2 .\" Copyright (c) 1998, Luigi Rizzo
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26 .\" $FreeBSD: src/share/man/man4/pcm.4,v 1.50 2006/11/29 17:07:02 joel Exp $
27 .\" $DragonFly: src/share/man/man4/pcm.4,v 1.6 2007/01/04 21:47:00 corecode Exp $
38 PCM audio device infrastructure
40 To compile this driver into the kernel, place the following line in your
41 kernel configuration file:
42 .Bd -ragged -offset indent
46 For non-PnP sound cards:
47 .Bd -literal -offset indent
48 .Cd "device pcm0 at isa? port? irq 5 drq 1 flags 0x15"
53 driver provides support for
55 audio play and capture.
56 This driver also supports various
61 sound cards, AC97 mixer and High Definition Audio.
64 driver attaches, supported devices provide audio record and
68 sound system provides dynamic mixing
72 True full duplex operation is available on most sound cards.
74 If the sound card is supported by a bridge driver, the
76 driver works in conjunction with the bridge driver.
78 Apart from the usual parameters, the flags field is used to specify
81 channel (generally used for capture in full duplex cards).
82 Flags are set to 0 for cards not using a secondary
84 channel, or to 0x10 + C to specify channel C.
86 The driver does its best to recognize the installed hardware and drive
87 it correctly so the user is not required to add specific settings to
88 the kernel config file.
94 cards this is actually easy
95 since they identify themselves.
98 cards, the driver looks for
100 cards at addresses 0x530 and 0x604 (unless overridden
101 in the kernel config file ) .
103 In general, the module
112 or from the command line using the
115 Options which can be specified in
116 .Pa /boot/loader.conf
118 .Bl -tag -width ".Va snd_emu10k1_load" -offset indent
119 .It Va snd_driver_load
123 this option loads all available drivers.
124 .It Va snd_emu10k1_load
128 only the SoundBlaster 5.1 driver and dependent modules will be loaded.
133 load driver for card/chipset foo.
136 Each device can optionally support more playback channels
137 than physical hardware provides by using
142 options can be configured via the
144 interface but can only be manipulated while the device is inactive.
145 .Ss Runtime Configuration
146 There are a number of
150 tunables are global settings and
153 .Bl -tag -width ".Va hw.snd.report_soft_formats" -offset indent
154 .It Va hw.snd.latency_profile
155 Define sets of buffering latency conversion tables for the
158 A value of 0 will use a low and aggressive latency profile which can result
159 in possible underruns if the application cannot keep up with a rapid irq
160 rate, especially during high workload.
161 The default value is 1, which is considered a moderate/safe latency profile.
162 .It Va hw.snd.latency
163 Configure the buffering latency.
164 Only affects applications that do not explicitly request
165 blocksize / fragments.
166 This tunable provides finer granularity than the
167 .Va hw.snd.latency_profile
169 Possible values range between 0 (lowest latency) and 10 (highest latency).
170 .It Va hw.snd.report_soft_formats
171 Controls the internal format conversion if it is
172 available transparently to the application software.
173 When disabled or not available, the application will
174 only be able to select formats the device natively supports.
175 .It Va hw.snd.feeder_rate_round
176 Sample rate rounding threshold, to avoid large prime division at the
178 All requested sample rates will be rounded to the nearest threshold value.
179 Possible values range between 0 (disabled) and 500.
181 .It Va hw.snd.feeder_rate_max
182 Maximum allowable sample rate.
183 .It Va hw.snd.feeder_rate_min
184 Minimum allowable sample rate.
185 .It Va hw.snd.verbose
186 Level of verbosity for the
189 Higher values include more output and the highest level,
190 four, should be used when reporting problems.
191 Other options include:
194 Installed devices and their allocated bus resources.
196 The number of playback, record, virtual channels, and
199 Channel information per device including the channel's
200 current format, speed, and pseudo device statistics such as
201 buffer overruns and buffer underruns.
203 File names and versions of the currently loaded sound modules.
205 Various messages intended for debugging.
207 .It Va hw.snd.maxautovchans
210 setting that only affects devices with only one playback channel available.
211 The sound system will dynamically create up this many
218 Maximum value is 255.
219 .It Va hw.snd.default_unit
220 Default sound card for systems with multiple sound cards.
223 the default device for
225 Equivalent to a symlink from
228 .Pa /dev/dsp Ns Va ${hw.snd.default_unit} .
229 .It Va dev.pcm.%d.vchans
230 The current number of
232 allocated per device.
233 This can be set to preallocate a certain number of
235 Setting this value to
240 .It Va dev.pcm.%d.vchanrate
241 Sample rate speed for
244 All playback paths will be converted to this sample rate before the mixing
246 .It Va dev.pcm.%d.vchanformat
250 All playback paths will be converted to this format before the mixing
252 .It Va dev.pcm.%d.polling
253 Experimental polling mode support where the driver operates by querying the
254 device state on each tick using a
257 Disabled by default and currently only available for a few device drivers.
259 .Ss Recording Channels
260 On devices that have more than one recording source (ie: mic and line),
261 there is a corresponding
265 Channel statistics are only kept while the device is open.
266 So with situations involving overruns and underruns, consider the output
267 while the errant application is open and running.
269 The driver supports most of the
272 functions, and most applications work unmodified.
273 A few differences exist, while memory mapped playback is
274 supported natively and in
276 emulation, memory mapped recording is
280 As a consequence, some applications may need to be recompiled
281 with a slightly modified audio module.
284 for a complete list of the supported
290 drivers may create the following
293 .Bl -tag -width ".Pa /dev/audio%d.%d" -compact
294 .It Pa /dev/audio%d.%d
295 Sparc-compatible audio device.
297 Digitized voice device.
298 .It Pa /dev/dspW%d.%d
301 but 16 bits per sample.
302 .It Pa /dev/dsp%d.p%d
304 .It Pa /dev/dsp%d.r%d
306 .It Pa /dev/dsp%d.v%d
311 status, including all channels and drivers.
314 The first number in the device node
315 represents the unit number of the
323 Additional messages are sometimes recorded when the
324 device is probed and attached, these messages can be viewed with the
329 .It pcm%d:play:%d:dsp%d.p%d: play interrupt timeout, channel dead
330 The hardware does not generate interrupts to serve incoming (play)
331 or outgoing (record) data.
332 .It unsupported subdevice XX
333 A device node is not created properly.
364 .Xr snd_via82c686 4 ,
373 .%O "http://www.opensound.com/pguide/oss.pdf"
378 device driver first appeared in
389 The API evolved from the VOXWARE
390 standard which later became OSS standard.
393 .An Luigi Rizzo Aq luigi@iet.unipi.it
396 device driver and this manual page.
397 .An Cameron Grant Aq gandalf@vilnya.demon.co.uk
398 later revised the device driver for
400 .An Seigo Tanimura Aq tanimura@r.dl.itc.u-tokyo.ac.jp
401 revised this manual page.
402 It was then rewritten for
405 Some features of your sound card (e.g., global volume control) might not
406 be supported on all devices.