Added -buffer_cell support for buffer_ports command.

e.g., "buffer_ports -buffer_cell <lib_cell>"

Author: jhkim-pii

.gitignore

@@ -11,6 +11,7 @@
 *.orig
 *.vscode
 *.sw[opqr]
+*.code-workspace
 TAGS
 *~
 \#*#

src/rsz/include/rsz/Resizer.hh

@@ -259,8 +259,8 @@ class Resizer : public dbStaState, public dbNetworkObserver
   // Remove all or selected buffers from the netlist.
   void removeBuffers(InstanceSeq insts);
   void unbufferNet(Net* net);
-  void bufferInputs();
-  void bufferOutputs();
+  void bufferInputs(LibertyCell* buffer_cell = nullptr);
+  void bufferOutputs(LibertyCell* buffer_cell = nullptr);
 
   // from sta::dbNetworkObserver callbacks
   void postReadLiberty() override;
@@ -457,6 +457,7 @@ class Resizer : public dbStaState, public dbNetworkObserver
                             float max_drive_resist);
   void findBuffers();
   void findFastBuffers();
+  LibertyCell* findLowestDriveBuffer(LibertyCell* buffer_cell = nullptr);
   bool isLinkCell(LibertyCell* cell) const;
   void findTargetLoads();
   void balanceBin(const std::vector<odb::dbInst*>& bin,

src/rsz/src/Resizer.cc

@@ -746,17 +746,47 @@ void Resizer::findBuffers()
   }
 }
 
+LibertyCell* Resizer::findLowestDriveBuffer(LibertyCell* buffer_cell)
+{
+  // Prefer user-specified buffer cell if provided.
+  if (buffer_cell) {
+    logger_->info(RSZ, 31, "Using the given buffer: {}", buffer_cell->name());
+    return buffer_cell;
+  }
+
+  // Otherwise, find the weakest buffer with the lowest drive resistance.
+  findBuffers(); // updates buffer_lowest_drive_
+
+  // No buffer?
+  if (buffer_lowest_drive_ == nullptr) {
+    logger_->error(RSZ, 23, "No buffers found.");
+    return nullptr;
+  } 
+
+  logger_->info(
+    RSZ, 52, 
+    "Using the buffer with the lowest driving resistance: {}", 
+    buffer_lowest_drive_->name());
+  return buffer_lowest_drive_;
+}
+
 bool Resizer::isLinkCell(LibertyCell* cell) const
 {
   return network_->findLibertyCell(cell->name()) == cell;
 }
 
 ////////////////////////////////////////////////////////////////
 
-void Resizer::bufferInputs()
+void Resizer::bufferInputs(LibertyCell* buffer_cell)
 {
   init();
-  findBuffers();
+  
+  // find the buffer to use
+  LibertyCell* buffer_to_use = findLowestDriveBuffer(buffer_cell);
+  if (buffer_to_use == nullptr) {
+    return;
+  }
+
   sta_->ensureClkNetwork();
   inserted_buffer_count_ = 0;
   buffer_moved_into_core_ = false;
@@ -776,14 +806,14 @@ void Resizer::bufferInputs()
           // Hands off special nets.
           && !db_network_->isSpecial(net) && hasPins(net)) {
         // repair_design will resize to target slew.
-        bufferInput(pin, buffer_lowest_drive_);
+        bufferInput(pin, buffer_to_use);
       }
     }
   }
 
+  logger_->info(
+      RSZ, 27, "Inserted {} input buffers.", inserted_buffer_count_);
   if (inserted_buffer_count_ > 0) {
-    logger_->info(
-        RSZ, 27, "Inserted {} input buffers.", inserted_buffer_count_);
     level_drvr_vertices_valid_ = false;
   }
 }
@@ -972,10 +1002,16 @@ Instance* Resizer::bufferInput(const Pin* top_pin, LibertyCell* buffer_cell)
   return buffer;
 }
 
-void Resizer::bufferOutputs()
+void Resizer::bufferOutputs(LibertyCell* buffer_cell)
 {
   init();
-  findBuffers();
+
+  // find the buffer to use
+  LibertyCell* buffer_to_use = findLowestDriveBuffer(buffer_cell);
+  if (buffer_to_use == nullptr) {
+    return;
+  }
+
   inserted_buffer_count_ = 0;
   buffer_moved_into_core_ = false;
 
@@ -995,14 +1031,14 @@ void Resizer::bufferOutputs()
           // drivers.
           && !hasTristateOrDontTouchDriver(net) && !vertex->isConstant()
           && hasPins(net)) {
-        bufferOutput(pin, buffer_lowest_drive_);
+        bufferOutput(pin, buffer_to_use);
       }
     }
   }
 
+  logger_->info(
+      RSZ, 28, "Inserted {} output buffers.", inserted_buffer_count_);
   if (inserted_buffer_count_ > 0) {
-    logger_->info(
-        RSZ, 28, "Inserted {} output buffers.", inserted_buffer_count_);
     level_drvr_vertices_valid_ = false;
   }
 }
@@ -1056,6 +1092,7 @@ void Resizer::bufferOutput(const Pin* top_pin, LibertyCell* buffer_cell)
   sta_->disconnectPin(const_cast<Pin*>(top_pin));
 
   LibertyPort *input, *output;
+  assert(buffer_cell);
   buffer_cell->bufferPorts(input, output);
 
   string buffer_name = makeUniqueInstName("output");

src/rsz/src/Resizer.i

@@ -409,19 +409,19 @@ set_dont_touch_net(Net *net,
 }
 
 void
-buffer_inputs()
+buffer_inputs(LibertyCell *buffer_cell)
 {
   ensureLinked();
   Resizer *resizer = getResizer();
-  resizer->bufferInputs();
+  resizer->bufferInputs(buffer_cell);
 }
 
 void
-buffer_outputs()
+buffer_outputs(LibertyCell *buffer_cell)
 {
   ensureLinked();
   Resizer *resizer = getResizer();
-  resizer->bufferOutputs();
+  resizer->bufferOutputs(buffer_cell);
 }
 
 void

src/rsz/src/Resizer.tcl

@@ -9,8 +9,36 @@ proc get_db_tech_checked { } {
   }
   return $tech
 }
+
+proc parse_buffer_cell { keys_var required } {
+  upvar 1 $keys_var keys
+  set buffer_cell "NULL"
+
+  if { [info exists keys(-buffer_cell)] } {
+    set buffer_cell_name $keys(-buffer_cell)
+    if { $buffer_cell_name ne "" } {
+      set buffer_cell [sta::get_lib_cell_error "-buffer_cell" $buffer_cell_name]
+
+      # the lib cell is a buffer?
+      if { $buffer_cell ne "NULL" && ![get_property $buffer_cell is_buffer] } {
+        utl::error RSZ 211 "[get_name $buffer_cell] is not a buffer."
+      }
+    }
+  }
+
+  # required argument is missing?
+  if { $buffer_cell == "NULL" && $required } {
+    utl::error RSZ 212 "-buffer_cell is required for buffer insertion."    
+  }
+
+  return $buffer_cell
+}
+
+# namespace eval rsz
 }
 
+
+
 # Units are from OpenSTA (ie Liberty file or set_cmd_units).
 sta::define_cmd_args "set_layer_rc" { [-layer layer]\
                                         [-via via_layer]\
@@ -441,8 +469,8 @@ proc report_dont_touch { args } {
 }
 
 sta::define_cmd_args "buffer_ports" {[-inputs] [-outputs]\
-                                       [-max_utilization util]\
-                                       [-buffer_cell buf_cell]}
+                                     [-max_utilization util]\
+                                     [-buffer_cell buf_cell]}
 
 proc buffer_ports { args } {
   sta::parse_key_args "buffer_ports" args \
@@ -455,14 +483,17 @@ proc buffer_ports { args } {
     set buffer_inputs 1
     set buffer_outputs 1
   }
+
   sta::check_argc_eq0 "buffer_ports" $args
 
   rsz::set_max_utilization [rsz::parse_max_util keys]
+  set buffer_cell [rsz::parse_buffer_cell keys 0] ; # 0: optional argument
+
   if { $buffer_inputs } {
-    rsz::buffer_inputs
+    rsz::buffer_inputs $buffer_cell
   }
   if { $buffer_outputs } {
-    rsz::buffer_outputs
+    rsz::buffer_outputs $buffer_cell
   }
 }
 
@@ -1056,7 +1087,7 @@ proc replace_arith_modules { args } {
   if { [info exists keys(-target)] } {
     set target $keys(-target)
     if { [lsearch -exact {setup hold power area} $target] == -1 } {
-      util::error "RSZ" 164 "-target needs to be one of setup, hold, power, area"
+      utl::error "RSZ" 164 "-target needs to be one of setup, hold, power, area"
     }
   } else {
     set target "setup"

src/rsz/test/CMakeLists.txt

@@ -12,6 +12,7 @@ or_integration_tests(
     buffer_ports6
     buffer_ports7
     buffer_ports8
+    buffer_ports9
     buffer_varying_lengths
     clone_flat
     clone_hier

src/rsz/test/buffer_ports1.ok

@@ -4,6 +4,8 @@
 [INFO ODB-0131]     Created 5 components and 27 component-terminals.
 [INFO ODB-0132]     Created 2 special nets and 10 connections.
 [INFO ODB-0133]     Created 12 nets and 14 connections.
+[INFO RSZ-0052] Using the buffer with the lowest driving resistance: BUF_X1
 [INFO RSZ-0027] Inserted 2 input buffers.
+[INFO RSZ-0052] Using the buffer with the lowest driving resistance: BUF_X1
 [INFO RSZ-0028] Inserted 1 output buffers.
 No differences found.

src/rsz/test/buffer_ports3.ok

@@ -4,4 +4,7 @@
 [INFO ODB-0130]     Created 8 pins.
 [INFO ODB-0131]     Created 1 components and 10 component-terminals.
 [INFO ODB-0133]     Created 8 nets and 8 connections.
+[INFO RSZ-0052] Using the buffer with the lowest driving resistance: BUF_X1
+[INFO RSZ-0027] Inserted 0 input buffers.
+[INFO RSZ-0052] Using the buffer with the lowest driving resistance: BUF_X1
 [INFO RSZ-0028] Inserted 4 output buffers.

src/rsz/test/buffer_ports4.ok

@@ -4,6 +4,7 @@
 [INFO ODB-0131]     Created 250 components and 2000 component-terminals.
 [INFO ODB-0132]     Created 2 special nets and 500 connections.
 [INFO ODB-0133]     Created 2 nets and 500 connections.
+[INFO RSZ-0052] Using the buffer with the lowest driving resistance: BUF_X1
 [INFO RSZ-0027] Inserted 1 input buffers.
 max slew
 

src/rsz/test/buffer_ports5.ok

@@ -4,5 +4,7 @@
 [INFO ODB-0131]     Created 5 components and 27 component-terminals.
 [INFO ODB-0132]     Created 2 special nets and 10 connections.
 [INFO ODB-0133]     Created 10 nets and 14 connections.
+[INFO RSZ-0052] Using the buffer with the lowest driving resistance: BUF_X1
 [INFO RSZ-0027] Inserted 2 input buffers.
+[INFO RSZ-0052] Using the buffer with the lowest driving resistance: BUF_X1
 [INFO RSZ-0028] Inserted 1 output buffers.