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