making SFN dependent on GPS time (when available)

executables/nr-ru.c

@@ -604,6 +604,7 @@ void *emulatedRF_thread(void *param) {
 void rx_rf(RU_t *ru,int *frame,int *slot) {
   RU_proc_t *proc = &ru->proc;
   NR_DL_FRAME_PARMS *fp = ru->nr_frame_parms;
+  openair0_config_t *cfg   = &ru->openair0_cfg;
   void *rxp[ru->nb_rx];
   unsigned int rxs;
   int i;
@@ -653,7 +654,13 @@ void rx_rf(RU_t *ru,int *frame,int *slot) {
     }
   }
 
-  proc->frame_rx    = (proc->timestamp_rx / (fp->samples_per_subframe*10))&1023;
+  //compute system frame number (SFN) according to O-RAN-WG4-CUS.0-v02.00 (using alpha=beta=0)
+  // this assumes that the USRP has been synchronized to the GPS time
+  // OAI uses timestamps in sample time stored in int64_t, but it will fit in double precision for many years to come. 
+  double gps_sec = ((double) ts)/cfg->sample_rate; 
+  proc->frame_rx = ((int64_t) (gps_sec/0.01)) & 1023;   
+  
+  //proc->frame_rx    = (proc->timestamp_rx / (fp->samples_per_subframe*10))&1023;
   proc->tti_rx = fp->get_slot_from_timestamp(proc->timestamp_rx,fp);
   // synchronize first reception to frame 0 subframe 0
   LOG_D(PHY,"RU %d/%d TS %llu , frame %d, slot %d.%d / %d\n",

targets/ARCH/USRP/USERSPACE/LIB/usrp_lib.cpp

@@ -203,8 +203,8 @@ static int sync_to_gps(openair0_device *device) {
 
       //Set to GPS time
       uhd::time_spec_t gps_time = uhd::time_spec_t(time_t(s->usrp->get_mboard_sensor("gps_time", mboard).to_int()));
-      //s->usrp->set_time_next_pps(gps_time+1.0, mboard);
-      s->usrp->set_time_next_pps(uhd::time_spec_t(0.0));
+      s->usrp->set_time_next_pps(gps_time+1.0, mboard);
+      //s->usrp->set_time_next_pps(uhd::time_spec_t(0.0));
       //Wait for it to apply
       //The wait is 2 seconds because N-Series has a known issue where
       //the time at the last PPS does not properly update at the PPS edge
@@ -215,10 +215,10 @@ static int sync_to_gps(openair0_device *device) {
       uhd::time_spec_t time_last_pps = s->usrp->get_time_last_pps(mboard);
       std::cout << "USRP time: " << (boost::format("%0.9f") % time_last_pps.get_real_secs()) << std::endl;
       std::cout << "GPSDO time: " << (boost::format("%0.9f") % gps_time.get_real_secs()) << std::endl;
-      //if (gps_time.get_real_secs() == time_last_pps.get_real_secs())
-      //    std::cout << std::endl << "SUCCESS: USRP time synchronized to GPS time" << std::endl << std::endl;
-      //else
-      //    std::cerr << std::endl << "ERROR: Failed to synchronize USRP time to GPS time" << std::endl << std::endl;
+      if (gps_time.get_real_secs() == time_last_pps.get_real_secs())
+          std::cout << std::endl << "SUCCESS: USRP time synchronized to GPS time" << std::endl << std::endl;
+      else
+          std::cerr << std::endl << "ERROR: Failed to synchronize USRP time to GPS time" << std::endl << std::endl;
     }
 
     if (num_gps_locked == num_mboards and num_mboards > 1) {