--- /dev/null
+ 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
+
+ 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.
+
+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.
+
+card*/pcm*/sub*/xrun_injection
+ Triggers an XRUN to the running stream when any value is
+ written to this proc file. Used for fault injection.
+ This entry is write-only.
+
+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/
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