enb,nr: rewrite UL PDU processing to handle CEs in reverse order but SDUs in order

this makes sure that C-RNTI CE gets processed before any SDU gets processed.
but it also makes sure that all SDUs then are processed in-order to
avoid reordering at higher layers.

srsenb/hdr/stack/mac/nr/ue_nr.h

@@ -71,6 +71,7 @@ public:
 private:
   // helper methods
   uint32_t buff_size_field_to_bytes(uint32_t buff_size_index, const srsran::bsr_format_nr_t& format);
+  int      process_ce_subpdu(srsran::mac_sch_subpdu_nr& subpdu);
 
   rlc_interface_mac*      rlc = nullptr;
   rrc_interface_mac_nr*   rrc = nullptr;

srsenb/src/stack/mac/nr/ue_nr.cc

@@ -74,16 +74,30 @@ int ue_nr::process_pdu(srsran::unique_byte_buffer_t pdu)
     logger.info("Rx PDU: rnti=0x%x, %s", rnti, srsran::to_c_str(str_buffer));
   }
 
-  // Reverse the order in which MAC subPDUs get processed.
+  // First, process MAC CEs in reverse order (CE like C-RNTI get handled first)
-  // First, process MAC CEs, then MAC MAC subPDUs with MAC SDUs
   for (uint32_t n = mac_pdu_ul.get_num_subpdus(), i = mac_pdu_ul.get_num_subpdus() - 1; n > 0; --n, i = n - 1) {
     srsran::mac_sch_subpdu_nr subpdu = mac_pdu_ul.get_subpdu(i);
-    logger.debug("Handling subPDU %d/%d: lcid=%d, sdu_len=%d",
+    if (not subpdu.is_sdu()) {
-                 i,
+      if (process_ce_subpdu(subpdu) != SRSRAN_SUCCESS) {
-                 mac_pdu_ul.get_num_subpdus(),
+        return SRSRAN_ERROR;
-                 subpdu.get_lcid(),
+      }
-                 subpdu.get_sdu_length());
+    }
+  }
+
+  // Second, handle all SDUs in order to avoid unnecessary reordering at higher layers
+  for (uint32_t i = 0; i < mac_pdu_ul.get_num_subpdus(); ++i) {
+    srsran::mac_sch_subpdu_nr subpdu = mac_pdu_ul.get_subpdu(i);
+    if (subpdu.is_sdu()) {
+      rrc->set_activity_user(rnti);
+      rlc->write_pdu(rnti, subpdu.get_lcid(), subpdu.get_sdu(), subpdu.get_sdu_length());
+    }
+  }
 
+  return SRSRAN_SUCCESS;
+}
+
+int ue_nr::process_ce_subpdu(srsran::mac_sch_subpdu_nr& subpdu)
+{
   // Handle MAC CEs
   switch (subpdu.get_lcid()) {
     case srsran::mac_sch_subpdu_nr::nr_lcid_sch_t::CRNTI: {
@@ -121,12 +135,9 @@ int ue_nr::process_pdu(srsran::unique_byte_buffer_t pdu)
       }
     } break;
     default:
-        if (subpdu.is_sdu()) {
+      logger.warning("Unhandled subPDU with LCID=%d", subpdu.get_lcid());
-          rrc->set_activity_user(rnti);
-          rlc->write_pdu(rnti, subpdu.get_lcid(), subpdu.get_sdu(), subpdu.get_sdu_length());
-        }
-    }
   }
+
   return SRSRAN_SUCCESS;
 }