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NAME    [Toc]    [Back]

     pcm, snd -- FreeBSD PCM audio device infrastructure

SYNOPSIS    [Toc]    [Back]

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

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

DESCRIPTION    [Toc]    [Back]

     The pcm 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 pcm 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 pcm 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    [Toc]    [Back]
     In general, the module snd_foo corresponds to device foo and can be
     loaded by the boot loader via boot/loader.conf 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.

   VCHANS    [Toc]    [Back]
     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    [Toc]    [Back]
     The following sysctl(8) tunables 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 reported problems.
				       Other options include: 0 - Installed
				       devices and their allocated bus
				       resources.  1 - The number of playback,
				       record, virtual channels, and flags per
				       device.	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 currently sound loaded

	   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 device.

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

   Statistics    [Toc]    [Back]
     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    [Toc]    [Back]
     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    [Toc]    [Back]
     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 formats 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)

FILES    [Toc]    [Back]

     The pcm 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 pcm status, including all channels and drivers.

     The first number in the device node represents the unit number of the PCM
     device.  All pcm PCM 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.

DIAGNOSTICS    [Toc]    [Back]

     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.

BUGS    [Toc]    [Back]

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

HISTORY    [Toc]    [Back]

     The pcm device driver first appeared in FreeBSD 2.2.6 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 standard.

SEE ALSO    [Toc]    [Back]

     csa(4), gusc(4), sbc(4), devfs(5), loader.conf(5), dmesg(8), kldload(8),

     The OSS API, http://www.opensound.com/pguide/oss.pdf.

AUTHORS    [Toc]    [Back]

     Luigi Rizzo <luigi@iet.unipi.it> initially wrote the pcm device driver
     and this manual page.  Cameron Grant <gandalf@vilnya.demon.co.uk> later
     revised the device driver for FreeBSD 4.0.  Seigo Tanimura
     <tanimura@r.dl.itc.u-tokyo.ac.jp> revised this manual page.  It was then
     rewritten for FreeBSD 5.2.

FreeBSD 5.2.1		       November 14, 2003		 FreeBSD 5.2.1
[ Back ]
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