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SOUND(4)		 BSD Kernel Interfaces Manual		      SOUND(4)

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

     To	compile	this driver into the kernel, place the following line in your
     kernel configuration file:

	   device sound

     Non-PnP sound cards require the following lines in	device.hints(5):"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, ISA, WSS/MSS compatible sound cards,
     AC97 mixer	and High Definition Audio.  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 sound

     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.	 In-
				       crease 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 de-
				       vice 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 de-

				       2   Channel information per device in-
					   cluding the channel's current for-
					   mat,	speed, and pseudo device sta-
					   tistics such	as buffer overruns and
					   buffer underruns.

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

	   hw.snd.maxautovchans	       Global VCHAN setting that only affects
				       devices with only one playback channel
				       available.  The sound system will dy-
				       namically 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 disable
				       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_envy24(4),
     snd_envy24ht(4), snd_es137x(4), snd_ess(4), snd_fm801(4), snd_gusc(4),
     snd_hda(4), snd_ich(4), snd_maestro(4), snd_maestro3(4), snd_mss(4),
     snd_neomagic(4), snd_sbc(4), snd_solo(4), snd_spicds(4), snd_t4dwave(4),
     snd_uaudio(4), snd_via8233(4), snd_via82c686(4), snd_vibes(4), devfs(5),
     device.hints(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 sound card (e.g., global volume control) might not
     be	supported on all devices.

BSD			       November	26, 2006			   BSD


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