/Documentation/sound/alsa/Procfile.txt

  1		Proc Files of ALSA Drivers
  2		==========================
  3		Takashi Iwai <tiwai@suse.de>
  4
  5General
  6-------
  7
  8ALSA has its own proc tree, /proc/asound.  Many useful information are
  9found in this tree.  When you encounter a problem and need debugging,
 10check the files listed in the following sections.
 11
 12Each card has its subtree cardX, where X is from 0 to 7. The
 13card-specific files are stored in the card* subdirectories.
 14
 15
 16Global Information
 17------------------
 18
 19cards
 20	Shows the list of currently configured ALSA drivers,
 21	index, the id string, short and long descriptions.
 22
 23version
 24	Shows the version string and compile date.
 25
 26modules
 27	Lists the module of each card
 28
 29devices
 30	Lists the ALSA native device mappings.
 31
 32meminfo
 33	Shows the status of allocated pages via ALSA drivers.
 34	Appears only when CONFIG_SND_DEBUG=y.
 35
 36hwdep
 37	Lists the currently available hwdep devices in format of
 38	<card>-<device>: <name>
 39
 40pcm
 41	Lists the currently available PCM devices in format of
 42	<card>-<device>: <id>: <name> : <sub-streams>
 43
 44timer
 45	Lists the currently available timer devices
 46
 47
 48oss/devices
 49	Lists the OSS device mappings.
 50
 51oss/sndstat
 52	Provides the output compatible with /dev/sndstat.
 53	You can symlink this to /dev/sndstat.
 54
 55
 56Card Specific Files
 57-------------------
 58
 59The card-specific files are found in /proc/asound/card* directories.
 60Some drivers (e.g. cmipci) have their own proc entries for the
 61register dump, etc (e.g. /proc/asound/card*/cmipci shows the register
 62dump).  These files would be really helpful for debugging.
 63
 64When PCM devices are available on this card, you can see directories
 65like pcm0p or pcm1c.  They hold the PCM information for each PCM
 66stream.  The number after 'pcm' is the PCM device number from 0, and
 67the last 'p' or 'c' means playback or capture direction.  The files in
 68this subtree is described later.
 69
 70The status of MIDI I/O is found in midi* files.  It shows the device
 71name and the received/transmitted bytes through the MIDI device.
 72
 73When the card is equipped with AC97 codecs, there are codec97#*
 74subdirectories (described later).
 75
 76When the OSS mixer emulation is enabled (and the module is loaded),
 77oss_mixer file appears here, too.  This shows the current mapping of
 78OSS mixer elements to the ALSA control elements.  You can change the
 79mapping by writing to this device.  Read OSS-Emulation.txt for
 80details.
 81
 82
 83PCM Proc Files
 84--------------
 85
 86card*/pcm*/info
 87	The general information of this PCM device: card #, device #,
 88	substreams, etc.
 89
 90card*/pcm*/xrun_debug
 91	This file appears when CONFIG_SND_DEBUG=y and
 92	CONFIG_PCM_XRUN_DEBUG=y.
 93	This shows the status of xrun (= buffer overrun/xrun) and
 94	invalid PCM position debug/check of ALSA PCM middle layer.
 95	It takes an integer value, can be changed by writing to this
 96	file, such as
 97
 98		 # echo 5 > /proc/asound/card0/pcm0p/xrun_debug
 99
100	The value consists of the following bit flags:
101	  bit 0 = Enable XRUN/jiffies debug messages
102	  bit 1 = Show stack trace at XRUN / jiffies check
103	  bit 2 = Enable additional jiffies check
104	  bit 3 = Log hwptr update at each period interrupt
105	  bit 4 = Log hwptr update at each snd_pcm_update_hw_ptr()
106
107	When the bit 0 is set, the driver will show the messages to
108	kernel log when an xrun is detected.  The debug message is
109	shown also when the invalid H/W pointer is detected at the
110	update of periods (usually called from the interrupt
111	handler).
112
113	When the bit 1 is set, the driver will show the stack trace
114	additionally.  This may help the debugging.
115
116	Since 2.6.30, this option can enable the hwptr check using
117	jiffies.  This detects spontaneous invalid pointer callback
118	values, but can be lead to too much corrections for a (mostly
119	buggy) hardware that doesn't give smooth pointer updates.
120	This feature is enabled via the bit 2.
121
122	Bits 3 and 4 are for logging the hwptr records.  Note that
123	these will give flood of kernel messages.
124
125card*/pcm*/sub*/info
126	The general information of this PCM sub-stream.
127
128card*/pcm*/sub*/status
129	The current status of this PCM sub-stream, elapsed time,
130	H/W position, etc.
131
132card*/pcm*/sub*/hw_params
133	The hardware parameters set for this sub-stream.
134
135card*/pcm*/sub*/sw_params
136	The soft parameters set for this sub-stream.
137
138card*/pcm*/sub*/prealloc
139	The buffer pre-allocation information.
140
141
142AC97 Codec Information
143----------------------
144
145card*/codec97#*/ac97#?-?
146	Shows the general information of this AC97 codec chip, such as
147	name, capabilities, set up.
148
149card*/codec97#0/ac97#?-?+regs
150	Shows the AC97 register dump.  Useful for debugging.
151
152	When CONFIG_SND_DEBUG is enabled, you can write to this file for
153	changing an AC97 register directly.  Pass two hex numbers.
154	For example,
155
156	# echo 02 9f1f > /proc/asound/card0/codec97#0/ac97#0-0+regs
157
158
159USB Audio Streams
160-----------------
161
162card*/stream*
163	Shows the assignment and the current status of each audio stream
164	of the given card.  This information is very useful for debugging.
165
166
167HD-Audio Codecs
168---------------
169
170card*/codec#*
171	Shows the general codec information and the attribute of each
172	widget node.
173
174card*/eld#*
175	Available for HDMI or DisplayPort interfaces.
176	Shows ELD(EDID Like Data) info retrieved from the attached HDMI sink,
177	and describes its audio capabilities and configurations.
178
179	Some ELD fields may be modified by doing `echo name hex_value > eld#*`.
180	Only do this if you are sure the HDMI sink provided value is wrong.
181	And if that makes your HDMI audio work, please report to us so that we
182	can fix it in future kernel releases.
183
184
185Sequencer Information
186---------------------
187
188seq/drivers
189	Lists the currently available ALSA sequencer drivers.
190
191seq/clients
192	Shows the list of currently available sequencer clients and
193	ports.  The connection status and the running status are shown
194	in this file, too.
195
196seq/queues
197	Lists the currently allocated/running sequencer queues.
198
199seq/timer
200	Lists the currently allocated/running sequencer timers.
201
202seq/oss
203	Lists the OSS-compatible sequencer stuffs.
204
205
206Help For Debugging?
207-------------------
208
209When the problem is related with PCM, first try to turn on xrun_debug
210mode.  This will give you the kernel messages when and where xrun
211happened.
212
213If it's really a bug, report it with the following information:
214
215  - the name of the driver/card, show in /proc/asound/cards
216  - the register dump, if available (e.g. card*/cmipci)
217
218when it's a PCM problem,
219
220  - set-up of PCM, shown in hw_parms, sw_params, and status in the PCM
221    sub-stream directory
222
223when it's a mixer problem,
224
225  - AC97 proc files, codec97#*/* files
226
227for USB audio/midi,
228
229  - output of lsusb -v
230  - stream* files in card directory
231
232
233The ALSA bug-tracking system is found at:
234
235    https://bugtrack.alsa-project.org/alsa-bug/