655 lines
20 KiB
Groff
655 lines
20 KiB
Groff
.\" $NetBSD: audio.4,v 1.24 1999/03/16 01:19:15 garbled Exp $
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.\"
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.\" Copyright (c) 1996 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by John T. Kohl.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the NetBSD
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.\" Foundation, Inc. and its contributors.
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.\" 4. Neither the name of The NetBSD Foundation nor the names of its
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.\" contributors may be used to endorse or promote products derived
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.\" from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd March 11, 1997
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.Dt AUDIO 4
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.Os
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.Sh NAME
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.Nm audio
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.Nd device-independent audio driver layer
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.Sh SYNOPSIS
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.Fd #include <sys/types.h>
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.Fd #include <sys/audioio.h>
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.Sh DESCRIPTION
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The
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.Nm
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driver provides support for various audio peripherals.
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It provides a uniform programming interface layer above different
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underlying audio hardware drivers.
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The audio layer provides full-duplex operation if the
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underlying hardware configuration supports it.
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.Pp
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There are four device files available for audio operation:
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.Pa /dev/audio ,
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.Pa /dev/sound ,
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.Pa /dev/audioctl ,
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and
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.Pa /dev/mixer .
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.Pa /dev/audio
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and
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.Pa /dev/sound
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are used for recording or playback of digital samples.
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.Pa /dev/mixer
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is used to manipulate volume, recording source, or other audio mixer
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functions.
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.Pa /dev/audioctl
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accepts the same
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.Xr ioctl 2
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operations as
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.Pa /dev/sound ,
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but no other operations.
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In contrast to
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.Pa /dev/sound
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which has the exclusive open property
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.Pa /dev/audioctl
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can be opened at any time and can be used to manipulate the audio device
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while it is in use.
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.Sh SAMPLING DEVICES
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When
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.Pa /dev/audio
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is opened, it automatically directs the underlying driver to manipulate
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monaural 8-bit mulaw samples.
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In addition, if it is opened read-only
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(write-only) the device is set to half-duplex record (play) mode with
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recording (playing) unpaused and playing (recording) paused.
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When
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.Pa /dev/sound
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is opened, it maintains the previous audio sample mode and
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record/playback mode.
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In all other respects
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.Pa /dev/audio
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and
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.Pa /dev/sound
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are identical.
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.Pp
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Only one process may hold open a sampling device at a given time
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(although file descriptors may be shared between processes once the
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first open completes).
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.Pp
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On a half-duplex device, writes while recording is in progress will be
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immediately discarded.
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Similarly, reads while playback is in progress
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will be filled with silence but delayed to return at the current
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sampling rate.
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If both playback and recording are requested on a half-duplex
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device, playback mode takes precedence and recordings will get silence.
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On a full-duplex device, reads and writes may operate
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concurrently without interference.
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If a full-duplex capable audio device is opened for both reading and writing
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it will start in half-duplex play mode; full-duplex mode has to be set
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explicitely.
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On either type of device, if the playback mode is paused then silence is
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played instead of the provided samples, and if recording is paused then
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the process blocks in
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.Xr read 2
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until recording is unpaused.
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.Pp
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If a writing process does not call
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.Xr write 2
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frequently enough to provide samples at the pace the hardware
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consumes them silence is inserted.
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If the
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.Dv AUMODE_PLAY_ALL
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mode is not set the writing process must
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provide enough data via
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subsequent write calls to ``catch up'' in time to the current audio
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block before any more process-provided samples will be played.
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If a reading process does not call
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.Xr read 2
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frequently enough, it will simply miss samples.
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.Pp
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The audio device is normally accessed with
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.Xr read 2
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or
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.Xr write 2
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calls, but it can also be mapped into user memory with
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.Xr mmap 2
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(when supported by the device).
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Once the device has been mapped it can no longer be accessed
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by read or write; all access is by reading and writing to
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the mapped memory.
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The device appears as a block of memory
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of size
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.Va buffersize
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(as available via
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.Dv AUDIO_GETINFO ) .
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The device driver will continuously move data from this buffer
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from/to the audio hardware, wrapping around at the end of the buffer.
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To find out where the hardware is currently accessing data in the buffer the
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.Dv AUDIO_GETIOFFS
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and
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.Dv AUDIO_GETOOFFS
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calls can be used.
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The playing and recording buffers are distinct and must be
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mapped separately if both are to be used.
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Only encodings that are not emulated (i.e. where
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.Dv AUDIO_ENCODINGFLAG_EMULATED
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is not set) work properly for a mapped device.
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.Pp
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The audio device, like most devices, can be used in
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.Va select,
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can be set in non-blocking mode and can be set to send a
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.Dv SIGIO
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when I/O is possible.
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The mixer device can be set to generate a
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.Dv SIGIO
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whenever a mixer value is changed.
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.Pp
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The following
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.Xr ioctl 2
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commands are supported on the sample devices:
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.Pp
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.Bl -tag -width indent -compact
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.It Dv AUDIO_FLUSH
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This command stops all playback and recording, clears all queued
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buffers, resets error counters, and restarts recording and playback as
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appropriate for the current sampling mode.
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.It Dv AUDIO_RERROR (int)
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This command fetches the count of dropped input samples into its integer
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argument.
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There is no information regarding when in the sample stream
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they were dropped.
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.It Dv AUDIO_WSEEK (int)
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This command fetches the count of samples are queued ahead of the
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first sample in the most recent sample block written into its integer argument.
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.It Dv AUDIO_DRAIN
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This command suspends the calling process until all queued playback
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samples have been played by the hardware.
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.It Dv AUDIO_GETDEV (audio_device_t)
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This command fetches the current hardware device information into the
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audio_device_t argument.
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.Bd -literal
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typedef struct audio_device {
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char name[MAX_AUDIO_DEV_LEN];
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char version[MAX_AUDIO_DEV_LEN];
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char config[MAX_AUDIO_DEV_LEN];
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} audio_device_t;
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.Ed
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.It Dv AUDIO_GETFD (int)
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The command returns the current setting of the full duplex mode.
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.It Dv AUDIO_GETENC (audio_encoding_t)
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This command is used iteratively to fetch sample encoding names and
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format_ids into the input/output audio_encoding_t argument.
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.Bd -literal
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typedef struct audio_encoding {
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int index; /* input: nth encoding */
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char name[MAX_AUDIO_DEV_LEN]; /* name of encoding */
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int encoding; /* value for encoding parameter */
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int precision; /* value for precision parameter */
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int flags;
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#define AUDIO_ENCODINGFLAG_EMULATED 1 /* software emulation mode */
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} audio_encoding_t;
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.Ed
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To query
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all the supported encodings, start with an index field of 0 and
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continue with successive encodings (1, 2, ...) until the command returns
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an error.
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.It Dv AUDIO_SETFD (int)
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This command sets the device into full-duplex operation if its integer
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argument has a non-zero value, or into half-duplex operation if it
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contains a zero value.
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If the device does not support full-duplex
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operation, attempting to set full-duplex mode returns an error.
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.It Dv AUDIO_GETPROPS (int)
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This command gets a bit set of hardware properties.
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If the hardware
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has a certain property the corresponding bit is set, otherwise it is not.
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The properties can have the following values:
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.Bl -tag -width indent -compact
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.It Dv AUDIO_PROP_FULLDUPLEX
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the device admits full duplex operation.
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.It Dv AUDIO_PROP_MMAP
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the device can be used with
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.Xr mmap 2 .
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.It Dv AUDIO_PROP_INDEPENDENT
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the device can set the playing and recording encoding parameters
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independently.
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.El
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.It Dv AUDIO_GETIOFFS (audio_offset_t)
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.It Dv AUDIO_GETOOFFS (audio_offset_t)
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This command fetches the current offset in the input(output) buffer where
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the hardware is putting(getting) data.
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It mostly useful when the device
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buffer is available in user space via the
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.Xr mmap 2
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call.
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The information is returned in the audio_offset structure.
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.Bd -literal
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typedef struct audio_offset {
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u_int samples; /* Total number of bytes transferred */
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u_int deltablks; /* Blocks transferred since last checked */
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u_int offset; /* Physical transfer offset in buffer */
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} audio_offset_t;
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.Ed
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.It Dv AUDIO_GETINFO (audio_info_t)
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.It Dv AUDIO_SETINFO (audio_info_t)
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Get or set audio information as encoded in the audio_info structure.
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.Bd -literal
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typedef struct audio_info {
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struct audio_prinfo play; /* info for play (output) side */
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struct audio_prinfo record; /* info for record (input) side */
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u_int monitor_gain;
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/* BSD extensions */
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u_int blocksize; /* H/W read/write block size */
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u_int hiwat; /* output high water mark */
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u_int lowat; /* output low water mark */
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u_int _ispare1;
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u_int mode; /* current device mode */
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#define AUMODE_PLAY 0x01
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#define AUMODE_RECORD 0x02
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#define AUMODE_PLAY_ALL 0x04 /* do not do real-time correction */
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};
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.Ed
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.Pp
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When setting the current state with
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.Dv AUDIO_SETINFO ,
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the audio_info structure should first be initialized with
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.Li Dv AUDIO_INITINFO Po &info Pc
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and then the particular values to be changed should be set.
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This allows the audio driver to only set those things that you wish
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to change and eliminates the need to query the device with
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.Dv AUDIO_GETINFO
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first.
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.Pp
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The
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.Va mode
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field should be set to
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.Dv AUMODE_PLAY ,
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.Dv AUMODE_RECORD ,
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.Dv AUMODE_PLAY_ALL ,
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or a bitwise OR combination of the three.
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Only full-duplex audio devices support
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simultaneous record and playback.
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.Pp
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.Va hiwat
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and
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.Va lowat
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are used to control write behavior.
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Writes to the audio devices will queue up blocks until the high-water
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mark is reached, at which point any more write calls will block
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until the queue is drained to the low-water mark.
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.Va hiwat
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and
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.Va lowat
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set those high- and low-water marks (in audio blocks).
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The default for
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.Va hiwat
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is the maximum value and for
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.Va lowat
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75 % of
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.Va hiwat .
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.Pp
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.Va blocksize
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sets the current audio blocksize.
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The generic audio driver layer and the hardware driver have the
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opportunity to adjust this block size to get it within
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implementation-required limits.
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Upon return from an
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.Dv AUDIO_SETINFO
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call, the actual blocksize set is returned in this field.
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Normally the
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.Va blocksize
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is calculated to correspond to 50ms of sound and it is recalculated
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when the encoding parameter changes, but if the
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.Va blocksize
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is set explicitely this value becomes sticky, i.e., it is remains
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even when the encoding is changed.
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The stickyness can be cleared by reopening the device or setting the
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.Va blocksize
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to 0.
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.Bd -literal
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struct audio_prinfo {
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u_int sample_rate; /* sample rate in samples/s */
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u_int channels; /* number of channels, usually 1 or 2 */
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u_int precision; /* number of bits/sample */
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u_int encoding; /* data encoding (AUDIO_ENCODING_* above) */
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u_int gain; /* volume level */
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u_int port; /* selected I/O port */
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u_long seek; /* BSD extension */
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u_int avail_ports; /* available I/O ports */
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u_int buffer_size; /* total size audio buffer */
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u_int _ispare[1];
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/* Current state of device: */
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u_int samples; /* number of samples */
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u_int eof; /* End Of File (zero-size writes) counter */
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u_char pause; /* non-zero if paused, zero to resume */
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u_char error; /* non-zero if underflow/overflow ocurred */
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u_char waiting; /* non-zero if another process hangs in open */
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u_char balance; /* stereo channel balance */
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u_char cspare[2];
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u_char open; /* non-zero if currently open */
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u_char active; /* non-zero if I/O is currently active */
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};
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.Ed
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.Pp
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Note: many hardware audio drivers require identical playback and
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recording sample rates, sample encodings, and channel counts.
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The playing information is always set last and will prevail on such hardware.
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If the hardware can handle different settings the
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.Dv AUDIO_PROP_INDEPENDENT
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property is set.
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.Pp
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The encoding parameter can have the following values:
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.Bl -tag -width indent -compact
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.It Dv AUDIO_ENCODING_ULAW
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mulaw encoding, 8 bits/sample
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.It Dv AUDIO_ENCODING_ALAW
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alaw encoding, 8 bits/sample
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.It Dv AUDIO_ENCODING_SLINEAR
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two's complement signed linear encoding with the platform byte order
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.It Dv AUDIO_ENCODING_ULINEAR
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unsigned linear encoding with the platform byte order
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.It Dv AUDIO_ENCODING_ADPCM
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ADPCM encoding, 8 bits/sample
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.It Dv AUDIO_ENCODING_SLINEAR_LE
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two's complement signed linear encoding with little endian byte order
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.It Dv AUDIO_ENCODING_SLINEAR_BE
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two's complement signed linear encoding with big endian byte order
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.It Dv AUDIO_ENCODING_ULINEAR_LE
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unsigned linear encoding with little endian byte order
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.It Dv AUDIO_ENCODING_ULINEAR_BE
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unsigned linear encoding with little big byte order
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.El
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.Pp
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The
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.Va gain ,
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.Va port
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and
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.Va balance
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settings provide simple shortcuts to the richer mixer
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interface described below.
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The gain should be in the range
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.Bq Dv AUDIO_MIN_GAIN , Dv AUDIO_MAX_GAIN
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and the balance in the range
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.Bq Dv AUDIO_LEFT_BALANCE , Dv AUDIO_RIGHT_BALANCE
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withe the normal setting at
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.Dv AUDIO_MID_BALANCE .
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.br
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The input port should be a combination of
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.Bl -tag -width indent -compact
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.It Dv AUDIO_MICROPHONE
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to select microphone input.
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.It Dv AUDIO_LINE_IN
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to select line input.
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.It Dv AUDIO_CD
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to select CD input.
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.El
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The output port should be a combination of
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.Bl -tag -width indent -compact
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.It Dv AUDIO_SPEAKER
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to select microphone output.
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.It Dv AUDIO_HEADPHONE
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to select headphone output.
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.It Dv AUDIO_LINE_OUT
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to select line output.
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.El
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The available ports can be found in
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.Va avail_ports .
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.Pp
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.Va buffer_size
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is the total size of the audio buffer.
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The buffer size divided by the
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.Va blocksize
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gives the maximum value for
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.Va hiwat .
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Currently the
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.Va buffer_size
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can only be read and not set.
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.Pp
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The
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.Va seek
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and
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.Va samples
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fields are only used for
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.Dv AUDIO_GETINFO .
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.Va seek
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represents the count of
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samples pending;
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.Va samples
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represents the total number of bytes recorded or played, less those
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that were dropped due to inadequate consumption/production rates.
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.Pp
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.Va pause
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returns the current pause/unpause state for recording or playback.
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For
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.Dv AUDIO_SETINFO ,
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if the pause value is specified it will either pause
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or unpause the particular direction.
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.El
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.Sh MIXER DEVICE
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The mixer device,
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.Pa /dev/mixer ,
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may be manipulated with
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.Xr ioctl 2
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but does not support
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.Xr read 2
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or
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.Xr write 2 .
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It supports the following
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.Xr ioctl 2
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commands:
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.Bl -tag -width indent -compact
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.It Dv AUDIO_GETDEV (audio_device_t)
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This command is the same as described above for the sampling devices.
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.It Dv AUDIO_MIXER_READ (mixer_ctrl_t)
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.It Dv AUDIO_MIXER_WRITE (mixer_ctrl_t)
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.Bd -literal
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#define AUDIO_MIXER_CLASS 0
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#define AUDIO_MIXER_ENUM 1
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#define AUDIO_MIXER_SET 2
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#define AUDIO_MIXER_VALUE 3
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typedef struct mixer_ctrl {
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int dev; /* input: nth device */
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int type;
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union {
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int ord; /* enum */
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int mask; /* set */
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mixer_level_t value; /* value */
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} un;
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} mixer_ctrl_t;
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.Ed
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.Bd -literal
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#define AUDIO_MIN_GAIN 0
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#define AUDIO_MAX_GAIN 255
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typedef struct mixer_level {
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int num_channels;
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u_char level[8]; /* [num_channels] */
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} mixer_level_t;
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#define AUDIO_MIXER_LEVEL_MONO 0
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#define AUDIO_MIXER_LEVEL_LEFT 0
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#define AUDIO_MIXER_LEVEL_RIGHT 1
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.Ed
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These commands read the current mixer state or set new mixer state for
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the specified device
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.Va dev .
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.Va type
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identifies which type of value is supplied in the
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.Va mixer_ctrl_t
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argument.
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For a mixer value, the
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.Va value
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field specifies both the number of channels and the values for each of
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the channels.
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If the channel count does not match the current channel count, the
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attempt to change the setting may fail (depending on the hardware
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device driver implementation).
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For an enumeration value, the
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.Va ord
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field should be set to one of the possible values as returned by a prior
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.Dv AUDIO_MIXER_DEVINFO
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command.
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The type
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.Dv AUDIO_MIXER_CLASS
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is only used for classifying particular mixer device
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types and is not used for
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.Dv AUDIO_MIXER_READ
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or
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.Dv AUDIO_MIXER_WRITE .
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.It Dv AUDIO_MIXER_DEVINFO (mixer_devinfo_t)
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This command is used iteratively to fetch audio mixer device information
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into the input/output mixer_devinfo_t argument.
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To query all the supported encodings, start with an index field of
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0 and continue with successive encodings (1, 2, ...) until the
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command returns an error.
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.Bd -literal
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typedef struct mixer_devinfo {
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int index; /* input: nth mixer device */
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audio_mixer_name_t label;
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int type;
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int mixer_class;
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int next, prev;
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#define AUDIO_MIXER_LAST -1
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union {
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struct audio_mixer_enum {
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int num_mem;
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struct {
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audio_mixer_name_t label;
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int ord;
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} member[32];
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} e;
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struct audio_mixer_set {
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int num_mem;
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struct {
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audio_mixer_name_t label;
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int mask;
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} member[32];
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} s;
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struct audio_mixer_value {
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audio_mixer_name_t units;
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int num_channels;
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} v;
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} un;
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} mixer_devinfo_t;
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.Ed
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The
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.Va label
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field identifies the name of this particular mixer control.
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The
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.Va index
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field may be used as the
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.Va dev
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field in
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.Dv AUDIO_MIXER_READ
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and
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.Dv AUDIO_MIXER_WRITE
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commands.
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The
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.Va type
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field identifies the type of this mixer control.
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Enumeration types are typically used for on/off style controls (e.g. a
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mute control) or for input/output device selection (e.g. select
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recording input source from CD, line in, or microphone).
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Set types are similar to enumeration types but any combination
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of the mask bits can be used.
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.Pp
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The
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.Va mixer_class
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field identifies what class of control this is.
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This value is set to the index value used to query the class itself.
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For example, a mixer level controlling the input gain on the ``line
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in'' circuit would be a class that matches an input class device
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with the name ``Inputs'' (AudioCInputs).
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Mixer controls which control audio circuitry for a particular audio
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source (e.g. line-in, CD in, DAC output) are collected under the input class,
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while those which control all audio sources (e.g. master volume,
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equalization controls) are under the output class.
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.Pp
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The
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.Va next
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and
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.Va prev
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may be used by the hardware device driver to provide hints for the next
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and previous devices in a related set (for example, the line in level
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control would have the line in mute as its "next" value).
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If there is no relevant next or previous value,
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.Dv AUDIO_MIXER_LAST
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is specified.
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.Pp
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For
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.Dv AUDIO_MIXER_ENUM
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mixer control types,
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the enumeration values and their corresponding names are filled in.
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For example, a mute control would return appropriate values paired with
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AudioNon and AudioNoff.
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For
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.Dv AUDIO_MIXER_VALUE
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and
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.Dv AUDIO_MIXER_SET
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mixer control types, the channel count is
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returned; the units name specifies what the level controls (typical
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values are AudioNvolume, AudioNtreble, AudioNbass).
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.\" For AUDIO_MIXER_SET mixer control types, what is what?
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.El
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.Pp
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By convention, all the mixer device can be distinguished from other
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mixer controls because they use a name from one of the AudioC* string values.
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.Sh FILES
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.Bl -tag -width /dev/audioctl -compact
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.It Pa /dev/audio
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.It Pa /dev/audioctl
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.It Pa /dev/sound
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.It Pa /dev/mixer
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.El
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.Sh SEE ALSO
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.Xr audioctl 1 ,
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.Xr mixerctl 1 .
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.br
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.Xr ioctl 2 ,
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.Xr midi 4 ,
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.Xr ossaudio 3 .
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.br
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For ports using the ISA bus:
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.Xr aria 4 ,
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.Xr ess 4 ,
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.Xr gus 4 ,
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.Xr guspnp 4 ,
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.Xr pas 4 ,
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.Xr pss 4 ,
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.Xr sb 4 ,
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.Xr wss 4 ,
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.Xr ym 4 .
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.br
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For ports using the PCI bus:
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.Xr eap 4 ,
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.Xr sv 4 .
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.Sh BUGS
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If the device is used in
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.Xr mmap 2
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it is currently always mapped for writing (playing) due to
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VM system weirdness.
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.Pp
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