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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
     following 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
     provide audio record and playback channels.  The FreeBSD sound system
     provides 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 works best with WSS/MSS cards, which have a very clean
     architecture and an orthogonal set of features.  They also happen to be
     among the cheapest audio cards on the market.

     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
     channel to the prefered 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 that 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

                                           0   Installed devices and their
                                               allocated 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

                                           3   File names and versions of the
                                               currently sound loaded modules.

           hw.snd.maxautovchans            Global VCHAN setting that only
                                           affects devices that have only one
                                           playback channel.  The sound system
                                           will dynamically 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 preallocate a certain number
                                           of VCHANs.  Setting this value to
                                           ``0'' will disable VCHANs for this

   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
     situations 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
     applications 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
     applications may need to be recompiled with a slightly modified audio
     module.  See <sys/soundcard.h> for a complete list of the supported
     ioctl() functions.

   Supported Cards
     Below we include a list of supported codecs/cards.  If your sound card is
     not listed here, it may be supported by a bridge driver.

     CS4237, CS4236, CS4232, CS4231 (ISA)
         All these cards work perfectly in full duplex using the MSS mode.
         This chipset is used, among others, on the A/Open AW35 and AW32, on
         some Intel motherboards, and (the CS4231) on some non-PnP cards.

         The CS4232 is reported as buggy in the Voxware documentation but I am
         not sure if this is true.  On one of my Intel motherboards, capture
         does not work simply because the capture DMA channel is not wired to
         the ISA DMA controller.

     Yamaha OPL-SAx (ISA)
         Works perfectly in all modes.  This chip is used in several PnP
         cards, but also (in non-PnP mode) on motherboards and laptops (e.g.,
         the Toshiba Libretto).

     OPTi931 (ISA)
         The chip is buggy, but the driver has many workarounds to make it
         work in full duplex because for some time these were the only full
         duplex cards I could find.  U-law format uses U8 format internally
         because of a bug in the chip.

     Trident 4DWave DX/NX (PCI)

     ENSONIQ AudioPCI ES1370/1371 (PCI)
         Creative Labs SoundBlaster PCI is supported as well.

     ESS Solo-1/1E (PCI)

     NeoMagic 256AV/ZX (PCI)

     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

     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.

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

     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

     snd_csa(4), snd_gusc(4), snd_sbc(4), devfs(5), loader.conf(5), dmesg(8),
     kldload(8), sysctl(8)

     The OSS API,

     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.

FreeBSD 11.0-PRERELEASE         August 28, 2004        FreeBSD 11.0-PRERELEASE


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