diff --git a/openair1/SIMULATION/NR_PHY/dlsim.c b/openair1/SIMULATION/NR_PHY/dlsim.c
index 1f597a3c0b..885684fe6e 100644
--- a/openair1/SIMULATION/NR_PHY/dlsim.c
+++ b/openair1/SIMULATION/NR_PHY/dlsim.c
@@ -537,8 +537,7 @@ int main(int argc, char **argv)
       break;
 
     case 'Y':
-      run_initial_sync=1;
-      //target_error_rate=0.1;
+      run_initial_sync = 1;
       slot = 0;
       break;
 
@@ -552,6 +551,7 @@ int main(int argc, char **argv)
       break;
 
     case 'H':
+      AssertFatal(run_initial_sync == 0, "Cannot use Y and H options at the same time\n");
       slot = atoi(optarg);
       break;
 
@@ -653,6 +653,11 @@ int main(int argc, char **argv)
   fill_scc_sim(scc, &ssb_bitmap, N_RB_DL, N_RB_DL, mu, mu);
   fix_scc(scc, ssb_bitmap);
 
+  frame_structure_t frame_structure = {0};
+  frame_type_t frame_type = TDD;
+  config_frame_structure(mu, scc, get_tdd_period_idx(scc->tdd_UL_DL_ConfigurationCommon), frame_type, &frame_structure);
+  AssertFatal(is_dl_slot(slot, &frame_structure), "The slot selected is not DL. Can't run DLSIM\n");
+
   // TODO do a UECAP for phy-sim
   nr_pdsch_AntennaPorts_t pdsch_AntennaPorts = {0};
   pdsch_AntennaPorts.N1 = n_tx > 1 ? n_tx >> 1 : 1;
diff --git a/openair1/SIMULATION/NR_PHY/ulsim.c b/openair1/SIMULATION/NR_PHY/ulsim.c
index 301beb19f5..5688253b8d 100644
--- a/openair1/SIMULATION/NR_PHY/ulsim.c
+++ b/openair1/SIMULATION/NR_PHY/ulsim.c
@@ -626,6 +626,11 @@ int main(int argc, char *argv[])
   fill_scc_sim(scc, &ssb_bitmap, N_RB_DL, N_RB_DL, mu, mu);
   fix_scc(scc,ssb_bitmap);
 
+  frame_structure_t frame_structure = {0};
+  frame_type_t frame_type = TDD;
+  config_frame_structure(mu, scc, get_tdd_period_idx(scc->tdd_UL_DL_ConfigurationCommon), frame_type, &frame_structure);
+  AssertFatal(is_ul_slot(slot, &frame_structure), "The slot selected is not UL. Can't run ULSIM\n");
+
   // TODO do a UECAP for phy-sim
   const nr_mac_config_t conf = {.pdsch_AntennaPorts = {.N1 = 1, .N2 = 1, .XP = 1},
                                 .pusch_AntennaPorts = n_rx,
diff --git a/openair2/LAYER2/NR_MAC_gNB/config.c b/openair2/LAYER2/NR_MAC_gNB/config.c
index fda1dc6c11..415cfc79e3 100644
--- a/openair2/LAYER2/NR_MAC_gNB/config.c
+++ b/openair2/LAYER2/NR_MAC_gNB/config.c
@@ -500,34 +500,28 @@ int get_ul_slot_offset(const frame_structure_t *fs, int idx, bool count_mixed)
  *
  * @param mu numerology
  * @param scc pointer to scc
- * @param cfg pointer to NFAPI config request
+ * @param tdd_period TDD period
+ * @param frame_type type of frame structure (FDD or TDD)
  * @param fs  pointer to the frame structure to update
- *
- * @return Number of periods in frame
  */
-static int config_frame_structure(int mu,
-                                  NR_ServingCellConfigCommon_t *scc,
-                                  nfapi_nr_config_request_scf_t *cfg,
-                                  frame_structure_t *fs)
+void config_frame_structure(int mu,
+                            NR_ServingCellConfigCommon_t *scc,
+                            uint8_t tdd_period,
+                            uint8_t frame_type,
+                            frame_structure_t *fs)
 {
   fs->numb_slots_frame = nr_slots_per_frame[mu];
-  if (cfg->cell_config.frame_duplex_type.value == TDD) {
-    cfg->tdd_table.tdd_period.tl.tag = NFAPI_NR_CONFIG_TDD_PERIOD_TAG;
-    cfg->num_tlv++;
-    cfg->tdd_table.tdd_period.value = get_tdd_period_idx(scc->tdd_UL_DL_ConfigurationCommon);
-    LOG_D(NR_MAC, "Setting TDD configuration period to %d\n", cfg->tdd_table.tdd_period.value);
-    fs->numb_period_frame = get_nb_periods_per_frame(cfg->tdd_table.tdd_period.value);
+  if (frame_type == TDD) {
+    fs->numb_period_frame = get_nb_periods_per_frame(tdd_period);
     fs->numb_slots_period = fs->numb_slots_frame / fs->numb_period_frame;
     fs->is_tdd = true;
     config_tdd_patterns(scc->tdd_UL_DL_ConfigurationCommon, fs);
-    set_tdd_config_nr(cfg, fs);
   } else { // FDD
     fs->is_tdd = false;
     fs->numb_period_frame = 1;
     fs->numb_slots_period = nr_slots_per_frame[mu];
   }
   AssertFatal(fs->numb_period_frame > 0, "Frame configuration cannot be configured!\n");
-  return fs->numb_period_frame;
 }
 
 static void config_common(gNB_MAC_INST *nrmac,
@@ -819,7 +813,16 @@ static void config_common(gNB_MAC_INST *nrmac,
 
   // Frame structure configuration
   uint8_t mu = frequencyInfoUL->scs_SpecificCarrierList.list.array[0]->subcarrierSpacing;
-  config_frame_structure(mu, scc, cfg, &nrmac->frame_structure);
+  if (cfg->cell_config.frame_duplex_type.value == TDD) {
+    cfg->tdd_table.tdd_period.tl.tag = NFAPI_NR_CONFIG_TDD_PERIOD_TAG;
+    cfg->num_tlv++;
+    cfg->tdd_table.tdd_period.value = get_tdd_period_idx(scc->tdd_UL_DL_ConfigurationCommon);
+    LOG_D(NR_MAC, "Setting TDD configuration period to %d\n", cfg->tdd_table.tdd_period.value);
+  }
+  frame_structure_t *fs = &nrmac->frame_structure;
+  config_frame_structure(mu, scc, cfg->tdd_table.tdd_period.value, cfg->cell_config.frame_duplex_type.value, fs);
+  if (cfg->cell_config.frame_duplex_type.value == TDD)
+    set_tdd_config_nr(cfg, fs);
 
   int nb_tx = config->nb_bfw[0]; // number of tx antennas
   int nb_beams = config->nb_bfw[1]; // number of beams
diff --git a/openair2/LAYER2/NR_MAC_gNB/mac_proto.h b/openair2/LAYER2/NR_MAC_gNB/mac_proto.h
index 4cd5563200..9be55c8dee 100644
--- a/openair2/LAYER2/NR_MAC_gNB/mac_proto.h
+++ b/openair2/LAYER2/NR_MAC_gNB/mac_proto.h
@@ -39,6 +39,11 @@ void set_cset_offset(uint16_t);
 void get_K1_K2(int N1, int N2, int *K1, int *K2, int layers);
 int get_NTN_Koffset(const NR_ServingCellConfigCommon_t *scc);
 
+void config_frame_structure(int mu,
+                            NR_ServingCellConfigCommon_t *scc,
+                            uint8_t tdd_period,
+                            uint8_t frame_type,
+                            frame_structure_t *fs);
 int get_first_ul_slot(const frame_structure_t *fs, bool mixed);
 int get_ul_slots_per_period(const frame_structure_t *fs);
 int get_ul_slots_per_frame(const frame_structure_t *fs);