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                Proc Files of ALSA Drivers

                ==========================

                Takashi Iwai 

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

        -: 

pcm

        Lists the currently available PCM devices in format of

        -: :  : 

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.

        This shows the status of xrun (= buffer overrun/xrun) debug of

        ALSA PCM middle layer, as an integer from 0 to 2.  The value

        can be changed by writing to this file, such as

                 # cat 2 > /proc/asound/card0/pcm0p/xrun_debug

        When this value is greater than 0, 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 this value is greater than 1, the driver will show the

        stack trace additionally.  This may help the debugging.

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.

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/