  Advanced Linux Sound Architecture - Library API
  Jaroslav Kysela <perex@jcu.cz> with assistance from Alan
  Robinson
  v0.0.3, 25 March 1998

  This document describes, in full detail, the Advanced Linux Sound
  Architecture library API.
  ______________________________________________________________________

  Table of Contents:

  1.      Introduction

  2.      Error Codes

  2.1.    Error Codes in Detail

  2.2.    Functions

  2.2.1.  const char *snd_strerror( int errnum )

  3.      Control Interface

  3.1.    Low-Level Layer

  3.1.1.  int snd_cards( void )

  3.1.2.  unsigned int snd_cards_mask( void )

  3.1.3.  int snd_ctl_open( void **handle, int card )

  3.1.4.  int snd_ctl_close( void *handle )

  3.1.5.  int snd_ctl_file_descriptor( void *handle )

  3.1.6.  int snd_ctl_hw_info( void *handle, struct snd_ctl_hw_info
  *info )

  3.1.7.  int snd_ctl_pcm_info( void *handle, int dev, snd_pcm_info_t
  *info )

  3.1.8.  int snd_ctl_pcm_playback_info( void *handle, int dev,
  snd_pcm_playback_info_t *info )

  3.1.9.  int snd_ctl_pcm_record_info( void *handle, int dev,
  snd_pcm_record_info_t *info )

  3.1.10. int snd_ctl_mixer_info( void *handle, int dev,
  snd_mixer_info_t *info )

  3.2.    Examples

  4.      Mixer Interface

  4.1.    Low-Level Layer

  4.1.1.  int snd_mixer_open( void **handle, int card, int device )

  4.1.2.  int snd_mixer_close( void *handle )

  4.1.3.  int snd_mixer_file_descriptor( void *handle )

  4.1.4.  int snd_mixer_channels( void *handle )

  4.1.5.  int snd_mixer_info( void *handle, snd_mixer_info_t *info )

  4.1.6.  int snd_mixer_channel( void *handle, const char *channel_id )

  4.1.7.  int snd_mixer_exact_mode( void *handle, int enable )

  4.1.8.  int snd_mixer_channel_info( void *handle, int channel,
  snd_mixer_channel_info_t *info )

  4.1.9.  int snd_mixer_channel_read( void *handle, int channel,
  snd_mixer_channel_t *data )

  4.1.10. int snd_mixer_channel_write( void *handle, int channel,
  snd_mixer_channel_t *data )

  4.1.11. int snd_mixer_special_read( void *handle, snd_mixer_special_t
  *special )

  4.1.12. int snd_mixer_special_write( void *handle, snd_mixer_special_t
  *special )

  4.1.13. int snd_mixer_read( void *handle, snd_mixer_callbacks_t
  *callbacks )

  4.2.    Examples

  5.      Digital Audio (PCM) Interface

  5.1.    Low-Level Layer

  5.1.1.  int snd_pcm_open( void **handle, int card, int device, int
  mode )

  5.1.2.  int snd_pcm_close( void *handle )

  5.1.3.  int snd_pcm_file_descriptor( void *handle )

  5.1.4.  int snd_pcm_block_mode( void *handle, int enable )

  5.1.5.  int snd_pcm_info( void *handle, snd_pcm_info_t *info )

  5.1.6.  int snd_pcm_playback_info( void *handle,
  snd_pcm_playback_info_t *info )

  5.1.7.  int snd_pcm_record_info( void *handle, snd_pcm_record_info_t
  *info )

  5.1.8.  int snd_pcm_playback_format( void *handle, snd_pcm_format_t
  *format )

  5.1.9.  int snd_pcm_record_format( void *handle, snd_pcm_format_t
  *format )

  5.1.10. int snd_pcm_playback_params( void *handle,
  snd_pcm_playback_params_t *params )

  5.1.11. int snd_pcm_record_params( void *handle,
  snd_pcm_record_params_t *params )

  5.1.12. int snd_pcm_playback_status( void *handle,
  snd_pcm_playback_status_t *status )

  5.1.13. int snd_pcm_record_status( void *handle,
  snd_pcm_record_status_t *status )

  5.1.14. int snd_pcm_drain_playback( void *handle )

  5.1.15. int snd_pcm_flush_playback( void *handle )

  5.1.16. int snd_pcm_flush_record( void *handle )

  5.1.17. int snd_pcm_playback_time( void *handle, int enable )

  5.1.18. int snd_pcm_record_time( void *handle, int enable )

  5.1.19. ssize_t snd_pcm_write( void *handle, const void *buffer,
  size_t size )

  5.1.20. ssize_t snd_pcm_read( void *handle, void *buffer, size_t size
  )

  5.2.    Examples
  ______________________________________________________________________

  11..  IInnttrroodduuccttiioonn

  The Advanced Linux Sound Architecture comes with a kernel API &
  library API.  This document describes the library API and how it
  interfaces with the kernel API.  The kernal API will probably never be
  documented in standalone form.

  Application programmers should use the library API rather than kernel
  API.  The Library offers 100% of the functionally of the kernel API,
  but add next major improvements in usability, making the application
  code simpler and better looking. In addition, some of the some
  fixes/compatibility code in, may be placed in the library code instead
  of the kernel driver.

  For a complete list of all variables and functions in the API you
  should look at the following header files:

  1. /usr/include/sys/asoundlib.h

  2. /usr/include/linux/asound.h

  3. /usr/include/linux/asoundid.h

  22..  EErrrroorr CCooddeess

  All functions return int (or some sort of signed value). If this value
  is negative it represents an error code. Codes up to SND_ERROR_BEGIN
  (500000) represents standard system errors. Codes equal or greather
  than this value represents sound library API errors. All error codes
  begin with the prefix _S_N_D___E_R_R_O_R__.

  22..11..  EErrrroorr CCooddeess iinn DDeettaaiill

     SSNNDD__EERRRROORR__UUNNCCOOMMPPAATTIIBBLLEE__VVEERRSSIIOONN ((550000000000))
        This error is caused if the driver uses an incompatible kernel
        API for this interface and hence the library doesn't know how
        this API can be used.

  22..22..  FFuunnccttiioonnss

  22..22..11..

  ccoonnsstt cchhaarr **ssnndd__ssttrreerrrroorr(( iinntt eerrrrnnuumm ))

  This functions converts error code to a string. Its functionality is
  the same as the _s_t_r_e_r_r_o_r function from the standard C library, but
  this function returns correct strings for sound error codes, too.

  33..  CCoonnttrrooll IInntteerrffaaccee

  The control interfaces gives application various information about the
  currently installed sound driver in the system. The interface should
  be used to detect if another sound interface is present for selected
  soundcard or, for example, to create a list of devices (MIXER, PCM
  etc) from which the user can select.

  33..11..  LLooww--LLeevveell LLaayyeerr

  33..11..11..

  iinntt ssnndd__ccaarrddss(( vvooiidd ))

  Returns the number of soundcards present in the system, if any.
  Otherwise it returns a negative value, which maps to an error code.
  This function will return 0 if no soundcards are detected.

  33..11..22..

  uunnssiiggnneedd iinntt ssnndd__ccaarrddss__mmaasskk(( vvooiidd ))

  Returns the bitmap of soundcards present in the system, if any.
  Otherwise it returns a negative value, which maps to an error code.
  This function will return 0 if no soundcards are detected. First
  soundcard is represented with bit 0.

  33..11..33..

  iinntt ssnndd__ccttll__ooppeenn(( vvooiidd ****hhaannddllee,, iinntt ccaarrdd ))

  Creates a new handle and opens communication with the kernel sound
  control interface for soundcard number _c_a_r_d (0-N). The function also
  checks if protocol is compatible, so as to prevent the use of old
  programs with a new kernel API. Function returns zero if successful,
  otherwise an error code is returned.

  33..11..44..

  iinntt ssnndd__ccttll__cclloossee(( vvooiidd **hhaannddllee ))

  Function frees all resources allocated with control handle and closes
  the kernel sound control interface. Function returns zero if
  successful, otherwise it returns an error code.

  33..11..55..

  iinntt ssnndd__ccttll__ffiillee__ddeessccrriippttoorr(( vvooiidd **hhaannddllee ))

  Function returns file descriptor for the kernel sound control
  interface.  This function should be used in very special cases.
  Function returns a negative error code if some error was encountered.
  33..11..66..

  iinntt ssnndd__ccttll__hhww__iinnffoo(( vvooiidd **hhaannddllee,, ssttrruucctt ssnndd__ccttll__hhww__iinnffoo **iinnffoo ))

  Fills the info structure with data about the sound hardware referenced
  by handle. Function returns zero if successful, otherwise it returns
  an error code.

  ______________________________________________________________________
    #define SND_CTL_GCAPS_MIDI              0x0000001       /* driver has MIDI interface */

    #define SND_CTL_LCAPS_SYNTH             0x0000001       /* soundcard has synthesizer */
    #define SND_CTL_LCAPS_RAWFM             0x0000002       /* soundcard has RAW FM/OPL3 */

    struct snd_ctl_hw_info {
      unsigned int type;            /* type of card - see SND_CARD_TYPE_XXXX */
      unsigned int gcaps;           /* see SND_CTL_GCAPS_XXXX */
      unsigned int lcaps;           /* see SND_CTL_LCAPS_XXXX */
      unsigned int pcmdevs;         /* count of PCM devices (0 to N) */
      unsigned int mixerdevs;       /* count of MIXER devices (0 to N) */
      unsigned int mididevs;        /* count of raw MIDI devices (0 to N) */
      char id[8];                   /* ID of card (user selectable) */
      char name[80];                /* name/info text about soundcard */
      unsigned char reserved[128];  /* reserved for future use */
    };

  ______________________________________________________________________

  33..11..77..

  iinntt ssnndd__ccttll__ppccmm__iinnffoo(( vvooiidd **hhaannddllee,, iinntt ddeevv,, ssnndd__ppccmm__iinnffoo__tt **iinnffoo ))

  Fills the *info structure with data about the PCM device. Function
  returns zero if successful, otherwise it returns an error code.
  Details about the snd_pcm_info_t structure are in the DDiiggiittaall AAuuddiioo
  ((PPCCMM)) IInntteerrffaaccee section. The argument _d_e_v selects the device number
  for the soundcard referenced by *handle. Its range is 0 to N where N
  is _s_t_r_u_c_t _s_n_d___c_t_l___h_w___i_n_f_o _-_> _p_c_m_d_e_v_s _- _1. This function will work if
  the selected PCM device is busy, too. It should be used to collect
  information about PCM devices without exclusive lock.

  33..11..88..

  iinntt ssnndd__ccttll__ppccmm__ppllaayybbaacckk__iinnffoo(( vvooiidd **hhaannddllee,, iinntt ddeevv,, ssnndd__ppccmm__ppllaayy--
  bbaacckk__iinnffoo__tt **iinnffoo ))

  Fills the *info structure with data about the PCM device and playback
  direction.  Function returns zero if successful, otherwise it returns
  an error code.  Details about the snd_pcm_playback_info_t structure
  are in the DDiiggiittaall AAuuddiioo ((PPCCMM)) IInntteerrffaaccee section. The argument _d_e_v
  selects the device number for the soundcard referenced by *handle. Its
  range is 0 to N where N is _s_t_r_u_c_t _s_n_d___c_t_l___h_w___i_n_f_o _-_> _p_c_m_d_e_v_s _- _1.
  This function will work if the selected PCM device is busy, too. It
  should be used to collect information about PCM devices without
  exclusive lock.

  33..11..99..

  iinntt ssnndd__ccttll__ppccmm__rreeccoorrdd__iinnffoo(( vvooiidd **hhaannddllee,, iinntt ddeevv,,
  ssnndd__ppccmm__rreeccoorrdd__iinnffoo__tt **iinnffoo ))

  Fills the *info structure with data about the PCM device and record
  direction.  Function returns zero if successful, otherwise it returns
  an error code.  Details about the snd_pcm_record_info_t structure are
  in the DDiiggiittaall AAuuddiioo ((PPCCMM)) IInntteerrffaaccee section. The argument _d_e_v selects
  the device number for the soundcard referenced by *handle. Its range
  is 0 to N where N is _s_t_r_u_c_t _s_n_d___c_t_l___h_w___i_n_f_o _-_> _p_c_m_d_e_v_s _- _1.  This
  function will work if the selected PCM device is busy, too. It should
  be used to collect information about PCM devices without exclusive
  lock.

  33..11..1100..

  iinntt ssnndd__ccttll__mmiixxeerr__iinnffoo(( vvooiidd **hhaannddllee,, iinntt ddeevv,, ssnndd__mmiixxeerr__iinnffoo__tt **iinnffoo
  ))

  Fills the *info structure with data about the mixer device. Returns
  zero if successful, otherwise it returns an error code. Details about
  the snd_mixer_info_t structure are in the MMiixxeerr IInntteerrffaaccee section.
  The argument _d_e_v specifies the device number for the appropriate
  soundcard. Its range is 0 to N where N found from _s_t_r_u_c_t
  _s_n_d___c_t_l___h_w___i_n_f_o _-_> _m_i_x_e_r_d_e_v_s _- _1.  It should be used to collect
  information about mixer devices.

  33..22..  EExxaammpplleess

  The following example shows how all PCM devices can be detected for
  the first soundcard (#0) in the system.

       ______________________________________________________________________
       int card = 0, err;
       void *handle;
       stuct snd_ctl_hw_info info;

       if ( (err = snd_ctl_open( &handle, card )) < 0 ) {
         fprintf( stderr, "open failed: %s\n", snd_strerror( err ) );
         return;
       }
       if ( (err = snd_ctl_hw_info( handle, &info )) < 0 ) {
         fprintf( stderr, "hw info failed: %s\n", snd_strerror( err ) );
         snd_ctl_close( handle );
         return;
       }
       printf( "Installed PCM devices for card #i: %i\n", card + 1, info.pcmdevs );
       snd_ctl_close( handle );
       ______________________________________________________________________

  44..  MMiixxeerr IInntteerrffaaccee

  The Mixer Interface allows applications to change the volume level of
  a soundcard's input/output channels in both the linear range (0-100)
  and in decibels. It also supports features like hardware mute, input
  sound source, etc.

  44..11..  LLooww--LLeevveell LLaayyeerr

  Mixer devices aren't opened exclusively. This allows applications to
  open a device multiple times with one or more processes.
  44..11..11..

  iinntt ssnndd__mmiixxeerr__ooppeenn(( vvooiidd ****hhaannddllee,, iinntt ccaarrdd,, iinntt ddeevviiccee ))

  Creates new handle and opens a connection to the kernel sound mixer
  interface for soundcard number _c_a_r_d (0-N) and mixer device number
  _d_e_v_i_c_e.  Also checks if protocol is compatible to prevent use of old
  programs with new kernel API. Function returns zero if successful,
  otherwise it returns an error code.

  44..11..22..

  iinntt ssnndd__mmiixxeerr__cclloossee(( vvooiidd **hhaannddllee ))

  Frees all resources allocated to the mixer handle and closes its
  connection to the kernel sound mixer interface. Function returns zero
  if successful, otherwise it returns an error code.

  44..11..33..

  iinntt ssnndd__mmiixxeerr__ffiillee__ddeessccrriippttoorr(( vvooiidd **hhaannddllee ))

  Returns the file descriptor for the connection to the kernel sound
  mixer interface. This function should be used only in very special
  cases. Function returns a negative error code if an error was
  encountered.

  The file descriptor should be used for the _s_e_l_e_c_t synchronous
  multiplexer function for deterimeing read direction. Applications
  should call _s_n_d___m_i_x_e_r___r_e_a_d function if some data is waiting to be
  read.  It is recomended that you do this, since it leaves place for
  this function to handle some new kernel API specifications.

  44..11..44..

  iinntt ssnndd__mmiixxeerr__cchhaannnneellss(( vvooiidd **hhaannddllee ))

  Returns the count of mixer channels for appropriate mixer device,
  otherwise the return value is negative, and signifies an error code.
  Never returns zero.

  44..11..55..

  iinntt ssnndd__mmiixxeerr__iinnffoo(( vvooiidd **hhaannddllee,, ssnndd__mmiixxeerr__iinnffoo__tt **iinnffoo ))

  Fills the *info structure with information about the mixer associated
  with *handle. Returns zero if successful, otherwise it returns an
  error code.

  ______________________________________________________________________
    #define SND_MIXER_INFO_CAP_EXCL_RECORD  0x00000001

    struct snd_mixer_info {
      unsigned int type;            /* type of soundcard - SND_CARD_TYPE_XXXX */
      unsigned int channels;        /* count of mixer devices */
      unsigned int caps;            /* some flags about this device (SND_MIXER_INFO_CAP_XXXX) */
      unsigned char id[32];         /* ID of this mixer */
      unsigned char name[80];       /* name of this device */
      char reserved[ 32 ];          /* reserved for future use */
    };

  ______________________________________________________________________

  44..11..66..

  iinntt ssnndd__mmiixxeerr__cchhaannnneell(( vvooiidd **hhaannddllee,, ccoonnsstt cchhaarr **cchhaannnneell__iidd ))

  Returns the channel number (index) associated with channel_id (channel
  name), or returns an error code.

  ______________________________________________________________________
    #define SND_MIXER_ID_MASTER             "Master"
    #define SND_MIXER_ID_BASS               "Bass"
    #define SND_MIXER_ID_TREBLE             "Treble"
    #define SND_MIXER_ID_SYNTHESIZER        "Synth"
    #define SND_MIXER_ID_SYNTHESIZER1       "Synth 1"
    #define SND_MIXER_ID_FM                 "FM"
    #define SND_MIXER_ID_EFFECT             "Effect"
    #define SND_MIXER_ID_PCM                "PCM"
    #define SND_MIXER_ID_PCM1               "PCM 1"
    #define SND_MIXER_ID_LINE               "Line-In"
    #define SND_MIXER_ID_MIC                "MIC"
    #define SND_MIXER_ID_CD                 "CD"
    #define SND_MIXER_ID_GAIN               "Record-Gain"
    #define SND_MIXER_ID_IGAIN              "In-Gain"
    #define SND_MIXER_ID_OGAIN              "Out-Gain"
    #define SND_MIXER_ID_LOOPBACK           "Loopback"
    #define SND_MIXER_ID_SPEAKER            "PC Speaker"
    #define SND_MIXER_ID_AUXA               "Aux A"
    #define SND_MIXER_ID_AUXB               "Aux B"
    #define SND_MIXER_ID_AUXC               "Aux C"

  ______________________________________________________________________

  44..11..77..

  iinntt ssnndd__mmiixxeerr__eexxaacctt__mmooddee(( vvooiidd **hhaannddllee,, iinntt eennaabbllee ))

  Turns on or off (by default) exact mode. This mode allows to
  application set/get volume values in exact range which uses hardware.
  In non-exact mode is range always from 0 to 100 and conversion to
  hardware range does driver. Function returns zero if successful,
  otherwise it returns an error code.

  44..11..88..

  iinntt ssnndd__mmiixxeerr__cchhaannnneell__iinnffoo(( vvooiidd **hhaannddllee,, iinntt cchhaannnneell,, ssnndd__mmiixxeerr__cchhaann--
  nneell__iinnffoo__tt **iinnffoo ))
  Fills the *info structure. The argument _c_h_a_n_n_e_l specifies channel (0
  to N) for which is the info requested. Function returns zero if
  successful, otherwise it returns an error code.

  ______________________________________________________________________
    #define SND_MIXER_CINFO_CAP_RECORD      0x00000001
    #define SND_MIXER_CINFO_CAP_STEREO      0x00000002
    #define SND_MIXER_CINFO_CAP_MUTE        0x00000004
    #define SND_MIXER_CINFO_CAP_HWMUTE      0x00000008      /* channel supports hardware mute */
    #define SND_MIXER_CINFO_CAP_DIGITAL     0x00000010      /* channel does digital (not analog) mixing */
    #define SND_MIXER_CINOF_CAP_INPUT       0x00000020      /* input channel */

    struct snd_mixer_channel_info {
      unsigned int channel;         /* channel # (filled by application) */
      unsigned int parent;          /* parent channel # or SND_MIXER_PARENT */
      unsigned char name[12];       /* name of this device */
      unsigned int caps;            /* some flags about this device (SND_MIXER_CINFO_XXXX) */
      int min;                      /* min. value when exact mode (or always 0) */
      int max;                      /* max. value when exact mode (or always 100) */
      int min_dB;                   /* minimum decibel value (*100) */
      int max_dB;                   /* maximum decibel value (*100) */
      int step_dB;                  /* step decibel value (*100) */
      unsigned char reserved[16];
    };

  ______________________________________________________________________

  44..11..99..

  iinntt ssnndd__mmiixxeerr__cchhaannnneell__rreeaadd(( vvooiidd **hhaannddllee,, iinntt cchhaannnneell,, ssnndd__mmiixxeerr__cchhaann--
  nneell__tt **ddaattaa ))

  Fills the *data structure. The argument _c_h_a_n_n_e_l specifies the channel
  (0 to N) for which is data requested. Function returns zero if
  successful, otherwise it returns an error code.

  ______________________________________________________________________
    #define SND_MIXER_FLG_RECORD            0x00000001      /* channel record source flag */
    #define SND_MIXER_FLG_MUTE_LEFT         0x00010000
    #define SND_MIXER_FLG_MUTE_RIGHT        0x00020000
    #define SND_MIXER_FLG_MUTE              0x00030000
    #define SND_MIXER_FLG_DECIBEL           0x40000000
    #define SND_MIXER_FLG_FORCE             0x80000000

    struct snd_mixer_channel {
      unsigned int channel;         /* channel # (filled by application) */
      unsigned int flags;           /* some flags to read/write (SND_MIXER_FLG_XXXX) */
      int left;                     /* min - max when exact mode (or 0 - 100) */
      int right;                    /* min - max when exact mode (or 0 - 100) */
      int left_dB;                  /* dB * 100 */
      int right_dB;                 /* dB * 100 */
      unsigned char reserved[16];
    };

  ______________________________________________________________________

     SSNNDD__MMIIXXEERR__FFLLGG__RREECCOORRDD
        Record source flag.

     SSNNDD__MMIIXXEERR__FFLLGG__DDEECCIIBBEELL
        If this bit is set, driver set volume from dB variables _l_e_f_t___d_B
        and _r_i_g_h_t___d_B.

     SSNNDD__MMIIXXEERR__FFLLGG__FFOORRCCEE
        Force set - this bit shouldn't be used from user space. Reserved
        for kernel.

  44..11..1100..

  iinntt ssnndd__mmiixxeerr__cchhaannnneell__wwrriittee(( vvooiidd **hhaannddllee,, iinntt cchhaannnneell,,
  ssnndd__mmiixxeerr__cchhaannnneell__tt **ddaattaa ))

  Writes the *data structure to kernel. The _c_h_a_n_n_e_l argument specifies
  the channel (0 to N) for which is data is to be applied.  Function
  returns zero if successful, otherwise it returns an error code.  This
  functions is the opposite of _s_n_d___m_i_x_e_r___c_h_a_n_n_e_l___r_e_a_d.

  44..11..1111..

  iinntt ssnndd__mmiixxeerr__ssppeecciiaall__rreeaadd(( vvooiidd **hhaannddllee,, ssnndd__mmiixxeerr__ssppeecciiaall__tt **ssppeecciiaall
  ))

  Not documented...

  44..11..1122..

  iinntt ssnndd__mmiixxeerr__ssppeecciiaall__wwrriittee(( vvooiidd **hhaannddllee,, ssnndd__mmiixxeerr__ssppeecciiaall__tt **ssppee--
  cciiaall ))

  Not documented...

  44..11..1133..

  iinntt ssnndd__mmiixxeerr__rreeaadd(( vvooiidd **hhaannddllee,, ssnndd__mmiixxeerr__ccaallllbbaacckkss__tt **ccaallllbbaacckkss ))

  This function reads and parses data from driver. Parsed actions are
  returned back to the application using the _c_a_l_l_b_a_c_k_s structure.
  Applications should not parse data from the driver in standard cases.
  This function returns immediately after all data is read from driver.
  Does not block process.

  ______________________________________________________________________
    typedef struct snd_mixer_callbacks {
      void *private_data;           /* should be used by application */
      void (*channel_was_changed)( void *private_data, int channel );
      void *reserved[15];           /* reserved for future use - must be NULL!!! */
    } snd_mixer_callbacks_t;

  ______________________________________________________________________

  44..22..  EExxaammpplleess

  The following example shows installed mixer channels for soundcard #0
  and mixer device #0 in the system, and also sets the master volume (if
  present) to 50.

  ______________________________________________________________________
  int card = 0, device = 0, err;
  void *handle;
  snd_mixer_info_t info;
  snd_mixer_channel_t channel;

  if ( (err = snd_mixer_open( &handle, card, device )) < 0 ) {
    fprintf( stderr, "open failed: %s\n", snd_strerror( err ) );
    return;
  }
  if ( (err = snd_mixer_info( handle, &info )) < 0 ) {
    fprintf( stderr, "info failed: %s\n", snd_strerror( err ) );
    snd_mixer_close( handle );
    return;
  }
  printf( "Installed MIXER channels for card #i and device %i: %i\n",
                                          card + 1, device, info.channels );
  master = snd_mixer_channel( handle, SND_MIXER_ID_MASTER );
  if ( master >= 0 ) {
    if ( (err = snd_mixer_read( handle, master, &channel )) < 0 ) {
      fprintf( stderr, "master read failed: %s\n", snd_strerror( err ) );
      snd_mixer_close( handle );
      return;
    }
    channel -> left = channel -> right = 50;
    if ( (err = snd_mixer_write( handle, master, &channel )) < 0 ) {
      fprintf( stderr, "master write failed: %s\n", snd_strerror( err ) );
      snd_mixer_close( handle );
      return;
    }
  }
  snd_mixer_close( handle );
  ______________________________________________________________________

  55..  DDiiggiittaall AAuuddiioo ((PPCCMM)) IInntteerrffaaccee

  Digital audio is the most commonly used method of representing sound
  inside a computer. In this method sound is stored as a sequence of
  samples taken from the audio signal using constant time intervals. A
  sample represents volume of the signal at the moment when it was
  measured. In uncompressed digital audio each sample require one or
  more bytes of storage. The number of bytes required depends on number
  of channels (mono, stereo) and sample format (8 or 16 bits, mu-Law,
  etc.). The length of this interval determines the sampling rate.
  Commonly used sampling rates are between 8 kHz (telephone quality) and
  48 kHz (DAT tapes).

  The physical devices used in digital audio are called the ADC (Analog
  to Digital Converter) and DAC (Digital to Analog Converter). A device
  containing both ADC and DAC is commonly known as a codec. The codec
  device used in a Sound Blaster cards is called a DSP which is somewhat
  misleading since DSP also stands for Digital Signal Processor (the SB
  DSP chip is very limited when compared to "true" DSP chips).

  Sampling parameters affect the quality of sound which can be
  reproduced from the recorded signal. The most fundamental parameter is
  sampling rate which limits the highest frequency than can be stored.
  It is well known (Nyquist's Sampling Theorem) that the highest
  frequency that can be stored in a sampled signal is at most 1/2 of the
  sampling frequency. For example, a 8 kHz sampling rate permits the
  recording of a signal in which the highest frequency is less than 4
  kHz. Higher frequency signals must be filtered out before feeding them
  to DAC.

  Sample encoding limits the dynamic range of recorded signal
  (difference between the faintest and the loudest signal that can be
  recorded). In theory the maximum dynamic range of signal is
  number_of_bits * 6 dB . This means that 8 bits sampling resolution
  gives dynamic range of 48 dB and 16 bit resolution gives 96 dB.

  Quality has price. The number of bytes required to store an audio
  sequence depends on sampling rate, number of channels and sampling
  resolution. For example just 8000 bytes of memory is required to store
  one second of sound using 8 kHz/8 bits/mono but 48 kHz/16bit/stereo
  takes 192 kilobytes. A 64 kbps ISDN channel is required to transfer a
  8kHz/8bit/mono audio stream in real time, and about 1.5 Mbps is
  required for DAT quality (48kHz/16bit/stereo).  On the other hand it
  is possible to store just 5.46 seconds of sound in a megabyte of
  memory when using 48kHz/16bit/stereo sampling. With 8kHz/8bits/mono it
  is possible to store 131 seconds of sound using the same amount of
  memory. It is possible to reduce memory and communication costs by
  compressing the recorded signal but this is out of the scope of this
  document.

  55..11..  LLooww--LLeevveell LLaayyeerr

  Audio devices are opened exclusively for a selected direction. This
  doesn't allow open from more than one processes for the same audio
  device in the same direction, but does allow one open call to each
  playback direction and second open call to record direction
  independently. Audio devices return EBUSY error to applications when
  other applications have already opened the requested direction.

  Low-Level layer supports these formats:

       ______________________________________________________________________
       #define SND_PCM_SFMT_MU_LAW             0
       #define SND_PCM_SFMT_A_LAW              1
       #define SND_PCM_SFMT_IMA_ADPCM          2
       #define SND_PCM_SFMT_U8                 3
       #define SND_PCM_SFMT_S16_LE             4
       #define SND_PCM_SFMT_S16_BE             5
       #define SND_PCM_SFMT_S8                 6
       #define SND_PCM_SFMT_U16_LE             7
       #define SND_PCM_SFMT_U16_BE             8
       #define SND_PCM_SFMT_MPEG               9
       #define SND_PCM_SFMT_GSM                10

       #define SND_PCM_FMT_MU_LAW              (1 << SND_PCM_SFMT_MU_LAW)
       #define SND_PCM_FMT_A_LAW               (1 << SND_PCM_SFMT_A_LAW)
       #define SND_PCM_FMT_IMA_ADPCM           (1 << SND_PCM_SFMT_IMA_ADPCM)
       #define SND_PCM_FMT_U8                  (1 << SND_PCM_SFMT_U8)
       #define SND_PCM_FMT_S16_LE              (1 << SND_PCM_SFMT_S16_LE)
       #define SND_PCM_FMT_S16_BE              (1 << SND_PCM_SFMT_S16_BE)
       #define SND_PCM_FMT_S8                  (1 << SND_PCM_SFMT_S8)
       #define SND_PCM_FMT_U16_LE              (1 << SND_PCM_SFMT_U16_LE)
       #define SND_PCM_FMT_U16_BE              (1 << SND_PCM_SFMT_U16_BE)
       #define SND_PCM_FMT_MPEG                (1 << SND_PCM_SFMT_MPEG)
       #define SND_PCM_FMT_GSM                 (1 << SND_PCM_SFMT_GSM)
       ______________________________________________________________________

  Constants with prefix SSNNDD__PPCCMM__FFMMTT__ are used in info structures and
  constants with prefix SSNNDD__PPCCMM__SSFFMMTT__ are used in format structures.
  55..11..11..

  iinntt ssnndd__ppccmm__ooppeenn(( vvooiidd ****hhaannddllee,, iinntt ccaarrdd,, iinntt ddeevviiccee,, iinntt mmooddee ))

  Creates a new handle and opens a connection to kernel sound audio
  interface for soundcard number _c_a_r_d (0-N) and audio device number
  _d_e_v_i_c_e. Function also checks if protocol is compatible to prevent use
  of old programs with a new kernel API. Function returns zero if
  successful,ful otherwise it returns an error code.  Error code -EBUSY
  is returned when some process ownes the selected direction.

  Default format after opening is mono _m_u_-_L_a_w at 8000Hz. This device can
  be used directly for playback of standard .au (Sparc) files.

  The following modes should be used for the _m_o_d_e argument:

  ______________________________________________________________________
    #define SND_PCM_OPEN_PLAYBACK   (O_WRONLY)
    #define SND_PCM_OPEN_RECORD     (O_RDONLY)
    #define SND_PCM_OPEN_DUPLEX     (O_RDWR)

  ______________________________________________________________________

  55..11..22..

  iinntt ssnndd__ppccmm__cclloossee(( vvooiidd **hhaannddllee ))

  Frees all resources allocated with audio handle and closes the
  connection to the kernel sound audio interface. Function returns zero
  if successful, otherwise it returns an error code.

  55..11..33..

  iinntt ssnndd__ppccmm__ffiillee__ddeessccrriippttoorr(( vvooiidd **hhaannddllee ))

  Returns the file descriptor of the connection to the kernel sound
  audio interface. Function returns an error code if an error was
  encountered.

  The file descriptor should be used for the _s_e_l_e_c_t synchronous
  multiplexer function for setting the read direction. Application
  should call _s_n_d___p_c_m___r_e_a_d or _s_n_d___p_c_m___w_r_i_t_e functions if some data is
  waiting for reading or a write can be performed. Calling this function
  is highly recomended, as it leaves a place for the API to things like
  data conversions, if needed.

  55..11..44..

  iinntt ssnndd__ppccmm__bblloocckk__mmooddee(( vvooiidd **hhaannddllee,, iinntt eennaabbllee ))

  Sets up block (default) or nonblock mode for a handle. Block mode
  suspends execution of a program when _s_n_d___p_c_m___r_e_a_d or _s_n_d___p_c_m___w_r_i_t_e is
  called for the time which is needed for the actual playback or record
  over of the entire buffer. In nonblock mode, programs aren't suspended
  and the above functions returns immediately with the count of bytes
  which were read or written by the driver. When used in this way, don't
  try to use the entire buffer after the call, but instead process the
  number of bytes returned, and call the function again.

  55..11..55..

  iinntt ssnndd__ppccmm__iinnffoo(( vvooiidd **hhaannddllee,, ssnndd__ppccmm__iinnffoo__tt **iinnffoo ))

  Fills the *info structure with data about the PCM device selected by
  *handle. Function returns zero if successful, otherwise it returns an
  error code.

  ______________________________________________________________________
    #define SND_PCM_INFO_CODEC              0x00000001
    #define SND_PCM_INFO_DSP                SND_PCM_INFO_CODEC
    #define SND_PCM_INFO_MMAP               0x00000002      /* reserved */
    #define SND_PCM_INFO_PLAYBACK           0x00000100
    #define SND_PCM_INFO_RECORD             0x00000200
    #define SND_PCM_INFO_DUPLEX             0x00000400
    #define SND_PCM_INFO_DUPLEX_LIMIT       0x00000800      /* rate for playback & record are same */

    struct snd_pcm_info {
      unsigned int type;                    /* soundcard type */
      unsigned int flags;                   /* see SND_PCM_INFO_XXXX */
      unsigned char id[32];                 /* ID of this PCM device */
      unsigned char name[80];               /* name of this device */
      unsigned char reserved[64];           /* reserved for future use */
    };

  ______________________________________________________________________

     SSNNDD__PPCCMM__IINNFFOO__MMMMAAPP
        This flag is reserved and should be never used. It remains for
        compatibility with Open Sound System driver.

     SSNNDD__PPCCMM__IINNFFOO__DDUUPPLLEEXX__LLIIMMIITT
        If this bit is set, rate must be same for playback and record
        direction.

  55..11..66..

  iinntt ssnndd__ppccmm__ppllaayybbaacckk__iinnffoo(( vvooiidd **hhaannddllee,, ssnndd__ppccmm__ppllaayybbaacckk__iinnffoo__tt **iinnffoo
  ))

  Fills the *info structure with data about PCM playback. Function
  returns zero if successful, otherwise it returns an error code.

  ______________________________________________________________________
    #define SND_PCM_PINFO_BATCH             0x00000001
    #define SND_PCM_PINFO_8BITONLY          0x00000002
    #define SND_PCM_PINFO_16BITONLY         0x00000004

    struct snd_pcm_playback_info {
      unsigned int flags;                   /* see SND_PCM_PINFO_XXXX */
      unsigned int formats;                 /* supported formats */
      unsigned int min_rate;                /* min rate (in Hz) */
      unsigned int max_rate;                /* max rate (in Hz) */
      unsigned int min_channels;            /* min channels (probably always 1) */
      unsigned int max_channels;            /* max channels */
      unsigned int buffer_size;             /* playback buffer size */
      unsigned int min_fragment_size;       /* min fragment size in bytes */
      unsigned int max_fragment_size;       /* max fragment size in bytes */
      unsigned int fragment_align;          /* align fragment value */
      unsigned char reserved[64];           /* reserved for future use */
    };

  ______________________________________________________________________

     SSNNDD__PPCCMM__PPIINNFFOO__BBAATTCCHH
        Driver implements double buffering with this device. This means
        that the chip used for data processing has its own memory, and
        output should be more delayed than if a traditional codec chip
        is used.

     SSNNDD__PPCCMM__PPIINNFFOO__88BBIITTOONNLLYY
        If this bit is set, the driver uses 8-bit format for 16-bit
        samples and does software conversion. This bit is set on broken
        SoundBlaster 16/AWE soundcards which can't do full 16-bit
        duplex. If this bit is set application or highter digital audio
        layer should do the conversion from 16-bit samples to 8-bit
        samples rather than making the driver to do it in the kernel.

     SSNNDD__PPCCMM__PPIINNFFOO__1166BBIITTOONNLLYY
        If this bit is set, driver uses 16-bit format for 8-bit samples
        and does software conversion. This bit is set on broken
        SoundBlaster 16/AWE soundcards which can't do full 8-bit duplex.
        If this bit is set the application or highter digital audio
        layer should do conversion from 8-bit samples to 16-bit samples
        rather than making the driver to do it in the kernel.

  55..11..77..

  iinntt ssnndd__ppccmm__rreeccoorrdd__iinnffoo(( vvooiidd **hhaannddllee,, ssnndd__ppccmm__rreeccoorrdd__iinnffoo__tt **iinnffoo ))

  Fills the *info structure. Returns zero if successful, otherwise it
  returns an error code.

  ______________________________________________________________________
    #define SND_PCM_RINFO_BATCH             0x00000001
    #define SND_PCM_RINFO_8BITONLY          0x00000002
    #define SND_PCM_RINFO_16BITONLY         0x00000004

    struct snd_pcm_record_info {
      unsigned int flags;                   /* see to SND_PCM_RINFO_XXXX */
      unsigned int formats;                 /* supported formats */
      unsigned int min_rate;                /* min rate (in Hz) */
      unsigned int max_rate;                /* max rate (in Hz) */
      unsigned int min_channels;            /* min channels (probably always 1) */
      unsigned int max_channels;            /* max channels */
      unsigned int buffer_size;             /* record buffer size */
      unsigned int min_fragment_size;       /* min fragment size in bytes */
      unsigned int max_fragment_size;       /* max fragment size in bytes */
      unsigned int fragment_align;          /* align fragment value */
      unsigned char reserved[64];           /* reserved for future... */
    };

  ______________________________________________________________________

     SSNNDD__PPCCMM__PPIINNFFOO__BBAATTCCHH
        Driver implements buffering for this device. This means that the
        chip used for data processing has its own memory and output
        should be more delayed than if a traditional codec chip is used.

     SSNNDD__PPCCMM__PPIINNFFOO__88BBIITTOONNLLYY
        If this bit is set, the device uses 8-bit format for 16-bit
        samples and does software conversion. This bit is set on broken
        SoundBlaster 16/AWE soundcards which can't do full 16-bit
        duplex. If this bit is set the application or highter digital
        audio layer should do conversion from 16-bit samples to 8-bit
        samples rather than making the driver to do it in the kernel.

     SSNNDD__PPCCMM__PPIINNFFOO__1166BBIITTOONNLLYY
        If this bit is set, the device uses a 16-bit format for 8-bit
        samples and does software conversion. This bit is set on broken
        SoundBlaster 16/AWE soundcards which can't do full 8-bit duplex.
        If this bit is set the application or highter digital audio
        layer should do the conversion from 8-bit samples to 16-bit
        samples rather than making the driver to do it in the kernel.

  55..11..88..

  iinntt ssnndd__ppccmm__ppllaayybbaacckk__ffoorrmmaatt(( vvooiidd **hhaannddllee,, ssnndd__ppccmm__ffoorrmmaatt__tt **ffoorrmmaatt ))

  Sets up format, rate (in Hz) and number of channels for playback, in
  the desired direction. Function returns zero if successful, otherwise
  it returns an error code.

  ______________________________________________________________________
    struct snd_pcm_format {
      unsigned int format;                  /* SND_PCM_SFMT_XXXX */
      unsigned int rate;                    /* rate in Hz */
      unsigned int channels;                /* channels (voices) */
      unsigned char reserved[16];
    };

  ______________________________________________________________________

  55..11..99..

  iinntt ssnndd__ppccmm__rreeccoorrdd__ffoorrmmaatt(( vvooiidd **hhaannddllee,, ssnndd__ppccmm__ffoorrmmaatt__tt **ffoorrmmaatt ))

  Sets up format, rate (in Hz) and number of channels for used for
  recording in the specified direction. Function returns zero if
  successful, otherwise it returns an error code.

  ______________________________________________________________________
    struct snd_pcm_format {
      unsigned int format;                  /* SND_PCM_SFMT_XXXX */
      unsigned int rate;                    /* rate in Hz */
      unsigned int channels;                /* channels (voices) */
      unsigned char reserved[16];
    };

  ______________________________________________________________________

  55..11..1100..

  iinntt ssnndd__ppccmm__ppllaayybbaacckk__ppaarraammss(( vvooiidd **hhaannddllee,, ssnndd__ppccmm__ppllaayybbaacckk__ppaarraammss__tt
  **ppaarraammss ))

  Sets various parameters for playback direction. Function returns zero
  if successful, otherwise it returns an error code.

  ______________________________________________________________________
    struct snd_pcm_playback_params {
      int fragment_size;
      int fragments_max;
      int fragments_room;
      unsigned char reserved[16];           /* must be filled with zero */
    };

  ______________________________________________________________________

     ffrraaggmmeenntt__ssiizzee
        Requested size of fragment. This value should be aligned for
        current format (for example to 4 if stereo 16-bit samples are
        used) or with the _f_r_a_g_m_e_n_t___a_l_i_g_n variable from
        _s_n_d___p_c_m___p_l_a_y_b_a_c_k___i_n_f_o___t structure. Its range can be from
        _m_i_n___f_r_a_g_m_e_n_t___s_i_z_e to _m_a_x___f_r_a_g_m_e_n_t___s_i_z_e.

     ffrraaggmmeennttss__mmaaxx
        Maximum number of fragments in queue for wakeup. This number
        doesn't counts partly used fragment. If current count of filled
        playback fragments is greater than this value driver block
        application or return immediately back if nonblock mode is
        active.

     ffrraaggmmeennttss__rroooomm
        Minumum number of fragments writeable for wakeup. This value
        should be in most cases 1 which means return back to application
        if at least one fragment is free for playback. This value
        includes partly used fragments, too.

  55..11..1111..

  iinntt ssnndd__ppccmm__rreeccoorrdd__ppaarraammss(( vvooiidd **hhaannddllee,, ssnndd__ppccmm__rreeccoorrdd__ppaarraammss__tt
  **ppaarraammss ))
  Function sets various parameters for the recording direction. Function
  returns zero if successful, otherwise it returns an error code.

  ______________________________________________________________________
    struct snd_pcm_record_params {
      int fragment_size;
      int fragments_min;
      unsigned char reserved[16];
    };

  ______________________________________________________________________

     ffrraaggmmeenntt__ssiizzee
        Requested size of fragment. This value should be aligned for
        current format (for example to 4 if stereo 16-bit samples are
        used) or set to the _f_r_a_g_m_e_n_t___a_l_i_g_n variable from
        _s_n_d___p_c_m___p_l_a_y_b_a_c_k___i_n_f_o___t structure. Its range can be from
        _m_i_n___f_r_a_g_m_e_n_t___s_i_z_e to _m_a_x___f_r_a_g_m_e_n_t___s_i_z_e.

     ffrraaggmmeennttss__mmiinn
        Minimum filled fragments for wakeup. Driver blocks the
        application (if block mode is selected) until it isn't filled
        with number of fragments specified with this value.

  55..11..1122..

  iinntt ssnndd__ppccmm__ppllaayybbaacckk__ssttaattuuss(( vvooiidd **hhaannddllee,, ssnndd__ppccmm__ppllaayybbaacckk__ssttaattuuss__tt
  **ssttaattuuss ))

  Fills the *status structure. Function returns zero if successful,
  otherwise it returns an error code.

  ______________________________________________________________________
    struct snd_pcm_playback_status {
      unsigned int rate;
      int fragments;
      int fragment_size;
      int count;
      int queue;
      int underrun;
      struct timeval time;
      struct timeval stime;
      unsigned char reserved[16];
    };

  ______________________________________________________________________

     rraattee
        Real playback rate. This value reflects hardware limitations.

     ffrraaggmmeennttss
        Currently allocated fragments by the driver for playback
        direction.

     ffrraaggmmeenntt__ssiizzee
        Current fragment size used by driver for the playback direction.

     ccoouunntt
        Count of bytes writeable without blocking.

     qquueeuuee
        Count of bytes in queue. Note: _(_f_r_a_g_m_e_n_t_s _* _f_r_a_g_m_e_n_t___s_i_z_e_) _-
        _q_u_e_u_e should not be equal to _c_o_u_n_t.

     uunnddeerrrruunn
        This value tells the application the number of underruns since
        the ast call of _s_n_d___p_c_m___p_l_a_y_b_a_c_k___s_t_a_t_u_s.

     ttiimmee
        Delay till played of the first sample from next write. This
        value should be used for time synchronization. Returned value is
        in the same format as returned from the standard C function
        _g_e_t_t_i_m_e_o_f_d_a_y_( _&_t_i_m_e_, _N_U_L_L _).  This variable contains right value
        only if playback time mode is enabled (look to
        _s_n_d___p_c_m___p_l_a_y_b_a_c_k___t_i_m_e function).

     ssttiimmee
        Time when playback was started.  This variable contains right
        value only if playback time mode is enabled (look to
        _s_n_d___p_c_m___p_l_a_y_b_a_c_k___t_i_m_e function).

  55..11..1133..

  iinntt ssnndd__ppccmm__rreeccoorrdd__ssttaattuuss(( vvooiidd **hhaannddllee,, ssnndd__ppccmm__rreeccoorrdd__ssttaattuuss__tt **ssttaa--
  ttuuss ))

  Fills the *status structure. Function returns zero if successful,
  otherwise it returns an error code.

  ______________________________________________________________________
    struct snd_pcm_record_status {
      unsigned int rate;
      int fragments;
      int fragment_size;
      int count;
      int free;
      int overrun;
      struct timeval time;
      unsigned char reserved[16];
    };

  ______________________________________________________________________

     rraattee
        Real record rate. This value reflects hardware limitations.

     ffrraaggmmeennttss
        Currently allocated fragments by driver for the record
        direction.

     ffrraaggmmeenntt__ssiizzee
        Current fragment size used by driver for the record direction.

     ccoouunntt
        Count of bytes readable without blocking.

     ffrreeee
        Count of bytes in buffer still free. Note: _(_f_r_a_g_m_e_n_t_s _*
        _f_r_a_g_m_e_n_t___s_i_z_e_) _- _f_r_e_e should not be equal to _c_o_u_n_t.

     oovveerrrruunn
        This value tells application the count of overruns since the
        last call to _s_n_d___p_c_m___r_e_c_o_r_d___s_t_a_t_u_s.
     ttiimmee
        Lag since the next sample read was recorded. This value should
        be used for time synchronization. Returned value is in the same
        format as returned by the from standard C function _g_e_t_t_i_m_e_o_f_d_a_y_(
        _&_t_i_m_e_, _N_U_L_L _). This variable contains right value only if record
        time mode is enabled (look to _s_n_d___p_c_m___r_e_c_o_r_d___t_i_m_e function).

     ssttiimmee
        Time when record was started. This variable contains right value
        only if record time mode is enabled (look to _s_n_d___p_c_m___r_e_c_o_r_d___t_i_m_e
        function).

  55..11..1144..

  iinntt ssnndd__ppccmm__ddrraaiinn__ppllaayybbaacckk(( vvooiidd **hhaannddllee ))

  This function drain playback buffers immediately. Function returns
  zero if successful, otherwise it returns an error code.

  55..11..1155..

  iinntt ssnndd__ppccmm__fflluusshh__ppllaayybbaacckk(( vvooiidd **hhaannddllee ))

  This function flushes the playback buffers. It blocks the program
  while the all the waiting samples in kernel playback buffers are
  processed. Function returns zero if successful, otherwise it returns
  an error code.

  55..11..1166..

  iinntt ssnndd__ppccmm__fflluusshh__rreeccoorrdd(( vvooiidd **hhaannddllee ))

  This function flushes (destroyes) record buffers. Function returns
  zero if successful, otherwise it returns an error code.

  55..11..1177..

  iinntt ssnndd__ppccmm__ppllaayybbaacckk__ttiimmee(( vvooiidd **hhaannddllee,, iinntt eennaabbllee ))

  This function enables or disables time mode for playback direction.
  Time mode allows to application better time synchronization. Function
  returns zero if successful, otherwise it returns an error code.

  55..11..1188..

  iinntt ssnndd__ppccmm__rreeccoorrdd__ttiimmee(( vvooiidd **hhaannddllee,, iinntt eennaabbllee ))

  This function enables or disables time mode for record direction. Time
  mode allows to application better time synchronization. Function
  returns zero if successful, otherwise it returns an error code.

  55..11..1199..

  ssssiizzee__tt ssnndd__ppccmm__wwrriittee(( vvooiidd **hhaannddllee,, ccoonnsstt vvooiidd **bbuuffffeerr,, ssiizzee__tt ssiizzee ))

  Writes samples to the device which must be in the proper format
  specified by the _s_n_d___p_c_m___p_l_a_y_b_a_c_k___f_o_r_m_a_t function. Function returns
  zero or positive value if playback was successful (value represents
  count of bytes which was successfuly written to device) or an error
  value if error occured. Function should suspend process if block mode
  is active.

  55..11..2200..

  ssssiizzee__tt ssnndd__ppccmm__rreeaadd(( vvooiidd **hhaannddllee,, vvooiidd **bbuuffffeerr,, ssiizzee__tt ssiizzee ))

  Function reads samples from driver. Samples are in format specified by
  _s_n_d___p_c_m___r_e_c_o_r_d___f_o_r_m_a_t function. Function returns zero or positive
  value if record was success (value represents count of bytes which was
  successfuly read from device) or negative error value if error
  occured. Function should suspend process if block mode is active.

  55..22..  EExxaammpplleess

  The following example shows how to play the first 512kB from the
  /tmp/test.au file with soundcard #0 and PCM device #0:

       ______________________________________________________________________
       int card = 0, device = 0, err, fd, count, size, idx;
       void *handle;
       snd_pcm_format_t format;
       char *buffer;

       buffer = (char *)malloc( 512 * 1024 );
       if ( !buffer ) return;
       if ( (err = snd_pcm_open( &handle, card, device, SND_PCM_OPEN_PLAYBACK )) < 0 ) {
         fprintf( stderr, "open failed: %s\n", snd_strerror( err ) );
         return;
       }
       format.format = SND_PCM_SFMT_MU_LAW;
       format.rate = 8000;
       format.channels = 1;
       if ( (err = snd_pcm_playback_format( handle, &format )) < 0 ) {
         fprintf( stderr, "format setup failed: %s\n", snd_strerror( err ) );
         snd_pcm_close( handle );
         return;
       }
       fd = open( "/tmp/test.au", O_RDONLY );
       if ( fd < 0 ) {
         perror( "open file" );
         snd_pcm_close( handle );
         return;
       }
       idx = 0;
       count = read( fd, buffer, 512 * 1024 );
       if ( count <= 0 ) {
         perror( "read from file" );
         snd_pcm_close( handle );
         return;
       }
       close( fd );
       if ( !memcmp( buffer, ".snd", 4 ) ) {
         idx = (buffer[4]<<24)|(buffer[5]<<16)|(buffer[6]<<8)|(buffer[7]);
         if ( idx > 128 ) idx = 128;
         if ( idx > count ) idx = count;
       }
       size = snd_pcm_write( handle, &buffer[ idx ], count - idx );
       printf( "Bytes written %i from %i...\n", size, count - idx );
       snd_pcm_close( handle );
       free( buffer );
       ______________________________________________________________________

