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.\" $FreeBSD$
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.Dd March 19, 2015
.Dt SND_UAUDIO 4
.Os
.Sh NAME
.Nm snd_uaudio
.Nd USB audio and MIDI device driver
.Sh SYNOPSIS
To compile this driver into the kernel, place the following lines in your
kernel configuration file:
.Bd -ragged -offset indent
.Cd "device sound"
.Cd "device usb"
.Cd "device snd_uaudio"
.Ed
.Pp
Alternatively, to load the driver as a module at boot time, place the
following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
snd_uaudio_load="YES"
.Ed
.Sh DESCRIPTION
The
.Nm
driver provides support for
.Tn USB
audio class devices and
.Tn USB
MIDI class devices.
.Pp
A
.Tn USB
audio device consists of a number of components:
input terminals (e.g.\& USB digital input), output terminals (e.g.\&
speakers), and a number of units in between (e.g.\& volume control).
.Pp
Refer to the
.Ql USB Audio Class Specification
for more information.
.Sh SEE ALSO
.Xr sound 4 ,
.Xr usb 4
.Rs
.%T "USB Audio Class Specifications"
.%U http://www.usb.org/developers/devclass_docs/
.Re
.Sh HISTORY
The
.Nm
driver first appeared in
.Fx 4.7 .
.Sh AUTHORS
This manual page was adopted from
.Nx 1.6
and modified for
.Fx
by
.An Hiten Pandya Aq hmp@FreeBSD.org .
.Sh BUGS
The
.Tn PCM
framework in
.Fx
only supports synchronous device detach.
That means all mixer and DSP character devices belonging to a given
USB audio device must be closed when receiving an error on a DSP read,
a DSP write or a DSP IOCTL request.
Else the USB audio driver will wait for this to happen, preventing
enumeration of new devices on the parenting USB controller.
.Pp
Some USB audio devices might refuse to work properly unless the sample
rate is configured the same for both recording and playback, even if
only simplex is used.
See the
.Va dev.pcm.%d.[play|rec].vchanrate
sysctls.
.Pp
The
.Tn PCM
framework in
.Fx
currently doesn't support the full set of USB audio mixer
controls.
Some mixer controls are only available as
.Va dev.pcm.%d.mixer
sysctls.