[AP][Timing] More Updates to Comments

Author: AlexandreSinger

vpr/src/analytical_place/analytical_solver.cpp

@@ -162,7 +162,9 @@ void AnalyticalSolver::update_net_weights(const PreClusterTimingManager& pre_clu
 
         // When optimizing for WL, the net weights are just set to 1 (meaning
         // that we want to minimize the WL of nets).
-        // When optimizing for timing, the net weights are set to the cirticality.
+        // When optimizing for timing, the net weights are set to the timing
+        // criticality, which is based on the lowest slack of any edge belonging
+        // to this net.
         // The intuition is that we care more about shrinking the wirelength of
         // more critical connections than less critical ones.
         // Use the AP timing trade-off term to linearly interpolate between these

vpr/src/analytical_place/global_placer.cpp

@@ -284,6 +284,9 @@ static void update_timing_info_with_gp_placement(PreClusterTimingManager& pre_cl
         // NOTE: We may not have enough information to know which pin the driver
         //       and sink block will use; however the delay models that we care
         //       about do not use this feature yet.
+        //       We do not know this information since those pins are cluster-
+        //       level pins, and the cluster-level blocks have not been created
+        //       yet.
         // TODO: Handle the from and to pins better.
         float delay = place_delay_model.delay(driver_block_loc,
                                               0 /*from_pin*/,

vpr/src/timing/PreClusterTimingManager.h

@@ -93,7 +93,7 @@ class PreClusterTimingManager {
      *        it terminates at.
      *
      * This method only updates an internal variable to this class and does not
-     * perform STA. Call the update_timing_info after updating the delays of all
+     * perform STA. Call update_timing_info after updating the delays of all
      * arcs to save time.
      */
     void set_timing_arc_delay(AtomPinId sink_pin_id, float delay) {
@@ -153,8 +153,8 @@ class PreClusterTimingManager {
     std::shared_ptr<SetupTimingInfo> timing_info_;
 
     /// @brief Delays of all timing arcs in the atom netlist. This is used to
-    ///        tell the delay calculator what delay to use for external net
-    ///        delays. Here, we use sink pins as unique identifiers for the the
-    ///        timing arc.
+    ///        hold the estimated delays of all atom connections so that the
+    ///        delay calculator can query them when Tatum performs a timing analysis.
+    ///        Here, we use sink pins as unique identifiers for the the timing arc.
     vtr::vector<AtomPinId, float> timing_arc_delays_;
 };