lib,rlc_am_nr: added processing of ACKs from status report

lib/include/srsran/rlc/rlc_am_base.h

@@ -191,6 +191,11 @@ public:
 protected:
   std::unique_ptr<rlc_am_base_tx> tx_base = {};
   std::unique_ptr<rlc_am_base_rx> rx_base = {};
+
+public:
+  // Getters for TX/RX entities. Useful for testing.
+  rlc_am_base_rx* get_rx() { return rx_base.get(); }
+  rlc_am_base_tx* get_tx() { return tx_base.get(); }
 };
 
 } // namespace srsran

lib/include/srsran/rlc/rlc_am_nr.h

@@ -35,7 +35,41 @@ namespace srsran {
 class rlc_am_nr_tx;
 class rlc_am_nr_rx;
 
-// Transmitter sub-class
+/****************************************************************************
+ * Tx state variables
+ * Ref: 3GPP TS 38.322 v10.0.0 Section 7.1
+ ***************************************************************************/
+struct rlc_am_nr_tx_state_t {
+  /*
+   * TX_Next_Ack: This state variable holds the value of the SN of the next RLC SDU for which a positive
+   * acknowledgment is to be received in-sequence, and it serves as the lower edge of the transmitting window. It is
+   * initially set to 0, and is updated whenever the AM RLC entity receives a positive acknowledgment for an RLC SDU
+   * with SN = TX_Next_Ack.
+   */
+  uint32_t tx_next_ack;
+  /*
+   * TX_Next: This state variable holds the value of the SN to be assigned for the next newly generated AMD PDU. It is
+   * initially set to 0, and is updated whenever the AM RLC entity constructs an AMD PDU with SN = TX_Next and
+   * contains an RLC SDU or the last segment of a RLC SDU.
+   */
+  uint32_t tx_next;
+  /*
+   * POLL_SN: This state variable holds the value of the highest SN of the AMD PDU among the AMD PDUs submitted to
+   * lower layer when POLL_SN is set according to sub clause 5.3.3.2. It is initially set to 0.
+   */
+  uint32_t poll_sn;
+  /*
+   * PDU_WITHOUT_POLL: This counter is initially set to 0. It counts the number of AMD PDUs sent since the most recent
+   * poll bit was transmitted.
+   */
+  uint32_t pdu_without_poll;
+  /*
+   * BYTE_WITHOUT_POLL: This counter is initially set to 0. It counts the number of data bytes sent since the most
+   * recent poll bit was transmitted.
+   */
+  uint32_t byte_without_poll;
+};
+
 class rlc_am_nr_tx : public rlc_am::rlc_am_base_tx
 {
 public:
@@ -80,17 +114,16 @@ private:
    * Tx state variables
    * Ref: 3GPP TS 38.322 v10.0.0 Section 7.1
    ***************************************************************************/
-  struct rlc_nr_tx_state_t {
-    uint32_t tx_next_ack;
-    uint32_t tx_next;
-    uint32_t poll_sn;
-    uint32_t pdu_without_poll;
-    uint32_t byte_without_poll;
-  } st = {};
+  struct rlc_am_nr_tx_state_t st = {};
 
   using rlc_amd_tx_pdu_nr = rlc_amd_tx_pdu<rlc_am_nr_pdu_header_t>;
   rlc_ringbuffer_t<rlc_amd_tx_pdu_nr, RLC_AM_WINDOW_SIZE> tx_window;
   pdu_retx_queue<RLC_AM_WINDOW_SIZE>                      retx_queue;
+
+public:
+  // Getters/Setters
+  rlc_am_nr_tx_state_t get_tx_state() { return st; }                     // This should only be used for testing.
+  uint32_t             get_tx_window_size() { return tx_window.size(); } // This should only be used for testing.
 };
 
 // Receiver sub-class

lib/src/rlc/rlc_am_nr.cc

@@ -237,6 +237,21 @@ void rlc_am_nr_tx::handle_control_pdu(uint8_t* payload, uint32_t nof_bytes)
    *   - consider the RLC SDU or the RLC SDU segment for which a negative acknowledgement was received for
    *     retransmission.
    */
+  // Process ACKs
+  uint32_t stop_sn = status.N_nack == 0
+                         ? st.tx_next
+                         : status.nacks[0].nack_sn; // Stop processing ACKs at the first NACK, if it exists.
+  if (status.ack_sn >= st.tx_next_ack) {
+    for (uint32_t sn = st.tx_next_ack; sn < stop_sn; sn++) {
+      if (tx_window.has_sn(sn)) {
+        tx_window.remove_pdu(sn);
+        st.tx_next_ack = sn + 1;
+      } else {
+        logger->error("Missing ACKed SN from TX window");
+        break;
+      }
+    }
+  }
   // Process N_acks
   for (uint32_t nack_idx = 0; nack_idx < status.N_nack; nack_idx++) {
     if (st.tx_next_ack <= status.nacks[nack_idx].nack_sn && status.nacks[nack_idx].nack_sn <= st.tx_next) {

lib/test/rlc/rlc_am_nr_test.cc

@@ -72,6 +72,11 @@ int basic_test()
   rlc_am rlc1(srsran_rat_t::nr, srslog::fetch_basic_logger("RLC_AM_1"), 1, &tester, &tester, &timers);
   rlc_am rlc2(srsran_rat_t::nr, srslog::fetch_basic_logger("RLC_AM_2"), 1, &tester, &tester, &timers);
 
+  rlc_am_nr_tx* tx1 = dynamic_cast<rlc_am_nr_tx*>(rlc1.get_tx());
+  rlc_am_nr_rx* rx1 = dynamic_cast<rlc_am_nr_rx*>(rlc1.get_rx());
+  rlc_am_nr_tx* tx2 = dynamic_cast<rlc_am_nr_tx*>(rlc2.get_tx());
+  rlc_am_nr_rx* rx2 = dynamic_cast<rlc_am_nr_rx*>(rlc2.get_rx());
+
   // before configuring entity
   TESTASSERT(0 == rlc1.get_buffer_state());
 
@@ -106,6 +111,10 @@ int basic_test()
   // Write status PDU to RLC1
   rlc1.write_pdu(status_buf.msg, status_buf.N_bytes);
 
+  // Check TX_NEXT_ACK
+  rlc_am_nr_tx_state_t st = tx1->get_tx_state();
+  TESTASSERT_EQ(5, st.tx_next_ack);
+  TESTASSERT_EQ(0, tx1->get_tx_window_size());
   // Check statistics
   TESTASSERT(rx_is_tx(rlc1.get_metrics(), rlc2.get_metrics()));
   return SRSRAN_SUCCESS;