freebsd-skq/share/man/man4/pcm.4

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.Dd November 14, 2003
.Dt PCM 4
.Os
.Sh NAME
.Nm pcm ,
.Nm snd
.Nd FreeBSD PCM audio device infrastructure
.Sh SYNOPSIS
For a card with bridge driver support, and a PnP card:
.Cd "device pcm"
.Pp
For a card without bridge driver support, and a non-PnP card,
the following lines may be required in
.Pa /boot/device.hints :
.Cd hint.pcm.0.at="isa"
.Cd hint.pcm.0.irq="5"
.Cd hint.pcm.0.drq="1"
.Cd hint.pcm.0.flags="0x0"
.Sh DESCRIPTION
The
.Nm
driver provides support for
.Tn PCM
audio play and capture.
This driver also supports various
.Tn PCI ,
.Tn WSS/MSS
compatible,
.Tn ISA
sound cards, and AC97 mixer.
Once the
.Nm
driver attaches, supported devices provide audio record and
playback channels.
The
.Fx
sound system provides dynamic mixing
.Dq VCHAN
and rate conversion
.Dq soft formats .
True full duplex operation is available on most 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 works best with
.Tn 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.
.Pp
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
.Pa /boot/device.hints .
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
.Pa /boot/device.hints ) .
.Ss Boot Variables
In general, the module
.Pa snd_foo
corresponds to device foo and can be
loaded by the boot loader via
.Pa boot/loader.conf
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 snd_emu10k1_load -offset indent
.It Va snd_driver_load
.Pq Dq NO
If set to
.Dq YES ,
this option loads all available drivers.
.It Va snd_emu10k1_load
.Pq Dq NO
If set to
.Dq YES ,
Only the SoundBlaster 5.1 driver and dependent modules will be loaded.
.It Va snd_foo_load
.Pq Dq NO
If set to
.Dq YES ,
load driver for card/chipset foo.
.El
.Ss VCHANS
Each device can optionally support more playback channels
that 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
tunables are available:
.Bl -tag -width ".It 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.unit
When using
.Xr devfs 5 ,
the default device for
.Pa /dev/dsp .
Equivalent to a symlink from
.Pa /dev/dsp
to
.Pa /dev/dsp${hw.snd.unit} .
.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 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 modules.
.It Va hw.snd.maxautovchans
Global
.Tn VCHAN
setting that only affects devices that have only one playback channel.
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 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.
.Ss 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.
.Bl -tag -width 2m
.It 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.
.Pp
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.
.It 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).
.It 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.
.It Trident 4DWave DX/NX (PCI)
.It ENSONIQ AudioPCI ES1370/1371 (PCI)
Creative Labs SoundBlaster PCI is supported as well.
.It ESS Solo-1/1E (PCI)
.It NeoMagic 256AV/ZX (PCI)
.El
.Sh FILES
The following commonly used symbolic links to real device nodes
should be present:
.Pp
.Bl -tag -width "/dev/dspr%d.%dXXX" -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
Each symbolic link refers to a device node of the same name,
but with a unit number appended.
The unit number for each device matches the unit number of the
device probed at boot time.
Device probe messages can be examined with the
.Xr dmesg 8
utility.
.Sh DIAGNOSTICS
.Bl -tag -width 2m
.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 BUGS
Some features of your cards (e.g. global volume control) might not
be supported on all devices.
.Sh HISTORY
The
.Nm
device driver first appeared in
.Fx 2.2.6 written by Luigi Rizzo.
It was later
rewritten in
.Fx 4.0 by Cameron Grant.
The API evolved from the VOXWARE
standard which later became OSS standard.
.Sh SEE ALSO
.Xr csa 4 ,
.Xr gusc 4 ,
.Xr sbc 4 ,
.Xr devfs 5 ,
.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 AUTHORS
.An -nosplit
.An Luigi Rizzo Aq luigi@iet.unipi.it
initially wrote the
.Nm
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 .