sched_nr: add dl_mac_ce() method to allow MAC to schedule CE

MAC can give the scheduler hints as to when to schedule certain
CEs in the DL. For example when receiving a CCCH on SRB0.

srsgnb/hdr/stack/mac/sched_nr.h

@@ -49,6 +49,7 @@ public:
   void ul_sr_info(uint16_t rnti) override;
   void ul_bsr(uint16_t rnti, uint32_t lcg_id, uint32_t bsr) override;
   void dl_buffer_state(uint16_t rnti, uint32_t lcid, uint32_t newtx, uint32_t retx);
+  void dl_mac_ce(uint16_t rnti, uint32_t ce_lcid) override;
   void dl_cqi_info(uint16_t rnti, uint32_t cc, uint32_t cqi_value);
 
   /// Called once per slot in a non-concurrent fashion

srsgnb/hdr/stack/mac/sched_nr_interface.h

@@ -149,6 +149,15 @@ public:
   virtual void ul_crc_info(uint16_t rnti, uint32_t cc, uint32_t pid, bool crc)                  = 0;
   virtual void ul_sr_info(uint16_t rnti)                                                        = 0;
   virtual void ul_bsr(uint16_t rnti, uint32_t lcg_id, uint32_t bsr)                             = 0;
+
+  /**
+   * Enqueue MAC CEs for DL transmission
+   *
+   * @param rnti user rnti
+   * @param ce_lcid lcid of the MAC CE
+   * @return error code
+   */
+  virtual void dl_mac_ce(uint16_t rnti, uint32_t ce_lcid) = 0;
 };
 
 } // namespace srsenb

srsgnb/hdr/stack/mac/sched_nr_ue.h

@@ -128,7 +128,7 @@ public:
   void            set_cfg(const ue_cfg_t& cfg);
   const ue_cfg_t& cfg() const { return ue_cfg; }
 
-  void mac_buffer_state(uint32_t ce_lcid, uint32_t nof_cmds = 1);
+  void add_dl_mac_ce(uint32_t ce_lcid, uint32_t nof_cmds = 1);
   void rlc_buffer_state(uint32_t lcid, uint32_t newtx, uint32_t retx);
 
   /// UE state feedback

srsgnb/src/stack/mac/sched_nr.cc

@@ -471,6 +471,15 @@ void sched_nr::ul_bsr(uint16_t rnti, uint32_t lcg_id, uint32_t bsr)
   });
 }
 
+void sched_nr::dl_mac_ce(uint16_t rnti, uint32_t ce_lcid)
+{
+  pending_events->enqueue_ue_event("dl_mac_ce", rnti, [ce_lcid](ue& u, event_manager::logger& event_logger) {
+    // CE is added to list of pending CE
+    u.add_dl_mac_ce(ce_lcid, 1);
+    event_logger.push("0x{:x}: dl_mac_ce(lcid={})", u.rnti, ce_lcid);
+  });
+}
+
 void sched_nr::dl_buffer_state(uint16_t rnti, uint32_t lcid, uint32_t newtx, uint32_t retx)
 {
   pending_events->enqueue_ue_event(

srsgnb/src/stack/mac/sched_nr_ue.cc

@@ -157,7 +157,7 @@ void ue::set_cfg(const ue_cfg_t& cfg)
   buffers.config_lcids(cfg.ue_bearers);
 }
 
-void ue::mac_buffer_state(uint32_t ce_lcid, uint32_t nof_cmds)
+void ue::add_dl_mac_ce(uint32_t ce_lcid, uint32_t nof_cmds)
 {
   for (uint32_t i = 0; i < nof_cmds; ++i) {
     // If not specified otherwise, the CE is transmitted in PCell
@@ -167,13 +167,6 @@ void ue::mac_buffer_state(uint32_t ce_lcid, uint32_t nof_cmds)
 
 void ue::rlc_buffer_state(uint32_t lcid, uint32_t newtx, uint32_t priotx)
 {
-  if (lcid == 0 and (newtx + priotx > 0) and buffers.get_dl_tx_total(0) == 0) {
-    // In case of DL-CCCH, schedule ConRes CE
-    // Note1: rlc_buffer_state may be called multiple times for the same CCCH. Thus, we need to confirm lcid=0 buffer
-    //        state is zero to avoid that multiple CEs being scheduled.
-    // Note2: use push_front because ConRes CE has priority
-    buffers.pending_ces.push_front({srsran::mac_sch_subpdu_nr::CON_RES_ID, cfg().carriers[0].cc});
-  }
   buffers.dl_buffer_state(lcid, newtx, priotx);
 }