sched-nr: fix scheduler to pass nr tests

Signed-off-by: Carlo Galiotto <carlo@srs.io>

srsgnb/hdr/stack/mac/sched_nr_ue.h

@@ -61,7 +61,7 @@ public:
   struct pdu_builder {
     pdu_builder() = default;
     explicit pdu_builder(uint32_t cc_, ue_buffer_manager& parent_) : cc(cc_), parent(&parent_) {}
-    bool alloc_subpdus(uint32_t rem_bytes, sched_nr_interface::dl_pdu_t& pdu);
+    bool alloc_subpdus(uint32_t rem_bytes, sched_nr_interface::dl_pdu_t& pdu, bool reset_buf_states = false);
 
   private:
     uint32_t           cc     = SRSRAN_MAX_CARRIERS;
@@ -180,9 +180,9 @@ public:
   ul_harq_proc* find_empty_ul_harq() { return ue->harq_ent.find_empty_ul_harq(); }
 
   /// Build PDU with MAC CEs and MAC SDUs
-  bool build_pdu(uint32_t rem_bytes, sched_nr_interface::dl_pdu_t& pdu)
+  bool build_pdu(uint32_t rem_bytes, sched_nr_interface::dl_pdu_t& pdu, bool reset_buf_states = false)
   {
-    return ue->pdu_builder.alloc_subpdus(rem_bytes, pdu);
+    return ue->pdu_builder.alloc_subpdus(rem_bytes, pdu, reset_buf_states);
   }
 
   /// Channel Information Getters

srsgnb/src/stack/mac/sched_nr_grant_allocator.cc

@@ -385,15 +385,22 @@ alloc_result bwp_slot_allocator::alloc_pdsch(slot_ue& ue, uint32_t ss_id, const
 
     // Select scheduled LCIDs and update UE buffer state
     bwp_pdsch_slot.dl.data.emplace_back();
-    // NOTE: ue.h_dl->tbs() has to be converted from bits to bytes
-    bool segmented_ccch_pdu = not ue.build_pdu(ue.h_dl->tbs() / 8, bwp_pdsch_slot.dl.data.back());
-    if (segmented_ccch_pdu) {
+    // NOTES: 1) ue.h_dl->tbs() has to be converted from bits to bytes
+    //        2) In case of CCCH segmentation, we'll need to repeat the scheduling with a higher MCS. Hence, the
+    //        function ue.build_pdu() will reset the LCIDs and UE buffer states as before its execution if the flag
+    //        "mcs<min_MCS_ccch" is true
+    bool segmented_ccch_pdu = not ue.build_pdu(ue.h_dl->tbs() / 8, bwp_pdsch_slot.dl.data.back(), mcs < min_MCS_ccch);
+    if (segmented_ccch_pdu and mcs < min_MCS_ccch) {
       // In case of segmented PDU for CCCH, set minimum MCS to 4 and re-run the outer while loop
       bwp_pdsch_slot.dl.data.pop_back();
       mcs           = min_MCS_ccch;
       pdcch.dci.mcs = mcs;
-      logger.warning(
-          "SCHED: MCS increased to min value %d to allocate SRB0/CCCH for rnti=0x%x", min_MCS_ccch, ue->rnti);
+      logger.info("SCHED: MCS increased to min value %d to allocate SRB0/CCCH for rnti=0x%x", min_MCS_ccch, ue->rnti);
+    } else if (segmented_ccch_pdu /* and mcs >= min_MCS_ccch */) {
+      // With MCS >= then min_MCS_ccch, it is not possible to allocate SRB0/CCCH without PDU segmentation
+      logger.error("SCHED: Insufficient resources to allocate SRB0/CCCH without PDU segmentation for rnti=0x%x",
+                   ue->rnti);
+      break;
     } else {
       break;
     }

srsgnb/src/stack/mac/sched_nr_ue.cc

@@ -27,8 +27,18 @@ int ue_buffer_manager::get_dl_tx_total() const
   return total_bytes;
 }
 
-// Return true if there is no SRB0/CCCH MAC PDU segmentation, false otherwise
-bool ue_buffer_manager::pdu_builder::alloc_subpdus(uint32_t rem_bytes, sched_nr_interface::dl_pdu_t& pdu)
+/**
+ * @brief Allocates LCIDs and update US buffer states depending on available resources and checks if there is SRB0/CCCH
+ MAC PDU segmentation
+
+ * @param rem_bytes TBS to be filled with MAC CEs and MAC SDUs [in bytes]
+ * @param reset_buf_states If true, when there is SRB0/CCCH MAC PDU segmentation, restore the UE buffers and scheduled
+ LCIDs as before running this function
+ * @return true if there is no SRB0/CCCH MAC PDU segmentation, false otherwise
+ */
+bool ue_buffer_manager::pdu_builder::alloc_subpdus(uint32_t                      rem_bytes,
+                                                   sched_nr_interface::dl_pdu_t& pdu,
+                                                   bool                          reset_buf_states)
 {
   // In case of SRB0/CCCH PDUs, we need to check whether there is PDU segmentation; if LCID = 0 has emtpy buffer, no
   // need to perform this check
@@ -47,10 +57,10 @@ bool ue_buffer_manager::pdu_builder::alloc_subpdus(uint32_t rem_bytes, sched_nr_
       rem_bytes -= size_ce;
       pdu.subpdus.push_back(ce.lcid);
       // If there is possibility of CCCH segmentation, we need to save the MAC CEs in a tmp queue to be later restored
-      if (check_ccch_pdu_segmentation) {
+      if (check_ccch_pdu_segmentation and reset_buf_states) {
         restore_ces.push_back(parent->pending_ces.front());
-        parent->pending_ces.pop_front();
       }
+      parent->pending_ces.pop_front();
     }
   }
 
@@ -60,12 +70,16 @@ bool ue_buffer_manager::pdu_builder::alloc_subpdus(uint32_t rem_bytes, sched_nr_
     // Verify if the TBS is big enough to store the entire CCCH buffer
     // Note: (pending_lcid_bytes > rem_bytes) implies (check_ccch_pdu_segmentation == true)
     if (lcid == srsran::mac_sch_subpdu_nr::nr_lcid_sch_t::CCCH and pending_lcid_bytes > rem_bytes) {
+      if (reset_buf_states) {
         // restore the MAC CEs as they were at the beginning of the function
         for (ce_t ce : restore_ces) {
           parent->pending_ces.push_back(ce);
         }
         // double check if this line is required
         pdu.subpdus.clear();
+      } else {
+        pdu.subpdus.push_back(lcid);
+      }
       return false;
     }
     if (pending_lcid_bytes > 0) {