/OpenROAD

OpenROAD's unified application implementing an RTL-to-GDS Flow

Primary LanguageVerilogOtherNOASSERTION

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 clang7
  • 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=<prefix_path>

Alternatively, you can use the DESTDIR variable with make.

make DESTDIR=<prefix_path> install

There are a set of regression tests in /test.

# run all tool unit tests
test/regression
# run all flow tests
test/regression flow
# run <tool> tests
test/regression <tool>
# run <tool> tool tests
src/<tool>/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_pins [-hor_layer h_layer]  
           [-ver_layer v_layer] 
           [-random_seed seed]
           [-exclude interval]
           [-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.
  • -exclude. Set an interval in one of the four edges of the die boundary where I/O pins cannot be assigned. Can be used multiple times.
  • -random. When this flag is enabled, the I/O pin assignment is random.

The exclude option syntax is -exclude edge:interval. The edge values are (top|bottom|left|right). The interval can be the whole edge, with the * value, or a range of values. Example: place_pins -hor_layer 2 -ver_layer 3 -exclude top:* -exclude right:15-60.5 -exclude left:*-50. In the example, three intervals were excluded: the whole top edge, the right edge from 15 microns to 60.5 microns, and the left edge from the beginning to the 50 microns.

set_io_pin_constraint -direction direction -names names -region edge:interval

The set_io_pin_constraint command sets region constraints for I/O pins according the direction or the pin name. This command can be called multiple times with different constraints. Only one condition should be used for each function call. The -names argument is a list of names. The -region syntax is the same as the -exclude syntax.

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]

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]

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. It also resizes gates to normalize slews. Use -max_wire_length to specify the maximum length 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 <fanout> [current_design]

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_timing [-setup]
              [-hold]
              [-allow_setup_violations]

The repair_timing command repair setup and hold violations. It should be run after clock tree synthesis with propagated clocks. While repairing hold violations buffers are not inserted that will cause setup violations unless '-allow_setup_violations' is specified.

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_dont_use {CLKBUF_* AOI211_X1 OAI211_X1}

buffer_ports
repair_design -max_wire_length 100
repair_tie_fanout LOGIC0_X1/Z
repair_tie_fanout LOGIC1_X1/Z
# clock tree synthesis...
repair_timing

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

repair_design

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 <tapcell_master>
        -endcap_master <endcap_master>
        -endcap_cpp <endcap_cpp>
        -distance <dist>
        -halo_width_x <halo_x>
        -halo_width_y <halo_y>
        -tap_nwin2_master <tap_nwin2_master>
        -tap_nwin3_master <tap_nwin3_master>
        -tap_nwout2_master <tap_nwout2_master>
        -tap_nwout3_master <tap_nwout3_master>
        -tap_nwintie_master <tap_nwintie_master>
        -tap_nwouttie_master <tap_nwouttie_master>
        -cnrcap_nwin_master <cnrcap_nwin_master>
        -cnrcap_nwout_master <cnrcap_nwout_master>
        -incnrcap_nwin_master <incnrcap_nwin_master>
        -incnrcap_nwout_master <incnrcap_nwout_master>
        -tbtie_cpp <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 == <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 <list_of_buffers> \
                     -sqr_cap <cap_per_sqr> \
                     -sqr_res <res_per_sqr> \
                     [-root_buf <root_buf>] \
                     [-max_slew <max_slew>] \
                     [-max_cap <max_cap>] \
                     [-slew_inter <slew_inter>] \
                     [-cap_inter <cap_inter>] \
                     [-wire_unit <wire_unit>] \
                     [-clk_nets <list_of_clk_nets>] \
                     [-out_path <lut_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 <lut_file> \
                     -sol_list <sol_list_file> \
                     -root_buf <root_buf> \
                     [-wire_unit <wire_unit>] \
                     [-clk_nets <list_of_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, 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.

global_route [-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] \
             [-macro_extension extension]
             [-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)
  • macro_extension: Set the number of GCells added to the obstacles boundaries from macros
  • 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 netName 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 clk 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

repair_antennas diodeCellName/diodePinName

The repair_antenna command evaluates the global routing results looking for antenna violations, and repairs the violations by inserting diodes. The input for this command is the diode cell and pin names. It uses the antennachecker tool to identify the antenna violations and return the exact number of diodes necessary to fix the antenna violation. Example: repair_antenna sky130_fd_sc_hs__diode_2/DIODE

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.

psn_repair_timing
        [-capacitance_violations]
        [-transition_violations]
        [-negative_slack_violations]
        [-iterations iteration_count]
        [-buffers buffer_cells]
        [-inverters inverter cells]
        [-auto_buffer_library <single|small|medium|large|all>]
        [-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 <single|small|medium|large|all>]: 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 <num_edits>]: 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 <unit_time>]: 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 on the power and ground nets.

PDNSim reports worst IR drop and worst current density in a power wire drop given a placed and PDN synthesized design.

PDNSim spice netlist writer for power wires.

Commands for the above three functionalities are below:

check_power_grid -net <net_name>
analyze_power_grid -vsrc <voltage_source_location_file> \
                   -net <net_name> \ 
                   [-outfile <filename>] \
                   [-enable_em] \
                   [-em_outfile <filename>]
write_pg_spice -vsrc <voltage_source_location_file> -outfile <netlist.sp> -net <net_name>

Options description:

  • vsrc: (mandatory) file to set the location of the power C4 bumps/IO pins
  • net: (mandatory) is the name of the net to analyze, power or ground net name
  • enable_em: (optional) is the flag to report current per power grid segment
  • outfile: (optional) filename specified per-instance voltage written into file
  • em_outfile: (optional) filename to write out the per segment current values into a file, can be specified only if enable_em is flag exists
Note: See the file Vsrc_aes.loc file for an example with a description specified here.