text: 
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #include <sched.h>
  #include <errno.h>
  #include <getopt.h>
  #include <alsa/asoundlib.h>
  #include <sys/time.h>
  #include <math.h>
  static char *device = "plughw:0,0";                     /* playback device */
  static snd_pcm_format_t format = SND_PCM_FORMAT_S16;    /* sample format */
  static unsigned int rate = 44100;                       /* stream rate */
  static unsigned int channels = 1;                       /* count of channels */
  static unsigned int buffer_time = 500000;               /* ring buffer length in us */
  static unsigned int period_time = 100000;               /* period time in us */
  static double freq = 440;                               /* sinusoidal wave frequency in Hz */
  static int verbose = 0;                                 /* verbose flag */
  static int resample = 1;                                /* enable alsa-lib resampling */
  static int period_event = 0;                            /* produce poll event after each period */
  static snd_pcm_sframes_t buffer_size;
  static snd_pcm_sframes_t period_size;
  static snd_output_t *output = NULL;
  static void generate_sine(const snd_pcm_channel_area_t *areas, 
                            snd_pcm_uframes_t offset,
                            int count, double *_phase)
  {
          static double max_phase = 2. * M_PI;
          double phase = *_phase;
          double step = max_phase*freq/(double)rate;
          unsigned char *samples[channels];
          int steps[channels];
          unsigned int chn;
          int format_bits = snd_pcm_format_width(format);
          unsigned int maxval = (1 << (format_bits - 1)) - 1;
          int bps = format_bits / 8;  /* bytes per sample */
          int phys_bps = snd_pcm_format_physical_width(format) / 8;
          int big_endian = snd_pcm_format_big_endian(format) == 1;
          int to_unsigned = snd_pcm_format_unsigned(format) == 1;
          int is_float = (format == SND_PCM_FORMAT_FLOAT_LE ||
                          format == SND_PCM_FORMAT_FLOAT_BE);
          /* verify and prepare the contents of areas */
          for (chn = 0; chn < channels; chn++) {
                  if ((areas[chn].first % 8) != 0) {
                          printf("areas[%i].first == %i, aborting...\n", chn, areas[chn].first);
                          exit(EXIT_FAILURE);
                  }
                  samples[chn] = /*(signed short *)*/(((unsigned char *)areas[chn].addr) + (areas[chn].first / 8));
                  if ((areas[chn].step % 16) != 0) {
                          printf("areas[%i].step == %i, aborting...\n", chn, areas[chn].step);
                          exit(EXIT_FAILURE);
                  }
                  steps[chn] = areas[chn].step / 8;
                  samples[chn] += offset * steps[chn];
          }
          /* fill the channel areas */
          while (count-- > 0) {
                  union {
                          float f;
                          int i;
                  } fval;
                  int res, i;
                  if (is_float) {
                          fval.f = sin(phase);
                          res = fval.i;
                  } else
                          res = sin(phase) * maxval;
                  if (to_unsigned)
                          res ^= 1U << (format_bits - 1);
                  for (chn = 0; chn < channels; chn++) {
                          /* Generate data in native endian format */
                          if (big_endian) {
                                  for (i = 0; i < bps; i++)
                                          *(samples[chn] + phys_bps - 1 - i) = (res >> i * 8) & 0xff;
                          } else {
                                  for (i = 0; i < bps; i++)
                                          *(samples[chn] + i) = (res >>  i * 8) & 0xff;
                          }
                          samples[chn] += steps[chn];
                  }
                  phase += step;
                  if (phase >= max_phase)
                          phase -= max_phase;
          }
          *_phase = phase;
  }
  static int set_hwparams(snd_pcm_t *handle,
                          snd_pcm_hw_params_t *params,
                          snd_pcm_access_t access)
  {
          unsigned int rrate;
          snd_pcm_uframes_t size;
          int err, dir;
          /* choose all parameters */
          err = snd_pcm_hw_params_any(handle, params);
          if (err < 0) {
                  printf("Broken configuration for playback: no configurations available: %s\n", snd_strerror(err));
                  return err;
          }
          /* set hardware resampling */
          err = snd_pcm_hw_params_set_rate_resample(handle, params, resample);
          if (err < 0) {
                  printf("Resampling setup failed for playback: %s\n", snd_strerror(err));
                  return err;
          }
          /* set the interleaved read/write format */
          err = snd_pcm_hw_params_set_access(handle, params, access);
          if (err < 0) {
                  printf("Access type not available for playback: %s\n", snd_strerror(err));
                  return err;
          }
          /* set the sample format */
          err = snd_pcm_hw_params_set_format(handle, params, format);
          if (err < 0) {
                  printf("Sample format not available for playback: %s\n", snd_strerror(err));
                  return err;
          }
          /* set the count of channels */
          err = snd_pcm_hw_params_set_channels(handle, params, channels);
          if (err < 0) {
                  printf("Channels count (%i) not available for playbacks: %s\n", channels, snd_strerror(err));
                  return err;
          }
          /* set the stream rate */
          rrate = rate;
          err = snd_pcm_hw_params_set_rate_near(handle, params, &rrate, 0);
          if (err < 0) {
                  printf("Rate %iHz not available for playback: %s\n", rate, snd_strerror(err));
                  return err;
          }
          if (rrate != rate) {
                  printf("Rate doesn't match (requested %iHz, get %iHz)\n", rate, err);
                  return -EINVAL;
          }
          /* set the buffer time */
          err = snd_pcm_hw_params_set_buffer_time_near(handle, params, &buffer_time, &dir);
          if (err < 0) {
                  printf("Unable to set buffer time %i for playback: %s\n", buffer_time, snd_strerror(err));
                  return err;
          }
          err = snd_pcm_hw_params_get_buffer_size(params, &size);
          if (err < 0) {
                  printf("Unable to get buffer size for playback: %s\n", snd_strerror(err));
                  return err;
          }
          buffer_size = size;
          /* set the period time */
          err = snd_pcm_hw_params_set_period_time_near(handle, params, &period_time, &dir);
          if (err < 0) {
                  printf("Unable to set period time %i for playback: %s\n", period_time, snd_strerror(err));
                  return err;
          }
          err = snd_pcm_hw_params_get_period_size(params, &size, &dir);
          if (err < 0) {
                  printf("Unable to get period size for playback: %s\n", snd_strerror(err));
                  return err;
          }
          period_size = size;
          /* write the parameters to device */
          err = snd_pcm_hw_params(handle, params);
          if (err < 0) {
                  printf("Unable to set hw params for playback: %s\n", snd_strerror(err));
                  return err;
          }
          return 0;
  }
  static int set_swparams(snd_pcm_t *handle, snd_pcm_sw_params_t *swparams)
  {
          int err;
          /* get the current swparams */
          err = snd_pcm_sw_params_current(handle, swparams);
          if (err < 0) {
                  printf("Unable to determine current swparams for playback: %s\n", snd_strerror(err));
                  return err;
          }
          /* start the transfer when the buffer is almost full: */
          /* (buffer_size / avail_min) * avail_min */
          err = snd_pcm_sw_params_set_start_threshold(handle, swparams, (buffer_size / period_size) * period_size);
          if (err < 0) {
                  printf("Unable to set start threshold mode for playback: %s\n", snd_strerror(err));
                  return err;
          }
          /* allow the transfer when at least period_size samples can be processed */
          /* or disable this mechanism when period event is enabled (aka interrupt like style processing) */
          err = snd_pcm_sw_params_set_avail_min(handle, swparams, period_event ? buffer_size : period_size);
          if (err < 0) {
                  printf("Unable to set avail min for playback: %s\n", snd_strerror(err));
                  return err;
          }
          /* enable period events when requested */
          if (period_event) {
                  err = snd_pcm_sw_params_set_period_event(handle, swparams, 1);
                  if (err < 0) {
                          printf("Unable to set period event: %s\n", snd_strerror(err));
                          return err;
                  }
          }
          /* write the parameters to the playback device */
          err = snd_pcm_sw_params(handle, swparams);
          if (err < 0) {
                  printf("Unable to set sw params for playback: %s\n", snd_strerror(err));
                  return err;
          }
          return 0;
  }
  /*
   *   Underrun and suspend recovery
   */
   
  static int xrun_recovery(snd_pcm_t *handle, int err)
  {
          if (verbose)
                  printf("stream recovery\n");
          if (err == -EPIPE) {    /* under-run */
                  err = snd_pcm_prepare(handle);
                  if (err < 0)
                          printf("Can't recovery from underrun, prepare failed: %s\n", snd_strerror(err));
                  return 0;
          } else if (err == -ESTRPIPE) {
                  while ((err = snd_pcm_resume(handle)) == -EAGAIN)
                          sleep(1);       /* wait until the suspend flag is released */
                  if (err < 0) {
                          err = snd_pcm_prepare(handle);
                          if (err < 0)
                                  printf("Can't recovery from suspend, prepare failed: %s\n", snd_strerror(err));
                  }
                  return 0;
          }
          return err;
  }
  /*
   *   Transfer method - write only
   */
  static int write_loop(snd_pcm_t *handle,
                        signed short *samples,
                        snd_pcm_channel_area_t *areas)
  {
          double phase = 0;
          signed short *ptr;
          int err, cptr;
          while (1) {
                  generate_sine(areas, 0, period_size, &phase);
                  ptr = samples;
                  cptr = period_size;
                  while (cptr > 0) {
                          err = snd_pcm_writei(handle, ptr, cptr);
                          if (err == -EAGAIN)
                                  continue;
                          if (err < 0) {
                                  if (xrun_recovery(handle, err) < 0) {
                                          printf("Write error: %s\n", snd_strerror(err));
                                          exit(EXIT_FAILURE);
                                  }
                                  break;  /* skip one period */
                          }
                          ptr += err * channels;
                          cptr -= err;
                  }
          }
  }
   
  /*
   *   Transfer method - write and wait for room in buffer using poll
   */
  static int wait_for_poll(snd_pcm_t *handle, struct pollfd *ufds, unsigned int count)
  {
          unsigned short revents;
          while (1) {
                  poll(ufds, count, -1);
                  snd_pcm_poll_descriptors_revents(handle, ufds, count, &revents);
                  if (revents & POLLERR)
                          return -EIO;
                  if (revents & POLLOUT)
                          return 0;
          }
  }
  static int write_and_poll_loop(snd_pcm_t *handle,
                                 signed short *samples,
                                 snd_pcm_channel_area_t *areas)
  {
          struct pollfd *ufds;
          double phase = 0;
          signed short *ptr;
          int err, count, cptr, init;
          count = snd_pcm_poll_descriptors_count (handle);
          if (count <= 0) {
                  printf("Invalid poll descriptors count\n");
                  return count;
          }
          ufds = malloc(sizeof(struct pollfd) * count);
          if (ufds == NULL) {
                  printf("No enough memory\n");
                  return -ENOMEM;
          }
          if ((err = snd_pcm_poll_descriptors(handle, ufds, count)) < 0) {
                  printf("Unable to obtain poll descriptors for playback: %s\n", snd_strerror(err));
                  return err;
          }
          init = 1;
          while (1) {
                  if (!init) {
                          err = wait_for_poll(handle, ufds, count);
                          if (err < 0) {
                                  if (snd_pcm_state(handle) == SND_PCM_STATE_XRUN ||
                                      snd_pcm_state(handle) == SND_PCM_STATE_SUSPENDED) {
                                          err = snd_pcm_state(handle) == SND_PCM_STATE_XRUN ? -EPIPE : -ESTRPIPE;
                                          if (xrun_recovery(handle, err) < 0) {
                                                  printf("Write error: %s\n", snd_strerror(err));
                                                  exit(EXIT_FAILURE);
                                          }
                                          init = 1;
                                  } else {
                                          printf("Wait for poll failed\n");
                                          return err;
                                  }
                          }
                  }
                  generate_sine(areas, 0, period_size, &phase);
                  ptr = samples;
                  cptr = period_size;
                  while (cptr > 0) {
                          err = snd_pcm_writei(handle, ptr, cptr);
                          if (err < 0) {
                                  if (xrun_recovery(handle, err) < 0) {
                                          printf("Write error: %s\n", snd_strerror(err));
                                          exit(EXIT_FAILURE);
                                  }
                                  init = 1;
                                  break;  /* skip one period */
                          }
                          if (snd_pcm_state(handle) == SND_PCM_STATE_RUNNING)
                                  init = 0;
                          ptr += err * channels;
                          cptr -= err;
                          if (cptr == 0)
                                  break;
                          /* it is possible, that the initial buffer cannot store */
                          /* all data from the last period, so wait awhile */
                          err = wait_for_poll(handle, ufds, count);
                          if (err < 0) {
                                  if (snd_pcm_state(handle) == SND_PCM_STATE_XRUN ||
                                      snd_pcm_state(handle) == SND_PCM_STATE_SUSPENDED) {
                                          err = snd_pcm_state(handle) == SND_PCM_STATE_XRUN ? -EPIPE : -ESTRPIPE;
                                          if (xrun_recovery(handle, err) < 0) {
                                                  printf("Write error: %s\n", snd_strerror(err));
                                                  exit(EXIT_FAILURE);
                                          }
                                          init = 1;
                                  } else {
                                          printf("Wait for poll failed\n");
                                          return err;
                                  }
                          }
                  }
          }
  }
  /*
   *   Transfer method - asynchronous notification
   */
  struct async_private_data {
          signed short *samples;
          snd_pcm_channel_area_t *areas;
          double phase;
  };
  static void async_callback(snd_async_handler_t *ahandler)
  {
          snd_pcm_t *handle = snd_async_handler_get_pcm(ahandler);
          struct async_private_data *data = snd_async_handler_get_callback_private(ahandler);
          signed short *samples = data->samples;
          snd_pcm_channel_area_t *areas = data->areas;
          snd_pcm_sframes_t avail;
          int err;
          
          avail = snd_pcm_avail_update(handle);
          while (avail >= period_size) {
                  generate_sine(areas, 0, period_size, &data->phase);
                  err = snd_pcm_writei(handle, samples, period_size);
                  if (err < 0) {
                          printf("Write error: %s\n", snd_strerror(err));
                          exit(EXIT_FAILURE);
                  }
                  if (err != period_size) {
                          printf("Write error: written %i expected %li\n", err, period_size);
                          exit(EXIT_FAILURE);
                  }
                  avail = snd_pcm_avail_update(handle);
          }
  }
  static int async_loop(snd_pcm_t *handle,
                        signed short *samples,
                        snd_pcm_channel_area_t *areas)
  {
          struct async_private_data data;
          snd_async_handler_t *ahandler;
          int err, count;
          data.samples = samples;
          data.areas = areas;
          data.phase = 0;
          err = snd_async_add_pcm_handler(&ahandler, handle, async_callback, &data);
          if (err < 0) {
                  printf("Unable to register async handler\n");
                  exit(EXIT_FAILURE);
          }
          for (count = 0; count < 2; count++) {
                  generate_sine(areas, 0, period_size, &data.phase);
                  err = snd_pcm_writei(handle, samples, period_size);
                  if (err < 0) {
                          printf("Initial write error: %s\n", snd_strerror(err));
                          exit(EXIT_FAILURE);
                  }
                  if (err != period_size) {
                          printf("Initial write error: written %i expected %li\n", err, period_size);
                          exit(EXIT_FAILURE);
                  }
          }
          if (snd_pcm_state(handle) == SND_PCM_STATE_PREPARED) {
                  err = snd_pcm_start(handle);
                  if (err < 0) {
                          printf("Start error: %s\n", snd_strerror(err));
                          exit(EXIT_FAILURE);
                  }
          }
          /* because all other work is done in the signal handler,
             suspend the process */
          while (1) {
                  sleep(1);
          }
  }
  /*
   *   Transfer method - asynchronous notification + direct write
   */
  static void async_direct_callback(snd_async_handler_t *ahandler)
  {
          snd_pcm_t *handle = snd_async_handler_get_pcm(ahandler);
          struct async_private_data *data = snd_async_handler_get_callback_private(ahandler);
          const snd_pcm_channel_area_t *my_areas;
          snd_pcm_uframes_t offset, frames, size;
          snd_pcm_sframes_t avail, commitres;
          snd_pcm_state_t state;
          int first = 0, err;
          
          while (1) {
                  state = snd_pcm_state(handle);
                  if (state == SND_PCM_STATE_XRUN) {
                          err = xrun_recovery(handle, -EPIPE);
                          if (err < 0) {
                                  printf("XRUN recovery failed: %s\n", snd_strerror(err));
                                  exit(EXIT_FAILURE);
                          }
                          first = 1;
                  } else if (state == SND_PCM_STATE_SUSPENDED) {
                          err = xrun_recovery(handle, -ESTRPIPE);
                          if (err < 0) {
                                  printf("SUSPEND recovery failed: %s\n", snd_strerror(err));
                                  exit(EXIT_FAILURE);
                          }
                  }
                  avail = snd_pcm_avail_update(handle);
                  if (avail < 0) {
                          err = xrun_recovery(handle, avail);
                          if (err < 0) {
                                  printf("avail update failed: %s\n", snd_strerror(err));
                                  exit(EXIT_FAILURE);
                          }
                          first = 1;
                          continue;
                  }
                  if (avail < period_size) {
                          if (first) {
                                  first = 0;
                                  err = snd_pcm_start(handle);
                                  if (err < 0) {
                                          printf("Start error: %s\n", snd_strerror(err));
                                          exit(EXIT_FAILURE);
                                  }
                          } else {
                                  break;
                          }
                          continue;
                  }
                  size = period_size;
                  while (size > 0) {
                          frames = size;
                          err = snd_pcm_mmap_begin(handle, &my_areas, &offset, &frames);
                          if (err < 0) {
                                  if ((err = xrun_recovery(handle, err)) < 0) {
                                          printf("MMAP begin avail error: %s\n", snd_strerror(err));
                                          exit(EXIT_FAILURE);
                                  }
                                  first = 1;
                          }
                          generate_sine(my_areas, offset, frames, &data->phase);
                          commitres = snd_pcm_mmap_commit(handle, offset, frames);
                          if (commitres < 0 || (snd_pcm_uframes_t)commitres != frames) {
                                  if ((err = xrun_recovery(handle, commitres >= 0 ? -EPIPE : commitres)) < 0) {
                                          printf("MMAP commit error: %s\n", snd_strerror(err));
                                          exit(EXIT_FAILURE);
                                  }
                                  first = 1;
                          }
                          size -= frames;
                  }
          }
  }
  static int async_direct_loop(snd_pcm_t *handle,
                               signed short *samples ATTRIBUTE_UNUSED,
                               snd_pcm_channel_area_t *areas ATTRIBUTE_UNUSED)
  {
          struct async_private_data data;
          snd_async_handler_t *ahandler;
          const snd_pcm_channel_area_t *my_areas;
          snd_pcm_uframes_t offset, frames, size;
          snd_pcm_sframes_t commitres;
          int err, count;
          data.samples = NULL;    /* we do not require the global sample area for direct write */
          data.areas = NULL;      /* we do not require the global areas for direct write */
          data.phase = 0;
          err = snd_async_add_pcm_handler(&ahandler, handle, async_direct_callback, &data);
          if (err < 0) {
                  printf("Unable to register async handler\n");
                  exit(EXIT_FAILURE);
          }
          for (count = 0; count < 2; count++) {
                  size = period_size;
                  while (size > 0) {
                          frames = size;
                          err = snd_pcm_mmap_begin(handle, &my_areas, &offset, &frames);
                          if (err < 0) {
                                  if ((err = xrun_recovery(handle, err)) < 0) {
                                          printf("MMAP begin avail error: %s\n", snd_strerror(err));
                                          exit(EXIT_FAILURE);
                                  }
                          }
                          generate_sine(my_areas, offset, frames, &data.phase);
                          commitres = snd_pcm_mmap_commit(handle, offset, frames);
                          if (commitres < 0 || (snd_pcm_uframes_t)commitres != frames) {
                                  if ((err = xrun_recovery(handle, commitres >= 0 ? -EPIPE : commitres)) < 0) {
                                          printf("MMAP commit error: %s\n", snd_strerror(err));
                                          exit(EXIT_FAILURE);
                                  }
                          }
                          size -= frames;
                  }
          }
          err = snd_pcm_start(handle);
          if (err < 0) {
                  printf("Start error: %s\n", snd_strerror(err));
                  exit(EXIT_FAILURE);
          }
          /* because all other work is done in the signal handler,
             suspend the process */
          while (1) {
                  sleep(1);
          }
  }
  /*
   *   Transfer method - direct write only
   */
  static int direct_loop(snd_pcm_t *handle,
                         signed short *samples ATTRIBUTE_UNUSED,
                         snd_pcm_channel_area_t *areas ATTRIBUTE_UNUSED)
  {
          double phase = 0;
          const snd_pcm_channel_area_t *my_areas;
          snd_pcm_uframes_t offset, frames, size;
          snd_pcm_sframes_t avail, commitres;
          snd_pcm_state_t state;
          int err, first = 1;
          while (1) {
                  state = snd_pcm_state(handle);
                  if (state == SND_PCM_STATE_XRUN) {
                          err = xrun_recovery(handle, -EPIPE);
                          if (err < 0) {
                                  printf("XRUN recovery failed: %s\n", snd_strerror(err));
                                  return err;
                          }
                          first = 1;
                  } else if (state == SND_PCM_STATE_SUSPENDED) {
                          err = xrun_recovery(handle, -ESTRPIPE);
                          if (err < 0) {
                                  printf("SUSPEND recovery failed: %s\n", snd_strerror(err));
                                  return err;
                          }
                  }
                  avail = snd_pcm_avail_update(handle);
                  if (avail < 0) {
                          err = xrun_recovery(handle, avail);
                          if (err < 0) {
                                  printf("avail update failed: %s\n", snd_strerror(err));
                                  return err;
                          }
                          first = 1;
                          continue;
                  }
                  if (avail < period_size) {
                          if (first) {
                                  first = 0;
                                  err = snd_pcm_start(handle);
                                  if (err < 0) {
                                          printf("Start error: %s\n", snd_strerror(err));
                                          exit(EXIT_FAILURE);
                                  }
                          } else {
                                  err = snd_pcm_wait(handle, -1);
                                  if (err < 0) {
                                          if ((err = xrun_recovery(handle, err)) < 0) {
                                                  printf("snd_pcm_wait error: %s\n", snd_strerror(err));
                                                  exit(EXIT_FAILURE);
                                          }
                                          first = 1;
                                  }
                          }
                          continue;
                  }
                  size = period_size;
                  while (size > 0) {
                          frames = size;
                          err = snd_pcm_mmap_begin(handle, &my_areas, &offset, &frames);
                          if (err < 0) {
                                  if ((err = xrun_recovery(handle, err)) < 0) {
                                          printf("MMAP begin avail error: %s\n", snd_strerror(err));
                                          exit(EXIT_FAILURE);
                                  }
                                  first = 1;
                          }
                          generate_sine(my_areas, offset, frames, &phase);
                          commitres = snd_pcm_mmap_commit(handle, offset, frames);
                          if (commitres < 0 || (snd_pcm_uframes_t)commitres != frames) {
                                  if ((err = xrun_recovery(handle, commitres >= 0 ? -EPIPE : commitres)) < 0) {
                                          printf("MMAP commit error: %s\n", snd_strerror(err));
                                          exit(EXIT_FAILURE);
                                  }
                                  first = 1;
                          }
                          size -= frames;
                  }
          }
  }
   
  /*
   *   Transfer method - direct write only using mmap_write functions
   */
  static int direct_write_loop(snd_pcm_t *handle,
                               signed short *samples,
                               snd_pcm_channel_area_t *areas)
  {
          double phase = 0;
          signed short *ptr;
          int err, cptr;
          while (1) {
                  generate_sine(areas, 0, period_size, &phase);
                  ptr = samples;
                  cptr = period_size;
                  while (cptr > 0) {
                          err = snd_pcm_mmap_writei(handle, ptr, cptr);
                          if (err == -EAGAIN)
                                  continue;
                          if (err < 0) {
                                  if (xrun_recovery(handle, err) < 0) {
                                          printf("Write error: %s\n", snd_strerror(err));
                                          exit(EXIT_FAILURE);
                                  }
                                  break;  /* skip one period */
                          }
                          ptr += err * channels;
                          cptr -= err;
                  }
          }
  }
   
  /*
   *
   */
  struct transfer_method {
          const char *name;
          snd_pcm_access_t access;
          int (*transfer_loop)(snd_pcm_t *handle,
                               signed short *samples,
                               snd_pcm_channel_area_t *areas);
  };
  static struct transfer_method transfer_methods[] = {
          { "write", SND_PCM_ACCESS_RW_INTERLEAVED, write_loop },
          { "write_and_poll", SND_PCM_ACCESS_RW_INTERLEAVED, write_and_poll_loop },
          { "async", SND_PCM_ACCESS_RW_INTERLEAVED, async_loop },
          { "async_direct", SND_PCM_ACCESS_MMAP_INTERLEAVED, async_direct_loop },
          { "direct_interleaved", SND_PCM_ACCESS_MMAP_INTERLEAVED, direct_loop },
          { "direct_noninterleaved", SND_PCM_ACCESS_MMAP_NONINTERLEAVED, direct_loop },
          { "direct_write", SND_PCM_ACCESS_MMAP_INTERLEAVED, direct_write_loop },
          { NULL, SND_PCM_ACCESS_RW_INTERLEAVED, NULL }
  };
  static void help(void)
  {
          int k;
          printf(
  "Usage: pcm [OPTION]... [FILE]...\n"
  "-h,--help      help\n"
  "-D,--device    playback device\n"
  "-r,--rate      stream rate in Hz\n"
  "-c,--channels  count of channels in stream\n"
  "-f,--frequency sine wave frequency in Hz\n"
  "-b,--buffer    ring buffer size in us\n"
  "-p,--period    period size in us\n"
  "-m,--method    transfer method\n"
  "-o,--format    sample format\n"
  "-v,--verbose   show the PCM setup parameters\n"
  "-n,--noresample  do not resample\n"
  "-e,--pevent    enable poll event after each period\n"
  "\n");
          printf("Recognized sample formats are:");
          for (k = 0; k < SND_PCM_FORMAT_LAST; ++k) {
                  const char *s = snd_pcm_format_name(k);
                  if (s)
                          printf(" %s", s);
          }
          printf("\n");
          printf("Recognized transfer methods are:");
          for (k = 0; transfer_methods[k].name; k++)
                  printf(" %s", transfer_methods[k].name);
          printf("\n");
  }
  int main(int argc, char *argv[])
  {
          struct option long_option[] =
          {
                  {"help", 0, NULL, 'h'},
                  {"device", 1, NULL, 'D'},
                  {"rate", 1, NULL, 'r'},
                  {"channels", 1, NULL, 'c'},
                  {"frequency", 1, NULL, 'f'},
                  {"buffer", 1, NULL, 'b'},
                  {"period", 1, NULL, 'p'},
                  {"method", 1, NULL, 'm'},
                  {"format", 1, NULL, 'o'},
                  {"verbose", 1, NULL, 'v'},
                  {"noresample", 1, NULL, 'n'},
                  {"pevent", 1, NULL, 'e'},
                  {NULL, 0, NULL, 0},
          };
          snd_pcm_t *handle;
          int err, morehelp;
          snd_pcm_hw_params_t *hwparams;
          snd_pcm_sw_params_t *swparams;
          int method = 0;
          signed short *samples;
          unsigned int chn;
          snd_pcm_channel_area_t *areas;
          snd_pcm_hw_params_alloca(&hwparams);
          snd_pcm_sw_params_alloca(&swparams);
          morehelp = 0;
          while (1) {
                  int c;
                  if ((c = getopt_long(argc, argv, "hD:r:c:f:b:p:m:o:vne", long_option, NULL)) < 0)
                          break;
                  switch (c) {
                  case 'h':
                          morehelp++;
                          break;
                  case 'D':
                          device = strdup(optarg);
                          break;
                  case 'r':
                          rate = atoi(optarg);
                          rate = rate < 4000 ? 4000 : rate;
                          rate = rate > 196000 ? 196000 : rate;
                          break;
                  case 'c':
                          channels = atoi(optarg);
                          channels = channels < 1 ? 1 : channels;
                          channels = channels > 1024 ? 1024 : channels;
                          break;
                  case 'f':
                          freq = atoi(optarg);
                          freq = freq < 50 ? 50 : freq;
                          freq = freq > 5000 ? 5000 : freq;
                          break;
                  case 'b':
                          buffer_time = atoi(optarg);
                          buffer_time = buffer_time < 1000 ? 1000 : buffer_time;
                          buffer_time = buffer_time > 1000000 ? 1000000 : buffer_time;
                          break;
                  case 'p':
                          period_time = atoi(optarg);
                          period_time = period_time < 1000 ? 1000 : period_time;
                          period_time = period_time > 1000000 ? 1000000 : period_time;
                          break;
                  case 'm':
                          for (method = 0; transfer_methods[method].name; method++)
                                          if (!strcasecmp(transfer_methods[method].name, optarg))
                                          break;
                          if (transfer_methods[method].name == NULL)
                                  method = 0;
                          break;
                  case 'o':
                          for (format = 0; format < SND_PCM_FORMAT_LAST; format++) {
                                  const char *format_name = snd_pcm_format_name(format);
                                  if (format_name)
                                          if (!strcasecmp(format_name, optarg))
                                          break;
                          }
                          if (format == SND_PCM_FORMAT_LAST)
                                  format = SND_PCM_FORMAT_S16;
                          if (!snd_pcm_format_linear(format) &&
                              !(format == SND_PCM_FORMAT_FLOAT_LE ||
                                format == SND_PCM_FORMAT_FLOAT_BE)) {
                                  printf("Invalid (non-linear/float) format %s\n",
                                         optarg);
                                  return 1;
                          }
                          break;
                  case 'v':
                          verbose = 1;
                          break;
                  case 'n':
                          resample = 0;
                          break;
                  case 'e':
                          period_event = 1;
                          break;
                  }
          }
          if (morehelp) {
                  help();
                  return 0;
          }
          err = snd_output_stdio_attach(&output, stdout, 0);
          if (err < 0) {
                  printf("Output failed: %s\n", snd_strerror(err));
                  return 0;
          }
          printf("Playback device is %s\n", device);
          printf("Stream parameters are %iHz, %s, %i channels\n", rate, snd_pcm_format_name(format), channels);
          printf("Sine wave rate is %.4fHz\n", freq);
          printf("Using transfer method: %s\n", transfer_methods[method].name);
          if ((err = snd_pcm_open(&handle, device, SND_PCM_STREAM_PLAYBACK, 0)) < 0) {
                  printf("Playback open error: %s\n", snd_strerror(err));
                  return 0;
          }
          
          if ((err = set_hwparams(handle, hwparams, transfer_methods[method].access)) < 0) {
                  printf("Setting of hwparams failed: %s\n", snd_strerror(err));
                  exit(EXIT_FAILURE);
          }
          if ((err = set_swparams(handle, swparams)) < 0) {
                  printf("Setting of swparams failed: %s\n", snd_strerror(err));
                  exit(EXIT_FAILURE);
          }
          if (verbose > 0)
                  snd_pcm_dump(handle, output);
          samples = malloc((period_size * channels * snd_pcm_format_physical_width(format)) / 8);
          if (samples == NULL) {
                  printf("No enough memory\n");
                  exit(EXIT_FAILURE);
          }
          
          areas = calloc(channels, sizeof(snd_pcm_channel_area_t));
          if (areas == NULL) {
                  printf("No enough memory\n");
                  exit(EXIT_FAILURE);
          }
          for (chn = 0; chn < channels; chn++) {
                  areas[chn].addr = samples;
                  areas[chn].first = chn * snd_pcm_format_physical_width(format);
                  areas[chn].step = channels * snd_pcm_format_physical_width(format);
          }
          err = transfer_methods[method].transfer_loop(handle, samples, areas);
          if (err < 0)
                  printf("Transfer failed: %s\n", snd_strerror(err));
          free(areas);
          free(samples);
          snd_pcm_close(handle);
          return 0;
  }
  