Proc Files of ALSA Drivers
  		==========================
  		Takashi Iwai <tiwai@suse.de>
  
  General
  -------
  
  ALSA has its own proc tree, /proc/asound.  Many useful information are
  found in this tree.  When you encounter a problem and need debugging,
  check the files listed in the following sections.
  
  Each card has its subtree cardX, where X is from 0 to 7. The
  card-specific files are stored in the card* subdirectories.
  
  
  Global Information
  ------------------
  
  cards
  	Shows the list of currently configured ALSA drivers,
  	index, the id string, short and long descriptions.
  
  version
  	Shows the version string and compile date.
  
  modules
  	Lists the module of each card
  
  devices
  	Lists the ALSA native device mappings.
  
  meminfo
  	Shows the status of allocated pages via ALSA drivers.
  	Appears only when CONFIG_SND_DEBUG=y.
  
  hwdep
  	Lists the currently available hwdep devices in format of
  	<card>-<device>: <name>
  
  pcm
  	Lists the currently available PCM devices in format of
  	<card>-<device>: <id>: <name> : <sub-streams>
  
  timer
  	Lists the currently available timer devices
  
  
  oss/devices
  	Lists the OSS device mappings.
  
  oss/sndstat
  	Provides the output compatible with /dev/sndstat.
  	You can symlink this to /dev/sndstat.
  
  
  Card Specific Files
  -------------------
  
  The card-specific files are found in /proc/asound/card* directories.
  Some drivers (e.g. cmipci) have their own proc entries for the
  register dump, etc (e.g. /proc/asound/card*/cmipci shows the register
  dump).  These files would be really helpful for debugging.
  
  When PCM devices are available on this card, you can see directories
  like pcm0p or pcm1c.  They hold the PCM information for each PCM
  stream.  The number after 'pcm' is the PCM device number from 0, and
  the last 'p' or 'c' means playback or capture direction.  The files in
  this subtree is described later.
  
  The status of MIDI I/O is found in midi* files.  It shows the device
  name and the received/transmitted bytes through the MIDI device.
  
  When the card is equipped with AC97 codecs, there are codec97#*
  subdirectories (described later).
  
  When the OSS mixer emulation is enabled (and the module is loaded),
  oss_mixer file appears here, too.  This shows the current mapping of
  OSS mixer elements to the ALSA control elements.  You can change the
  mapping by writing to this device.  Read OSS-Emulation.txt for
  details.
  
  
  PCM Proc Files
  --------------
  
  card*/pcm*/info
  	The general information of this PCM device: card #, device #,
  	substreams, etc.
  
  card*/pcm*/xrun_debug
  	This file appears when CONFIG_SND_DEBUG=y and
  	CONFIG_PCM_XRUN_DEBUG=y.
  	This shows the status of xrun (= buffer overrun/xrun) and
  	invalid PCM position debug/check of ALSA PCM middle layer.
  	It takes an integer value, can be changed by writing to this
  	file, such as
  
  		 # echo 5 > /proc/asound/card0/pcm0p/xrun_debug
  
  	The value consists of the following bit flags:
  	  bit 0 = Enable XRUN/jiffies debug messages
  	  bit 1 = Show stack trace at XRUN / jiffies check
  	  bit 2 = Enable additional jiffies check
  	  bit 3 = Log hwptr update at each period interrupt
  	  bit 4 = Log hwptr update at each snd_pcm_update_hw_ptr()
  	  bit 5 = Show last 10 positions on error
  	  bit 6 = Do above only once
  
  	When the bit 0 is set, the driver will show the messages to
  	kernel log when an xrun is detected.  The debug message is
  	shown also when the invalid H/W pointer is detected at the
  	update of periods (usually called from the interrupt
  	handler).
  
  	When the bit 1 is set, the driver will show the stack trace
  	additionally.  This may help the debugging.
  
  	Since 2.6.30, this option can enable the hwptr check using
  	jiffies.  This detects spontaneous invalid pointer callback
  	values, but can be lead to too much corrections for a (mostly
  	buggy) hardware that doesn't give smooth pointer updates.
  	This feature is enabled via the bit 2.
  
  	Bits 3 and 4 are for logging the hwptr records.  Note that
  	these will give flood of kernel messages.
  
  	When bit 5 is set, the driver logs the last 10 xrun errors and
  	the proc file shows each jiffies, position, period_size,
  	buffer_size, old_hw_ptr, and hw_ptr_base values.
  
  	When bit 6 is set, the full xrun log is shown only once.
  
  card*/pcm*/sub*/info
  	The general information of this PCM sub-stream.
  
  card*/pcm*/sub*/status
  	The current status of this PCM sub-stream, elapsed time,
  	H/W position, etc.
  
  card*/pcm*/sub*/hw_params
  	The hardware parameters set for this sub-stream.
  
  card*/pcm*/sub*/sw_params
  	The soft parameters set for this sub-stream.
  
  card*/pcm*/sub*/prealloc
  	The buffer pre-allocation information.
  
  
  AC97 Codec Information
  ----------------------
  
  card*/codec97#*/ac97#?-?
  	Shows the general information of this AC97 codec chip, such as
  	name, capabilities, set up.
  
  card*/codec97#0/ac97#?-?+regs
  	Shows the AC97 register dump.  Useful for debugging.
  
  	When CONFIG_SND_DEBUG is enabled, you can write to this file for
  	changing an AC97 register directly.  Pass two hex numbers.
  	For example,
  
  	# echo 02 9f1f > /proc/asound/card0/codec97#0/ac97#0-0+regs
  
  
  USB Audio Streams
  -----------------
  
  card*/stream*
  	Shows the assignment and the current status of each audio stream
  	of the given card.  This information is very useful for debugging.
  
  
  HD-Audio Codecs
  ---------------
  
  card*/codec#*
  	Shows the general codec information and the attribute of each
  	widget node.
  
  card*/eld#*
  	Available for HDMI or DisplayPort interfaces.
  	Shows ELD(EDID Like Data) info retrieved from the attached HDMI sink,
  	and describes its audio capabilities and configurations.
  
  	Some ELD fields may be modified by doing `echo name hex_value > eld#*`.
  	Only do this if you are sure the HDMI sink provided value is wrong.
  	And if that makes your HDMI audio work, please report to us so that we
  	can fix it in future kernel releases.
  
  
  Sequencer Information
  ---------------------
  
  seq/drivers
  	Lists the currently available ALSA sequencer drivers.
  
  seq/clients
  	Shows the list of currently available sequencer clients and
  	ports.  The connection status and the running status are shown
  	in this file, too.
  
  seq/queues
  	Lists the currently allocated/running sequencer queues.
  
  seq/timer
  	Lists the currently allocated/running sequencer timers.
  
  seq/oss
  	Lists the OSS-compatible sequencer stuffs.
  
  
  Help For Debugging?
  -------------------
  
  When the problem is related with PCM, first try to turn on xrun_debug
  mode.  This will give you the kernel messages when and where xrun
  happened.
  
  If it's really a bug, report it with the following information:
  
    - the name of the driver/card, show in /proc/asound/cards
    - the register dump, if available (e.g. card*/cmipci)
  
  when it's a PCM problem,
  
    - set-up of PCM, shown in hw_parms, sw_params, and status in the PCM
      sub-stream directory
  
  when it's a mixer problem,
  
    - AC97 proc files, codec97#*/* files
  
  for USB audio/midi,
  
    - output of lsusb -v
    - stream* files in card directory
  
  
  The ALSA bug-tracking system is found at:
  
      https://bugtrack.alsa-project.org/alsa-bug/