Bf -emphasis
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.
Ef
The
driver provides support for
PCM
audio play and capture.
This driver also supports various
PCIISAWSS/MSS
compatible
sound cards, AC97 mixer and High Definition Audio.
Once the
driver attaches, supported devices provide audio record and
playback channels.
The
Fx sound system provides dynamic mixing
``VCHAN''
and rate conversion
``soft formats''
True full duplex operation is available on most sound cards.
If the sound card is supported by a bridge driver, the
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
ISAPnP
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/device.hints )
Boot Variables
In general, the module
snd_foo
corresponds to
device snd_foo
and can be
loaded by the boot
loader(8)
via
loader.conf5
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 preferred value using hints, e.g.:
hint.pcm.0.line = Qq 0
This will mute the input channel per default.
VCHAEach device can optionally support more playback and recording channels
than physical hardware provides by using
``virtual channels''
or
VCHAVCHAN
options can be configured via the
sysctl(8)
interface but can only be manipulated while the device is inactive.
Runtime Configuration
There are a number of
sysctl(8)
variables available.
hw.snd.*
tunables are global settings and
dev.pcm.*
are device specific.
hw.snd.latency_profile
Define sets of buffering latency conversion tables for the
hw.snd.latency
tunable.
A value of 0 will use a low and aggressive latency profile which can result
in possible underruns if the application cannot keep up with a rapid irq
rate, especially during high workload.
The default value is 1, which is considered a moderate/safe latency profile.
hw.snd.latency
Configure the buffering latency.
Only affects applications that do not explicitly request
blocksize / fragments.
This tunable provides finer granularity than the
hw.snd.latency_profile
tunable.
Possible values range between 0 (lowest latency) and 10 (highest latency).
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.compat_linux_mmap
Enable to allow PROT_EXEC page mappings.
All Linux applications using sound and
mmap(2)
require this.
hw.snd.feeder_rate_round
Sample rate rounding threshold, to avoid large prime division at the
cost of accuracy.
All requested sample rates will be rounded to the nearest threshold value.
Possible values range between 0 (disabled) and 500.
Default is 25.
hw.snd.feeder_rate_max
Maximum allowable sample rate.
hw.snd.feeder_rate_min
Minimum allowable sample rate.
hw.snd.verbose
Level of verbosity for the
/dev/sndstat
device.
Higher values include more output and the highest level,
four, should be used when reporting 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 loaded sound modules.
4
Various messages intended for debugging.
hw.snd.maxautovchans
Global
VCHAN
setting that only affects devices with at least one playback or recording channel available.
The sound system will dynamically create up this many
VCHA
Set to
``0''
if no
VCHANS
are desired.
Maximum value is 256.
hw.snd.default_unit
Default sound card for systems with multiple sound cards.
When using
devfs(5),
the default device for
/dev/dsp
Equivalent to a symlink from
/dev/dsp
to
/dev/dsp ${hw.snd.default_unit}
hw.snd.default_auto
Enable to automatically assign default sound unit to the most recent
attached device.
dev.pcm.%d.[play|rec].vchans
The current number of
VCHAallocated per device.
This can be set to preallocate a certain number of
VCHA
Setting this value to
``0''
will disable
VCHAfor this device.
dev.pcm.%d.[play|rec].vchanrate
Sample rate speed for
VCHAN
mixing.
All playback paths will be converted to this sample rate before the mixing
process begins.
dev.pcm.%d.[play|rec].vchanformat
Format for
VCHAN
mixing.
All playback paths will be converted to this format before the mixing
process begins.
dev.pcm.%d.polling
Experimental polling mode support where the driver operates by querying the
device state on each tick using a
callout(9)
mechanism.
Disabled by default and currently only available for a few device drivers.
Recording Channels
On devices that have more than one recording source (ie: mic and line),
there is a corresponding
/dev/dsp%d.r%d
device.
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.
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
#include <sys/soundcard.h>
for a complete list of the supported
ioctl ();
functions.
FILES
The
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/dsp%d.p%d
Playback channel.
/dev/dsp%d.r%d
Record channel.
/dev/dsp%d.vp%d
Virtual playback channel.
/dev/dsp%d.vr%d
Virtual recording channel.
/dev/sndstat
Current
status, including all channels and drivers.
The first number in the device node
represents the unit number of the
device.
All
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.
The above device nodes are only created on demand through the dynamic
devfs(5)
clone handler.
Users are strongly discouraged to access them directly.
For specific sound card access, please instead use
/dev/dsp
or
/dev/dsp%d
DIAGNOSTICS
pcm%d:play:%d:dsp%d.p%d: play interrupt timeout, channel dead
The hardware does not generate interrupts to serve incoming (play)
or outgoing (record) data.
The
device driver first appeared in
Fx 2.2.6
as
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.
AUTHORS
An -nosplit
An Luigi Rizzo Aq luigi@iet.unipi.it
initially wrote the
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 .
BUGS
Some features of your sound card (e.g., global volume control) might not
be supported on all devices.
