Documentation/sound/alsa/Procfile.txt - linux - Git at Google

 		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/
	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/