man/man4/pcm.4

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.\" $FreeBSD: src/share/man/man4/pcm.4,v 1.39.2.6 2007/05/23 19:45:49 brueffer Exp $
.\" $DragonFly: src/share/man/man4/pcm.4,v 1.7 2007/06/16 17:44:33 hasso Exp $
.\"
.Dd November 26, 2006
.Dt SOUND 4
.Os
.Sh NAME
.Nm sound ,
.Nm pcm ,
.Nm snd
.Nd
.Dx
PCM audio device infrastructure
.Sh SYNOPSIS
To compile this driver into the kernel, place the following line in your
kernel configuration file:
.Bd -ragged -offset indent
.Cd "device pcm"
.Ed
.Pp
For non-PnP sound cards:
.Bd -literal -offset indent
.Cd "device pcm0 at isa? port? irq 5 drq 1 flags 0x15"
.Ed
.Sh DESCRIPTION
The
.Nm
driver provides support for
.Tn PCM
audio play and capture.
This driver also supports various
.Tn PCI ,
.Tn ISA ,
.Tn WSS/MSS
compatible
sound cards, AC97 mixer and High Definition Audio.
Once the
.Nm
driver attaches, supported devices provide audio record and
playback channels.
The
.Dx
sound system provides dynamic mixing
.Dq VCHAN
and rate conversion
.Dq soft formats .
True full duplex operation is available on most sound cards.
.Pp
If the sound card is supported by a bridge driver, the
.Nm
driver works in conjunction with the bridge driver.
.Pp
Apart from the usual parameters, the flags field is used to specify
the secondary
.Tn DMA
channel (generally used for capture in full duplex cards).
Flags are set to 0 for cards not using a secondary
.Tn DMA
channel, or to 0x10 + C to specify channel C.
.Pp
The driver does its best to recognize the installed hardware and drive
it correctly so the user is not required to add specific settings to
the kernel config file.
For
.Tn PCI
and
.Tn ISA
.Tn PnP
cards this is actually easy
since they identify themselves.
For legacy
.Tn ISA
cards, the driver looks for
.Tn MSS
cards at addresses 0x530 and 0x604 (unless overridden
in the kernel config file ) .
.Ss Boot Variables
In general, the module
.Pa snd_foo
corresponds to
.Cd "device snd_foo"
and can be
loaded by the boot
.Xr loader 8
via
.Xr loader.conf 5
or from the command line using the
.Xr kldload 8
utility.
Options which can be specified in
.Pa /boot/loader.conf
include:
.Bl -tag -width ".Va snd_emu10k1_load" -offset indent
.It Va snd_driver_load
.Pq Dq Li NO
If set to
.Dq Li YES ,
this option loads all available drivers.
.It Va snd_emu10k1_load
.Pq Dq Li NO
If set to
.Dq Li YES ,
only the SoundBlaster 5.1 driver and dependent modules will be loaded.
.It Va snd_foo_load
.Pq Dq Li NO
If set to
.Dq Li YES ,
load driver for card/chipset foo.
.El
.Ss VCHANs
Each device can optionally support more playback channels
than physical hardware provides by using
.Dq virtual channels
or
.Tn VCHANs .
.Tn VCHAN
options can be configured via the
.Xr sysctl 8
interface but can only be manipulated while the device is inactive.
.Ss Runtime Configuration
The following
.Xr sysctl 8
variables are available:
.Bl -tag -width ".Va hw.snd.report_soft_formats" -offset indent
.It Va hw.snd.pcm%d.buffersize
Configure the amount of
.Tn DMA
bufferspace available for a device.
.It Va hw.snd.targetirqrate
Set the default block size such that continuous
playback will achieve this
.Tn 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.
.It Va 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.
.It Va hw.snd.verbose
Level of verbosity for the
.Pa /dev/sndstat
device.
Higher values include more output and the highest level,
three, should be used when reporting problems.
Other options include:
.Bl -tag -width 2n
.It 0
Installed devices and their allocated bus resources.
.It 1
The number of playback, record, virtual channels, and
flags per device.
.It 2
Channel information per device including the channel's
current format, speed, and pseudo device statistics such as
buffer overruns and buffer underruns.
.It 3
File names and versions of the currently loaded sound modules.
.El
.It Va hw.snd.maxautovchans
Global
.Tn VCHAN
setting that only affects devices with only one playback channel available.
The sound system will dynamically create up this many
.Tn VCHANs .
Set to
.Dq 0
if no
.Tn VCHANS
are desired.
.It Va hw.snd.pcm%d.vchans
The current number of
.Tn VCHANs
allocated per device.
This can be set to preallocate a certain number of
.Tn VCHANs .
Setting this value to
.Dq 0
will disable
.Tn VCHANs
for this device.
.El
.Ss Recording Channels
On devices that have more than one recording source (ie: mic and line),
there is a corresponding
.Pa /dev/dspr%d.%d
device.
.Ss Statistics
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.
.Ss IOCTL Support
The driver supports most of the
.Tn OSS
.Fn ioctl
functions, and most applications work unmodified.
A few differences exist, while memory mapped playback is
supported natively and in
.Tn Linux
emulation, memory mapped recording is
not due to
.Tn VM
system design.
As a consequence, some applications may need to be recompiled
with a slightly modified audio module.
See
.In sys/soundcard.h
for a complete list of the supported
.Fn ioctl
functions.
.Sh FILES
The
.Nm
drivers may use the following
device nodes:
.Pp
.Bl -tag -width ".Pa /dev/audio%d.%d" -compact
.It Pa /dev/audio%d.%d
Sparc-compatible audio device.
.It Pa /dev/dsp%d.%d
Digitized voice device.
.It Pa /dev/dspW%d.%d
Like
.Pa /dev/dsp ,
but 16 bits per sample.
.It Pa /dev/dspr%d.%d
Should be connected to a record codec.
.It Pa /dev/sndstat
Current
.Nm
status, including all channels and drivers.
.El
.Pp
The first number in the device node
represents the unit number of the
.Nm
device.
All
.Nm
devices are listed
in
.Pa /dev/sndstat .
Additional messages are sometimes recorded when the
device is probed and attached, these messages can be viewed with the
.Xr dmesg 8
utility.
.Sh DIAGNOSTICS
.Bl -diag
.It ac97: dac not ready
AC97 codec is not likely to be accompanied with the sound card.
.It unsupported subdevice XX
A device node is not created properly.
.El
.Sh SEE ALSO
.Xr snd_ad1816 4 ,
.Xr snd_als4000 4 ,
.Xr snd_atiixp 4 ,
.Xr snd_cmi 4 ,
.Xr snd_cs4281 4 ,
.Xr snd_csa 4 ,
.Xr snd_ds1 4 ,
.Xr snd_emu10k1 4 ,
.Xr snd_envy24 4 ,
.Xr snd_envy24ht 4 ,
.Xr snd_es137x 4 ,
.Xr snd_ess 4 ,
.Xr snd_fm801 4 ,
.Xr snd_gusc 4 ,
.Xr snd_hda 4 ,
.Xr snd_ich 4 ,
.Xr snd_maestro 4 ,
.Xr snd_maestro3 4 ,
.Xr snd_mss 4 ,
.Xr snd_neomagic 4 ,
.Xr snd_sbc 4 ,
.Xr snd_solo 4 ,
.Xr snd_spicds 4 ,
.Xr snd_t4dwave 4 ,
.Xr snd_uaudio 4 ,
.Xr snd_via8233 4 ,
.Xr snd_via82c686 4 ,
.Xr snd_vibes 4 ,
.Xr loader.conf 5 ,
.Xr dmesg 8 ,
.Xr kldload 8 ,
.Xr sysctl 8
.Rs
.%T "The OSS API"
.%O "http://www.opensound.com/pguide/oss.pdf"
.Re
.Sh HISTORY
The
.Nm
device driver first appeared in
.Fx 2.2.6
as
.Nm pcm ,
written by
.An Luigi Rizzo .
It was later
rewritten in
.Fx 4.0
by
.An Cameron Grant .
The API evolved from the VOXWARE
standard which later became OSS standard.
.Sh AUTHORS
.An -nosplit
.An Luigi Rizzo Aq luigi@iet.unipi.it
initially wrote the
.Nm pcm
device driver and this manual page.
.An Cameron Grant Aq gandalf@vilnya.demon.co.uk
later revised the device driver for
.Fx 4.0 .
.An Seigo Tanimura Aq tanimura@r.dl.itc.u-tokyo.ac.jp
revised this manual page.
It was then rewritten for
.Fx 5.2 .
.Sh BUGS
Some features of your sound card (e.g., global volume control) might not
be supported on all devices.