From ab7515e2804bc416df6f16e285590eb90628bf6a Mon Sep 17 00:00:00 2001
From: Cedric Roux <cedric.roux@eurecom.fr>
Date: Fri, 14 Sep 2018 14:58:15 +0200
Subject: [PATCH 1/2] basic simulator: handle discontinuities in output

In TDD mode the eNB does not output data all the time,
only in downlink and special subframes.

The basic simulator needs a continuous stream of samples.

So let's fill the blank with silence.
---
 targets/ARCH/tcp_bridge/tcp_bridge_oai.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/targets/ARCH/tcp_bridge/tcp_bridge_oai.c b/targets/ARCH/tcp_bridge/tcp_bridge_oai.c
index 4d7d49d9c7..32fddb9c2d 100644
--- a/targets/ARCH/tcp_bridge/tcp_bridge_oai.c
+++ b/targets/ARCH/tcp_bridge/tcp_bridge_oai.c
@@ -44,6 +44,7 @@ typedef struct {
   int sock;
   int samples_per_subframe;
   uint64_t timestamp;
+  uint64_t next_tx_timestamp;
   int is_enb;
 } tcp_bridge_state_t;
 
@@ -141,11 +142,27 @@ int tcp_bridge_write(openair0_device *device, openair0_timestamp timestamp, void
 {
   if (cc != 1) { printf("tcp_bridge: only 1 antenna supported\n"); exit(1); }
   tcp_bridge_state_t *t = device->priv;
+  /* deal with discontinuities in output (think: eNB in TDD mode) */
+  if (t->next_tx_timestamp && timestamp != t->next_tx_timestamp) {
+    uint32_t b[4096];
+    uint64_t to_send = timestamp - t->next_tx_timestamp;
+    memset(b, 0, 4096 * sizeof(uint32_t));
+    while (to_send) {
+      int len = to_send > 4096 ? 4096 : to_send;
+      int n = fullwrite(t->sock, b, len * 4);
+      if (n != len * 4) {
+        printf("tcp_bridge: write error ret %d error %s\n", n, strerror(errno));
+        abort();
+      }
+      to_send -= len;
+    }
+  }
   int n = fullwrite(t->sock, buff[0], nsamps * 4);
   if (n != nsamps * 4) {
     printf("tcp_bridge: write error ret %d (wanted %d) error %s\n", n, nsamps*4, strerror(errno));
     abort();
   }
+  t->next_tx_timestamp = timestamp + nsamps;
   return nsamps;
 }
 

From 824f62d8bfa8949dfa550245bdb3e26be36ddcd5 Mon Sep 17 00:00:00 2001
From: Cedric Roux <cedric.roux@eurecom.fr>
Date: Fri, 14 Sep 2018 15:01:55 +0200
Subject: [PATCH 2/2] basic simulator: support TDD mode

For whatever reason we need N_TA_offset to be 0 for the basic simulator
to function properly.

This is more a hack than a proper solution. More analysis is needed
to understand what happens and what should be really done.
---
 openair1/PHY/INIT/lte_param_init.c | 7 +++++++
 targets/RT/USER/lte-ru.c           | 6 ++++++
 targets/RT/USER/lte-ue.c           | 7 +++++++
 3 files changed, 20 insertions(+)

diff --git a/openair1/PHY/INIT/lte_param_init.c b/openair1/PHY/INIT/lte_param_init.c
index 0830058a8f..dd8c2e54db 100644
--- a/openair1/PHY/INIT/lte_param_init.c
+++ b/openair1/PHY/INIT/lte_param_init.c
@@ -169,6 +169,13 @@ void lte_param_init(PHY_VARS_eNB **eNBp,
   }
   else ru->N_TA_offset=0;
 
+#if BASIC_SIMULATOR
+  /* this is required for the basic simulator in TDD mode
+   * TODO: find a proper cleaner solution
+   */
+  UE->N_TA_offset = 0;
+#endif
+
   printf("Done lte_param_init\n");
 
 
diff --git a/targets/RT/USER/lte-ru.c b/targets/RT/USER/lte-ru.c
index d20b614ad7..1ff97386ac 100644
--- a/targets/RT/USER/lte-ru.c
+++ b/targets/RT/USER/lte-ru.c
@@ -1456,6 +1456,12 @@ int setup_RU_buffers(RU_t *ru) {
     if      (frame_parms->N_RB_DL == 100) ru->N_TA_offset = 624;
     else if (frame_parms->N_RB_DL == 50)  ru->N_TA_offset = 624/2;
     else if (frame_parms->N_RB_DL == 25)  ru->N_TA_offset = 624/4;
+#if BASIC_SIMULATOR
+    /* this is required for the basic simulator in TDD mode
+     * TODO: find a proper cleaner solution
+     */
+    ru->N_TA_offset = 0;
+#endif
   } 
   if (ru->openair0_cfg.mmapped_dma == 1) {
     // replace RX signal buffers with mmaped HW versions
diff --git a/targets/RT/USER/lte-ue.c b/targets/RT/USER/lte-ue.c
index 66107d79a4..c49a54b98a 100644
--- a/targets/RT/USER/lte-ue.c
+++ b/targets/RT/USER/lte-ue.c
@@ -333,6 +333,13 @@ void init_UE(int nb_inst,int eMBMS_active, int uecap_xer_in, int timing_correcti
     }
     else UE->N_TA_offset = 0;
 
+#if BASIC_SIMULATOR
+    /* this is required for the basic simulator in TDD mode
+     * TODO: find a proper cleaner solution
+     */
+    UE->N_TA_offset = 0;
+#endif
+
     if (simL1flag == 1) init_ue_devices(UE);
     LOG_I(PHY,"Intializing UE Threads for instance %d (%p,%p)...\n",inst,PHY_vars_UE_g[inst],PHY_vars_UE_g[inst][0]);
     init_UE_threads(inst);