nas: fix airplane mode simulation

the current implementation was somehow broken after a
NAS refactor. It was undetected because we didn't really
use it.

this fixes the simulation by using a single timer to simulate
airplane mode transitions.
the timer is rearmed in the timer_expire() function
if the correspondig event is set.

Has been tested to work well with, e.g.:

--sim.airplane_t_on_ms 5000 --sim.airplane_t_off_ms 10000

srsue/hdr/stack/upper/nas.h

@@ -163,6 +163,7 @@ private:
   // Airplane mode simulation
   typedef enum { DISABLED = 0, ENABLED } airplane_mode_state_t;
   airplane_mode_state_t airplane_mode_state = {};
+  srslte::timer_handler::unique_timer airplane_mode_sim_timer;
 
   // PCAP
   srslte::nas_pcap* pcap = nullptr;
@@ -226,7 +227,6 @@ private:
 
   // Other internal helpers
   void enter_state(emm_state_t state_);
-  void handle_airplane_mode_sim();
   void enter_emm_deregistered();
 
   // security context persistence file

srsue/src/stack/upper/nas.cc

@@ -245,6 +245,7 @@ nas::nas(srslte::task_sched_handle task_sched_) :
   t3411(task_sched_.get_unique_timer()),
   t3421(task_sched_.get_unique_timer()),
   reattach_timer(task_sched_.get_unique_timer()),
+  airplane_mode_sim_timer(task_sched_.get_unique_timer()),
   nas_log{"NAS"}
 {}
 
@@ -302,7 +303,10 @@ void nas::init(usim_interface_nas* usim_, rrc_interface_nas* rrc_, gw_interface_
   t3421.set(t3421_duration_ms, [this](uint32_t tid) { timer_expired(tid); });
   reattach_timer.set(reattach_timer_duration_ms, [this](uint32_t tid) { timer_expired(tid); });
 
-  handle_airplane_mode_sim();
+  if (cfg.sim.airplane_t_on_ms > 0) {
+    airplane_mode_sim_timer.set(cfg.sim.airplane_t_on_ms, [this](uint32_t tid) { timer_expired(tid); });
+    airplane_mode_sim_timer.run();
+  }
 
   running = true;
 }
@@ -372,6 +376,26 @@ void nas::timer_expired(uint32_t timeout_id)
   } else if (timeout_id == reattach_timer.id()) {
     nas_log->info("Reattach timer expired: trying to attach again\n");
     start_attach_proc(nullptr, srslte::establishment_cause_t::mo_sig);
+  } else if (timeout_id == airplane_mode_sim_timer.id()) {
+    if (airplane_mode_state == DISABLED) {
+      // Enabling air-plane mode
+      send_detach_request(true);
+      airplane_mode_state = ENABLED;
+
+      if (cfg.sim.airplane_t_on_ms > 0) {
+        airplane_mode_sim_timer.set(cfg.sim.airplane_t_on_ms, [this](uint32_t tid) { timer_expired(tid); });
+        airplane_mode_sim_timer.run();
+      }
+    } else if (airplane_mode_state == ENABLED) {
+      // Disabling airplane mode again
+      start_attach_proc(nullptr, srslte::establishment_cause_t::mo_sig);
+      airplane_mode_state = DISABLED;
+
+      if (cfg.sim.airplane_t_off_ms > 0) {
+        airplane_mode_sim_timer.set(cfg.sim.airplane_t_off_ms, [this](uint32_t tid) { timer_expired(tid); });
+        airplane_mode_sim_timer.run();
+      }
+    }
   } else {
     nas_log->error("Timeout from unknown timer id %d\n", timeout_id);
   }
@@ -2488,40 +2512,6 @@ void nas::send_close_ue_test_loop_complete()
   ctxt.tx_count++;
 }
 
-/*
- * Handles the airplane mode simulation by triggering a UE switch off/on
- * in user-definable time intervals
- */
-void nas::handle_airplane_mode_sim()
-{
-  if (cfg.sim.airplane_t_on_ms > 0 && airplane_mode_state == DISABLED) {
-    // check if we're already attached, if so, schedule airplane mode command
-    if (state == EMM_STATE_REGISTERED) {
-      // NAS is attached
-      task_sched.defer_callback(cfg.sim.airplane_t_on_ms, [&]() {
-        // Enabling air-plane mode
-        send_detach_request(true);
-        airplane_mode_state = ENABLED;
-      });
-    }
-  } else if (cfg.sim.airplane_t_off_ms > 0 && airplane_mode_state == ENABLED) {
-    // check if we are already deregistered, if so, schedule command to turn off airplone mode again
-    if (state == EMM_STATE_DEREGISTERED) {
-      // NAS is deregistered
-      task_sched.defer_callback(cfg.sim.airplane_t_off_ms, [&]() {
-        // Disabling airplane mode again
-        start_attach_proc(nullptr, srslte::establishment_cause_t::mo_sig);
-        airplane_mode_state = DISABLED;
-      });
-    }
-  }
-
-  // schedule another call
-  if (cfg.sim.airplane_t_on_ms > 0 || cfg.sim.airplane_t_off_ms > 0) {
-    task_sched.defer_callback(1000, [&]() { handle_airplane_mode_sim(); });
-  }
-}
-
 /*******************************************************************************
  * Security context persistence file
  ******************************************************************************/