diff --git a/openfpga/src/annotation/vpr_clustering_annotation.cpp b/openfpga/src/annotation/vpr_clustering_annotation.cpp
index e0c7ab575..8dbc2d6f4 100644
--- a/openfpga/src/annotation/vpr_clustering_annotation.cpp
+++ b/openfpga/src/annotation/vpr_clustering_annotation.cpp
@@ -86,5 +86,10 @@ void VprClusteringAnnotation::add_physical_pb(const ClusterBlockId& block_id,
   physical_pbs_[block_id] = physical_pb;
 }
 
+PhysicalPb& VprClusteringAnnotation::mutable_physical_pb(const ClusterBlockId& block_id) {
+  VTR_ASSERT(physical_pbs_.end() != physical_pbs_.find(block_id));
+
+  return physical_pbs_.at(block_id);
+}
 
 } /* End namespace openfpga*/
diff --git a/openfpga/src/annotation/vpr_clustering_annotation.h b/openfpga/src/annotation/vpr_clustering_annotation.h
index b72173e1d..f8e84bb02 100644
--- a/openfpga/src/annotation/vpr_clustering_annotation.h
+++ b/openfpga/src/annotation/vpr_clustering_annotation.h
@@ -41,6 +41,7 @@ class VprClusteringAnnotation {
                     const ClusterNetId& net_id);
     void adapt_truth_table(t_pb* pb, const AtomNetlist::TruthTable& tt);
     void add_physical_pb(const ClusterBlockId& block_id, const PhysicalPb& physical_pb);
+    PhysicalPb& mutable_physical_pb(const ClusterBlockId& block_id);
   private: /* Internal data */
     /* Pair a regular pb_type to its physical pb_type */
     std::map<ClusterBlockId, std::map<int, ClusterNetId>> net_names_;
diff --git a/openfpga/src/repack/physical_pb.cpp b/openfpga/src/repack/physical_pb.cpp
index a29b6d401..59417080e 100644
--- a/openfpga/src/repack/physical_pb.cpp
+++ b/openfpga/src/repack/physical_pb.cpp
@@ -16,6 +16,17 @@ PhysicalPb::physical_pb_range PhysicalPb::pbs() const {
   return vtr::make_range(pb_ids_.begin(), pb_ids_.end());
 }
 
+std::vector<PhysicalPbId> PhysicalPb::primitive_pbs() const {
+  std::vector<PhysicalPbId> results; 
+  /* The primitive pbs are those without any children */
+  for (auto pb : pbs()) {
+    if (true == child_pbs_[pb].empty()) {
+      results.push_back(pb);
+    } 
+  }
+  return results;
+}
+
 std::string PhysicalPb::name(const PhysicalPbId& pb) const {
   VTR_ASSERT(true == valid_pb_id(pb));
   return names_[pb];
diff --git a/openfpga/src/repack/physical_pb.h b/openfpga/src/repack/physical_pb.h
index d5f5b00a3..caea0a0b9 100644
--- a/openfpga/src/repack/physical_pb.h
+++ b/openfpga/src/repack/physical_pb.h
@@ -39,6 +39,7 @@ class PhysicalPb {
     typedef vtr::Range<physical_pb_iterator> physical_pb_range;
   public: /* Public aggregators */
     physical_pb_range pbs() const;
+    std::vector<PhysicalPbId> primitive_pbs() const;
     std::string name(const PhysicalPbId& pb) const;
     PhysicalPbId find_pb(const t_pb_graph_node* name) const;
     PhysicalPbId parent(const PhysicalPbId& pb) const;