srsue: limit sync queue length to 1 for ZMQ radio

apply same change that we've done on the eNB also on the UE
to avoid the PHY processing TTIs faster than the stack.

Without that, we see lots of those in the logs:

...
08:39:17.580325 [STCK] [W] Detected slow task processing (sync_queue_len=7).
...

srsue/hdr/stack/ue_stack_base.h

@@ -68,6 +68,7 @@ typedef struct {
   std::string      ue_category_str;
   nas_args_t       nas;
   gw_args_t        gw;
+  uint32_t         sync_queue_size; // Max allowed difference between PHY and Stack clocks (in TTI)
   bool             have_tti_time_stats;
 } stack_args_t;
 

srsue/src/main.cc

@@ -558,6 +558,14 @@ static int parse_args(all_args_t* args, int argc, char* argv[])
     }
   }
 
+  // Set sync queue capacity to 1 for ZMQ
+  if (args->rf.device_name == "zmq") {
+    args->stack.sync_queue_size = 1;
+  } else {
+    // use default size
+    args->stack.sync_queue_size = MULTIQUEUE_DEFAULT_CAPACITY;
+  }
+
   return SRSLTE_SUCCESS;
 }
 

srsue/src/stack/ue_stack_lte.cc

@@ -49,10 +49,10 @@ ue_stack_lte::ue_stack_lte() :
   tti_tprof("tti_tprof", "STCK", TTI_STAT_PERIOD)
 {
   ue_queue_id         = pending_tasks.add_queue();
-  sync_queue_id       = pending_tasks.add_queue();
   gw_queue_id         = pending_tasks.add_queue();
   stack_queue_id      = pending_tasks.add_queue();
   background_queue_id = pending_tasks.add_queue();
+  // sync_queue is added in init()
 
   background_tasks.start();
 }
@@ -125,6 +125,9 @@ int ue_stack_lte::init(const stack_args_t& args_, srslte::logger* logger_)
     return SRSLTE_ERROR;
   }
 
+  // add sync queue
+  sync_queue_id = pending_tasks.add_queue(args.sync_queue_size);
+
   mac.init(phy, &rlc, &rrc, this);
   rlc.init(&pdcp, &rrc, &timers, 0 /* RB_ID_SRB0 */);
   pdcp.init(&rlc, &rrc, gw);

srsue/test/ttcn3/src/ttcn3_dut.cc

@@ -106,6 +106,8 @@ all_args_t parse_args(ttcn3_dut_args_t* args, int argc, char* argv[])
   all_args.stack.log.gw_hex_limit   = args->log_hex_level;
   all_args.stack.log.usim_hex_limit = args->log_hex_level;
 
+  all_args.stack.sync_queue_size = 1;
+
   return all_args;
 }