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SOUND(4)               FreeBSD Kernel Interfaces Manual               SOUND(4)

     sound, pcm, snd -- FreeBSD PCM audio device infrastructure

     For a card with bridge driver support, and a PnP card:
     device sound

     For a card without bridge driver support, and a non-PnP card, the follow-
     ing lines may be required in /boot/device.hints:"isa"

     Note: There exists some ambiguity in the naming at the moment (sound,
     pcm, snd).  It will be resolved soon by renaming device sound to device
     snd, and doing associated changes.

     The sound driver provides support for PCM audio play and capture.  This
     driver also supports various PCI, WSS/MSS compatible, ISA sound cards,
     and AC97 mixer.  Once the sound driver attaches, supported devices pro-
     vide audio record and playback channels.  The FreeBSD sound system pro-
     vides dynamic mixing ``VCHAN'' and rate conversion ``soft formats''.
     True full duplex operation is available on most cards.

     If the sound card is supported by a bridge driver, the sound driver works
     in conjunction with the bridge driver.

     Apart from the usual parameters, the flags field is used to specify the
     secondary DMA channel (generally used for capture in full duplex cards).
     Flags are set to 0 for cards not using a secondary DMA channel, or to
     0x10 + C to specify channel C.

     The driver does its best to recognize the installed hardware and drive it
     correctly so the user is not required to add several lines in
     /boot/device.hints.  For PCI and ISA PnP cards this is actually easy
     since they identify themselves.  For legacy ISA cards, the driver looks
     for MSS cards at addresses 0x530 and 0x604 (unless overridden in

   Boot Variables
     In general, the module snd_foo corresponds to device snd_foo and can be
     loaded by the boot loader(8) via loader.conf(5) or from the command line
     using the kldload(8) utility.  Options which can be specified in
     /boot/loader.conf include:

           snd_driver_load   (``NO'') If set to ``YES'', this option loads all
                             available drivers.

           snd_emu10k1_load  (``NO'') If set to ``YES'', only the SoundBlaster
                             5.1 driver and dependent modules will be loaded.

           snd_foo_load      (``NO'') If set to ``YES'', load driver for
                             card/chipset foo.

     To define default values for the different mixer channels, set the chan-
     nel to the preferred value using hints, e.g.: hint.pcm.0.line="0".  This
     will mute the input channel per default.

     Each device can optionally support more playback channels than physical
     hardware provides by using ``virtual channels'' or VCHANs.  VCHAN options
     can be configured via the sysctl(8) interface but can only be manipulated
     while the device is inactive.

   Runtime Configuration
     The following sysctl(8) variables are available:

           hw.snd.pcm%d.buffersize     Configure the amount of DMA bufferspace
                                       available for a device.

           hw.snd.targetirqrate        Set the default block size such that
                                       continuous playback will achieve this
                                       IRQ rate.  This value can be tuned to
                                       improve application performance.
                                       Increase this value when the sound lags
                                       and decrease it if sound stutters or
                                       breaks up.

           hw.snd.unit                 When using devfs(5), the default device
                                       for /dev/dsp.  Equivalent to a symlink
                                       from /dev/dsp to

           hw.snd.report_soft_formats  Controls the internal format conversion
                                       if it is available transparently to the
                                       application software.  When disabled or
                                       not available, the application will
                                       only be able to select formats the
                                       device natively supports.

           hw.snd.verbose              Level of verbosity for the /dev/sndstat
                                       device.  Higher values include more
                                       output and the highest level, three,
                                       should be used when reporting problems.
                                       Other options include:

                                       0   Installed devices and their allo-
                                           cated bus resources.

                                       1   The number of playback, record,
                                           virtual channels, and flags per

                                       2   Channel information per device
                                           including the channel's current
                                           format, speed, and pseudo device
                                           statistics such as buffer overruns
                                           and buffer underruns.

                                       3   File names and versions of the cur-
                                           rently sound loaded modules.

           hw.snd.maxautovchans        Global VCHAN setting that only affects
                                       devices that have only one playback
                                       channel.  The sound system will dynami-
                                       cally create up this many VCHANs.  Set
                                       to ``0'' if no VCHANS are desired.

           hw.snd.pcm%d.vchans         The current number of VCHANs allocated
                                       per device.  This can be set to preal-
                                       locate a certain number of VCHANs.
                                       Setting this value to ``0'' will dis-
                                       able VCHANs for this device.

   Recording Channels
     On devices that have more than one recording source (ie: mic and line),
     there is a corresponding /dev/dspr%d.%d device.

     Channel statistics are only kept while the device is open.  So with situ-
     ations involving overruns and underruns, consider the output while the
     errant application is open and running.

   IOCTL Support
     The driver supports most of the OSS ioctl() functions, and most applica-
     tions work unmodified.  A few differences exist, while memory mapped
     playback is supported natively and in Linux emulation, memory mapped
     recording is not due to VM system design.  As a consequence, some appli-
     cations may need to be recompiled with a slightly modified audio module.
     See <sys/soundcard.h> for a complete list of the supported ioctl() func-

     The sound drivers may create the following device nodes:

     /dev/audio%d.%d  Sparc-compatible audio device.
     /dev/dsp%d.%d    Digitized voice device.
     /dev/dspW%d.%d   Like /dev/dsp, but 16 bits per sample.
     /dev/dspr%d.%d   Should be connected to a record codec.
     /dev/sndstat     Current sound status, including all channels and driv-

     The first number in the device node represents the unit number of the
     sound device.  All sound devices are listed in /dev/sndstat.  Additional
     messages are sometimes recorded when the device is probed and attached,
     these messages can be viewed with the dmesg(8) utility.

     ac97: dac not ready  AC97 codec is not likely to be accompanied with the
     sound card.

     unsupported subdevice XX  A device node is not created properly.

     snd_ad1816(4), snd_als4000(4), snd_atiixp(4), snd_audiocs(4), snd_cmi(4),
     snd_cs4281(4), snd_csa(4), snd_ds1(4), snd_emu10k1(4), snd_es137x(4),
     snd_ess(4), snd_fm801(4), snd_gusc(4), snd_ich(4), snd_maestro(4),
     snd_maestro3(4), snd_mss(4), snd_neomagic(4), snd_sbc(4), snd_solo(4),
     snd_t4dwave(4), snd_uaudio(4), snd_via8233(4), snd_via82c686(4),
     snd_vibes(4), devfs(5), loader.conf(5), dmesg(8), kldload(8), sysctl(8)

     The OSS API,

     The sound device driver first appeared in FreeBSD 2.2.6 as pcm, written
     by Luigi Rizzo.  It was later rewritten in FreeBSD 4.0 by Cameron Grant.
     The API evolved from the VOXWARE standard which later became OSS stan-

     Luigi Rizzo <> initially wrote the pcm device driver
     and this manual page.  Cameron Grant <> later
     revised the device driver for FreeBSD 4.0.  Seigo Tanimura
     <> revised this manual page.  It was then
     rewritten for FreeBSD 5.2.

     Some features of your cards (e.g., global volume control) might not be
     supported on all devices.

FreeBSD 6.2                    November 28, 2005                   FreeBSD 6.2


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