channel_simulator: synch eNBs in time and some bugs fixed

By default, eNB are now frame/subframe synchronized in time (that is they
all transmit the exact same frame and subframe at the same time).
Use -no-sync to disable synchronization.

Some bugs were fixed:
- memory initialized to 0
- ignore SIGPIPE that was delivered sometimes when an eNB disconnects
- set tx_sample_advance to 40, which is used in the usrp lib of openair
  (srsUE did not connect well with 0)

channel_simulator/channel_simulator.c

@@ -97,6 +97,7 @@ static int find_or_create_channel(channel_simulator *c, uint64_t freq,
   chan->sample_advance = sample_advance;
   if (posix_memalign((void **)&chan->data, 32, c->n_samples * 4) != 0)
     goto oom;
+  memset(chan->data, 0, c->n_samples * 4);
   chan->connection_count = 0;
 
   return i;
@@ -124,12 +125,14 @@ void channel_simulator_add_connection(channel_simulator *c,
   con->socket = socket;
   if (posix_memalign((void **)&con->iq_buffer, 32, c->n_samples * 4) != 0)
     goto oom;
+  memset(con->iq_buffer, 0, c->n_samples * 4);
   con->rx_frequency = rx_frequency;
   con->tx_frequency = tx_frequency;
   con->rx_channel_index = find_or_create_channel(c, rx_frequency,
                                                  rx_sample_advance);
   con->tx_channel_index = find_or_create_channel(c, tx_frequency,
                                                  tx_sample_advance);
+  con->running = 0;
 
   c->channels[con->rx_channel_index].connection_count++;
   c->channels[con->tx_channel_index].connection_count++;

channel_simulator/channel_simulator.h

@@ -20,6 +20,8 @@ typedef struct {
   int      tx_channel_index;
   /* gain to apply to rx and tx data */
   void     *gain;           /* actually __m256i * */
+  /* running: used to synchronize eNB in time */
+  int      running;
 } connection;
 
 typedef struct {

channel_simulator/main.c

@@ -2,15 +2,35 @@
 #include "connection_manager.h"
 
 #include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
 #include <unistd.h>
 #include <sys/socket.h>
+#include <signal.h>
 
-int main(void)
+void usage(void)
+{
+  printf("options:\n");
+  printf("    -no-sync\n");
+  printf("        do not synchronize eNBs in time\n");
+  exit(0);
+}
+
+int main(int n, char **v)
 {
   channel_simulator c;
   connection_manager cm;
   int i;
   int samplerate = 7680000;
+  int do_synchronize = 1;
+
+  for (i = 1; i < n; i++) {
+    if (!strcmp(v[i], "-h") || !strcmp(v[i], "--help")) usage();
+    if (!strcmp(v[i], "-no-sync")) { do_synchronize = 0; continue; }
+    usage();
+  }
+
+  signal(SIGPIPE, SIG_IGN);
 
   init_connection_manager(&cm, "0.0.0.0", 4024);
   init_channel_simulator(&c, samplerate, 512);
@@ -39,6 +59,11 @@ int main(void)
       connection *con = &c.connections[i];
       channel    *ch_rx  = &c.channels[con->rx_channel_index];
       channel    *ch_tx  = &c.channels[con->tx_channel_index];
+      if (do_synchronize && con->running == 0) {
+        if (c.timestamp % (samplerate/1000*1024*10))
+          continue;
+        con->running = 1;
+      }
       connection_send_rx(con, c.timestamp + ch_rx->sample_advance,
                          ch_rx->data, c.n_samples);
       connection_receive_tx(&c, con, c.timestamp + ch_tx->sample_advance

channel_simulator/usrp/main.c

@@ -128,7 +128,7 @@ int main(void)
   uint64_t sim_timestamp;
   uint64_t usrp_timestamp;
   int samples_per_subframe = 7680;
-  int tx_sample_advance = 0; //40;
+  int tx_sample_advance = 40;
   char *usrp_data;
 
   go_realtime();
@@ -145,6 +145,7 @@ int main(void)
     printf("ERROR: out of memory\n");
     exit(1);
   }
+  memset(usrp_data, 0, buf.n_samples * 4);
 
   send_to_channel_simulator(sock, usrp_data, buf.n_samples, sim_timestamp);
   sim_timestamp += buf.n_samples;