Fix and tidy up time offset in srsue

lib/include/srslte/radio/radio.h

@@ -334,7 +334,10 @@ private:
 
   channel_mapping rx_channel_mapping = {}, tx_channel_mapping = {};
 
-  bool map_channels(channel_mapping& map, const rf_buffer_interface& buffer, void* radio_buffers[SRSLTE_MAX_CHANNELS]);
+  bool map_channels(channel_mapping&           map,
+                    uint32_t                   sample_offset,
+                    const rf_buffer_interface& buffer,
+                    void*                      radio_buffers[SRSLTE_MAX_CHANNELS]);
   bool start_agc(bool tx_gain_same_rx = false);
   void set_tx_adv(int nsamples);
   void set_tx_adv_neg(bool tx_adv_is_neg);

lib/src/radio/radio.cc

@@ -222,7 +222,7 @@ bool radio::rx_now(rf_buffer_interface& buffer, const uint32_t& nof_samples, srs
   double* frac_secs = rxd_time ? &rxd_time->frac_secs : NULL;
 
   void* radio_buffers[SRSLTE_MAX_CHANNELS] = {};
-  if (!map_channels(rx_channel_mapping, buffer, radio_buffers)) {
+  if (!map_channels(rx_channel_mapping, 0, buffer, radio_buffers)) {
     log_h->error("Mapping logical channels to physical channels for transmission\n");
     return false;
   }
@@ -260,8 +260,11 @@ bool radio::has_rssi()
   return srslte_rf_has_rssi(&rf_device);
 }
 
-bool radio::tx(rf_buffer_interface& buffer, const uint32_t& nof_samples, const srslte_timestamp_t& tx_time_)
+bool radio::tx(rf_buffer_interface& buffer, const uint32_t& nof_samples_, const srslte_timestamp_t& tx_time_)
 {
+  uint32_t nof_samples   = nof_samples_;
+  uint32_t sample_offset = 0;
+
   if (!is_initialized) {
     return false;
   }
@@ -272,12 +275,32 @@ bool radio::tx(rf_buffer_interface& buffer, const uint32_t& nof_samples, const s
     srslte_timestamp_add(&tx_time, 0, tx_adv_sec);
   }
 
+  // Calculate Tx gap if it is not start of the burst
+  if (not is_start_of_burst) {
+    srslte_timestamp_t tx_gap = end_of_burst_time;
+    srslte_timestamp_sub(&tx_gap, tx_time.full_secs, tx_time.frac_secs);
+    int32_t past_nsamples = (int32_t)round(cur_tx_srate * srslte_timestamp_real(&tx_gap));
+
+    // Negative gap, trimming first samples by setting a sample offset. Otherwise, ignore
+    if (past_nsamples > 0) {
+      // If the gap is larger than the amount of samples to transmit, return without doing anything else
+      if ((int32_t)nof_samples < past_nsamples) {
+        return true;
+      }
+
+      // Update transmission parameters
+      tx_time = end_of_burst_time;
+      nof_samples -= past_nsamples;
+      sample_offset = (uint32_t)past_nsamples;
+    }
+  }
+
   // Save possible end of burst time
   srslte_timestamp_copy(&end_of_burst_time, &tx_time);
   srslte_timestamp_add(&end_of_burst_time, 0, (double)nof_samples / cur_tx_srate);
 
   void* radio_buffers[SRSLTE_MAX_CHANNELS] = {};
-  if (!map_channels(rx_channel_mapping, buffer, radio_buffers)) {
+  if (!map_channels(rx_channel_mapping, sample_offset, buffer, radio_buffers)) {
     log_h->error("Mapping logical channels to physical channels for transmission\n");
     return false;
   }
@@ -285,11 +308,7 @@ bool radio::tx(rf_buffer_interface& buffer, const uint32_t& nof_samples, const s
   int ret = srslte_rf_send_timed_multi(
       &rf_device, radio_buffers, nof_samples, tx_time.full_secs, tx_time.frac_secs, true, is_start_of_burst, false);
   is_start_of_burst = false;
-  if (ret > 0) {
-    return true;
-  } else {
-    return false;
-  }
+  return ret > SRSLTE_SUCCESS;
 }
 
 void radio::tx_end()
@@ -616,6 +635,7 @@ void radio::rf_msg_callback(void* arg, srslte_rf_error_t error)
 }
 
 bool radio::map_channels(channel_mapping&           map,
+                         uint32_t                   sample_offset,
                          const rf_buffer_interface& buffer,
                          void*                      radio_buffers[SRSLTE_MAX_CHANNELS])
 {
@@ -630,7 +650,7 @@ bool radio::map_channels(channel_mapping&           map,
       uint32_t physical_idx = map.get_carrier_idx(i);
       for (uint32_t j = 0; j < nof_antennas; j++) {
         if (physical_idx * nof_antennas + j < SRSLTE_MAX_CHANNELS) {
-          radio_buffers[physical_idx * nof_antennas + j] = buffer.get(i, j, nof_antennas);
+          radio_buffers[physical_idx * nof_antennas + j] = buffer.get(i, j, nof_antennas) + sample_offset;
         } else {
           return false;
         }

srsue/hdr/phy/ta_control.h

@@ -35,9 +35,6 @@ private:
   mutable std::mutex mutex;
   uint32_t           next_base_nta    = 0;
   float              next_base_sec    = 0.0f;
-  float              current_base_sec = 0.0f;
-  float              prev_base_sec    = 0.0f;
-  int32_t            pending_nsamples = 0;
 
 public:
   /**
@@ -62,9 +59,6 @@ public:
     // Update base in nta
     next_base_nta = static_cast<uint32_t>(roundf(next_base_sec / SRSLTE_LTE_TS));
 
-    // Resets pending samples
-    pending_nsamples = 0;
-
     // Log information information if available
     if (log_h) {
       log_h->info("PHY:   Set TA base: n_ta: %d, ta_usec: %.1f\n", next_base_nta, next_base_sec * 1e6f);
@@ -138,43 +132,17 @@ public:
     }
   }
 
-  /**
-   * Increments/Decrements the number pending samples for next transmission
-   *
-   * @param nsamples is the number of samples
-   */
-  void set_pending_nsamples(int32_t nsamples)
-  {
-    std::lock_guard<std::mutex> lock(mutex);
-
-    // Increment number of pending samples
-    pending_nsamples += nsamples;
-  }
-
-  /**
-   * Get the previous time alignment in seconds
-   *
-   * @return Time alignment in seconds
-   */
-  float get_previous_sec() const
-  {
-    std::lock_guard<std::mutex> lock(mutex);
-
-    // Returns the previous base
-    return prev_base_sec;
-  }
-
   /**
    * Get the current time alignment in seconds
    *
    * @return Time alignment in seconds
    */
-  float get_current_sec() const
+  float get_sec() const
   {
     std::lock_guard<std::mutex> lock(mutex);
 
     // Returns the current base
-    return current_base_sec;
+    return next_base_sec;
   }
 
   /**
@@ -182,12 +150,12 @@ public:
    *
    * @return Time alignment in microseconds
    */
-  float get_current_usec() const
+  float get_usec() const
   {
     std::lock_guard<std::mutex> lock(mutex);
 
     // Returns the current base
-    return current_base_sec * 1e6f;
+    return next_base_sec * 1e6f;
   }
 
   /**
@@ -195,41 +163,12 @@ public:
    *
    * @return Distance based on the current time base
    */
-  float get_current_km() const
+  float get_km() const
   {
     std::lock_guard<std::mutex> lock(mutex);
 
     // Returns the current base, one direction distance
-    return current_base_sec * (3.6f * 3e8f / 2.0f);
-  }
-
-  /**
-   * Get the total number of pending samples to transmit, considering the time difference between the next base and the
-   * current base.
-   *
-   * Attention: this method changes the internal state of the class.
-   *
-   * @return the total number of pending samples considering the sampling rate
-   */
-  int32_t get_pending_nsamples(uint32_t sampling_rate_hz)
-  {
-    std::lock_guard<std::mutex> lock(mutex);
-
-    // Convert sampling rate to float
-    float srate = static_cast<float>(sampling_rate_hz);
-
-    // Calculate number of samples
-    int32_t nsamples = static_cast<int32_t>(roundf(srate * (current_base_sec - next_base_sec)));
-
-    // Update current base
-    prev_base_sec    = current_base_sec;
-    current_base_sec = next_base_sec;
-
-    // Reset pending samples
-    pending_nsamples = 0;
-
-    // Return number of samples
-    return nsamples;
+    return next_base_sec * (3.6f * 3e8f / 2.0f);
   }
 };
 

srsue/src/phy/phy_common.cc

@@ -532,6 +532,9 @@ void phy_common::worker_end(void*                tx_sem_id,
   // Wait for the green light to transmit in the current TTI
   semaphore.wait(tx_sem_id);
 
+  // Add Time Alignment
+  srslte_timestamp_sub(&tx_time, 0, ta.get_sec());
+
   // For each radio, transmit
   if (tx_enable && !srslte_timestamp_iszero(&tx_time)) {
 

srsue/src/phy/sf_worker.cc

@@ -206,7 +206,6 @@ void sf_worker::work_imp()
   bool     rx_signal_ok    = false;
   bool     tx_signal_ready = false;
   uint32_t nof_samples     = SRSLTE_SF_LEN_PRB(cell.nof_prb);
-  int32_t  next_offset     = 0;
 
   {
     std::lock_guard<std::mutex> lock(mutex);
@@ -231,9 +230,6 @@ void sf_worker::work_imp()
       }
     }
 
-    // Load TA
-    next_offset = phy->ta.get_pending_nsamples(nof_samples * 1000U);
-
     /***** Uplink Generation + Transmission *******/
 
     /* If TTI+4 is an uplink subframe (TODO: Support short PRACH and SRS in UpPts special subframes) */
@@ -250,12 +246,7 @@ void sf_worker::work_imp()
           tx_signal_ready |= cc_workers[carrier_idx]->work_ul(&uci_data);
 
           // Set signal pointer based on offset
-          cf_t* b = cc_workers[carrier_idx]->get_tx_buffer(0);
-          if (next_offset > 0) {
-            tx_signal_ptr.set(carrier_idx, 0, phy->args->nof_rx_ant, b);
-          } else {
-            tx_signal_ptr.set(carrier_idx, 0, phy->args->nof_rx_ant, &b[-next_offset]);
-          }
+          tx_signal_ptr.set((uint32_t)carrier_idx, 0, phy->args->nof_rx_ant, cc_workers[carrier_idx]->get_tx_buffer(0));
         }
       }
     }
@@ -263,13 +254,9 @@ void sf_worker::work_imp()
 
   // Set PRACH buffer signal pointer
   if (prach_ptr) {
-    srslte_timestamp_sub(&tx_time, 0, phy->ta.get_current_sec());
     tx_signal_ready = true;
     tx_signal_ptr.set(0, prach_ptr);
     prach_ptr = nullptr;
-  } else {
-    srslte_timestamp_sub(&tx_time, 0, phy->ta.get_previous_sec());
-    nof_samples += next_offset;
   }
 
   // Call worker_end to transmit the signal

srsue/src/phy/sync.cc

@@ -473,7 +473,7 @@ void sync::run_thread()
 
               metrics.sfo   = srslte_ue_sync_get_sfo(&ue_sync);
               metrics.cfo   = srslte_ue_sync_get_cfo(&ue_sync);
-              metrics.ta_us = worker_com->ta.get_current_usec();
+              metrics.ta_us = worker_com->ta.get_usec();
               for (uint32_t i = 0; i < worker_com->args->nof_carriers; i++) {
                 worker_com->set_sync_metrics(i, metrics);
               }
@@ -862,13 +862,6 @@ int sync::radio_recv_fnc(srslte::rf_buffer_t& data, uint32_t nsamples, srslte_ti
       }
     }
 
-    int offset = nsamples - current_sflen;
-    if (abs(offset) < 10 && offset != 0) {
-      worker_com->ta.set_pending_nsamples(offset);
-    } else if (nsamples < 10) {
-      worker_com->ta.set_pending_nsamples(nsamples);
-    }
-
     log_h->debug("SYNC:  received %d samples from radio\n", nsamples);
 
     return nsamples;