doxygen comment for e_route_type and improve comments for NetCostHandler::estimate_routing_chan_util()

Author: soheilshahrouz

libs/librrgraph/src/base/rr_graph_type.h

@@ -1,5 +1,4 @@
-#ifndef RR_GRAPH_TYPE_H
-#define RR_GRAPH_TYPE_H
+#pragma once
 
 #include <vector>
 #include "physical_types.h"
@@ -14,6 +13,7 @@ struct t_chan_width {
     std::vector<int> y_list;
 };
 
+/// @brief Specifies whether global routing or combined global and detailed routing is performed.
 enum class e_route_type {
     GLOBAL,
     DETAILED
@@ -46,5 +46,3 @@ enum class e_graph_type {
  * @see get_parallel_segs for more details.
  */
 typedef std::unordered_multimap<size_t, std::pair<size_t, e_parallel_axis>> t_unified_to_parallel_seg_index;
-
-#endif

vpr/src/place/net_cost_handler.cpp

@@ -1770,6 +1770,14 @@ std::pair<vtr::NdMatrix<double, 3>, vtr::NdMatrix<double, 3>> NetCostHandler::es
                                                  device_ctx.grid.height()}},
                                                0);
 
+
+    // For each net, this function estimates routing channel utilization by distributing
+    // the net's expected wirelength across its bounding box. The expected wirelength
+    // for each dimension (x, y) is computed proportionally based on the bounding box size
+    // in each direction. The wirelength in each dimension is then **evenly spread** across
+    // all grid locations within the bounding box, and the demand is accumulated in
+    // the channel utilization matrices.
+
     for (ClusterNetId net_id : cluster_ctx.clb_nlist.nets()) {
         if (!cluster_ctx.clb_nlist.net_is_ignored(net_id)) {
 

vpr/src/place/net_cost_handler.h

@@ -129,9 +129,11 @@ class NetCostHandler {
      * @brief Estimates routing channel utilization.
      *
      * For each net, distributes estimated wirelength across its bounding box
-     * and accumulates demand for different routing channels. Normalizes by channel widths.
+     * and accumulates demand for different routing channels. Normalizes by channel widths
+     * (e.g. a value of 0.5 means 50% of the wiring in a channel is expected to be used).
      *
      * @return Pair of matrices with relative CHANX and CHANY utilization.
+     *         The dimension order for each matrix is [layer][x][y].
      */
     std::pair<vtr::NdMatrix<double, 3>, vtr::NdMatrix<double, 3>> estimate_routing_chan_util() const;