latency.cc

/*
 *  Latency test program
 *
 *     Author: Jaroslav Kysela <perex@perex.cz>
 *
 *     Author of bandpass filter sweep effect:
 *         Maarten de Boer <mdeboer@iua.upf.es>
 *
 *  This small demo program can be used for measuring latency between
 *  capture and playback. This latency is measured from driver (diff when
 *  playback and capture was started). Scheduler is set to SCHED_RR.
 *
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation; either version 2 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program; if not, write to the Free Software
 *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 *
 */

#include <stdio.h>
#include <stdint.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 unsigned char header[4] = { 0xff, 0xff, 0xff, 0xff };
const char *pdevice = "hw:0,0";
const char *cdevice = "hw:0,0";
snd_pcm_format_t format = SND_PCM_FORMAT_S16_LE;
int rate = 22050;
int channels = 2;
int buffer_size = 0;    /* auto */
int period_size = 0;    /* auto */
int latency_min = 32;    /* in frames / 2 */
int latency_max = 2048;    /* in frames / 2 */
int loop_sec = 30;    /* seconds */
int block = 0;      /* block mode */
int use_poll = 0;
int resample = 1;
unsigned long loop_limit;
double end_to_end_latency = 0;
uint64_t end_to_end_samples = 0;

snd_output_t *output = NULL;

int setparams_stream(snd_pcm_t *handle,
         snd_pcm_hw_params_t *params,
         const char *id)
{
  int err;
  unsigned int rrate;

  err = snd_pcm_hw_params_any(handle, params);
  if (err < 0) {
    printf("Broken configuration for %s PCM: no configurations available: %s\n", snd_strerror(err), id);
    return err;
  }
  err = snd_pcm_hw_params_set_rate_resample(handle, params, resample);
  if (err < 0) {
    printf("Resample setup failed for %s (val %i): %s\n", id, resample, snd_strerror(err));
    return err;
  }
  err = snd_pcm_hw_params_set_access(handle, params, SND_PCM_ACCESS_RW_INTERLEAVED);
  if (err < 0) {
    printf("Access type not available for %s: %s\n", id, snd_strerror(err));
    return err;
  }
  err = snd_pcm_hw_params_set_format(handle, params, format);
  if (err < 0) {
    printf("Sample format not available for %s: %s\n", id, snd_strerror(err));
    return err;
  }
  err = snd_pcm_hw_params_set_channels(handle, params, channels);
  if (err < 0) {
    printf("Channels count (%i) not available for %s: %s\n", channels, id, snd_strerror(err));
    return err;
  }
  rrate = rate;
  err = snd_pcm_hw_params_set_rate_near(handle, params, &rrate, 0);
  if (err < 0) {
    printf("Rate %iHz not available for %s: %s\n", rate, id, snd_strerror(err));
    return err;
  }
  if ((int)rrate != rate) {
    printf("Rate doesn't match (requested %iHz, get %iHz)\n", rate, err);
    return -EINVAL;
  }
  return 0;
}

int setparams_bufsize(snd_pcm_t *handle,
          snd_pcm_hw_params_t *params,
          snd_pcm_hw_params_t *tparams,
          snd_pcm_uframes_t bufsize,
          const char *id)
{
  int err;
  snd_pcm_uframes_t periodsize;

  snd_pcm_hw_params_copy(params, tparams);
  periodsize = bufsize * 2;
  err = snd_pcm_hw_params_set_buffer_size_near(handle, params, &periodsize);
  if (err < 0) {
    printf("Unable to set buffer size %li for %s: %s\n", bufsize * 2, id, snd_strerror(err));
    return err;
  }
  if (period_size > 0)
    periodsize = period_size;
  else
    periodsize /= 2;
  err = snd_pcm_hw_params_set_period_size_near(handle, params, &periodsize, 0);
  if (err < 0) {
    printf("Unable to set period size %li for %s: %s\n", periodsize, id, snd_strerror(err));
    return err;
  }
  return 0;
}

int setparams_set(snd_pcm_t *handle,
      snd_pcm_hw_params_t *params,
      snd_pcm_sw_params_t *swparams,
      const char *id)
{
  int err;
  snd_pcm_uframes_t val;

  err = snd_pcm_hw_params(handle, params);
  if (err < 0) {
    printf("Unable to set hw params for %s: %s\n", id, snd_strerror(err));
    return err;
  }
  err = snd_pcm_sw_params_current(handle, swparams);
  if (err < 0) {
    printf("Unable to determine current swparams for %s: %s\n", id, snd_strerror(err));
    return err;
  }
  err = snd_pcm_sw_params_set_start_threshold(handle, swparams, 0x7fffffff);
  if (err < 0) {
    printf("Unable to set start threshold mode for %s: %s\n", id, snd_strerror(err));
    return err;
  }
  if (!block)
    val = 4;
  else
    snd_pcm_hw_params_get_period_size(params, &val, NULL);
  err = snd_pcm_sw_params_set_avail_min(handle, swparams, val);
  if (err < 0) {
    printf("Unable to set avail min for %s: %s\n", id, snd_strerror(err));
    return err;
  }
  err = snd_pcm_sw_params(handle, swparams);
  if (err < 0) {
    printf("Unable to set sw params for %s: %s\n", id, snd_strerror(err));
    return err;
  }
  return 0;
}

int setparams(snd_pcm_t *phandle, snd_pcm_t *chandle, int *bufsize)
{
  int err, last_bufsize = *bufsize;
  snd_pcm_hw_params_t *pt_params, *ct_params;  /* templates with rate, format and channels */
  snd_pcm_hw_params_t *p_params, *c_params;
  snd_pcm_sw_params_t *p_swparams, *c_swparams;
  snd_pcm_uframes_t p_size, c_size, p_psize, c_psize;
  unsigned int p_time, c_time;
  unsigned int val;

  snd_pcm_hw_params_alloca(&p_params);
  snd_pcm_hw_params_alloca(&c_params);
  snd_pcm_hw_params_alloca(&pt_params);
  snd_pcm_hw_params_alloca(&ct_params);
  snd_pcm_sw_params_alloca(&p_swparams);
  snd_pcm_sw_params_alloca(&c_swparams);
  if ((err = setparams_stream(phandle, pt_params, "playback")) < 0) {
    printf("Unable to set parameters for playback stream: %s\n", snd_strerror(err));
    exit(0);
  }
  if ((err = setparams_stream(chandle, ct_params, "capture")) < 0) {
    printf("Unable to set parameters for playback stream: %s\n", snd_strerror(err));
    exit(0);
  }

  if (buffer_size > 0) {
    *bufsize = buffer_size;
    goto __set_it;
  }

      __again:
        if (buffer_size > 0)
          return -1;
        if (last_bufsize == *bufsize)
    *bufsize += 4;
  last_bufsize = *bufsize;
  if (*bufsize > latency_max)
    return -1;
      __set_it:
        
  if ((err = setparams_bufsize(phandle, p_params, pt_params, *bufsize, "playback")) < 0) {
    printf("Unable to set sw parameters for playback stream: %s\n", snd_strerror(err));
     exit(0);
  }
  if ((err = setparams_bufsize(chandle, c_params, ct_params, *bufsize, "capture")) < 0) {
    printf("Unable to set sw parameters for playback stream: %s\n", snd_strerror(err));
    exit(0);
  }

  snd_pcm_hw_params_get_period_size(p_params, &p_psize, NULL);
  if (p_psize > (unsigned int)*bufsize)
    *bufsize = p_psize;
  snd_pcm_hw_params_get_period_size(c_params, &c_psize, NULL);
  if (c_psize > (unsigned int)*bufsize)
    *bufsize = c_psize;
  snd_pcm_hw_params_get_period_time(p_params, &p_time, NULL);
  snd_pcm_hw_params_get_period_time(c_params, &c_time, NULL);
  if (p_time != c_time)
    goto __again;

  //printf("p period_time = %u\n", p_time);
  //printf("p period_size = %lu\n", p_size);
  //printf("c period_time = %u\n", c_time);
  //printf("c period_size = %lu\n", c_size);

  snd_pcm_hw_params_get_buffer_size(p_params, &p_size);
  if (p_psize * 2 < p_size) {
    snd_pcm_hw_params_get_periods_min(p_params, &val, NULL);
    //printf("p period_min = %u\n", val);
    if (val > 2) {
      //printf("playback device does not support 2 periods per buffer\n");
      //exit(0);
    }
    //goto __again;
  }
  snd_pcm_hw_params_get_buffer_size(c_params, &c_size);
  if (c_psize * 2 < c_size) {
    snd_pcm_hw_params_get_periods_min(c_params, &val, NULL);
    //printf("c period_min = %u\n", val);
    if (val > 2 ) {
      //printf("capture device does not support 2 periods per buffer\n");
      //exit(0);
    }
    //goto __again;
  }
  if ((err = setparams_set(phandle, p_params, p_swparams, "playback")) < 0) {
    printf("Unable to set sw parameters for playback stream: %s\n", snd_strerror(err));
    exit(0);
  }
  if ((err = setparams_set(chandle, c_params, c_swparams, "capture")) < 0) {
    printf("Unable to set sw parameters for playback stream: %s\n", snd_strerror(err));
    exit(0);
  }

  if ((err = snd_pcm_prepare(phandle)) < 0) {
    printf("Prepare error: %s\n", snd_strerror(err));
    exit(0);
  }

  snd_pcm_dump(phandle, output);
  snd_pcm_dump(chandle, output);
  fflush(stdout);
  return 0;
}

void showstat(snd_pcm_t *handle, size_t frames)
{
  int err;
  snd_pcm_status_t *status;

  snd_pcm_status_alloca(&status);
  if ((err = snd_pcm_status(handle, status)) < 0) {
    printf("Stream status error: %s\n", snd_strerror(err));
    exit(0);
  }
  printf("*** frames = %li ***\n", (long)frames);
  snd_pcm_status_dump(status, output);
}

void showlatency(size_t latency)
{
  double d;
  latency *= 2;
  d = (double)latency / (double)rate;
  printf("Trying latency %li frames, %.3fus, %.6fms (%.4fHz)\n", (long)latency, d * 1000000, d * 1000, (double)1 / d);
}

void showinmax(size_t in_max)
{
  double d;

  printf("Maximum read: %li frames\n", (long)in_max);
  d = (double)in_max / (double)rate;
  printf("Maximum read latency: %.3fus, %.6fms (%.4fHz)\n", d * 1000000, d * 1000, (double)1 / d);
}

void gettimestamp(snd_pcm_t *handle, snd_timestamp_t *timestamp)
{
  int err;
  snd_pcm_status_t *status;

  snd_pcm_status_alloca(&status);
  if ((err = snd_pcm_status(handle, status)) < 0) {
    printf("Stream status error: %s\n", snd_strerror(err));
    exit(0);
  }
  snd_pcm_status_get_trigger_tstamp(status, timestamp);
}

void setscheduler(void)
{
  struct sched_param sched_param;

  if (sched_getparam(0, &sched_param) < 0) {
    printf("Scheduler getparam failed...\n");
    return;
  }
  sched_param.sched_priority = sched_get_priority_max(SCHED_RR);
  if (!sched_setscheduler(0, SCHED_RR, &sched_param)) {
    printf("Scheduler set to Round Robin with priority %i...\n", sched_param.sched_priority);
    fflush(stdout);
    return;
  }
  printf("!!!Scheduler set to Round Robin with priority %i FAILED!!!\n", sched_param.sched_priority);
}

long timediff(snd_timestamp_t t1, snd_timestamp_t t2)
{
  signed long l;

  t1.tv_sec -= t2.tv_sec;
  l = (signed long) t1.tv_usec - (signed long) t2.tv_usec;
  if (l < 0) {
    t1.tv_sec--;
    l = 1000000 + l;
    l %= 1000000;
  }
  return (t1.tv_sec * 1000000) + l;
}

long readbuf(snd_pcm_t *handle, char *buf, long len, size_t *frames, size_t *max)
{
  long r;
  long nread = 0;

  if (!block) {
    do {
      r = snd_pcm_readi(handle, buf, len);
    } while (r == -EAGAIN);
    if (r > 0) {
      nread += r;
      if ((long)*max < r)
        *max = r;
    }
    // printf("read = %li\n", r);
  } else {
    int frame_bytes = (snd_pcm_format_width(format) / 8) * channels;
    do {
      r = snd_pcm_readi(handle, buf, len);
      if (r > 0) {
        buf += r * frame_bytes;
        len -= r;
        nread += r;
        if ((long)*max < r)
          *max = r;
      }
      // printf("r = %li, len = %li\n", r, len);
    } while (r >= 1 && len > 0);
  }
  *frames += nread;

  timespec tp;
  if (clock_gettime(CLOCK_MONOTONIC, &tp) != 0) {
    printf("Cannot read monotonic clock\n");
    exit(1);
  }

  uint64_t sentMs, recvMs = tp.tv_sec * 1000000 + tp.tv_nsec / 1000;
  for (int i = 0; i < (nread - 12); i++) {
    if (!memcmp(buf + i, header, 4)) {
      memcpy(&sentMs, buf + i + 4, 8);
      if ((recvMs - sentMs) < 1000000) {
        end_to_end_latency += ((double)recvMs - (double)sentMs) / 1000;
        end_to_end_samples++;
      }
    }
  }

  // showstat(handle, 0);
  return r;
}

long writebuf(snd_pcm_t *handle, char *buf, long len, size_t *frames, bool add_ts)
{
  long r;
  int frame_bytes = (snd_pcm_format_width(format) / 8) * channels;

  if (add_ts) {
    timespec tp;
    if (clock_gettime(CLOCK_MONOTONIC, &tp) != 0) {
      printf("Cannot read monotonic clock\n");
      exit(1);
    }

    uint64_t ms = tp.tv_sec * 1000000 + tp.tv_nsec / 1000;
    memcpy(buf, header, 4);
    memcpy(buf + 4, &ms, sizeof(ms));
  }

  while (len > 0) {
    r = snd_pcm_writei(handle, buf, len);
    if (r == -EAGAIN)
      continue;
    // printf("write = %li\n", r);
    if (r < 0)
      return r;
    // showstat(handle, 0);
    buf += r * frame_bytes;
    len -= r;
    *frames += r;
  }
  return 0;
}
      
#define FILTERSWEEP_LFO_CENTER 2000.
#define FILTERSWEEP_LFO_DEPTH 1800.
#define FILTERSWEEP_LFO_FREQ 0.2
#define FILTER_BANDWIDTH 50

/* filter the sweep variables */
float lfo,dlfo,fs,fc,BW,C,D,a0,a1,a2,b1,b2,*x[3],*y[3];

void applyeffect(char* buffer,int r)
{
  short* samples = (short*) buffer;
  int i;
  for (i=0;i<r;i++)
  {
    int chn;

    fc = sin(lfo)*FILTERSWEEP_LFO_DEPTH+FILTERSWEEP_LFO_CENTER;
    lfo += dlfo;
    if (lfo>2.*M_PI) lfo -= 2.*M_PI;
    C = 1./tan(M_PI*BW/fs);
    D = 2.*cos(2*M_PI*fc/fs);
    a0 = 1./(1.+C);
    a1 = 0;
    a2 = -a0;
    b1 = -C*D*a0;
    b2 = (C-1)*a0;

    for (chn=0;chn<channels;chn++)
    {
      x[chn][2] = x[chn][1];
      x[chn][1] = x[chn][0];

      y[chn][2] = y[chn][1];
      y[chn][1] = y[chn][0];

      x[chn][0] = samples[i*channels+chn];
      y[chn][0] = a0*x[chn][0] + a1*x[chn][1] + a2*x[chn][2] 
        - b1*y[chn][1] - b2*y[chn][2];
      samples[i*channels+chn] = y[chn][0];
    }
  }
}

void help(void)
{
  int k;
  printf(
"Usage: latency [OPTION]... [FILE]...\n"
"-h,--help      help\n"
"-P,--pdevice   playback device\n"
"-C,--cdevice   capture device\n"
"-m,--min       minimum latency in frames\n"
"-M,--max       maximum latency in frames\n"
"-F,--frames    frames to transfer\n"
"-f,--format    sample format\n"
"-c,--channels  channels\n"
"-r,--rate      rate\n"
"-B,--buffer    buffer size in frames\n"
"-E,--period    period size in frames\n"
"-s,--seconds   duration of test in seconds\n"
"-b,--block     block mode\n"
"-p,--poll      use poll (wait for event - reduces CPU usage)\n"
"-e,--effect    apply an effect (bandpass filter sweep)\n"
);
        printf("Recognized sample formats are:");
        for (k = 0; k < SND_PCM_FORMAT_LAST; ++k) {
                const char *s = snd_pcm_format_name((snd_pcm_format_t)k);
                if (s)
                        printf(" %s", s);
        }
        printf("\n\n");
        printf(
"Tip #1 (usable latency with large periods, non-blocking mode, good CPU usage,\n"
"        superb xrun prevention):\n"
"  latency -m 8192 -M 8192 -t 1 -p\n"
"Tip #2 (superb latency, non-blocking mode, but heavy CPU usage):\n"
"  latency -m 128 -M 128\n"
);
}

int main(int argc, char *argv[])
{
  struct option long_option[] =
  {
    {"help", 0, NULL, 'h'},
    {"pdevice", 1, NULL, 'P'},
    {"cdevice", 1, NULL, 'C'},
    {"min", 1, NULL, 'm'},
    {"max", 1, NULL, 'M'},
    {"frames", 1, NULL, 'F'},
    {"format", 1, NULL, 'f'},
    {"channels", 1, NULL, 'c'},
    {"rate", 1, NULL, 'r'},
    {"buffer", 1, NULL, 'B'},
    {"period", 1, NULL, 'E'},
    {"seconds", 1, NULL, 's'},
    {"block", 0, NULL, 'b'},
    {"poll", 0, NULL, 'p'},
    {"effect", 0, NULL, 'e'},
    {NULL, 0, NULL, 0},
  };
  snd_pcm_t *phandle, *chandle;
  char *buffer;
  int err, latency, morehelp;
  int ok;
  snd_timestamp_t p_tstamp, c_tstamp;
  ssize_t r;
  size_t frames_in, frames_out, in_max;
  int effect = 0;
  morehelp = 0;
  while (1) {
    int c;
    if ((c = getopt_long(argc, argv, "hP:C:m:M:F:f:c:r:B:E:s:bpen", long_option, NULL)) < 0)
      break;
    switch (c) {
    case 'h':
      morehelp++;
      break;
    case 'P':
      pdevice = strdup(optarg);
      break;
    case 'C':
      cdevice = strdup(optarg);
      break;
    case 'm':
      err = atoi(optarg) / 2;
      latency_min = err >= 4 ? err : 4;
      if (latency_max < latency_min)
        latency_max = latency_min;
      break;
    case 'M':
      err = atoi(optarg) / 2;
      latency_max = latency_min > err ? latency_min : err;
      break;
    case 'f':
      format = snd_pcm_format_value(optarg);
      if (format == SND_PCM_FORMAT_UNKNOWN) {
        printf("Unknown format, setting to default S16_LE\n");
        format = SND_PCM_FORMAT_S16_LE;
      }
      break;
    case 'c':
      err = atoi(optarg);
      channels = err >= 1 && err < 1024 ? err : 1;
      break;
    case 'r':
      err = atoi(optarg);
      rate = err >= 4000 && err < 400000 ? err : 44100;
      break;
    case 'B':
      err = atoi(optarg);
      buffer_size = err >= 32 && err < 200000 ? err : 0;
      break;
    case 'E':
      err = atoi(optarg);
      period_size = err >= 32 && err < 200000 ? err : 0;
      break;
    case 's':
      err = atoi(optarg);
      loop_sec = err >= 1 && err <= 100000 ? err : 30;
      break;
    case 'b':
      block = 1;
      break;
    case 'p':
      use_poll = 1;
      break;
    case 'e':
      effect = 1;
      break;
    case 'n':
      resample = 0;
      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;
  }

  loop_limit = loop_sec * rate;
  latency = latency_min - 4;
  buffer = (char*)malloc((latency_max * 4 * snd_pcm_format_width(format) / 8) * channels);

  setscheduler();

  printf("Playback device is %s\n", pdevice);
  printf("Capture device is %s\n", cdevice);
  printf("Parameters are %iHz, %s, %i channels, %s mode\n", rate, snd_pcm_format_name(format), channels, block ? "blocking" : "non-blocking");
  printf("Poll mode: %s\n", use_poll ? "yes" : "no");
  printf("Loop limit is %lu frames, minimum latency = %i, maximum latency = %i\n", loop_limit, latency_min * 2, latency_max * 2);

  if ((err = snd_pcm_open(&phandle, pdevice, SND_PCM_STREAM_PLAYBACK, block ? 0 : SND_PCM_NONBLOCK)) < 0) {
    printf("Playback open error: %s\n", snd_strerror(err));
    return 0;
  }
  if ((err = snd_pcm_open(&chandle, cdevice, SND_PCM_STREAM_CAPTURE, block ? 0 : SND_PCM_NONBLOCK)) < 0) {
    printf("Record open error: %s\n", snd_strerror(err));
    return 0;
  }

  /* initialize the filter sweep variables */
  if (effect) {
    fs = (float) rate;
    BW = FILTER_BANDWIDTH;

    lfo = 0;
    dlfo = 2.*M_PI*FILTERSWEEP_LFO_FREQ/fs;

    x[0] = (float*) malloc(channels*sizeof(float));    
    x[1] = (float*) malloc(channels*sizeof(float));    
    x[2] = (float*) malloc(channels*sizeof(float));    
    y[0] = (float*) malloc(channels*sizeof(float));    
    y[1] = (float*) malloc(channels*sizeof(float));    
    y[2] = (float*) malloc(channels*sizeof(float));    
  }
        
  while (1) {
    frames_in = frames_out = 0;
    if (setparams(phandle, chandle, &latency) < 0)
      break;
    showlatency(latency);
    if ((err = snd_pcm_link(chandle, phandle)) < 0) {
      printf("Streams link error: %s\n", snd_strerror(err));
      exit(0);
    }
    if (snd_pcm_format_set_silence(format, buffer, latency*channels) < 0) {
      fprintf(stderr, "silence error\n");
      break;
    }
    if (writebuf(phandle, buffer, latency, &frames_out, false) < 0) {
      fprintf(stderr, "write error\n");
      break;
    }
    if (writebuf(phandle, buffer, latency, &frames_out, false) < 0) {
      fprintf(stderr, "write error\n");
      break;
    }

    if ((err = snd_pcm_start(chandle)) < 0) {
      printf("Go error: %s\n", snd_strerror(err));
      exit(0);
    }
    gettimestamp(phandle, &p_tstamp);
    gettimestamp(chandle, &c_tstamp);
#if 0
    printf("Playback:\n");
    showstat(phandle, frames_out);
    printf("Capture:\n");
    showstat(chandle, frames_in);
#endif

    ok = 1;
    in_max = 0;
    while (ok && frames_in < loop_limit) {
      if (use_poll) {
        /* use poll to wait for next event */
        snd_pcm_wait(chandle, 1000);
      }
      if ((r = readbuf(chandle, buffer, latency, &frames_in, &in_max)) < 0)
        ok = 0;
      else {
        if (effect)
          applyeffect(buffer,r);
         if (writebuf(phandle, buffer, r, &frames_out, true) < 0)
          ok = 0;
      }
    }
    if (ok)
      printf("Success\n");
    else
      printf("Failure\n");
    printf("Playback:\n");
    showstat(phandle, frames_out);
    printf("Capture:\n");
    showstat(chandle, frames_in);
    showinmax(in_max);
    if (p_tstamp.tv_sec == c_tstamp.tv_sec &&
        p_tstamp.tv_usec == c_tstamp.tv_usec)
      printf("Hardware sync\n");
    snd_pcm_drop(chandle);
    snd_pcm_nonblock(phandle, 0);
    snd_pcm_drain(phandle);
    snd_pcm_nonblock(phandle, !block ? 1 : 0);
    if (ok) {
#if 1
      printf("Playback time = %li.%i, Record time = %li.%i, diff = %li\n",
             p_tstamp.tv_sec,
             (int)p_tstamp.tv_usec,
             c_tstamp.tv_sec,
             (int)c_tstamp.tv_usec,
             timediff(p_tstamp, c_tstamp));
#endif
      break;
    }
    snd_pcm_unlink(chandle);
    snd_pcm_hw_free(phandle);
    snd_pcm_hw_free(chandle);
  }

  if (end_to_end_samples)
    printf("End to end latency: %.3f msecs\n", end_to_end_latency / end_to_end_samples);
  else
    printf("End to end latency: no samples collected\n");
  snd_pcm_close(phandle);
  snd_pcm_close(chandle);
  return 0;
}