SOUND(4) BSD Kernel Interfaces Manual SOUND(4)NAME
sound, pcm, snd — DragonFly PCM audio device infrastructure
SYNOPSIS
To compile this driver into the kernel, place the following line in your
kernel configuration file:
device pcm
For non-PnP sound cards:
device pcm0 at isa? port? irq 5 drq 1 flags 0x15
DESCRIPTION
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
DragonFly sound system provides dynamic mixing “VCHAN” and rate conver‐
sion “soft formats”. True full duplex operation is available on most
sound cards.
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 specific settings to the
kernel config file. 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 the ker‐
nel config file ) .
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.
VCHANs
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.
Increase this value when the sound lags
and decrease it if sound stutters or
breaks up.
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 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
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 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
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 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.
Statistics
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‐
tions.
FILES
The sound drivers may use 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‐
ers.
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.
DIAGNOSTICS
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.
SEE ALSOsnd_ad1816(4), snd_als4000(4), snd_atiixp(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), loader.conf(5), dmesg(8),
kldload(8), sysctl(8)
The OSS API, http://www.opensound.com/pguide/oss.pdf.
HISTORY
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‐
dard.
AUTHORS
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.
BUGS
Some features of your sound card (e.g., global volume control) might not
be supported on all devices.
BSD November 26, 2006 BSD
