nr,gnb,mac: prioritize CRNTI CE handling over remaining SDUs and CEs in gNB mac receiver

lib/include/srsran/mac/mac_sch_pdu_nr.h

@@ -29,7 +29,7 @@ class mac_sch_subpdu_nr
 {
 public:
   // 3GPP 38.321 v15.3.0 Combined Tables 6.2.1-1, 6.2.1-2
-  typedef enum {
+  enum nr_lcid_sch_t {
     // Values for DL-SCH
     CCCH       = 0b000000,
     DRX_CMD    = 0b111100,
@@ -44,12 +44,14 @@ public:
     CCCH_SIZE_64    = 0b000000,
     SE_PHR          = 0b111001, // Single Entry PHR
 
+    MIN_LCID  = 0b000001,
+    MAX_LCID  = 0b100000,
     SHORT_BSR = 0b111101,
     LONG_BSR  = 0b111110,
 
     // Common
     PADDING = 0b111111,
-  } nr_lcid_sch_t;
+  };
 
   // SDUs up to 256 B can use the short 8-bit L field
   static const int32_t MAC_SUBHEADER_LEN_THRESHOLD = 256;
@@ -188,7 +190,7 @@ public:
 
   void                     pack();
   int                      unpack(const uint8_t* payload, const uint32_t& len);
-  uint32_t                 get_num_subpdus();
+  uint32_t                 get_num_subpdus() const { return subpdus.size(); }
   const mac_sch_subpdu_nr& get_subpdu(const uint32_t& index) const;
   mac_sch_subpdu_nr&       get_subpdu(uint32_t index);
   bool                     is_ulsch();

lib/src/mac/mac_sch_pdu_nr.cc

@@ -444,11 +444,6 @@ int mac_sch_pdu_nr::unpack(const uint8_t* payload, const uint32_t& len)
   return SRSRAN_SUCCESS;
 }
 
-uint32_t mac_sch_pdu_nr::get_num_subpdus()
-{
-  return subpdus.size();
-}
-
 const mac_sch_subpdu_nr& mac_sch_pdu_nr::get_subpdu(const uint32_t& index) const
 {
   return subpdus.at(index);

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

@@ -71,7 +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);
+  int      process_ce_subpdu(const 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

@@ -74,29 +74,35 @@ 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));
   }
 
-  // First, process MAC CEs in reverse order (CE like C-RNTI get handled first)
-  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);
-    if (not subpdu.is_sdu()) {
+  // Process MAC CRNTI CE first, if it exists
+  uint32_t crnti_ce_pos = mac_pdu_ul.get_num_subpdus();
+  for (uint32_t n = mac_pdu_ul.get_num_subpdus(); n > 0; --n) {
+    srsran::mac_sch_subpdu_nr& subpdu = mac_pdu_ul.get_subpdu(n - 1);
+    if (subpdu.is_sdu() and subpdu.get_lcid() == srsran::mac_sch_subpdu_nr::nr_lcid_sch_t::CRNTI) {
       if (process_ce_subpdu(subpdu) != SRSRAN_SUCCESS) {
         return SRSRAN_ERROR;
       }
+      crnti_ce_pos = n - 1;
     }
   }
 
-  // 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);
+  // Process SDUs and remaining MAC CEs
+  for (uint32_t n = 0; n < mac_pdu_ul.get_num_subpdus(); ++n) {
+    srsran::mac_sch_subpdu_nr& subpdu = mac_pdu_ul.get_subpdu(n);
     if (subpdu.is_sdu()) {
       rrc->set_activity_user(rnti);
       rlc->write_pdu(rnti, subpdu.get_lcid(), subpdu.get_sdu(), subpdu.get_sdu_length());
+    } else if (n != crnti_ce_pos) {
+      if (process_ce_subpdu(subpdu) != SRSRAN_SUCCESS) {
+        return SRSRAN_ERROR;
+      }
     }
   }
 
   return SRSRAN_SUCCESS;
 }
 
-int ue_nr::process_ce_subpdu(srsran::mac_sch_subpdu_nr& subpdu)
+int ue_nr::process_ce_subpdu(const srsran::mac_sch_subpdu_nr& subpdu)
 {
   // Handle MAC CEs
   switch (subpdu.get_lcid()) {