ue,mac_nr: fix generation of padding BSRs

* in Msg3 don't add explicit SBSR (rely on padding BSR to add)
* fix padding BSR generation to always use padding bytes to add it

srsue/hdr/stack/mac_nr/mac_nr.h

@@ -98,6 +98,7 @@ public:
 
   /// Interface for MUX
   srsran::mac_sch_subpdu_nr::lcg_bsr_t generate_sbsr();
+  void                                 set_padding_bytes(uint32_t nof_bytes);
 
   void msg3_flush() { mux.msg3_flush(); }
   bool msg3_is_transmitted() { return mux.msg3_is_transmitted(); }

srsue/hdr/stack/mac_nr/mac_nr_interfaces.h

@@ -54,11 +54,17 @@ public:
 class mac_interface_mux_nr
 {
 public:
+  // MUX can ask MAC if a C-RNTI is present
+  virtual bool has_crnti() = 0;
+
   // MUX can query MAC for current C-RNTI for Msg3 transmission
   virtual uint16_t get_crnti() = 0;
 
   // MUX queries MAC to return LCG state for SBSR
   virtual srsran::mac_sch_subpdu_nr::lcg_bsr_t generate_sbsr() = 0;
+
+  // MUX informs MAC about padding bytes so BSR proc can decide whether to create BSR or not
+  virtual void set_padding_bytes(uint32_t nof_bytes) = 0;
 };
 
 /**

srsue/hdr/stack/mac_nr/proc_bsr_nr.h

@@ -69,7 +69,7 @@ public:
 
   /// MUX interface for BSR generation
   srsran::mac_sch_subpdu_nr::lcg_bsr_t generate_sbsr();
-  bool                                 generate_padding_bsr(uint32_t nof_padding_bytes);
+  void                                 set_padding_bytes(uint32_t nof_bytes);
 
 private:
   const static int QUEUE_STATUS_PERIOD_MS = 1000;

srsue/src/stack/mac_nr/mac_nr.cc

@@ -209,6 +209,11 @@ srsran::mac_sch_subpdu_nr::lcg_bsr_t mac_nr::generate_sbsr()
   return proc_bsr.generate_sbsr();
 }
 
+void mac_nr::set_padding_bytes(uint32_t nof_bytes)
+{
+  proc_bsr.set_padding_bytes(nof_bytes);
+}
+
 void mac_nr::bch_decoded_ok(uint32_t tti, srsran::unique_byte_buffer_t payload)
 {
   // Send MIB to RLC

srsue/src/stack/mac_nr/mux_nr.cc

@@ -63,14 +63,15 @@ srsran::unique_byte_buffer_t mux_nr::get_pdu(uint32_t max_pdu_len)
   tx_pdu.init_tx(phy_tx_pdu.get(), max_pdu_len, true);
 
   if (msg3_is_pending()) {
-    // If Msg3 is pending, pack it
-    // Use the CRNTI which is provided in the RRC reconfiguration (only for DC mode maybe other)
+    // only C-RNTI or CCCH SDU can be transmitted in Msg3
+    if (mac.has_crnti()) {
       tx_pdu.add_crnti_ce(mac.get_crnti());
-    tx_pdu.add_sbsr_ce(mac.generate_sbsr());
+    }
+    // TODO: add CCCH check
     msg3_transmitted();
   } else {
     // Pack normal UL data PDU
-    int32_t remaining_len = tx_pdu.get_remaing_len(); // local variable to reserv space for CEs
+    int32_t remaining_len = tx_pdu.get_remaing_len(); // local variable to reserve space for CEs
 
     if (add_bsr_ce == sbsr_ce) {
       // reserve space for SBSR
@@ -115,15 +116,25 @@ srsran::unique_byte_buffer_t mux_nr::get_pdu(uint32_t max_pdu_len)
         }
       }
     }
+  }
+
+  // check if
+  if (add_bsr_ce == no_bsr) {
+    // tell BSR proc we still have space in PDU and let it decide to create a padding BSR
+    mac.set_padding_bytes(tx_pdu.get_remaing_len());
+  }
 
   // Second add fixed-sized MAC CEs (e.g. SBSR)
   if (add_bsr_ce == sbsr_ce) {
     tx_pdu.add_sbsr_ce(mac.generate_sbsr());
     add_bsr_ce = no_bsr;
+  } else if (add_bsr_ce == lbsr_ce) {
+    // TODO: implement LBSR support
+    tx_pdu.add_sbsr_ce(mac.generate_sbsr());
+    add_bsr_ce = no_bsr;
   }
 
   // Lastly, add variable-sized MAC CEs
-  }
 
   // Pack PDU
   tx_pdu.pack();

srsue/src/stack/mac_nr/proc_bsr_nr.cc

@@ -209,8 +209,8 @@ void proc_bsr_nr::new_grant_ul(uint32_t grant_size)
   sr->reset();
 }
 
-// This function is called by MUX only if Regular BSR has not been triggered before
-bool proc_bsr_nr::generate_padding_bsr(uint32_t nof_padding_bytes)
+// This function is called by MUX only if no BSR has been triggered before
+void proc_bsr_nr::set_padding_bytes(uint32_t nof_bytes)
 {
   std::lock_guard<std::mutex> lock(mutex);
 
@@ -219,16 +219,14 @@ bool proc_bsr_nr::generate_padding_bsr(uint32_t nof_padding_bytes)
   const uint32_t LBSR_CE_SUBHEADER_LEN = 1;
   // if the number of padding bits is equal to or larger than the size of the Short BSR plus its subheader but smaller
   // than the size of the Long BSR plus its subheader
-  if (nof_padding_bytes >= SBSR_CE_SUBHEADER_LEN + srsran::mac_sch_subpdu_nr::sizeof_ce(SHORT_BSR, true) &&
-      nof_padding_bytes <= LBSR_CE_SUBHEADER_LEN + srsran::mac_sch_subpdu_nr::sizeof_ce(LONG_BSR, true)) {
-    // generate padding BSR
-    set_trigger(PADDING);
-    // generate_bsr(bsr, nof_padding_bytes);
-    set_trigger(NONE);
-    return true;
+  if (nof_bytes >= SBSR_CE_SUBHEADER_LEN + srsran::mac_sch_subpdu_nr::sizeof_ce(SHORT_BSR, true) &&
+      nof_bytes < LBSR_CE_SUBHEADER_LEN + srsran::mac_sch_subpdu_nr::sizeof_ce(LONG_BSR, true)) {
+    // generate short padding BSR
+    mux->generate_bsr_mac_ce(SHORT_BSR);
+  } else if (nof_bytes >= LBSR_CE_SUBHEADER_LEN + srsran::mac_sch_subpdu_nr::sizeof_ce(LONG_BSR, true)) {
+    // report Long BSR if more than one LCG has data to send
+    mux->generate_bsr_mac_ce(LONG_BSR);
   }
-
-  return false;
 }
 
 int proc_bsr_nr::setup_lcid(uint32_t lcid, uint32_t new_lcg, uint32_t priority)