Example #1
0
/** Manages acquisition searches and starts tracking channels after successful acquisitions. */
static void manage_acq()
{
  /* Decide which PRN to try and then start it acquiring. */
  u8 prn = choose_prn();
  if (prn == (u8)-1)
    return;
  gnss_signal_t sid = {.sat = prn};

  u32 timer_count;
  float cn0, cp, cf;

  acq_set_prn(prn);

  /* We have our PRN chosen, now load some fresh data
   * into the acquisition ram on the Swift NAP for
   * an initial coarse acquisition.
   */
  do {
    timer_count = nap_timing_count() + 20000;
    /* acq_load could timeout if we're preempted and miss the timing strobe */
  } while (!acq_load(timer_count));

  /* Check for NaNs in dopp hints, or low > high */
  if (!(acq_prn_param[prn].dopp_hint_low
        <= acq_prn_param[prn].dopp_hint_high)) {
    log_error("Acq: caught bogus dopp_hints (%f, %f)",
              acq_prn_param[prn].dopp_hint_low,
              acq_prn_param[prn].dopp_hint_high);
    acq_prn_param[prn].dopp_hint_high = ACQ_FULL_CF_MAX;
    acq_prn_param[prn].dopp_hint_low = ACQ_FULL_CF_MIN;
  }
  acq_search(acq_prn_param[prn].dopp_hint_low,
             acq_prn_param[prn].dopp_hint_high,
             ACQ_FULL_CF_STEP);

  /* Done with the coarse acquisition, check if we have found a
   * satellite, if so save the results and start the loading
   * for the fine acquisition. If not, start again choosing a
   * different PRN.
   */
  acq_get_results(&cp, &cf, &cn0);
  /* Send result of an acquisition to the host. */
  acq_send_result(sid, cn0, cp, cf);
  if (cn0 < ACQ_THRESHOLD) {
    /* Didn't find the satellite :( */
    /* Double the size of the doppler search space for next time. */
    float dilute = (acq_prn_param[prn].dopp_hint_high -
                    acq_prn_param[prn].dopp_hint_low) / 2;
    acq_prn_param[prn].dopp_hint_high =
        MIN(acq_prn_param[prn].dopp_hint_high + dilute, ACQ_FULL_CF_MAX);
    acq_prn_param[prn].dopp_hint_low =
        MAX(acq_prn_param[prn].dopp_hint_low - dilute, ACQ_FULL_CF_MIN);
    /* Decay hint scores */
    for (u8 i = 0; i < ACQ_HINT_NUM; i++)
      acq_prn_param[prn].score[i] = (acq_prn_param[prn].score[i] * 3) / 4;
    /* Reset hint score for acquisition. */
    acq_prn_param[prn].score[ACQ_HINT_PREV_ACQ] = 0;
    return;
  }

  u8 chan = manage_track_new_acq();
  if (chan == MANAGE_NO_CHANNELS_FREE) {
    /* No channels are free to accept our new satellite :( */
    /* TODO: Perhaps we can try to warm start this one
     * later using another fine acq.
     */
    if (cn0 > ACQ_RETRY_THRESHOLD) {
      acq_prn_param[prn].score[ACQ_HINT_PREV_ACQ] =
        SCORE_ACQ + (cn0 - ACQ_THRESHOLD);
      acq_prn_param[prn].dopp_hint_low = cf - ACQ_FULL_CF_STEP;
      acq_prn_param[prn].dopp_hint_high = cf + ACQ_FULL_CF_STEP;
    }
    return;
  }
  /* Transition to tracking. */
  u32 track_count = nap_timing_count() + 20000;
  cp = propagate_code_phase(cp, cf, track_count - timer_count);

  // Contrive for the timing strobe to occur at or close to a PRN edge (code phase = 0)
  track_count += 16*(1023.0-cp)*(1.0 + cf / GPS_L1_HZ);

  /* Start the tracking channel */
  tracking_channel_init(chan, sid, cf, track_count, cn0,
                        TRACKING_ELEVATION_UNKNOWN);
  /* TODO: Initialize elevation from ephemeris if we know it precisely */

  acq_prn_param[prn].state = ACQ_PRN_TRACKING;
  nap_timing_strobe_wait(100);
}
Example #2
0
/** Manages acquisition searches and starts tracking channels after successful acquisitions. */
static void manage_acq()
{
  /* Decide which PRN to try and then start it acquiring. */
  u8 prn = choose_prn();
  if (prn == (u8)-1)
    return;

  u32 timer_count;
  float snr, cp, cf;

  acq_set_prn(prn);

  /* We have our PRN chosen, now load some fresh data
   * into the acquisition ram on the Swift NAP for
   * an initial coarse acquisition.
   */
  do {
    timer_count = nap_timing_count() + 20000;
    /* acq_load could timeout if we're preempted and miss the timing strobe */
  } while (!acq_load(timer_count));

  acq_search(acq_prn_param[prn].dopp_hint_low,
             acq_prn_param[prn].dopp_hint_high,
             ACQ_FULL_CF_STEP);

  /* Done with the coarse acquisition, check if we have found a
   * satellite, if so save the results and start the loading
   * for the fine acquisition. If not, start again choosing a
   * different PRN.
   */
  acq_get_results(&cp, &cf, &snr);
  /* Send result of an acquisition to the host. */
  acq_send_result(prn, snr, cp, cf);
  if (snr < ACQ_THRESHOLD) {
    /* Didn't find the satellite :( */
    /* Double the size of the doppler search space for next time. */
    float dilute = (acq_prn_param[prn].dopp_hint_high -
                    acq_prn_param[prn].dopp_hint_low) / 2;
    acq_prn_param[prn].dopp_hint_high =
        MIN(acq_prn_param[prn].dopp_hint_high + dilute, ACQ_FULL_CF_MAX);
    acq_prn_param[prn].dopp_hint_low =
        MAX(acq_prn_param[prn].dopp_hint_low - dilute, ACQ_FULL_CF_MIN);
    /* Decay hint scores */
    for (u8 i = 0; i < ACQ_HINT_NUM; i++)
      acq_prn_param[prn].score[i] = (acq_prn_param[prn].score[i] * 3) / 4;
    /* Reset hint score for acuisition. */
    acq_prn_param[prn].score[ACQ_HINT_ACQ] = 0;
    return;
  }

  log_info("acq: PRN %d found @ %d Hz, %d SNR\n", prn + 1, (int)cf, (int)snr);

  u8 chan = manage_track_new_acq();
  if (chan == MANAGE_NO_CHANNELS_FREE) {
    /* No channels are free to accept our new satellite :( */
    /* TODO: Perhaps we can try to warm start this one
     * later using another fine acq.
     */
    log_info("No channels free :(\n");
    if (snr > ACQ_RETRY_THRESHOLD) {
      acq_prn_param[prn].score[ACQ_HINT_ACQ] = SCORE_ACQ + (snr - 20) / 20;
      acq_prn_param[prn].dopp_hint_low = cf - ACQ_FULL_CF_STEP;
      acq_prn_param[prn].dopp_hint_high = cf + ACQ_FULL_CF_STEP;
    }
    return;
  }
  /* Transition to tracking. */
  u32 track_count = nap_timing_count() + 20000;
  cp = propagate_code_phase(cp, cf, track_count - timer_count);

  // Contrive for the timing strobe to occur at or close to a PRN edge (code phase = 0)
  track_count += 16*(1023.0-cp)*(1.0 + cf / GPS_L1_HZ);

  tracking_channel_init(chan, prn, cf, track_count, snr);
  acq_prn_param[prn].state = ACQ_PRN_TRACKING;
  nap_timing_strobe_wait(100);
}
Example #3
0
/** Manages acquisition searches and starts tracking channels after successful acquisitions. */
void manage_acq()
{
  /* Decide which PRN to try and then start it acquiring. */
  u8 prn = best_prn();
  if (prn == (u8)-1)
    return;

  u32 timer_count;
  float snr, cp, cf;

  acq_set_prn(prn);

  /* We have our PRN chosen, now load some fresh data
   * into the acquisition ram on the Swift NAP for
   * an initial coarse acquisition.
   */
  acq_prn_param[prn].state = ACQ_PRN_ACQUIRING;
  do {
    timer_count = nap_timing_count() + 20000;
    /* acq_load could timeout if we're preempted and miss the timing strobe */
  } while (!acq_load(timer_count));

  /* Done loading, now lets set that coarse acquisition going. */
  if (almanac[prn].valid && time_quality == TIME_COARSE) {
    gps_time_t t = rx2gpstime(timer_count);

    double dopp = -calc_sat_doppler_almanac(&almanac[prn], t.tow, t.wn, position_solution.pos_ecef);
    /* TODO: look into accuracy of prediction and possibilities for
     * improvement, e.g. use clock bias estimated by PVT solution. */
    /*log_info("Expecting PRN %02d @ %.1f\n", prn+1, dopp);*/
    acq_search(dopp - 4000, dopp + 4000, ACQ_FULL_CF_STEP);
  } else {
    acq_search(ACQ_FULL_CF_MIN, ACQ_FULL_CF_MAX, ACQ_FULL_CF_STEP);
  }

  /* Done with the coarse acquisition, check if we have found a
   * satellite, if so save the results and start the loading
   * for the fine acquisition. If not, start again choosing a
   * different PRN.
   */
  acq_get_results(&cp, &cf, &snr);
  /* Send result of an acquisition to the host. */
  acq_send_result(prn, snr, cp, cf);
  if (snr < ACQ_THRESHOLD) {
    /* Didn't find the satellite :( */
    acq_prn_param[prn].state = ACQ_PRN_TRIED;
    return;
  }

  log_info("acq: PRN %d found @ %d Hz, %d SNR\n", prn + 1, (int)cf, (int)snr);

  u8 chan = manage_track_new_acq(snr);
  if (chan == MANAGE_NO_CHANNELS_FREE) {
    /* No channels are free to accept our new satellite :( */
    /* TODO: Perhaps we can try to warm start this one
     * later using another fine acq.
     */
    log_info("No channels free :(\n");
    acq_prn_param[prn].state = ACQ_PRN_TRIED;
    return;
  }
  /* Transition to tracking. */
  u32 track_count = nap_timing_count() + 20000;
  cp = propagate_code_phase(cp, cf, track_count - timer_count);

  // Contrive for the timing strobe to occur at or close to a PRN edge (code phase = 0)
  track_count += 16*(1023.0-cp)*(1.0 + cf / GPS_L1_HZ);

  tracking_channel_init(chan, prn, cf, track_count, snr);
  acq_prn_param[prn].state = ACQ_PRN_TRACKING;
  nap_timing_strobe_wait(100);
}