diff --git a/openfpga/src/annotation/route_clock_rr_graph.cpp b/openfpga/src/annotation/route_clock_rr_graph.cpp
index fe1b61ed3..b26122a9f 100644
--- a/openfpga/src/annotation/route_clock_rr_graph.cpp
+++ b/openfpga/src/annotation/route_clock_rr_graph.cpp
@@ -10,12 +10,68 @@
 namespace openfpga {
 
 /********************************************************************
- * Append a programmable clock network to an existing routing resource graph
+ * Route a clock tree on an existing routing resource graph
+ * The strategy is to route spine one by one
+ * - route the spine from the starting point to the ending point
+ * - route the spine-to-spine switching points
+ * - route the spine-to-IPIN connections (only for the last level)
+ *******************************************************************/
+static 
+int route_clock_tree_rr_graph() {
+  for (auto ispine : clk_ntwk.spines(clk_tree)) {
+    for (auto ipin : clk_ntwk.pins(clk_tree)) {
+      /* Route the spine from starting point to ending point */
+      std::vector<vtr::Point<size_t>> spine_coords = clk_ntwk.spine_coords(ispine);
+      for (size_t icoord = 0; icoord < spine_coords.size() - 1; ++icoord) {
+        vtr::Point<size_t> src_coord = spine_coords[icoord];
+        vtr::Point<size_t> des_coord = spine_coords[icoord + 1];
+        Direction src_spine_direction = clk_ntwk.spine_direction(ispine);
+        Direction des_spine_direction = clk_ntwk.spine_direction(ispine);
+        ClockLevelId src_spine_level = clk_ntwk.spine_level(ispine); 
+        ClockLevelId des_spine_level = clk_ntwk.spine_level(ispine); 
+        RRNodeId src_node = clk_rr_lookup.find_node(src_coord.x(), src_coord.y(), clk_tree, src_spine_level, ipin, src_spine_direction);
+        RRNodeId des_node = clk_rr_lookup.find_node(des_coord.x(), des_coord.y(), clk_tree, des_spine_level, ipin, des_spine_direction);
+        vpr_routing_annotation.set_rr_node_prev_node(rr_graph, des_node, src_node);
+      }
+      /* Route the spine-to-spine switching points */
+      for (ClockSwitchPointId switch_point_id : clk_ntwk.spine_switch_points(ispine)) {
+        vtr::Point<size_t> src_coord = clk_ntwk.spine_switch_point(ispine, switch_point_id);
+        ClockSpineId des_spine = clk_ntwk.spine_switch_point_tap(ispine, switch_point_id);
+        vtr::Point<size_t> des_coord = clk_ntwk.spine_start_point(des_spine);
+        Direction src_spine_direction = clk_ntwk.spine_direction(ispine);
+        Direction des_spine_direction = clk_ntwk.spine_direction(des_spine);
+        ClockLevelId src_spine_level = clk_ntwk.spine_level(ispine); 
+        ClockLevelId des_spine_level = clk_ntwk.spine_level(des_spine); 
+        RRNodeId src_node = clk_rr_lookup.find_node(src_coord.x(), src_coord.y(), clk_tree, src_spine_level, ipin, src_spine_direction);
+        RRNodeId des_node = clk_rr_lookup.find_node(des_coord.x(), des_coord.y(), clk_tree, des_spine_level, ipin, des_spine_direction);
+        vpr_routing_annotation.set_rr_node_prev_node(rr_graph, des_node, src_node);
+      }
+      /* Route the spine-to-IPIN connections (only for the last level) */
+      if (clk_ntwk.is_last_level(clk_tree, ispine)) {
+        /* Connect to any fan-out node which is IPIN */
+        for (size_t icoord = 0; icoord < spine_coords.size(); ++icoord) {
+          vtr::Point<size_t> src_coord = spine_coords[icoord];
+          Direction src_spine_direction = clk_ntwk.spine_direction(ispine);
+          ClockLevelId src_spine_level = clk_ntwk.spine_level(ispine); 
+          RRNodeId src_node = clk_rr_lookup.find_node(src_coord.x(), src_coord.y(), clk_tree, src_spine_level, ipin, src_spine_direction);
+          for (RREdgeId edge : rr_graph.edges(src_node)) {
+            RRNodeId des_node = rr_graph.edge_sink_node(edge);
+            if (rr_graph.node_type(des_node) == IPIN) {
+              vpr_routing_annotation.set_rr_node_prev_node(rr_graph, des_node, src_node);
+            }
+          }
+        }
+      }
+    }
+  }
+  return CMD_EXEC_SUCCESS;
+}
+
+/********************************************************************
+ * Route a clock network based on an existing routing resource graph
  * This function will do the following jobs:
- * - Estimate the number of clock nodes and pre-allocate memory
- * - Add clock nodes
- * - Build edges between clock nodes
- * - Sanity checks
+ * - configure the routing annotation w.r.t. the clock node connections
+ * - quick check to ensure routing is valid
  *******************************************************************/
 int route_clock_rr_graph(VprRoutingAnnotation& vpr_routing_annotation,
                          const DeviceContext& vpr_device_ctx,
@@ -41,6 +97,12 @@ int route_clock_rr_graph(VprRoutingAnnotation& vpr_routing_annotation,
   }
 
   /* TODO: Route spines one by one */
+  for (auto itree : clk_ntwk.trees()) {
+    int status = route_clock_tree_rr_graph();
+    if (status == CMD_EXEC_FATAL_ERROR) {
+      return status;
+    }
+  }
 
   /* TODO: Sanity checks */