Skip DL HARQ feedbacks if the timing does not match

As the precedent commit, this commit deals with the realtime problems
that we currently have on the CI bench.

For DL HARQ feedback, nFAPI does not give us the HARQ process ID.
Instead, we have to figure this out "from timing", i.e., if we trigger
PUCCH reception, we will get a message with HARQ if we instructed the
PHY to do so. If we have real-time problems, it seems (I cannot verify:
don't have real time problems) that we do not get the nFAPI message with
HARQ feedback. Thus, we need to skip the HARQ processes that should have
been processed in the past, which happens in this commit.

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_uci.c

@@ -336,14 +336,27 @@ void handle_nr_uci_pucch_0_1(module_id_t mod_id,
     for (int harq_bit = 0; harq_bit < uci_01->harq->num_harq; harq_bit++) {
       const uint8_t harq_value = uci_01->harq->harq_list[harq_bit].harq_value;
       const uint8_t harq_confidence = uci_01->harq->harq_confidence_level;
-      const int8_t pid = sched_ctrl->feedback_dl_harq.head;
+      const int feedback_slot = (slot - 1 + num_slots) % num_slots;
+      /* In case of realtime problems: we can only identify a HARQ process by
+       * timing. If the HARQ process's feedback_slot is not the one we
+       * expected, we assume that processing has been aborted and we need to
+       * skip this HARQ process, which is what happens in the loop below. If
+       * you don't experience real-time problems, you might simply revert the
+       * commit that introduced these changes. */
+      int8_t pid = sched_ctrl->feedback_dl_harq.head;
       DevAssert(pid >= 0);
+      while (sched_ctrl->harq_processes[pid].feedback_slot != feedback_slot) {
+        LOG_W(MAC,
+              "expected feedback slot %d, but found %d instead\n",
+              sched_ctrl->harq_processes[pid].feedback_slot,
+              feedback_slot);
+        remove_front_nr_list(&sched_ctrl->feedback_dl_harq);
+        handle_dl_harq(mod_id, UE_id, pid, 0);
+        pid = sched_ctrl->feedback_dl_harq.head;
+        DevAssert(pid >= 0);
+      }
       remove_front_nr_list(&sched_ctrl->feedback_dl_harq);
       NR_UE_harq_t *harq = &sched_ctrl->harq_processes[pid];
-      const int feedback_slot = (slot - 1 + num_slots) % num_slots;
-      AssertFatal(harq->feedback_slot == feedback_slot,
-                  "expected feedback slot %d, but found %d instead\n",
-                  harq->feedback_slot, feedback_slot);
       DevAssert(harq->is_waiting);
       handle_dl_harq(mod_id, UE_id, pid, harq_value == 1 && harq_confidence == 0);
     }
@@ -374,14 +387,28 @@ void handle_nr_uci_pucch_2_3_4(module_id_t mod_id,
     // iterate over received harq bits
     for (int harq_bit = 0; harq_bit < uci_234->harq.harq_bit_len; harq_bit++) {
       const int acknack = ((uci_234->harq.harq_payload[harq_bit >> 3]) >> harq_bit) & 0x01;
-      const int8_t pid = sched_ctrl->feedback_dl_harq.head;
+      const int feedback_slot = (slot - 1 + num_slots) % num_slots;
+      /* In case of realtime problems: we can only identify a HARQ process by
+       * timing. If the HARQ process's feedback_slot is not the one we
+       * expected, we assume that processing has been aborted and we need to
+       * skip this HARQ process, which is what happens in the loop below. If
+       * you don't experience real-time problems, you might simply revert the
+       * commit that introduced these changes. */
+      int8_t pid = sched_ctrl->feedback_dl_harq.head;
       DevAssert(pid >= 0);
+      while (sched_ctrl->harq_processes[pid].feedback_slot != feedback_slot) {
+        LOG_W(MAC,
+              "expected feedback slot %d, but found %d instead\n",
+              sched_ctrl->harq_processes[pid].feedback_slot,
+              feedback_slot);
+        remove_front_nr_list(&sched_ctrl->feedback_dl_harq);
+        handle_dl_harq(mod_id, UE_id, pid, 0);
+        pid = sched_ctrl->feedback_dl_harq.head;
+        DevAssert(pid >= 0);
+      }
       remove_front_nr_list(&sched_ctrl->feedback_dl_harq);
       NR_UE_harq_t *harq = &sched_ctrl->harq_processes[pid];
-      const int feedback_slot = (slot - 1 + num_slots) % num_slots;
-      AssertFatal(harq->feedback_slot == feedback_slot,
-                  "expected feedback slot %d, but found %d instead\n",
-                  harq->feedback_slot, feedback_slot);
+      DevAssert(harq->is_waiting);
       handle_dl_harq(mod_id, UE_id, pid, uci_234->harq.harq_crc != 1 && acknack);
     }
   }