.\"	$NetBSD$
.\"
.\" Copyright (c) 2008 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" Written by Cherry G. Mathew <cherry@zyx.in> with bits and pieces
.\" from auich(4) and ym(4)
.\"
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.Dd September 19, 2008
.Dt PWMAUDIO 4
.Os
.Sh NAME
.Nm pwmaudio
.Nd pwmaudio PC Speaker audio(4) device driver using Pulse Width Modulation
.Sh SYNOPSIS
.Cd audio* at pcppi?
.Sh DESCRIPTION
The
.Nm
pwmaudio device driver uses the attimer(4) and the pcppi(4) device
to drive the PC Speaker on ISA architecture motherboards, via Pulse
Width Modulation. PWM allows PCM encoded waveforms to be played with
dubious quality, via the PC speaker.
.Pp
A sysctl node 'hw.attimer?.samplingrate' is provided to fine tune the
sampling rate from between 8000Hz to 44000Hz.
.Pp
A mixer interface provides a single control,  "Speaker". Note that
most modern PC audio hardware routes the PC Speaker output via a sound
card, which has a separate mixer control, as well as mute/unmute for
that channel. 
.Pp
This driver differs from the
.Xr spkr 4
driver, which uses a custom,
.Xr ioctl 2
based interface to play monotonic sounds, while this driver interfaces
to the
.Xr audio 4
driver to export a full fledged sound interface via /dev/audio
.Sh SEE ALSO
.Xr spkr 4 ,
.Xr pcppi 4 ,
.Xr attimer 4 ,
.Xr audio 4
.Sh HISTORY
The
.Nm
device driver appeared in
.Nx 6.0 .
.Sh BUGS
Switching the system timecounter back and forth between i8254 and 
APIC-Fast seems affect playback sometimes.
.Sh AUTHORS
The
.Nm
driver was written by
.An Cherry G. Mathew <cherry@zyx.in>