- Calculate PRACH buffers on the fly when required instead of pregenerating all of them.

srsue/hdr/phy/prach.h

@@ -22,6 +22,7 @@
 #ifndef SRSUE_PRACH_H
 #define SRSUE_PRACH_H
 
+#include <bitset>
 #include <string.h>
 
 #include "srslte/common/log.h"
@@ -57,6 +58,19 @@ public:
 
   phy_interface_mac_lte::prach_info_t get_info();
 
+private:
+  bool generate_buffer(uint32_t f_idx);
+
+  bool is_buffer_generated(uint32_t f_idx, uint32_t preamble_index) const
+  {
+    return buffer_bitmask.test(f_idx * 64 + preamble_index);
+  }
+
+  void set_buffer_as_generated(uint32_t f_idx, uint32_t preamble_index)
+  {
+    buffer_bitmask.set(f_idx * 64 + preamble_index);
+  }
+
 private:
   const static int MAX_LEN_SF = 3;
 
@@ -67,12 +81,14 @@ private:
   bool                 cell_initiated;
   uint32_t             len;
   cf_t*                buffer[12][64];
+  std::bitset<12 * 64> buffer_bitmask;
   srslte_prach_t       prach_obj;
   int                  transmitted_tti;
   srslte_cell_t        cell;
   cf_t*                signal_buffer;
   srslte_cfo_t         cfo_h;
   float                target_power_dbm;
+  srslte_prach_cfg_t   cfg = {};
 };
 
 } // namespace srsue

srsue/src/phy/prach.cc

@@ -104,6 +104,7 @@ bool prach::set_cell(srslte_cell_t cell_, srslte_prach_cfg_t prach_cfg)
     // TODO: Check if other PRACH parameters changed
     if (cell.id != cell_.id || !cell_initiated) {
       cell         = cell_;
+      cfg          = prach_cfg;
       preamble_idx = -1;
 
       if (6 + prach_cfg.freq_offset > cell.nof_prb) {
@@ -125,33 +126,7 @@ bool prach::set_cell(srslte_cell_t cell_, srslte_prach_cfg_t prach_cfg)
         return false;
       }
 
-      uint32_t nof_f_idx = 1;
+      buffer_bitmask.reset();
-      if (cell.frame_type == SRSLTE_TDD) {
-        nof_f_idx = srslte_prach_nof_f_idx_tdd(prach_cfg.config_idx, prach_cfg.tdd_config.sf_config);
-        // For format4, generate prach for even and odd position
-        if (prach_cfg.config_idx >= 48) {
-          nof_f_idx *= 2;
-        }
-      }
-
-      for (int i = 0; i < 64; i++) {
-        for (uint32_t f = 0; f < nof_f_idx; f++) {
-          uint32_t freq_offset = prach_cfg.freq_offset;
-          if (cell.frame_type == SRSLTE_TDD) {
-            freq_offset = srslte_prach_f_ra_tdd(prach_cfg.config_idx,
-                                                prach_cfg.tdd_config.sf_config,
-                                                (f / 6) * 10,
-                                                f % 6,
-                                                prach_cfg.freq_offset,
-                                                cell.nof_prb);
-          }
-          if (srslte_prach_gen(&prach_obj, i, freq_offset, buffer[f][i])) {
-            Error("Generating PRACH preamble %d\n", i);
-            return false;
-          }
-        }
-      }
-
       len             = prach_obj.N_seq + prach_obj.N_cp;
       transmitted_tti = -1;
       cell_initiated  = true;
@@ -163,6 +138,28 @@ bool prach::set_cell(srslte_cell_t cell_, srslte_prach_cfg_t prach_cfg)
   }
 }
 
+bool prach::generate_buffer(uint32_t f_idx)
+{
+  if (is_buffer_generated(f_idx, preamble_idx)) {
+    printf("generation was already done\n");
+    return true;
+  }
+
+  uint32_t freq_offset = cfg.freq_offset;
+  if (cell.frame_type == SRSLTE_TDD) {
+    freq_offset = srslte_prach_f_ra_tdd(
+        cfg.config_idx, cfg.tdd_config.sf_config, (f_idx / 6) * 10, f_idx % 6, cfg.freq_offset, cell.nof_prb);
+  }
+  if (srslte_prach_gen(&prach_obj, preamble_idx, freq_offset, buffer[f_idx][preamble_idx])) {
+    Error("Generating PRACH preamble %d\n", preamble_idx);
+    return false;
+  }
+
+  set_buffer_as_generated(f_idx, preamble_idx);
+
+  return true;
+}
+
 bool prach::prepare_to_send(uint32_t preamble_idx_, int allowed_subframe_, float target_power_dbm_)
 {
   if (cell_initiated && preamble_idx_ < 64) {
@@ -237,6 +234,15 @@ cf_t* prach::generate(float cfo, uint32_t* nof_sf, float* target_power)
       }
     }
 
+    if (!generate_buffer(f_idx)) {
+      return NULL;
+    }
+
+    if (!is_buffer_generated(f_idx, preamble_idx)) {
+      Error("PRACH Buffer not generated: f_idx=%d preamble_idx=%d\n", f_idx, preamble_idx);
+      return NULL;
+    }
+
     // Correct CFO before transmission
     srslte_cfo_correct(&cfo_h, buffer[f_idx][preamble_idx], signal_buffer, cfo / srslte_symbol_sz(cell.nof_prb));