# OpenROAD **Repository Path**: Flians/OpenROAD ## Basic Information - **Project Name**: OpenROAD - **Description**: No description available - **Primary Language**: Unknown - **License**: BSD-3-Clause - **Default Branch**: master - **Homepage**: None - **GVP Project**: No ## Statistics - **Stars**: 0 - **Forks**: 0 - **Created**: 2020-10-09 - **Last Updated**: 2024-06-23 ## Categories & Tags **Categories**: Uncategorized **Tags**: None ## README # OpenROAD OpenROAD is a chip physical design tool. It uses the OpenDB database as a design database and representation. OpenSTA is used for static timing analysis. #### Build The OpenROAD build requires the following packages: Tools * cmake 3.14 * gcc 8.3.0 or clang * bison 3.0.5 * flex 2.6.4 * swig 4.0 Libraries * boost 1.68 * tcl 8.6 * zlib * eigen * lemon * qt5 * CImg (optional for replace) See `Dockerfile` for an example of how to install these packages. ``` git clone --recursive https://github.com/The-OpenROAD-Project/OpenROAD.git cd OpenROAD mkdir build cd build cmake .. make ``` OpenROAD git submodules (cloned by the --recursive flag) are located in `/src`. The default build type is RELEASE to compile optimized code. The resulting executable is in `build/src/openroad`. Optional CMake variables passed as -D= arguments to CMake are show below. ``` CMAKE_BUILD_TYPE DEBUG|RELEASE CMAKE_CXX_FLAGS - additional compiler flags TCL_LIB - path to tcl library TCL_HEADER - path to tcl.h ZLIB_ROOT - path to zlib CMAKE_INSTALL_PREFIX ``` The default install directory is `/usr/local`. To install in a different directory with CMake use: ``` cmake .. -DCMAKE_INSTALL_PREFIX= ``` Alternatively, you can use the `DESTDIR` variable with make. ``` make DESTDIR= install ``` There are a set of regression tests in `/test`. ``` test/regression src/resizer/test/regression ``` #### Run ``` openroad -help show help and exit -version show version and exit -no_init do not read .openroad init file -no_splash do not show the license splash at startup -exit exit after reading cmd_file cmd_file source cmd_file ``` OpenROAD sources the Tcl command file `~/.openroad` unless the command line option `-no_init` is specified. OpenROAD then sources the command file cmd_file if it is specified on the command line. Unless the `-exit` command line flag is specified it enters and interactive Tcl command interpreter. OpenROAD is run using Tcl scripts. The following commands are used to read and write design data. ``` read_lef [-tech] [-library] filename read_def filename write_def [-version 5.8|5.6|5.5|5.4|5.3] filename read_verilog filename write_verilog filename read_db filename write_db filename ``` Use the Tcl `source` command to read commands from a file. ``` source [-echo] file ``` If an error is encountered in a command while reading the command file, the error is printed and no more commands are read from the file. If `file_continue_on_error` is `1` OpenROAD will continue reading commands after the error. If `exit_on_error` is `1` OpenROAD will exit when it encounters an error. OpenROAD can be used to make a OpenDB database from LEF/DEF, or Verilog (flat or hierarchical). Once the database is made it can be saved as a file with the `write_db` command. OpenROAD can then read the database with the `read_db` command without reading LEF/DEF or Verilog. The `read_lef` and `read_def` commands can be used to build an OpenDB database as shown below. The `read_lef -tech` flag reads the technology portion of a LEF file. The `read_lef -library` flag reads the MACROs in the LEF file. If neither of the `-tech` and `-library` flags are specified they default to `-tech -library` if no technology has been read and `-library` if a technology exists in the database. ``` read_lef liberty1.lef read_def reg1.def # Write the db for future runs. write_db reg1.db ``` The `read_verilog` command is used to build an OpenDB database as shown below. Multiple verilog files for a hierarchical design can be read. The `link_design` command is used to flatten the design and make a database. ``` read_lef liberty1.lef read_verilog reg1.v link_design top # Write the db for future runs. write_db reg1.db ``` #### Example Scripts Example scripts demonstrating how to run OpenROAD on sample designs can be found in /test. Flow tests taking sample designs from synthesis verilog to routed design in the open source technologies Nangate45 and Sky130 are shown below. ``` gcd_nangate45.tcl aes_nangate45.tcl tinyRocket_nangate45.tcl gcd_sky130.tcl aes_sky130.tcl ibex_sky130.tcl ``` Each of these designs use the common script `flow.tcl`. #### Initialize Floorplan ``` initialize_floorplan [-site site_name] LEF site name for ROWS [-tracks tracks_file] routing track specification -die_area "lx ly ux uy" die area in microns [-core_area "lx ly ux uy"] core area in microns or -utilization util utilization (0-100 percent) [-aspect_ratio ratio] height / width, default 1.0 [-core_space space or "bottom top left right"] space around core. Should either be one value for all margins or 4 values for each margin. default 0.0 (microns) ``` The die area and core size used to write ROWs can be specified explicitly with the -die_area and -core_area arguments. Alternatively, the die and core area can be computed from the design size and utilization as show below: If no -tracks file is used the routing layers from the LEF are used. ``` core_area = design_area / (utilization / 100) core_width = sqrt(core_area / aspect_ratio) core_height = core_width * aspect_ratio core = ( core_space_left, core_space_bottom ) ( core_space_left + core_width, core_space_bottom + core_height ) die = ( 0, 0 ) ( core_width + core_space_left + core_space_right, core_height + core_space_bottom + core_space_top ) ``` Place pins around core boundary. ``` auto_place_pins pin_layer ``` #### I/O pin assignment Assign I/O pins to on-track locations at the boundaries of the core while optimizing I/O nets wirelength. I/O pin assignment also creates a metal shape for each I/O pin using min-area rules. Use the following command to perform I/O pin assignment: ``` place_ios [-hor_layer h_layer] [-ver_layer v_layer] [-random_seed seed] [-random] ``` - ``-hor_layer`` (mandatory). Set the layer to create the metal shapes of I/O pins assigned to horizontal tracks. - ``-ver_layer`` (mandatory). Set the layer to create the metal shapes of I/O pins assigned to vertical tracks. - ``-random_seed``. Set the seed for random operations. - ``-random``. When this flag is enabled, the I/O pin assignment is random. #### Gate Resizer Gate resizer commands are described below. The resizer commands stop when the design area is `-max_utilization util` percent of the core area. `util` is between 0 and 100. ``` set_wire_rc [-clock] [-data] [-layer layer_name] [-resistance res ] [-capacitance cap] [-corner corner_name] ``` The `set_wire_rc` command sets the resistance and capacitance used to estimate delay of routing wires. Separate values can be specified for clock and data nets with the `-data` and `-clock` flags. Without either `-data` or `-clock` the resistance and capacitance for clocks and data nets are set. Use `-layer` or `-resistance` and `-capacitance`. If `-layer` is used, the LEF technology resistance and area/edge capacitance values for the layer are used for a minimum width wire on the layer. The resistance and capacitance values per length of wire, not per square or per square micron. The units for `-resistance` and `-capacitance` are from the first liberty file read, resistance_unit/distance_unit (typically kohms/micron) and liberty capacitance_unit/distance_unit (typically pf/micron or ff/micron). If no distance units are not specied in the liberty file microns are used. ``` estimate_parasitics -placement ``` Estimate RC parasitics based on placed component pin locations. If there are no component locations no parasitics are added. The resistance and capacitance are per distance unit of a routing wire. Use the `set_units` command to check units or `set_cmd_units` to change units. They should represent "average" routing layer resistance and capacitance. If the set_wire_rc command is not called before resizing, the default_wireload model specified in the first liberty file or with the SDC set_wire_load command is used to make parasitics. ``` set_dont_use lib_cells ``` The `set_dont_use` command removes library cells from consideration by the resizer. `lib_cells` is a list of cells returned by `get_lib_cells` or a list of cell names (wildcards allowed). For example, `DLY*` says do not use cells with names that begin with `DLY` in all libraries. ``` buffer_ports [-inputs] [-outputs] -buffer_cell buffer_cell ``` The `buffer_ports -inputs` command adds a buffer between the input and its loads. The `buffer_ports -outputs` adds a buffer between the port driver and the output port. If The default behavior is `-inputs` and `-outputs` if neither is specified. ``` repair_design [-max_wire_length max_length] -buffer_cell buffer_cell ``` The `repair_design` inserts buffers on nets to repair max slew, max capacitance, max fanout violations, and on long wires to reduce RC delay in the wire. Use `-max_wire_length` to specify the maximum lenth of wires. The resistance/capacitance values in `set_wire_rc` are used to find the wire delays. Use the `set_max_fanout` SDC command to set the maximum fanout for the design. ``` set_max_fanout [current_design] ``` ``` resize [-libraries resize_libraries] [-max_utilization util] ``` The `resize` command resizes gates to normalize slews. The `-libraries` option specifies which libraries to use when resizing. `resize_libraries` defaults to all of the liberty libraries that have been read. Some designs have multiple libraries with different transistor thresholds (Vt) and are used to trade off power and speed. Chosing a low Vt library uses more power but results in a faster design after the resizing step. ``` repair_tie_fanout [-separation dist] [-verbose] lib_port ``` The `repair_tie_fanout` command connects each tie high/low load to a copy of the tie high/low cell. `lib_port` is the tie high/low port, which can be a library/cell/port name or object returned by `get_lib_pins`. The tie high/low instance is separaated from the load by `dist` (in liberty units, typically microns). ``` repair_hold_violations -buffer_cell buffer_cell [-max_utilization util] ``` The `repair_hold_violations` command inserts buffers to repair hold check violations. ``` report_design_area ``` The `report_design_area` command reports the area of the design's components and the utilization. ``` report_floating_nets [-verbose] ``` The `report_floating_nets` command reports nets with only one pin connection. Use the `-verbose` flag to see the net names. A typical resizer command file is shown below. ``` # resizer/test/gcd_resize.tcl read_liberty Nangate_typ.lib read_lef Nangate.lef read_def gcd_placed.def read_sdc gcd.sdc set_wire_rc -layer metal2 set buffer_cell BUF_X4 set_dont_use {CLKBUF_* AOI211_X1 OAI211_X1} buffer_ports -buffer_cell $buffer_cell repair_design -max_wire_length 100 -buffer_cell $buffer_cell resize repair_tie_fanout LOGIC0_X1/Z repair_tie_fanout LOGIC1_X1/Z repair_hold_violations -buffer_cell $buffer_cell resize ``` Note that OpenSTA commands can be used to report timing metrics before or after resizing the design. ``` set_wire_rc -layer metal2 report_checks report_tns report_wns report_checks resize report_checks report_tns report_wns ``` #### Timing Analysis Timing analysis commands are documented in src/OpenSTA/doc/OpenSTA.pdf. After the database has been read from LEF/DEF, Verilog or an OpenDB database, use the `read_liberty` command to read Liberty library files used by the design. The example script below timing analyzes a database. ``` read_liberty liberty1.lib read_db reg1.db create_clock -name clk -period 10 {clk1 clk2 clk3} set_input_delay -clock clk 0 {in1 in2} set_output_delay -clock clk 0 out report_checks ``` #### Tapcell Tapcell and endcap insertion. ``` tapcell -tapcell_master -endcap_master -endcap_cpp -distance -halo_width_x -halo_width_y -tap_nwin2_master -tap_nwin3_master -tap_nwout2_master -tap_nwout3_master -tap_nwintie_master -tap_nwouttie_master -cnrcap_nwin_master -cnrcap_nwout_master -incnrcap_nwin_master -incnrcap_nwout_master -tbtie_cpp -no_cell_at_top_bottom -add_boundary_cell ``` You can find script examples for both 45nm/65nm and 14nm in ```tapcell/etc/scripts``` #### Global Placement RePlAce global placement. ``` global_placement [-timing_driven] [-bin_grid_count grid_count] ``` - **timing_driven**: Enable timing-driven mode - **grid_count**: [64,128,256,512,..., int]. Default: Defined by internal algorithm. Use the `set_wire_rc` command to set resistance and capacitance of estimated wires used for timing. #### Detailed Placement The `detailed_placement` command does detailed placement of instances to legal locations after global placement. ``` set_placement_padding -global|-instances insts|-masters masters [-left pad_left] [-right pad_right] detailed_placement [-max_displacement rows] check_placement [-verbose] filler_placement filler_masters optimimize_mirroring ``` The `set_placement_padding` command sets left and right padding in multiples of the row site width. Use the `set_placement_padding` command before legalizing placement to leave room for routing. Use the `-global` flag for padding that applies to all instances. Use the `instances` argument for instances specific padding. The instances can be a list of instance name, or instance object returned by the SDC `get_cells` command. To specify padding for all instances of a common master, use the `-filter "ref_name == " option to `get_cells`. The `set_power_net` command is used to set the power and ground special net names. The defaults are `VDD` and `VSS`. The `check_placement` command checks the placement legality. It returns `1` if the placement is legal. The `filler_placement` command fills gaps between detail placed instances to connect the power and ground rails in the rows. `filler_masters` is a list of master/macro names to use for filling the gaps. Wildcard matching is supported, so `FILL*` will match `FILLCELL_X1 FILLCELL_X16 FILLCELL_X2 FILLCELL_X32 FILLCELL_X4 FILLCELL_X8`. The `optimimize_mirroring` command mirrors instances about the Y axis in vane attempt to minimize the total wire length (hpwl). #### Clock Tree Synthesis Create clock tree subnets. There are currently two ways one can run this command. The first is if the user does not have a characterization file. Thus, the wire segments are created manually based on the user parameters. ``` clock_tree_synthesis -buf_list \ -sqr_cap \ -sqr_res \ [-root_buf ] \ [-max_slew ] \ [-max_cap ] \ [-slew_inter ] \ [-cap_inter ] \ [-wire_unit ] \ [-clk_nets ] \ [-out_path ] \ [-characterization_only] ``` - ``-buf_list`` are the master cells (buffers) that will be considered when making the wire segments. - ``-sqr_cap`` is the capacitance (in picofarad) per micrometer (thus, the same unit that is used in the LEF syntax) to be used in the wire segments. - ``-sqr_res`` is the resistance (in ohm) per micrometer (thus, the same unit that is used in the LEF syntax) to be used in the wire segments. - ``-root_buffer`` is the master cell of the buffer that serves as root for the clock tree. If this parameter is omitted, the first master cell from ``-buf_list`` is taken. - ``-max_slew`` is the max slew value (in seconds) that the characterization will test. If this parameter is omitted, the code tries to obtain the value from the liberty file. - ``-max_cap`` is the max capacitance value (in farad) that the characterization will test. If this parameter is omitted, the code tries to obtain the value from the liberty file. - ``-slew_inter`` is the time value (in seconds) that the characterization will consider for results. If this parameter is omitted, the code gets the default value (5.0e-12). Be careful that this value can be quite low for bigger technologies (>65nm). - ``-cap_inter`` is the capacitance value (in farad) that the characterization will consider for results. If this parameter is omitted, the code gets the default value (5.0e-15). Be careful that this value can be quite low for bigger technologies (>65nm). - ``-wire_unit`` is the minimum unit distance between buffers for a specific wire. If this parameter is omitted, the code gets the value from ten times the height of ``-root_buffer``. - ``-clk_nets`` is a string containing the names of the clock roots. If this parameter is omitted, TritonCTS looks for the clock roots automatically. - ``-out_path`` is the output path (full) that the lut.txt and sol_list.txt files will be saved. This is used to load an existing characterization, without creating one from scratch. - ``-only_characterization`` is a flag that, when specified, makes so that only the library characterization step is run and no clock tree is inserted in the design. Instead of creating a characterization, you can use use the following parameters to load a characterization file. ``` clock_tree_synthesis -lut_file \ -sol_list \ -root_buf \ [-wire_unit ] \ [-clk_nets ] ``` - ``-lut_file`` (mandatory) is the file containing delay, power and other metrics for each segment. - ``-sol_list`` (mandatory) is the file containing the information on the topology of each segment (wirelengths and buffer masters). - ``-sqr_res`` (mandatory) is the resistance (in ohm) per database units to be used in the wire segments. - ``-root_buffer`` (mandatory) is the master cell of the buffer that serves as root for the clock tree. If this parameter is omitted, you can use the ``-buf_list`` argument, using the first master cell. If both arguments are omitted, an error is raised. - ``-wire_unit`` (optional) is the minimum unit distance between buffers for a specific wire, based on your ``-lut_file``. If this parameter is omitted, the code gets the value from the header of the ``-lut_file``. For the old technology characterization, described [here](https://github.com/The-OpenROAD-Project/TritonCTS/blob/master/doc/Technology_characterization.md), this argument is mandatory, and omitting it raises an error. - ``-clk_nets`` (optional) is a string containing the names of the clock roots. If this parameter is omitted, TritonCTS looks for the clock roots automatically. Another command available from TritonCTS is ``report_cts``. It is used to extract metrics after a successful ``clock_tree_synthesis`` run. These are: Number of Clock Roots, Number of Buffers Inserted, Number of Clock Subnets, and Number of Sinks. ``` read_lef "mylef.lef" read_liberty "myliberty.lib" read_def "mydef.def" read_verilog "myverilog.v" read_sdc "mysdc.sdc" report_checks clock_tree_synthesis -lut_file "lut.txt" \ -sol_list "sol_list.txt" \ -root_buf "BUF_X4" \ -wire_unit 20 report_cts [-out_file "file.txt"] ``` - ``-out_file`` (optional) is the file containing the TritonCTS reports. If this parameter is omitted, the metrics are shown on the standard output. #### Global Routing Global router options and commands are described below. ``` fastroute [-guide_file out_file] \ [-layers min-max] [-tile_size tile_size] \ [-verbose verbose] \ [-overflow_iterations iterations] \ [-grid_origin {x y}] \ [-report_congestion congest_file] \ [-clock_layers min-max] \ [-clock_pdrev_fanout fanout] \ [-clock_topology_priority priority] \ [-unidirectional_routing] \ [-allow_overflow] ``` Options description: - **guide_file**: Set the output guides file name (e.g.: -guide_file route.guide") - **layers**: Set the minimum and maximum routing layers (e.g.: -layers 2-10) - **tile_size**: Set the number of pitches inside a GCell (e.g.: -tile_size *20*) - **verbose**: Set verbose of report. 0 for less verbose, 1 for medium verbose, 2 for full verbose (e.g.: -verbose *1*) - **overflow_iterations**: Set the number of iterations to remove the overflow of the routing (e.g.: -overflow_iterations *50*) - **grid_origin**: Set the origin of the routing grid (e.g.: -grid_origin {1 1}) - **report_congestion**: Create a text file with the congestion report of the GCells (e.g.: -report_congestion "congest") - **clock_layers min-max**: Set the minimum and maximum routing layers for clock nets (e.g.: -clock_layers 4-9) - **clock_pdrev_fanout**: Set the minimum fanout to use PDRev for the routing topology construction of the clock nets (e.g.: -clock_pdrev_fanout 5) - **clock_topology_priority**: Set the PDRev routing topology construction priority for clock nets. See `set_pdrev_topology_priority` command description for more details about PDRev and topology priority (e.g.: -topology_priority 0.6) - **unidirectional_routing**: Avoid routing in layer 1, using it only for pin access - **allow_overflow**: Allow global routing results with overflow ``` set_global_routing_layer_adjustment layer adjustment ``` The `set_global_routing_layer_adjustment` command sets routing resources adjustments in the routing layers of the design. You can set adjustment for a specific layer, e.g.: `set_global_routing_layer_adjustment 4 0.5` reduces the routing resources of routing layer 4 in 50%. You can set adjustment for all layers at once using `*`, e.g.: `set_global_routing_layer_adjustment * 0.3` reduces the routing resources of all routing layers in 30%. You can set adjustment for a layer range, e.g.: `set_global_routing_layer_adjustment 4-8 0.3` reduces the routing resources of routing layers 4, 5, 6 7 and 8 in 30%. ``` set_global_routing_layer_pitch layer pitch ``` The `set_global_routing_layer_pitch` command sets the pitch for routing tracks in a specific layer. You can call it multiple times for different layers. Example: `set_global_routing_layer_pitch 6 1.34`. ``` set_pdrev_topology_priority -net netName -alpha alpha ``` FastRoute has an alternative tool for the routing topology construction, called PDRev. You can define the topology construction priority of PDRev between wire length and skew, using the `alpha` parameter. The `set_pdrev_topology_priority` command sets the PDRev routing topology construction priority for specific nets. Alpha is a positive float between 0.0 and 1.0, where alpha close to 0.0 generates topologies with shorter wire length, and alpha close to 1.0 generates topologies with lower skew. For more information about PDRev, check the paper in `src/FastRoute/src/pdrev/papers/PDRev.pdf` You can call it multiple times for different nets. Example: `set_pdrev_topology_priority -net "clk" -alpha 0.3` sets an alpha value of 0.3 for net *clk*. ``` set_global_routing_region_adjustment {lower_left_x lower_left_y upper_right_x upper_right_y} -layer layer -adjustment adjustment ``` The `set_global_routing_region_adjustment` command sets routing resources adjustments in a specific region of the design. The region is defined as a rectangle in a routing layer. Example: `set_global_routing_region_adjustment {1.5 2 20 30.5} -layer 4 -adjustment 0.7` ``` write_guides file_name ``` The `write_guides` generates the guide file from the routing results. Example: `write_guides route.guide`. To estimate RC parasitics based on global route results, use the `-global_routing` option of the `estimate_parasitics` command. ``` estimate_parasitics -global_routing ``` #### Logical and Physical Optimizations OpenPhySyn performs additional timing and area optimization. ``` optimize_logic [-tiehi tiehi_cell_name] [-tielo tielo_cell_name] ``` The `optimize_logic` command should be run after the logic synthesis on hierarical designs to perform logic optimization; currently, it performs constant propagation to reduce the design area. You can optionally specify the name of tie-hi/tie-lo liberty cell names to use for the optimization. ``` repair_timing [-capacitance_violations] [-transition_violations] [-negative_slack_violations] [-iterations iteration_count] [-buffers buffer_cells] [-inverters inverter cells] [-auto_buffer_library ] [-no_minimize_buffer_library] [-auto_buffer_library_inverters_enabled] [-buffer_disabled] [-resize_disabled] [-pin_swap_disabled] [-capacitance_pessimism_factor factor] [-transition_pessimism_factor factor] [-minimum_cost_buffer_enabled] [-legalization_frequency num_edits] [-legalize_each_iteration iterations] [-legalize_eventually] [-post_place] [-post_route] [-minimum_gain gain] [-high_effort] [-maximum_negative_slack_paths count] [-maximum_negative_slack_path_depth count] [-pins pin_names] ``` The `repair_timing` command repairs negative slack, maximum capacitance and transition violations by buffer tree insertion, gate sizing, and pin-swapping. `repair_timing` options: - `[-capacitance_violations]`: Repair capacitance violations. - `[-transition_violations]`: Repair transition violations. - `[-negative_slack_violations]`: Repair paths with negative slacks. - `[-iterations iterations]`: Maximum number of iterations. - `[-buffers buffer_cells]`: Manually specify buffer cells to use. - `[-inverters inverter cells]`: Manually specify inverter cells to use. - `[-auto_buffer_library ]`: Auto-select buffer library. - `[-no_minimize_buffer_library]`: Do not run initial pruning phase for buffer selection. - `[-auto_buffer_library_inverters_enabled]`: Include inverters in the selected buffer library. - `[-buffer_disabled]`: Disable all buffering. - `[-resize_disabled]`: Disable driver sizing. - `[-pin_swap_disabled]`: Disable pin-swapping. - `[-transition_pessimism_factor factor]` Scaling factor for transition violation limits, default is 1.0, should be non-negative, < 1.0 is pessimistic, 1.0 is ideal, > 1.0 is optimistic (default is 1.0). - `[-capacitance_pessimism_factor factor]` Scaling factor for capacitance violation limits, default is 1.0, should be non-negative, < 1.0 is pessimistic, 1.0 is ideal, > 1.0 is optimistic (default is 1.0). - `[-minimum_cost_buffer_enabled]`: Enable minimum cost buffering. - `[-legalization_frequency ]`: Legalize after how many edits. - `[-legalize_eventually]`: Legalize at the end of the optimization. - `[-legalize_each_iteration]`: Legalize after each iteration. - `[-post_place|-post_route]`: Post-placement phase mode or post-routing phase mode (not currently supported). - `[-minimum_gain ]`: Minimum slack gain to accept an optimization. - `[-high_effort]`: Trade-off runtime versus optimization quality by weaker pruning. - `[-no_resize_for_negative_slack]`: Disable resizing when solving negative slack violations (enhances runtime). - `[-maximum_negative_slack_paths count]`: Maximum number of negative slack paths to try to optimize. - `[-maximum_negative_slack_path_depth count]`: Maximum depth per negative slack path to try to optimize. - `[-pins pin_names]`: Manually select the pins to optimize. ``` pin_swap -path_count count [-power] ``` The `pin_swap` command performs additional timing optimization by commutative pin swapping. ``` optimize_fanout -buffer_cell buffer_cell_name -max_fanout max_fanout ``` The `optimize_fanout` command can be run after the logical synthesis to perform basic buffering based on the number of fanout pins. ``` cluster_buffers [-cluster_threshold diameter] [-cluster_size single|small|medium|large|all] ``` The `cluster_buffers` command can be used to automatically select representative set of buffers through k-center clustering. #### PDN analysis PDNSim PDN checker searches for floating PDN stripes. PDNSim reports worst IR drop given a placed and PDN synthesized design. ``` check_power_grid -net analyze_power_grid -vsrc write_pg_spice -vsrc -outfile ``` Options description: - **vsrc**: Set the location of the power C4 bumps/IO pins ###### Note: See the file [Vsrc_aes.loc file](https://github.com/The-OpenROAD-Project/PDNSim/blob/master/test/aes/Vsrc.loc) for an example with a description specified [here](https://github.com/The-OpenROAD-Project/PDNSim/blob/master/doc/Vsrc_description.md).