From 8b265883e40edfb357a67cf021c54abf47eb037a Mon Sep 17 00:00:00 2001
From: Xavier Arteaga <xavier@softwareradiosystems.com>
Date: Thu, 9 Apr 2020 12:43:55 +0200
Subject: [PATCH] SRSENB: UL TA measurement waits for a start order before
 start measuring

---
 srsenb/hdr/stack/mac/ta.h   | 52 +++++++++++++++++++------------------
 srsenb/hdr/stack/mac/ue.h   |  7 +----
 srsenb/src/stack/mac/mac.cc |  3 +++
 3 files changed, 31 insertions(+), 31 deletions(-)

diff --git a/srsenb/hdr/stack/mac/ta.h b/srsenb/hdr/stack/mac/ta.h
index 46fdd4c04..4fe9970ea 100644
--- a/srsenb/hdr/stack/mac/ta.h
+++ b/srsenb/hdr/stack/mac/ta.h
@@ -42,17 +42,18 @@ public:
 /**
  * UE's FSM for controlling Time Aligment command generation.
  *
- * Initially the FSM starts at none state which automatically transitions to Measure. Measurements are collected while
- * the FSM is in Measure state. Up to MAX_NOF_MEAS are stored. The FSM uses a minimum of MIN_NOF_MEAS measurements to
- * compute the TA average. The TA command is triggered as soon as the TA average is higher than TA_N_THRESHOLD. After
- * triggering a TA command, holds in prohibit state for PROHIBIT_PERIOD_MS before start collecting measurements.
+ * Initially the FSM starts at idle state which transitions to Measure as soon as start is called. Measurements are
+ * collected while the FSM is in Measure state. Up to MAX_NOF_MEAS are stored. The FSM uses a minimum of MIN_NOF_MEAS
+ * measurements to compute the TA average. The TA command is triggered as soon as the TA average is higher than
+ * TA_N_THRESHOLD. After triggering a TA command, holds in prohibit state for PROHIBIT_PERIOD_MS before start collecting
+ * measurements.
  *
- *  +------+  First call   +---------+   Trigger   +----------+
- *  | None | ------------->| Measure |------------>| Prohibit |
- *  +------+               +---------+             +----------+
- *     ^                        ^                        |
- *     |                        |    Prohibit expires    |
- *   --+                        +------------------------+
+ *  +------+  Start  +---------+   Trigger   +----------+
+ *  | Idle | ------->| Measure |------------>| Prohibit |
+ *  +------+         +---------+             +----------+
+ *     ^                  ^                        |
+ *     |                  |    Prohibit expires    |
+ *   --+                  +------------------------+
  *
  *
  */
@@ -82,11 +83,11 @@ private:
 
   // FSM states
   typedef enum {
-    state_none = 0, ///< NO state has been set yet
+    state_idle = 0, ///< Waits for start order
     state_measure,  ///< Performing measurement
     state_prohibit  ///< Waiting for HARQ to transmit CE command, NO measurement shall be stored
   } state_t;
-  state_t state = state_none;
+  state_t state = state_idle;
 
   /**
    * Reset Measurement and timer counter
@@ -120,17 +121,6 @@ private:
     return static_cast<int>(std::roundf(ta_us * 1e-6f / SRSLTE_LTE_TS / 16.0f));
   }
 
-  /**
-   * Runs initial state none
-   * @return 0
-   */
-  uint32_t run_state_none()
-  {
-    reset_measurements();
-    state = state_measure;
-    return 0;
-  }
-
   /**
    * Runs measure state
    * @return the number of enqueued MAC CE carrying TA commands
@@ -187,8 +177,9 @@ private:
   uint32_t run_fsm()
   {
     switch (state) {
-      case state_none:
-        return run_state_none();
+      case state_idle:
+        // Waits for Start order, do nothing
+        return 0;
       case state_measure:
         return run_state_measure();
       case state_prohibit:
@@ -210,6 +201,17 @@ public:
     run_fsm();
   }
 
+  /**
+   * Gives an start order to the FSM
+   */
+  void start()
+  {
+    // Transition to idle only if the current state is idle
+    if (state == state_idle) {
+      state = state_measure;
+    }
+  }
+
   /**
    * Pushes TA measurement and runs internal FSM
    *
diff --git a/srsenb/hdr/stack/mac/ue.h b/srsenb/hdr/stack/mac/ue.h
index 7074313bb..ab65d8a9c 100644
--- a/srsenb/hdr/stack/mac/ue.h
+++ b/srsenb/hdr/stack/mac/ue.h
@@ -59,15 +59,10 @@ public:
 
   uint32_t set_ta(int ta) override;
 
+  void     start_ta() { ta_fsm.start(); };
   uint32_t set_ta_us(float ta_us) { return ta_fsm.push_value(ta_us); };
   uint32_t tick_ta_fsm() { return ta_fsm.tick(); };
 
-  void     config(uint16_t           rnti,
-                  uint32_t           nof_prb,
-                  sched_interface*   sched,
-                  rrc_interface_mac* rrc_,
-                  rlc_interface_mac* rlc,
-                  srslte::log*       log_h);
   uint8_t* generate_pdu(uint32_t                        ue_cc_idx,
                         uint32_t                        harq_pid,
                         uint32_t                        tb_idx,
diff --git a/srsenb/src/stack/mac/mac.cc b/srsenb/src/stack/mac/mac.cc
index 96ccf0e4c..8dc1cdcd8 100644
--- a/srsenb/src/stack/mac/mac.cc
+++ b/srsenb/src/stack/mac/mac.cc
@@ -202,6 +202,9 @@ int mac::ue_cfg(uint16_t rnti, sched_interface::ue_cfg_t* cfg)
   }
   ue_ptr = it->second.get();
 
+  // Start TA FSM in UE entity
+  ue_ptr->start_ta();
+
   // Add RNTI to the PHY (pregenerate signals) now instead of after PRACH
   if (not ue_ptr->is_phy_added) {
     Info("Registering RNTI=0x%X to PHY...\n", rnti);