nonblock_open=0 |
| 195 | |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 196 | The ``partial-frag`` and ``no-silence`` commands have been added recently. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 197 | Both commands are for optimization use only. The former command |
| 198 | specifies to invoke the write transfer only when the whole fragment is |
| 199 | filled. The latter stops writing the silence data ahead |
| 200 | automatically. Both are disabled as default. |
| 201 | |
| 202 | You can check the currently defined configuration by reading the proc |
| 203 | file. The read image can be sent to the proc file again, hence you |
| 204 | can save the current configuration |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 205 | :: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 206 | |
| 207 | % cat /proc/asound/card0/pcm0p/oss > /somewhere/oss-cfg |
| 208 | |
| 209 | and restore it like |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 210 | :: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 211 | |
| 212 | % cat /somewhere/oss-cfg > /proc/asound/card0/pcm0p/oss |
| 213 | |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 214 | Also, for clearing all the current configuration, send ``erase`` command |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 215 | as below: |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 216 | :: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 217 | |
| 218 | % echo "erase" > /proc/asound/card0/pcm0p/oss |
| 219 | |
| 220 | |
| 221 | Mixer Elements |
| 222 | ============== |
| 223 | |
| 224 | Since ALSA has completely different mixer interface, the emulation of |
| 225 | OSS mixer is relatively complicated. ALSA builds up a mixer element |
| 226 | from several different ALSA (mixer) controls based on the name |
| 227 | string. For example, the volume element SOUND_MIXER_PCM is composed |
| 228 | from "PCM Playback Volume" and "PCM Playback Switch" controls for the |
| 229 | playback direction and from "PCM Capture Volume" and "PCM Capture |
| 230 | Switch" for the capture directory (if exists). When the PCM volume of |
| 231 | OSS is changed, all the volume and switch controls above are adjusted |
| 232 | automatically. |
| 233 | |
| 234 | As default, ALSA uses the following control for OSS volumes: |
| 235 | |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 236 | ==================== ===================== ===== |
| 237 | OSS volume ALSA control Index |
| 238 | ==================== ===================== ===== |
| 239 | SOUND_MIXER_VOLUME Master 0 |
| 240 | SOUND_MIXER_BASS Tone Control - Bass 0 |
| 241 | SOUND_MIXER_TREBLE Tone Control - Treble 0 |
| 242 | SOUND_MIXER_SYNTH Synth 0 |
| 243 | SOUND_MIXER_PCM PCM 0 |
| 244 | SOUND_MIXER_SPEAKER PC Speaker 0 |
| 245 | SOUND_MIXER_LINE Line 0 |
| 246 | SOUND_MIXER_MIC Mic 0 |
| 247 | SOUND_MIXER_CD CD 0 |
| 248 | SOUND_MIXER_IMIX Monitor Mix 0 |
| 249 | SOUND_MIXER_ALTPCM PCM 1 |
| 250 | SOUND_MIXER_RECLEV (not assigned) |
| 251 | SOUND_MIXER_IGAIN Capture 0 |
| 252 | SOUND_MIXER_OGAIN Playback 0 |
| 253 | SOUND_MIXER_LINE1 Aux 0 |
| 254 | SOUND_MIXER_LINE2 Aux 1 |
| 255 | SOUND_MIXER_LINE3 Aux 2 |
| 256 | SOUND_MIXER_DIGITAL1 Digital 0 |
| 257 | SOUND_MIXER_DIGITAL2 Digital 1 |
| 258 | SOUND_MIXER_DIGITAL3 Digital 2 |
| 259 | SOUND_MIXER_PHONEIN Phone 0 |
| 260 | SOUND_MIXER_PHONEOUT Phone 1 |
| 261 | SOUND_MIXER_VIDEO Video 0 |
| 262 | SOUND_MIXER_RADIO Radio 0 |
| 263 | SOUND_MIXER_MONITOR Monitor 0 |
| 264 | ==================== ===================== ===== |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 265 | |
| 266 | The second column is the base-string of the corresponding ALSA |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 267 | control. In fact, the controls with ``XXX [Playback|Capture] |
| 268 | [Volume|Switch]`` will be checked in addition. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 269 | |
| 270 | The current assignment of these mixer elements is listed in the proc |
| 271 | file, /proc/asound/cardX/oss_mixer, which will be like the following |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 272 | :: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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 element, the second column |
| 282 | the base-string of the corresponding ALSA control, and the third the |
| 283 | control index. When the string is empty, it means that the |
| 284 | corresponding OSS control is not available. |
| 285 | |
| 286 | For changing the assignment, you can write the configuration to this |
| 287 | proc file. For example, to map "Wave Playback" to the PCM volume, |
| 288 | send the command like the following: |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 289 | :: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 290 | |
| 291 | % echo 'VOLUME "Wave Playback" 0' > /proc/asound/card0/oss_mixer |
| 292 | |
| 293 | The command is exactly as same as listed in the proc file. You can |
| 294 | change one or more elements, one volume per line. In the last |
| 295 | example, both "Wave Playback Volume" and "Wave Playback Switch" will |
| 296 | be affected when PCM volume is changed. |
| 297 | |
| 298 | Like the case of PCM proc file, the permission of proc files depend on |
| 299 | the module options of snd. you'll likely need to be superuser for |
| 300 | sending the command above. |
| 301 | |
| 302 | As well as in the case of PCM proc file, you can save and restore the |
| 303 | current mixer configuration by reading and writing the whole file |
| 304 | image. |
| 305 | |
| 306 | |
Alan Horstmann | 1919de0 | 2007-06-04 23:11:23 +0200 | [diff] [blame] | 307 | Duplex Streams |
| 308 | ============== |
| 309 | |
| 310 | Note that when attempting to use a single device file for playback and |
| 311 | capture, the OSS API provides no way to set the format, sample rate or |
| 312 | number of channels different in each direction. Thus |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 313 | :: |
| 314 | |
Alan Horstmann | 1919de0 | 2007-06-04 23:11:23 +0200 | [diff] [blame] | 315 | io_handle = open("device", O_RDWR) |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 316 | |
Alan Horstmann | 1919de0 | 2007-06-04 23:11:23 +0200 | [diff] [blame] | 317 | will only function correctly if the values are the same in each direction. |
| 318 | |
| 319 | To use different values in the two directions, use both |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 320 | :: |
| 321 | |
Alan Horstmann | 1919de0 | 2007-06-04 23:11:23 +0200 | [diff] [blame] | 322 | input_handle = open("device", O_RDONLY) |
| 323 | output_handle = open("device", O_WRONLY) |
Takashi Iwai | 0c266c4 | 2016-11-09 16:18:14 +0100 | [diff] [blame] | 324 | |
Alan Horstmann | 1919de0 | 2007-06-04 23:11:23 +0200 | [diff] [blame] | 325 | and set the values for the corresponding handle. |
| 326 | |
| 327 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 328 | Unsupported Features |
| 329 | ==================== |
| 330 | |
| 331 | MMAP on ICE1712 driver |
| 332 | ---------------------- |
| 333 | ICE1712 supports only the unconventional format, interleaved |
| 334 | 10-channels 24bit (packed in 32bit) format. Therefore you cannot mmap |
| 335 | the buffer as the conventional (mono or 2-channels, 8 or 16bit) format |
| 336 | on OSS. |