ue,phy,nr: fix race condition when setting UL grant for Msg3

the Msg3 UL grant requires the TTI in which the RAR has been received
to calcualte the correct timing. There was a race between PHY and Stack
thread.

This patch circumvents the issue by removing a PHY state member that only holds
the RAR Rx timing. In the new interface the RA proc passes the Rx TTI
to the PHY again when setting the UL grant so the PHY can calculate the
correct timing without any state.

lib/include/srsran/interfaces/ue_nr_interfaces.h

@@ -54,6 +54,7 @@ public:
   } mac_nr_grant_dl_t;
 
   typedef struct {
+    uint32_t                     rx_slot_idx; // Slot when DL TB has been decoded
     srsran::unique_byte_buffer_t payload;     // TB when decoded successfully, nullptr otherwise
     bool                         ack;         // HARQ information
   } tb_action_dl_result_t;
@@ -212,7 +213,8 @@ public:
   } tx_request_t;
 
   // MAC informs PHY about UL grant included in RAR PDU
-  virtual int set_ul_grant(std::array<uint8_t, SRSRAN_RAR_UL_GRANT_NBITS> packed_ul_grant,
+  virtual int set_ul_grant(uint32_t                                       rar_slot_idx,
+                           std::array<uint8_t, SRSRAN_RAR_UL_GRANT_NBITS> packed_ul_grant,
                            uint16_t                                       rnti,
                            srsran_rnti_type_t                             rnti_type) = 0;
 

srsue/hdr/phy/nr/state.h

@@ -90,8 +90,6 @@ public:
   /// Semaphore for aligning UL work
   srsran::tti_semaphore<void*> dl_ul_semaphore;
 
-  srsran_slot_cfg_t rar_grant_slot = {};
-
   state()
   {
     // Hard-coded values, this should be set when the measurements take place

srsue/hdr/phy/nr/worker_pool.h

@@ -41,7 +41,8 @@ public:
                         const int      preamble_index,
                         const float    preamble_received_target_power,
                         const float    ta_base_sec = 0.0f) override;
-  int        set_ul_grant(std::array<uint8_t, SRSRAN_RAR_UL_GRANT_NBITS> array,
+  int        set_ul_grant(uint32_t                                       rx_tti,
+                          std::array<uint8_t, SRSRAN_RAR_UL_GRANT_NBITS> array,
                           uint16_t                                       rnti,
                           srsran_rnti_type_t                             rnti_type) override;
   bool       set_config(const srsran::phy_cfg_nr_t& cfg) override;

srsue/hdr/phy/phy.h

@@ -165,7 +165,8 @@ public:
 
   int  init(const phy_args_nr_t& args_, stack_interface_phy_nr* stack_, srsran::radio_interface_phy* radio_) final;
   bool set_config(const srsran::phy_cfg_nr_t& cfg) final;
-  int  set_ul_grant(std::array<uint8_t, SRSRAN_RAR_UL_GRANT_NBITS> packed_ul_grant,
+  int  set_ul_grant(uint32_t                                       rx_tti,
+                    std::array<uint8_t, SRSRAN_RAR_UL_GRANT_NBITS> packed_ul_grant,
                     uint16_t                                       rnti,
                     srsran_rnti_type_t                             rnti_type) final;
   void send_prach(const uint32_t prach_occasion,

srsue/src/phy/nr/cc_worker.cc

@@ -336,14 +336,11 @@ bool cc_worker::decode_pdsch_dl()
 
   // Notify MAC about PDSCH decoding result
   mac_interface_phy_nr::tb_action_dl_result_t mac_dl_result = {};
+  mac_dl_result.rx_slot_idx = dl_slot_cfg.idx; // Rx TTI for this TB (required for correct Msg3 timing)
   mac_dl_result.ack         = pdsch_res.tb[0].crc;
   mac_dl_result.payload     = mac_dl_result.ack ? std::move(data) : nullptr; // only pass data when successful
   phy.stack->tb_decoded(cc_idx, mac_dl_grant, std::move(mac_dl_result));
 
-  if (pdsch_cfg.grant.rnti_type == srsran_rnti_type_ra) {
-    phy.rar_grant_slot = dl_slot_cfg;
-  }
-
   if (pdsch_res.tb[0].crc) {
     // Generate DL metrics
     dl_metrics_t dl_m = {};

srsue/src/phy/nr/worker_pool.cc

@@ -99,7 +99,9 @@ void worker_pool::send_prach(const uint32_t prach_occasion,
   prach_buffer->prepare_to_send(preamble_index);
 }
 
-int worker_pool::set_ul_grant(std::array<uint8_t, SRSRAN_RAR_UL_GRANT_NBITS> packed_ul_grant,
+// called from Stack thread when processing RAR PDU
+int worker_pool::set_ul_grant(uint32_t                                       rar_slot_idx,
+                              std::array<uint8_t, SRSRAN_RAR_UL_GRANT_NBITS> packed_ul_grant,
                               uint16_t                                       rnti,
                               srsran_rnti_type_t                             rnti_type)
 {
@@ -113,21 +115,24 @@ int worker_pool::set_ul_grant(std::array<uint8_t, SRSRAN_RAR_UL_GRANT_NBITS> pac
   srsran_vec_u8_copy(dci_msg.payload, packed_ul_grant.data(), SRSRAN_RAR_UL_GRANT_NBITS);
 
   srsran_dci_ul_nr_t dci_ul = {};
-
   if (srsran_dci_nr_ul_unpack(NULL, &dci_msg, &dci_ul) < SRSRAN_SUCCESS) {
     logger.error("Couldn't unpack UL grant");
     return SRSRAN_ERROR;
   }
 
+  // initialize with Rx TTI of RAR
+  srsran_slot_cfg_t msg3_slot_cfg = {};
+  msg3_slot_cfg.idx               = rar_slot_idx;
+
   if (logger.info.enabled()) {
     std::array<char, 512> str;
     srsran_dci_nr_t       dci = {};
     srsran_dci_ul_nr_to_str(&dci, &dci_ul, str.data(), str.size());
-    logger.set_context(phy_state.rar_grant_slot.idx);
+    logger.set_context(msg3_slot_cfg.idx);
     logger.info("Setting RAR Grant: %s", str.data());
   }
 
-  phy_state.set_ul_pending_grant(phy_state.rar_grant_slot, dci_ul);
+  phy_state.set_ul_pending_grant(msg3_slot_cfg, dci_ul);
 
   return SRSRAN_SUCCESS;
 }

srsue/src/phy/phy.cc

@@ -622,11 +622,12 @@ int phy::init(const phy_args_nr_t& args_, stack_interface_phy_nr* stack_, srsran
   return SRSRAN_SUCCESS;
 }
 
-int phy::set_ul_grant(std::array<uint8_t, SRSRAN_RAR_UL_GRANT_NBITS> packed_ul_grant,
+int phy::set_ul_grant(uint32_t                                       rar_slot_idx,
+                      std::array<uint8_t, SRSRAN_RAR_UL_GRANT_NBITS> packed_ul_grant,
                       uint16_t                                       rnti,
                       srsran_rnti_type_t                             rnti_type)
 {
-  return nr_workers.set_ul_grant(packed_ul_grant, rnti, rnti_type);
+  return nr_workers.set_ul_grant(rar_slot_idx, packed_ul_grant, rnti, rnti_type);
 }
 
 void phy::send_prach(const uint32_t prach_occasion,

srsue/src/stack/mac_nr/proc_ra_nr.cc

@@ -207,7 +207,7 @@ void proc_ra_nr::ra_response_reception(const mac_interface_phy_nr::tb_action_dl_
         temp_crnti = subpdu.get_temp_crnti();
 
         // Set Temporary-C-RNTI if provided, otherwise C-RNTI is ok
-        phy->set_ul_grant(subpdu.get_ul_grant(), temp_crnti, srsran_rnti_type_ra);
+        phy->set_ul_grant(tb.rx_slot_idx, subpdu.get_ul_grant(), temp_crnti, srsran_rnti_type_ra);
 
         // reset all parameters that are used before rar
         rar_rnti = SRSRAN_INVALID_RNTI;

srsue/src/stack/mac_nr/test/mac_nr_test.cc

@@ -36,7 +36,10 @@ public:
     preamble_received_target_power = preamble_received_target_power_;
   }
   int tx_request(const tx_request_t& request) override { return 0; }
-  int set_ul_grant(std::array<uint8_t, SRSRAN_RAR_UL_GRANT_NBITS>, uint16_t rnti, srsran_rnti_type_t rnti_type) override
+  int set_ul_grant(uint32_t rar_slot_idx,
+                   std::array<uint8_t, SRSRAN_RAR_UL_GRANT_NBITS>,
+                   uint16_t           rnti,
+                   srsran_rnti_type_t rnti_type) override
   {
     return 0;
   }

srsue/src/stack/mac_nr/test/proc_ra_nr_test.cc

@@ -30,7 +30,10 @@ public:
     preamble_received_target_power = preamble_received_target_power_;
   }
   int tx_request(const tx_request_t& request) override { return 0; }
-  int set_ul_grant(std::array<uint8_t, SRSRAN_RAR_UL_GRANT_NBITS>, uint16_t rnti, srsran_rnti_type_t rnti_type) override
+  int set_ul_grant(uint32_t rar_slot_idx,
+                   std::array<uint8_t, SRSRAN_RAR_UL_GRANT_NBITS>,
+                   uint16_t           rnti,
+                   srsran_rnti_type_t rnti_type) override
   {
     return 0;
   }

srsue/src/stack/mac_nr/test/proc_sr_nr_test.cc

@@ -31,7 +31,10 @@ public:
     preamble_received_target_power = preamble_received_target_power_;
   }
   int tx_request(const tx_request_t& request) override { return 0; }
-  int set_ul_grant(std::array<uint8_t, SRSRAN_RAR_UL_GRANT_NBITS>, uint16_t rnti, srsran_rnti_type_t rnti_type) override
+  int set_ul_grant(uint32_t rar_slot_idx,
+                   std::array<uint8_t, SRSRAN_RAR_UL_GRANT_NBITS>,
+                   uint16_t           rnti,
+                   srsran_rnti_type_t rnti_type) override
   {
     return 0;
   }