proc_phr: rename start_periodic_timer() and make sure its only started if a valid config is present

srsue/hdr/stack/mac/proc_phr.h

@@ -44,7 +44,7 @@ public:
   bool is_extended();
   void timer_expired(uint32_t timer_id);
 
-  void start_timer();
+  void start_periodic_timer();
 
 private:
   bool pathloss_changed();

srsue/src/stack/mac/mac.cc

@@ -515,10 +515,10 @@ void mac::new_grant_ul(uint32_t                               cc_idx,
                        mac_interface_phy_lte::mac_grant_ul_t  grant,
                        mac_interface_phy_lte::tb_action_ul_t* action)
 {
-  /* Start PHR Periodic timer on first UL dci */
+  // Start PHR Periodic timer on first UL DCI (See TS 36.321 Sec 5.4.6)
   if (is_first_ul_grant) {
     is_first_ul_grant = false;
-    phr_procedure.start_timer();
+    phr_procedure.start_periodic_timer();
   }
 
   // Assert UL HARQ entity

srsue/src/stack/mac/proc_phr.cc

@@ -100,16 +100,19 @@ bool phr_proc::pathloss_changed()
   }
 }
 
-void phr_proc::start_timer()
+void phr_proc::start_periodic_timer()
 {
+  if (phr_cfg.enabled && phr_cfg.periodic_timer > 0) {
     timer_periodic.run();
   }
+}
 
 /* Trigger PHR when timers exires */
 void phr_proc::timer_expired(uint32_t timer_id)
 {
   if (!phr_cfg.enabled) {
-    Warning("PHR:   Timer triggered but PHR has been disabled\n");
+    Warning("PHR:   %s timer triggered but PHR has been disabled\n",
+            timer_id == timer_periodic.id() ? "Periodic" : "Prohibit");
     return;
   }
   if (timer_id == timer_periodic.id()) {