diff --git a/executables/nr-ru.c b/executables/nr-ru.c
index 46f2ff7b2e..fc34e68bae 100644
--- a/executables/nr-ru.c
+++ b/executables/nr-ru.c
@@ -623,6 +623,7 @@ void rx_rf(RU_t *ru,int *frame,int *slot) {
   unsigned int rxs;
   int i;
   uint32_t samples_per_slot = fp->get_samples_per_slot(*slot,fp);
+  uint32_t samples_per_slot_prev ;
   openair0_timestamp ts,old_ts;
   AssertFatal(*slot<fp->slots_per_frame && *slot>=0, "slot %d is illegal (%d)\n",*slot,fp->slots_per_frame);
 
@@ -658,16 +659,16 @@ void rx_rf(RU_t *ru,int *frame,int *slot) {
     ru->ts_offset = proc->timestamp_rx;
     proc->timestamp_rx = 0;
   } else {
-    if (proc->timestamp_rx - old_ts != fp->get_samples_per_slot((*slot-1)%fp->slots_per_frame,fp)) {
-      LOG_D(PHY,"rx_rf: rfdevice timing drift of %"PRId64" samples (ts_off %"PRId64")\n",proc->timestamp_rx - old_ts - samples_per_slot,ru->ts_offset);
-      ru->ts_offset += (proc->timestamp_rx - old_ts - samples_per_slot);
+    samples_per_slot_prev = fp->get_samples_per_slot((*slot-1)%fp->slots_per_frame,fp);
+    if (proc->timestamp_rx - old_ts != samples_per_slot_prev) {
+      LOG_D(PHY,"rx_rf: rfdevice timing drift of %"PRId64" samples (ts_off %"PRId64")\n",proc->timestamp_rx - old_ts - samples_per_slot_prev,ru->ts_offset);
+      ru->ts_offset += (proc->timestamp_rx - old_ts - samples_per_slot_prev);
       proc->timestamp_rx = ts-ru->ts_offset;
     }
   }
 
   proc->frame_rx    = (proc->timestamp_rx / (fp->samples_per_subframe*10))&1023;
-  uint32_t idx_sf = proc->timestamp_rx / fp->samples_per_subframe;
-  proc->tti_rx = (idx_sf * fp->slots_per_subframe + (int)round((float)(proc->timestamp_rx % fp->samples_per_subframe) / fp->samples_per_slot0))%(fp->slots_per_frame);
+  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 (off %d), frame %d, slot %d.%d / %d\n",
         ru->idx,
@@ -688,7 +689,7 @@ void rx_rf(RU_t *ru,int *frame,int *slot) {
     }
 
     if (proc->frame_rx != *frame) {
-      LOG_E(PHY,"Received Timestamp (%llu) doesn't correspond to the time we think it is (proc->frame_rx %d frame %d)\n",(long long unsigned int)proc->timestamp_rx,proc->frame_rx,*frame);
+      LOG_E(PHY,"Received Timestamp (%llu) doesn't correspond to the time we think it is (proc->frame_rx %d frame %d, proc->tti_rx %d, slot %d)\n",(long long unsigned int)proc->timestamp_rx,proc->frame_rx,*frame,proc->tti_rx,*slot);
       exit_fun("Exiting");
     }
   } else {
diff --git a/openair1/PHY/INIT/nr_parms.c b/openair1/PHY/INIT/nr_parms.c
index 6045930b17..e2d39bc89f 100644
--- a/openair1/PHY/INIT/nr_parms.c
+++ b/openair1/PHY/INIT/nr_parms.c
@@ -233,6 +233,20 @@ uint32_t get_samples_per_slot(int slot, NR_DL_FRAME_PARMS* fp)
   return samp_count;
 }
 
+
+uint32_t get_slot_from_timestamp(openair0_timestamp timestamp_rx, NR_DL_FRAME_PARMS* fp)
+{
+   uint32_t slot_idx = 0;
+   int samples_till_the_slot = 0;
+   timestamp_rx = timestamp_rx%fp->samples_per_frame;
+
+    while (timestamp_rx > samples_till_the_slot) {
+        samples_till_the_slot += fp->get_samples_per_slot(slot_idx,fp);
+        slot_idx++;
+     }
+   return slot_idx; 
+}
+
 uint32_t get_samples_slot_timestamp(int slot, NR_DL_FRAME_PARMS* fp, uint8_t sl_ahead)
 {
   uint32_t samp_count = 0;
@@ -289,6 +303,7 @@ int nr_init_frame_parms(nfapi_nr_config_request_scf_t* cfg,
                              (fp->nb_prefix_samples + fp->ofdm_symbol_size) * (fp->symbols_per_slot * fp->slots_per_subframe - 2); 
   fp->get_samples_per_slot = &get_samples_per_slot;
   fp->get_samples_slot_timestamp = &get_samples_slot_timestamp;
+  fp->get_slot_from_timestamp = &get_slot_from_timestamp;
   fp->samples_per_frame = 10 * fp->samples_per_subframe;
   fp->freq_range = (fp->dl_CarrierFreq < 6e9)? nr_FR1 : nr_FR2;
 
diff --git a/openair1/PHY/NR_TRANSPORT/pucch_rx.c b/openair1/PHY/NR_TRANSPORT/pucch_rx.c
index 71132b64c5..d68a64ec04 100644
--- a/openair1/PHY/NR_TRANSPORT/pucch_rx.c
+++ b/openair1/PHY/NR_TRANSPORT/pucch_rx.c
@@ -414,7 +414,7 @@ void nr_decode_pucch0(PHY_VARS_gNB *gNB,
     uci_pdu->harq->harq_confidence_level = (no_conf) ? 1 : 0;
     uci_pdu->harq->harq_list = (nfapi_nr_harq_t*)malloc(1);
     uci_pdu->harq->harq_list[0].harq_value = index&0x01;
-    LOG_I(PHY, "HARQ value %d with confidence level (0 is good, 1 is bad) %d\n",
+    LOG_D(PHY, "HARQ value %d with confidence level (0 is good, 1 is bad) %d\n",
           uci_pdu->harq->harq_list[0].harq_value,uci_pdu->harq->harq_confidence_level);
     if (pucch_pdu->sr_flag == 1) {
       uci_pdu->sr = calloc(1,sizeof(*uci_pdu->sr));
@@ -429,7 +429,7 @@ void nr_decode_pucch0(PHY_VARS_gNB *gNB,
     uci_pdu->harq->harq_list = (nfapi_nr_harq_t*)malloc(2);
     uci_pdu->harq->harq_list[1].harq_value = index&0x01;
     uci_pdu->harq->harq_list[0].harq_value = (index>>1)&0x01;
-    LOG_I(PHY, "HARQ values %d and %d with confidence level (0 is good, 1 is bad) %d\n",
+    LOG_D(PHY, "HARQ values %d and %d with confidence level (0 is good, 1 is bad) %d\n",
           uci_pdu->harq->harq_list[1].harq_value,uci_pdu->harq->harq_list[0].harq_value,uci_pdu->harq->harq_confidence_level);
     if (pucch_pdu->sr_flag == 1) {
       uci_pdu->sr = calloc(1,sizeof(*uci_pdu->sr));
diff --git a/openair1/PHY/defs_nr_common.h b/openair1/PHY/defs_nr_common.h
index a21af3fa03..bdcf38752c 100644
--- a/openair1/PHY/defs_nr_common.h
+++ b/openair1/PHY/defs_nr_common.h
@@ -233,6 +233,7 @@ typedef struct {
 typedef struct NR_DL_FRAME_PARMS NR_DL_FRAME_PARMS;
 
 typedef uint32_t (*get_samples_per_slot_t)(int slot, NR_DL_FRAME_PARMS* fp);
+typedef uint32_t (*get_slot_from_timestamp_t)(openair0_timestamp timestamp_rx, NR_DL_FRAME_PARMS* fp);
 
 typedef uint32_t (*get_samples_slot_timestamp_t)(int slot, NR_DL_FRAME_PARMS* fp, uint8_t sl_ahead);
 
@@ -289,6 +290,8 @@ struct NR_DL_FRAME_PARMS {
   uint32_t samples_per_subframe;
   /// Number of samples in current slot
   get_samples_per_slot_t get_samples_per_slot;
+  /// slot calculation from timestamp
+  get_slot_from_timestamp_t get_slot_from_timestamp;
   /// Number of samples before slot
   get_samples_slot_timestamp_t get_samples_slot_timestamp;
   /// Number of samples in 0th and center slot of a subframe
diff --git a/targets/ARCH/USRP/USERSPACE/LIB/usrp_lib.cpp b/targets/ARCH/USRP/USERSPACE/LIB/usrp_lib.cpp
index b43c2769eb..dd29d01fae 100644
--- a/targets/ARCH/USRP/USERSPACE/LIB/usrp_lib.cpp
+++ b/targets/ARCH/USRP/USERSPACE/LIB/usrp_lib.cpp
@@ -693,10 +693,10 @@ static int trx_usrp_read(openair0_device *device, openair0_timestamp *ptimestamp
   *ptimestamp = s->rx_timestamp;
 
   // push GPIO bits 7-9 from flags_msb
-   s->usrp->set_command_time(uhd::time_spec_t::from_ticks((s->rx_timestamp+(2*nsamps)),s->sample_rate));
+   /*s->usrp->set_command_time(uhd::time_spec_t::from_ticks((s->rx_timestamp+(2*nsamps)),s->sample_rate));
    s->usrp->set_gpio_attr("FP0", "OUT", gpio789<<7, 0x380);
    s->usrp->clear_command_time();
-   gpio789 = (gpio789+1)&7;
+   gpio789 = (gpio789+1)&7;*/
 
   if (device->recplay_state != NULL) { // record mode
     // Copy subframes to memory (later dump on a file)
diff --git a/targets/PROJECTS/GENERIC-LTE-EPC/CONF/gnb.band257.tm1.32PRB.usrpx300.conf b/targets/PROJECTS/GENERIC-LTE-EPC/CONF/gnb.band257.tm1.32PRB.usrpx300.conf
index fdaa965ae9..ea38aba1b2 100644
--- a/targets/PROJECTS/GENERIC-LTE-EPC/CONF/gnb.band257.tm1.32PRB.usrpx300.conf
+++ b/targets/PROJECTS/GENERIC-LTE-EPC/CONF/gnb.band257.tm1.32PRB.usrpx300.conf
@@ -239,6 +239,8 @@ RUs = (
          eNB_instances  = [0];
 	 sdr_addrs = "addr=192.168.10.2,second_addr=192.168.20.2";
          if_freq = 5300000000L;
+         #time_source = "external";
+         clock_source = "external";
     }
 );