snd4

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 channel to the prefered value using hints, e.g.: hint.pcm.0.line="0". This will mute the input channel per default.

VCHANs

Each device can optionally support more playback channels that 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.unit

When using devfs(5), the default device for /dev/dsp. Equivalent to a symlink from /dev/dsp to /dev/dsp${hw.snd.unit}.

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 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.

hw.snd.maxautovchans

Global VCHAN setting that only affects devices that have only one playback channel. 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 preallocate 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 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 ⟨sys/soundcard.h⟩ for a complete list of the supported ioctl() functions.