diff --git a/common/utils/LOG/vcd_signal_dumper.c b/common/utils/LOG/vcd_signal_dumper.c
index 103cf1cd94..5ba54f1536 100644
--- a/common/utils/LOG/vcd_signal_dumper.c
+++ b/common/utils/LOG/vcd_signal_dumper.c
@@ -248,7 +248,8 @@ const char* eurecomVariablesNames[] = {
   "slot_number_TX1_gNB",
   "slot_number_RX0_gNB",
   "slot_number_RX1_gNB",
-  "ru_tx_ofdm_mask"
+  "ru_tx_ofdm_mask",
+  "usrp_send_return"
 };
 
 const char* eurecomFunctionsNames[] = {
@@ -282,6 +283,8 @@ const char* eurecomFunctionsNames[] = {
   "lock_mutex_ru",
   "lock_mutex_ru1",
   "lock_mutex_ru2",
+  /* uhd signals */
+  "trx_write_thread",
   /* simulation signals */
   "do_DL_sig",
   "do_UL_sig",
diff --git a/common/utils/LOG/vcd_signal_dumper.h b/common/utils/LOG/vcd_signal_dumper.h
index 9383b39b1e..d2efdda098 100644
--- a/common/utils/LOG/vcd_signal_dumper.h
+++ b/common/utils/LOG/vcd_signal_dumper.h
@@ -226,6 +226,7 @@ typedef enum {
   VCD_SIGNAL_DUMPER_VARIABLES_SLOT_NUMBER_RX0_GNB,
   VCD_SIGNAL_DUMPER_VARIABLES_SLOT_NUMBER_RX1_GNB,
   VCD_SIGNAL_DUMPER_VARIABLES_RU_TX_OFDM_MASK,
+  VCD_SIGNAL_DUMPER_VARIABLES_USRP_SEND_RETURN,
 
 
   VCD_SIGNAL_DUMPER_VARIABLES_END
@@ -262,6 +263,8 @@ typedef enum {
   VCD_SIGNAL_DUMPER_FUNCTIONS_LOCK_MUTEX_RU,
   VCD_SIGNAL_DUMPER_FUNCTIONS_LOCK_MUTEX_RU1,
   VCD_SIGNAL_DUMPER_FUNCTIONS_LOCK_MUTEX_RU2,
+  /* uhd signals */
+  VCD_SIGNAL_DUMPER_FUNCTIONS_TRX_WRITE_THREAD,
   /* SIMULATION signals */ 
   VCD_SIGNAL_DUMPER_FUNCTIONS_SIM_DO_DL_SIGNAL,
   VCD_SIGNAL_DUMPER_FUNCTIONS_SIM_DO_UL_SIGNAL,
diff --git a/common/utils/T/T_defs.h b/common/utils/T/T_defs.h
index b59fae2a0c..ad21819c7d 100644
--- a/common/utils/T/T_defs.h
+++ b/common/utils/T/T_defs.h
@@ -73,10 +73,10 @@ typedef struct {
 } T_cache_t;
 
 /* number of VCD functions (to be kept up to date! see in T_messages.txt) */
-#define VCD_NUM_FUNCTIONS (247)
+#define VCD_NUM_FUNCTIONS (248)
 
 /* number of VCD variables (to be kept up to date! see in T_messages.txt) */
-#define VCD_NUM_VARIABLES (186)
+#define VCD_NUM_VARIABLES (187)
 
 /* first VCD function (to be kept up to date! see in T_messages.txt) */
 #define VCD_FIRST_FUNCTION    ((uintptr_t)T_VCD_FUNCTION_RT_SLEEP)
diff --git a/common/utils/T/T_messages.txt b/common/utils/T/T_messages.txt
index 387257d145..5374c09712 100644
--- a/common/utils/T/T_messages.txt
+++ b/common/utils/T/T_messages.txt
@@ -2138,6 +2138,11 @@ ID = VCD_VARIABLE_RU_TX_OFDM_MASK
     GROUP = ALL:VCD:ENB:VCD_VARIABLE
     FORMAT = ulong,value
     VCD_NAME = ru_tx_ofdm_mask
+ID = VCD_VARIABLE_USRP_SEND_RETURN
+    DESC = VCD variable USRP_SEND_RETURN
+    GROUP = ALL:VCD:ENB:VCD_VARIABLE
+    FORMAT = ulong,value
+    VCD_NAME = usrp_send_return
 
 #functions
 
@@ -2286,6 +2291,11 @@ ID = VCD_FUNCTION_LOCK_MUTEX_RU2
     GROUP = ALL:VCD:UE:VCD_FUNCTION
     FORMAT = int,value
     VCD_NAME = lock_mutex_ru2
+ID = VCD_FUNCTION_TRX_WRITE_THREAD
+    DESC = VCD function TRX_WRITE_THREAD
+    GROUP = ALL:VCD:ENB:VCD_FUNCTION
+    FORMAT = int,value
+    VCD_NAME = trx_write_thread
 ID = VCD_FUNCTION_SIM_DO_DL_SIGNAL
     DESC = VCD function SIM_DO_DL_SIGNAL
     GROUP = ALL:VCD:ENB:VCD_FUNCTION
diff --git a/executables/nr-ru.c b/executables/nr-ru.c
index f7d63a94ad..2355c78534 100644
--- a/executables/nr-ru.c
+++ b/executables/nr-ru.c
@@ -735,6 +735,8 @@ void tx_rf(RU_t *ru,int frame,int slot, uint64_t timestamp) {
     else
       flags=4;
 
+    VCD_SIGNAL_DUMPER_DUMP_VARIABLE_BY_NAME( VCD_SIGNAL_DUMPER_VARIABLES_TRX_WRITE_FLAGS, flags );
+
     /*
         if (SF_type == SF_S) {
           siglen = fp->dl_symbols_in_S_subframe*(fp->ofdm_symbol_size+fp->nb_prefix_samples0);
diff --git a/targets/ARCH/USRP/USERSPACE/LIB/usrp_lib.cpp b/targets/ARCH/USRP/USERSPACE/LIB/usrp_lib.cpp
index 78f76b6a21..d48755266c 100644
--- a/targets/ARCH/USRP/USERSPACE/LIB/usrp_lib.cpp
+++ b/targets/ARCH/USRP/USERSPACE/LIB/usrp_lib.cpp
@@ -49,6 +49,8 @@
 #include "common_lib.h"
 #include "assertions.h"
 
+#include "common/utils/LOG/vcd_signal_dumper.h"
+
 #include <sys/resource.h>
 
 #include "usrp_lib.h"
@@ -443,7 +445,7 @@ static int trx_usrp_write(openair0_device *device, openair0_timestamp timestamp,
   pthread_mutex_lock(&write_thread->mutex_write);
 
   if(write_thread->count_write >= MAX_WRITE_THREAD_PACKAGE){
-    LOG_W(HW,"Buffer overflow, resetting write package\n");
+    LOG_W("Buffer overflow, count_write = %d, start = %d end = %d, resetting write package\n", write_thread->count_write, write_thread->start, write_thread->end);
     write_thread->end = write_thread->start;
     write_thread->count_write = 0;
   }
@@ -495,6 +497,7 @@ void *trx_usrp_write_thread(void * arg){
     while (write_thread->count_write == 0) {
       pthread_cond_wait(&write_thread->cond_write,&write_thread->mutex_write); // this unlocks mutex_rxtx while waiting and then locks it again
     }
+    VCD_SIGNAL_DUMPER_DUMP_FUNCTION_BY_NAME( VCD_SIGNAL_DUMPER_FUNCTIONS_TRX_WRITE_THREAD, 1 );
     s = (usrp_state_t *)device->priv;
     start = write_thread->start;
     timestamp    = write_package[start].timestamp;
@@ -506,6 +509,9 @@ void *trx_usrp_write_thread(void * arg){
     write_thread->start = (write_thread->start + 1)% MAX_WRITE_THREAD_PACKAGE;
     write_thread->count_write--;
     pthread_mutex_unlock(&write_thread->mutex_write);
+    if(write_thread->count_write != 0){
+      LOG_W(HW,"count write = %d, start = %d, end = %d\n", write_thread->count_write, write_thread->start, write_thread->end);
+    }
 
     #if defined(__x86_64) || defined(__i386__)
       #ifdef __AVX2__
@@ -552,6 +558,8 @@ void *trx_usrp_write_thread(void * arg){
       ret = (int)s->tx_stream->send(buff_ptrs, nsamps, s->tx_md);
     } else ret = (int)s->tx_stream->send(&(((int16_t *)buff_tx[0])[0]), nsamps, s->tx_md);
     if (ret != nsamps) LOG_E(HW,"[xmit] tx samples %d != %d\n",ret,nsamps);
+    VCD_SIGNAL_DUMPER_DUMP_VARIABLE_BY_NAME( VCD_SIGNAL_DUMPER_VARIABLES_USRP_SEND_RETURN, ret );
+    VCD_SIGNAL_DUMPER_DUMP_FUNCTION_BY_NAME( VCD_SIGNAL_DUMPER_FUNCTIONS_TRX_WRITE_THREAD, 0 );
 
     if(0) break;
   }
@@ -567,7 +575,7 @@ int trx_write_init(openair0_device *device){
 
   write_thread->start              = 0;
   write_thread->end                = 0;
-  write_thread->count_write = 0;
+  write_thread->count_write        = 0;
   printf("end of tx write thread\n");
 
   pthread_create(&write_thread->pthread_write,NULL,trx_usrp_write_thread,(void *)device);
diff --git a/targets/RT/USER/gNB_usrp.gtkw b/targets/RT/USER/gNB_usrp.gtkw
index e6726e7d9f..6ece894bb6 100644
--- a/targets/RT/USER/gNB_usrp.gtkw
+++ b/targets/RT/USER/gNB_usrp.gtkw
@@ -1,21 +1,25 @@
 [*]
 [*] GTKWave Analyzer v3.3.61 (w)1999-2014 BSI
-[*] Tue Dec 17 15:31:51 2019
+[*] Wed Mar  4 14:05:43 2020
 [*]
-[dumpfile] "/tmp/gNB.vcd"
-[dumpfile_mtime] "Tue Dec 17 15:25:49 2019"
-[dumpfile_size] 6343431
+[dumpfile] "/tmp/gNB_trx_thread.vcd"
+[dumpfile_mtime] "Wed Mar  4 14:05:10 2020"
+[dumpfile_size] 10750468
 [savefile] "/home/wangts/openairinterface5g/targets/RT/USER/gNB_usrp.gtkw"
-[timestart] 1517712000
-[size] 1920 1018
-[pos] -9 -33
-*-19.276148 1518358451 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
+[timestart] 31148700000
+[size] 1916 1002
+[pos] -1 -25
+*-23.852516 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
 [sst_width] 386
 [signals_width] 344
 [sst_expanded] 1
-[sst_vpaned_height] 267
+[sst_vpaned_height] 262
 @28
 functions.trx_read
+functions.trx_write_thread
+@25
+variables.trx_write_flags[63:0]
+@28
 functions.trx_write
 @420
 variables.frame_number_TX0_UE[63:0]