OSS emulation

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#REDIRECT [[OSSEmulation]]
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== OSS Emulation in Alsa ==
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One of the aims of ALSA is to provide full OSS compatibility for OSS applications.  ALSA has an '''OSS emulation''' which supports all of the [[OSS device]]s listed below.
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There are two different OSS emulation methods in ALSA (and several not in ALSA itself; see the "Alternatives" section below):
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# Kernel-level OSS emulation via the <code>[[snd-pcm-oss]]</code> and <code>[[snd-mixer-oss]]</code> and <code>[[snd-seq-oss]]</code> modules
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# The <code>[[aoss]]</code> script from the <code>[[alsa-oss]]</code> package.
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The latter has the advantage of being able to use any device from ALSA's [[PCM plugin]] layer during the emulation. This enables software-based mixing of streams for OSS apps. See the [[DmixPlugin]] page for more details of how to do software mixing.
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Note that neither method works for all OSS apps.
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== Issues and Limitations ==
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Particular issues include:
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* the OSS sequencer <code>/dev/sequencer</code> only half works (playback works but recording from [[MIDI keyboards]] is broken -- ''see Alsa-devel [http://bugtrack.alsa-project.org/alsa-bug/bug_view_advanced_page.php?bug_id=28 2004/02/02] 2002/8/26 and 2003/12/7'').
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* apps that use libc's FILE* functionality (fopen(), etc..). A fix for this should now be in alsa cvs (as of what version/date?)
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* things that use OSS via memory mapping (mmap). See [[ALSA PCM proc commands]] for some hints on this.
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* The ''ICE1712'' chipset supports only an unconventional format, interleaved 10-channels 24bit (packed in 32bit). Therefore you cannot mmap the buffer in a conventional (mono or 2-channels, 8 or 16bit) format using OSS emulation.
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* Some USB devices support only 24bit format packed in 3bytes. This format is not supported by OSS and no conversion is provided by kernel OSS emulation. You can, however, use the user-space OSS emulation via libaoss instead.
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== OSS Emulation Topics ==
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* [http://alsa.opensrc.org/OSS+device List of Supported OSS devices] (such as /dev/dsp)
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* Kernel [[module device mapping options]] control which ALSA PCM and MIDI devices OSS devices like /dev/dsp get mapped to.
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* Some [[ALSA PCM proc commands]] can be used to control behaviors important for OSS emulation. Check these out if your problems may be related to:
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** apps that uses MMAP
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** sample rate conversion
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** fragment size
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** i/o blocking issues
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** apps that can't handle duplex streams properly
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* Takashi Iwai's documentation on the OSS MIDI emulation may be found at [[OssSequencerEmulation]].
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* All about [[Mapping oss mixer controls to alsa mixer]]
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== More Info ==
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Much of this page and it's sub-topic pages is derived from  http://alsa-project.org/~iwai/OSS-Emulation.html from the official ALSA docs. It may be more frequently updated or contain more extensive information than this wiki.
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[[DmixPlugin]] includes some tips on using dmix with OSS.
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[[OSS and dmix]] by Richard is an a step by step guide on how to use xmms while playing Unreal Tournament. It probably will also help with Enemy Territory, Quake3, and other things that use OSS, fopen(), and/or mmap.
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== Alternatives ==
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ALSA is not the first sound system (and probably not the last) to have a need to capture and convert output from programs written for OSS. If ALSA's OSS Emulation is not doing it for you, you can look into:
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* the artsdsp wrapper for KDE's arts sound server
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* the esddsp wrapper for esd (Enlighted Sound Daemon) sound server
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* the libjackasyn and bio2jack libraries for use with jackit (Jack Audio Connection Kit) (bio2jack requires recompiling)
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[[Category:OSS]]

Latest revision as of 23:16, 14 February 2007

Contents

OSS Emulation in Alsa

One of the aims of ALSA is to provide full OSS compatibility for OSS applications. ALSA has an OSS emulation which supports all of the OSS devices listed below.

There are two different OSS emulation methods in ALSA (and several not in ALSA itself; see the "Alternatives" section below):

  1. Kernel-level OSS emulation via the snd-pcm-oss and snd-mixer-oss and snd-seq-oss modules
  2. The aoss script from the alsa-oss package.

The latter has the advantage of being able to use any device from ALSA's PCM plugin layer during the emulation. This enables software-based mixing of streams for OSS apps. See the DmixPlugin page for more details of how to do software mixing.

Note that neither method works for all OSS apps.

Issues and Limitations

Particular issues include:

OSS Emulation Topics

More Info

Much of this page and it's sub-topic pages is derived from http://alsa-project.org/~iwai/OSS-Emulation.html from the official ALSA docs. It may be more frequently updated or contain more extensive information than this wiki.

DmixPlugin includes some tips on using dmix with OSS.

OSS and dmix by Richard is an a step by step guide on how to use xmms while playing Unreal Tournament. It probably will also help with Enemy Territory, Quake3, and other things that use OSS, fopen(), and/or mmap.

Alternatives

ALSA is not the first sound system (and probably not the last) to have a need to capture and convert output from programs written for OSS. If ALSA's OSS Emulation is not doing it for you, you can look into:

Retrieved from "http://alsa.opensrc.org/OSS_emulation"
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