Documentation/sound/alsa/Procfile.txt

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