Problem with triggered TX

[nils]

Hi,
I am trying to send a signal synchronously and periodically with trigger input. For each trigger, I want to emit a fixed number of samples. So, if the trigger occurs every 10 milliseconds and I have samples for a 5-millisecond transmission, there will be a 5-millisecond gap between transmissions.
I have tried to achieve this using the gating mechanism, but I am unable to have a transmission where the tx burst does not drift and is always a constant distance relative to the trigger input.
I might have missed some functionality / misconfigured the radio, therefore any pointers would be greatly appreciated. Thanks
For reference this is the code i have used to try to get the specified behaviour:

Code: Select all

  status = bladerf_open(&dev, nullptr);
  if (status != 0) {
    fprintf(stderr, "Unable to open bladeRF: %s\n", bladerf_strerror(status));
    return 1;
  }

  status = bladerf_set_frequency(dev, BLADERF_CHANNEL_TX(0), frequency);
  if (status == 0) {
    status = bladerf_set_sample_rate(dev, BLADERF_CHANNEL_TX(0), (bladerf_sample_rate)requested_rate, &actual_rate);
  }
  if (status == 0) {
    status = bladerf_set_bandwidth(dev, BLADERF_CHANNEL_TX(0), actual_rate, &actual_bandwidth);
  }
  if (status == 0) {
    status = bladerf_set_gain(dev, BLADERF_CHANNEL_TX(0), (bladerf_gain)tx_gain_db);
  }
  if (status != 0) {
    fprintf(stderr, "Device configuration failed: %s\n", bladerf_strerror(status));
    goto cleanup;
  }

  if (actual_rate % 100 != 0) {
    fprintf(stderr, "Actual sample rate must produce an integral 10 ms frame.\n");
    status = BLADERF_ERR_INVAL;
    goto cleanup;
  }

  frame_samples = (size_t)(actual_rate / 100);
  trigger_samples = (size_t)llround((double)actual_rate * (double)trigger_high_us / 1000000.0);
  if (trigger_samples == 0 || trigger_samples >= frame_samples) {
    fprintf(stderr, "Trigger pulse width is outside the usable frame.\n");
    status = BLADERF_ERR_INVAL;
    goto cleanup;
  }

  playback_samples = frame_samples - trigger_samples;
  start_sample = (size_t)llround((double)actual_rate * start_ms / 1000.0);
  duration_samples = (size_t)llround((double)actual_rate * duration_ms / 1000.0);
  requested_end = start_sample + duration_samples;
  if (duration_samples == 0 || requested_end > frame_samples) {
    fprintf(stderr,
            "Requested interval must contain samples and end within "
            "the 10 ms frame.\n");
    status = BLADERF_ERR_INVAL;
    goto cleanup;
  }
  if (start_sample < trigger_samples) {
    start_sample = trigger_samples;
    if (start_sample >= requested_end) {
      fprintf(stderr,
              "Requested interval is entirely inside the "
              "trigger-high portion.\n");
      status = BLADERF_ERR_INVAL;
      goto cleanup;
    }
    fprintf(stderr,
            "Requested interval clipped at the trigger falling "
            "edge; TX is gated while the trigger is high.\n");
  }
  duration_samples = requested_end - start_sample;
  start_sample -= trigger_samples;

  if (tone_hz >= (double)actual_rate / 2.0 || start_sample + duration_samples > playback_samples) {
    fprintf(stderr, "Tone or interval is outside the playable range.\n");
    status = BLADERF_ERR_INVAL;
    goto cleanup;
  }

  if (playback_samples > UINT_MAX || playback_samples > SIZE_MAX / (2 * sizeof(*samples))) {
    fprintf(stderr, "Computed playback frame is too large.\n");
    status = BLADERF_ERR_INVAL;
    goto cleanup;
  }

  samples = (int16_t *)malloc(playback_samples * 2 * sizeof(*samples));
  if (samples == NULL) {
    perror("malloc");
    status = BLADERF_ERR_MEM;
    goto cleanup;
  }

  // NOTE: Generate the playback frame with the specified tone and interval.
  make_frame(samples, playback_samples, start_sample, duration_samples, actual_rate, tone_hz);

  status = bladerf_sync_config(dev, BLADERF_TX_X1, BLADERF_FORMAT_SC16_Q11, 16, TX_BUFFER_SIZE, 8, 1000);
  if (status != 0) {
    fprintf(stderr, "TX stream configuration failed: %s\n", bladerf_strerror(status));
    goto cleanup;
  }

  status = bladerf_trigger_init(dev, BLADERF_CHANNEL_TX(0), BLADERF_TRIGGER_MINI_EXP_1, &trigger);
  if (status != 0) {
    fprintf(stderr, "Trigger initialization failed: %s\n", bladerf_strerror(status));
    goto cleanup;
  }
  trigger.role = BLADERF_TRIGGER_ROLE_SLAVE;
  status = bladerf_trigger_arm(dev, &trigger, true, 0, 0);
  if (status != 0) {
    fprintf(stderr, "Unable to arm TX trigger: %s\n", bladerf_strerror(status));
    goto cleanup;
  }
  trigger_armed = true;

  status = bladerf_enable_module(dev, BLADERF_CHANNEL_TX(0), true);
  if (status != 0) {
    fprintf(stderr, "Unable to enable TX: %s\n", bladerf_strerror(status));
    goto cleanup;
  }
  tx_enabled = true;

  // NOTE: stop_requested is wired to a signal handler for SIGINT 
  while (!stop_requested) {
    status = bladerf_sync_tx(dev, samples, (unsigned int)playback_samples, NULL, 1000);
    if (status != 0) {
      fprintf(stderr, "TX stream failed: %s\n", bladerf_strerror(status));
      goto cleanup;
    }
  }

  // NOTE: cleanup omitted for brevity

[jennyarora]

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