OpenROAD

OpenROAD is an integrated chip physical design tool that takes a design from synthesized Verilog to routed layout.

An outline of steps used to build a chip using OpenROAD are shown below.

• Initialize floorplan - define the chip size and cell rows
• Place pins (for designs without pads )
• Place macro cells (RAMs, embedded macros)
• Insert substrate tap cells
• Insert power distribution network
• Macro Placement of macro cells
• Global placement of standard cells
• Repair max slew, max capacitance, and max fanout violations and long wires
• Clock tree synthesis
• Optimize setup/hold timing
• Insert fill cells
• Global routing (route guides for detailed routing)
• Detailed routing

OpenROAD uses the OpenDB database and OpenSTA for static timing analysis.

Install dependencies

The etc/DependencyInstaller.sh script supports Centos7 and Ubuntu 20.04. You need root access to correctly install the dependencies with the script.

Install dependencies

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 (1.75 will not compile)
• tcl 8.6
• zlibc
• eigen3
• spdlog
• lemon(graph library, not the parser)
• qt5
• cimg (optional for replace)

For a limited number of configurations the following script can be used to install dependencies.

./etc/DependencyInstaller.sh -dev

Build

git clone --recursive https://github.com/The-OpenROAD-Project/OpenROAD.git
cd OpenROAD

Build by hand

$ mkdir build
$ cd build
$ cmake ..
$ make

Build using support script

$ ./etc/Build.sh

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

Example with support script

$ ./etc/Build.sh --cmake="-DCMAKE_BUILD_TYPE=DEBUG -DTCL_LIB=/path/to/tcl/lib"

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

The flow tests check results such as worst slack against reference values. Use report_flow_metrics [test]... to see the all of the metrics. Use save_flow_metrics [test]... to add margins to the metrics and save them to .metrics_limits.

> report_flow_metrics gcd_nangate45
                       insts    area util slack_min slack_max  tns_max clk_skew max_slew max_cap max_fanout DPL ANT drv
gcd_nangate45            368     564  8.8     0.112    -0.015     -0.1    0.004        0       0          0   0   0   0

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
  -threads count|max number of threads to use
  -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
write_abstract_lef 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

Abstract Lef Support

OpenROAD contains an abstract lef writer that can take your current design and emit an abstract lef representing the external pins of your design and metal obstructions.

read reg1.db
write_abstract_lef reg1_abstract.lef

Limitations of the Abstract Lef Writer

Currently the writer will place an obstruction over the entire block area on any metal layer if there is any object on that metal layer.

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
  -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:

 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 )

The initialize_floorplan command removes existing tracks. Use the make_tracks command to add routing tracks to a floorplan.

make_tracks [layer]
            [-x_pitch x_pitch]
            [-y_pitch y_pitch]
            [-x_offset x_offset]
            [-y_offset y_offset]

With no arguments make_tracks adds X and Y tracks for each routing layer. With a -layer argument make_tracks adds X and Y tracks for layer with options to override the LEF technology X and Y pitch and offset.

Place pins around core boundary.

auto_place_pins pin_layer

Pin placement

Place pins on the boundary of the die on the track grid to minimize net wire lengths. Pin placement also creates a metal shape for each pin using min-area rules.

For designs with unplaced cells, the net wire length is computed considering the center of the die area as the unplaced cells' position.

Use the following command to perform pin placement:

place_pins [-hor_layers h_layers]  
           [-ver_layers v_layers] 
           [-random_seed seed]
           [-exclude interval]
           [-random]
           [-group_pins pins]
           [-corner_avoidance length]
           [-min_distance distance]
           [-min_distance_in_tracks]

• -hor_layers (mandatory). Specify the layers to create the metal shapes of pins placed in horizontal tracks. Can be a single layer or a list of layer names.
• -ver_layers (mandatory). Specify the layers to create the metal shapes of pins placed in vertical tracks. Can be a single layer or a list of layer names.
• -random_seed. Specify the seed for random operations.
• -exclude. Specify an interval in one of the four edges of the die boundary where pins cannot be placed. Can be used multiple times.
• -random. When this flag is enabled, the pin placement is random.
• -group_pins. Specify a list of pins to be placed together on the die boundary.
• -corner_avoidance distance. Specify the distance (in micron) from each corner to avoid placing pins.
• -min_distance distance. Specify the minimum distance between pins in the die boundary. It can be in microns (default) or in number of tracks between each pin.
• -min_distance_in_tracks. Flag that allows set the min distance in number of tracks instead of microns.

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_layers metal2 -ver_layers metal3 -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.

place_pin [-pin_name pin_name]
          [-layer layer]
          [-location {x y}]
          [-pin_size {width height}]

The place_pin command places a specific pin in the specified location, with the specified size. The -pin_name option is the name of a pin of the design. The -layer defines the routing layer where the pin is placed. The -location defines the center of the pin. The -pin_size option defines the width and height of the pin.

define_pin_shape_pattern [-layer layer]
                         [-x_step x_step]
                         [-y_step y_step]
                         [-region {llx lly urx ury}]
                         [-size {width height}]
                         [-pin_keepout dist]

The define_pin_shape_pattern command defines a pin placement grid at the specified layer. This grid has positions inside the die area, not only at the edges of the die boundary. The -layer option defines a single top most routing layer of the placement grid. The -region option defines the {llx, lly, urx, ury} region of the placement grid. The -x_step and -y_step options define the distance between each valid position on the grid. The -size option defines the width and height of the pins assigned to this grid. The center of the pins are placed on the grid positions. Pins may have half of their shapes outside the defined region. The -pin_keepout option defines the boundary (microns) around existing routing obstructions the pins should avoid, defaults to the layer minimum spacing.

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

The set_io_pin_constraint command sets region constraints for 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 command call. The -direction argument is the pin direction (input, output, inout, or feedthru). The -pin_names argument is a list of names. The -region syntax is the same as the -exclude syntax. To restrict pins to the positions defined with define_pin_shape_pattern, use -region up:{llx lly urx ury} or -region up:*.

clear_io_pin_constraints

The clear_io_pin_constraints command clear all the previous defined constraints and pin shape pattern for top layer placement.

Chip level connections

At the top level of the chip, special padcells are use to connect signals to the external package. Additional commands are provided to specify the placement of padcells, bondpads and bumps

Tapcell

Tapcell and endcap insertion.

tapcell [-tapcell_master tapcell_master]
        [-endcap_master endcap_master]
        [-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]
        [-tap_prefix tap_prefix]
        [-endcap_prefix endcap_prefix]

You can find script examples for both 45nm/65nm and 14nm in tapcell/etc/scripts

Global Placement

RePlAce global placement.

global_placement
    [-timing_driven]
    [-routability_driven]
    [-skip_initial_place]
    [-disable_timing_driven]
    [-disable_routability_driven]
    [-incremental]
    [-bin_grid_count grid_count]
    [-density target_density]
    [-init_density_penalty init_density_penalty]
    [-init_wirelength_coef init_wirelength_coef]
    [-min_phi_coef min_phi_conef]
    [-max_phi_coef max_phi_coef]
    [-overflow overflow]
    [-initial_place_max_iter initial_place_max_iter]
    [-initial_place_max_fanout initial_place_max_fanout]
    [-routability_check_overflow routability_check_overflow]
    [-routability_max_density routability_max_density]
    [-routability_max_bloat_iter routability_max_bloat_iter]
    [-routability_max_inflation_iter routability_max_inflation_iter]
    [-routability_target_rc_metric routability_target_rc_metric]
    [-routability_inflation_ratio_coef routability_inflation_ratio_coef]
    [-routability_pitch_scale routability_pitch_scale]
    [-routability_max_inflation_ratio routability_max_inflation_ratio]
    [-routability_rc_coefficients routability_rc_coefficients]
    [-pad_left pad_left]
    [-pad_right pad_right]
    [-verbose_level level]

• timing_driven: Enable timing-driven mode

• skip_initial_place : Skip the initial placement (BiCGSTAB solving) before Nesterov placement. IP improves HPWL by ~5% on large designs. Equal to '-initial_place_max_iter 0'
• incremental : Enable the incremental global placement. Users would need to tune other parameters (e.g. init_density_penalty) with pre-placed solutions.

• grid_count: [64,128,256,512,..., int]. Default: Defined by internal algorithm.

Tuning Parameters

• bin_grid_count : Set bin grid's counts. Default: Defined by internal algorithm. [64,128,256,512,..., int]
• density : Set target density. Default: 0.70 [0-1, float]
• init_density_penalty : Set initial density penalty. Default: 8e-5 [1e-6 - 1e6, float]
• init_wire_length__coef : Set initial wirelength coefficient. Default: 0.25 [unlimited, float]
• min_phi_coef : Set pcof_min(µ_k Lower Bound). Default: 0.95 [0.95-1.05, float]
• max_phi_coef : Set pcof_max(µ_k Upper Bound). Default: 1.05 [1.00-1.20, float]
• overflow : Set target overflow for termination condition. Default: 0.1 [0-1, float]
• initial_place_max_iter : Set maximum iterations in initial place. Default: 20 [0-, int]
• initial_place_max_fanout : Set net escape condition in initial place when 'fanout >= initial_place_max_fanout'. Default: 200 [1-, int]
• verbose_level : Set verbose level for RePlAce. Default: 1 [0-10, int]

-timing_driven does a virtual 'repair_design' to find slacks and weight nets with low slack. Use the set_wire_rc command to set resistance and capacitance of estimated wires used for timing.

Macro Placement

ParquetFP based macro cell placer. Run global_placement before macro placement. The macro placer places macros/blocks honoring halos, channels and cell row "snapping".

Approximately ceil((#macros/3)^(3/2)) sets corresponding to quadrisections of the initial placed mixed-size layout are explored and packed using ParquetFP-based annealing. The best resulting floorplan according to a heuristic evaluation function kept.

macro_placement [-halo {halo_x halo_y}]
                [-channel {channel_x channel_y}]
                [-fence_region {lx ly ux uy}]
                [-snap_layer snap_layer_number]

-halo horizontal/vertical halo around macros (microns) -channel horizontal/vertical channel width between macros (microns) -fence_region - restrict macro placements to a region (microns). Defaults to the core area. -snap_layer_number - snap macro origins to this routing layer track

Macros will be placed with max(halo * 2, channel) spacing between macros and the fence/die boundary. If not solutions are found, try reducing the channel/halo.

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 disp|{disp_x disp_y}]
check_placement [-verbose]
filler_placement [-prefix prefix] 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 -max_displacement argument to detailed_placement specifies how far to move an instance to find a site to place it. The default values are {500 100} sites. The x/y displacement arguments are in microns.

The check_placement command checks the placement legality. It returns 0 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. To specify a different naming prefix from FILLER_ use -prefix <new prefix>.

The optimimize_mirroring command mirrors instances about the Y axis in vane attempt to minimize the total wire length (hpwl).

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. The resizer stops and reports and error if the max utilization is exceeded.

set_wire_rc [-clock] [-signal]
            [-layer layer_name]
            [-resistance res]
            [-capacitance cap]

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 -signal and -clock flags. Without either -signal 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 distance units are not specified in the liberty file microns are used.

The set_layer_rc command can be used to set the resistance and capacitance for a layer or via. This is useful if they are missing from the LEF file or to override the values in the LEF.

set_layer_rc [-layer layer]
             [-via via_layer]
             [-capacitance cap]
             [-resistance res]
             [-corner corner]

For layers the resistance and capacitance units are the same as set_wire_rc (per length of minimum width wire). layer must be the name of a routing layer.

Via resistance can also be set with the set_layer_rc command with the -via keyword. -capacitance is not supported for vias. via_layer is the name of a via layer. Via resistance is per cut/via, not area based.

remove_buffers

Use the remove_buffers command to remove buffers inserted by synthesis. This step is recommended before using repair_design so it has more flexibility in buffering nets.

estimate_parasitics -placement|-global_routing

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.

After the global_route command has been called the global routing topology and layers can be used to estimate parasitics with the -global_routing flag.

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]
             [-max_utilization util]

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]
              [-max_slew_margin slew_margin]
              [-max_cap_margin cap_margin]
              [-max_utilization util]

The repair_design command 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 estimate_parasitics -placement before repair_design to estimate parasitics considered during repair. Placement based parasitics cannot accurately predict routed parasitics, so a margin can be used to "over-repair" the design to compensate. Use -max_slew_margin to add a margin to the slews, and -max_cap_margin to add a margin to the capacitances, Use -max_wire_length to specify the maximum length of wires. The maximum wire length defaults to a value that minimizes the wire delay for the wire resistance/capacitance values specified by set_wire_rc.

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 separated from the load by dist (in liberty units, typically microns).

repair_timing [-setup]
              [-hold]
              [-slack_margin slack_margin]
              [-allow_setup_violations]
              [-max_utilization util]
              [-max_buffer_percent buffer_percent]

The repair_timing command repairs 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. Use -slack_margin to add additional slack margin. To specify different slack margins use separate repair_timing commands for setup and hold. Use -max_buffer_percent to specify a maximum number of buffers to insert to repair hold violations as a percent of the number of instances in the design. The default value for buffer_percent is 20, for 20%.

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 (after a design and liberty libraries have been read) is shown below.

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

Clock Tree Synthesis

TritonCTS 2.0 is available under the OpenROAD app as clock_tree_synthesis command. The following tcl snippet shows how to call TritonCTS. TritonCTS 2.0 performs on-the-fly characterization. Thus there is no need to generate characterization data. On-the-fly characterization feature could still be optionally controlled by parameters specified to configure_cts_characterization command. Use set_wire_rc command to set clock routing layer.

read_sdc "design.sdc"
set_wire_rc -clock -layer metal5

configure_cts_characterization [-max_slew <max_slew>] \
                               [-max_cap <max_cap>] \
                               [-slew_inter <slew_inter>] \
                               [-cap_inter <cap_inter>]

clock_tree_synthesis -buf_list <list_of_buffers> \
                     [-root_buf <root_buf>] \
                     [-wire_unit <wire_unit>] \
                     [-clk_nets <list_of_clk_nets>] \
                     [-out_path <lut_path>] \
                     [-post_cts_disable] \
                     [-distance_between_buffers] \
                     [-branching_point_buffers_distance] \
                     [-clustering_exponent] \
                     [-clustering_unbalance_ratio] \
                     [-sink_clustering_enable] \
                     [-sink_clustering_size <cluster_size>] \
                     [-sink_clustering_max_diameter <max_diameter>]


write_def "final.def"

Argument description:

• -buf_list are the master cells (buffers) that will be considered when making 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 would use max slew value for specified buffer in buf_list from liberty file.
• -max_cap is the max capacitance value (in farad) that the characterization will test. If this parameter is omitted, the code would use max cap value for specified buffer in buf_list from 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.
• -post_cts_disable is a flag that, when specified, disables the post-processing operation for outlier sinks (buffer insertion on 10% of the way between source and sink).
• -distance_between_buffers is the distance (in micron) between buffers that TritonCTS should use when creating the tree. When using this parameter, the clock tree algorithm is simplified, and only uses a fraction of the segments from the LUT.
• -branching_point_buffers_distance is the distance (in micron) that a branch has to have in order for a buffer to be inserted on a branch end-point. This requires the -distance_between_buffers value to be set.
• -clustering_exponent is a value that determines the power used on the difference between sink and means on the CKMeans clustering algorithm. If this parameter is omitted, the code gets the default value (4).
• -clustering_unbalance_ratio is a value that determines the maximum capacity of each cluster during CKMeans. A value of 50% means that each cluster will have exactly half of all sinks for a specific region (half for each branch). If this parameter is omitted, the code gets the default value (0.6).
• -sink_clustering_enable enables pre-clustering of sinks to create one level of sub-tree before building H-tree. Each cluster is driven by buffer which becomes end point of H-tree structure.
• -sink_clustering_size specifies the maximum number of sinks per cluster. Default value is 20.
• sink_clustering_max_diameter specifies maximum diameter (in micron) of sink cluster. Default value is 50.
• -clk_nets 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. The following tcl snippet shows how to call report_cts.

clock_tree_synthesis -root_buf "BUF_X4" \
                     -buf_list "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] \
             [-verbose verbose] \
             [-congestion_iterations iterations] \
             [-grid_origin {x y}] \
             [-allow_congestion]

Options description:

• guide_file: Set the output guides file name (e.g.: -guide_file route.guide")
• verbose: Set verbose of report. 0 for less verbose, 1 for medium verbose, 2 for full verbose (e.g.: -verbose 1)
• congestion_iterations: Set the number of iterations to remove the overflow of the routing (e.g.: -congestion_iterations 50)
• grid_origin: Set the origin of the routing grid (e.g.: -grid_origin {1 1})
• allow_congestion: Allow global routing results with congestion

set_routing_layers [-signal min-max] \
                   [-clock min-max]

The set_routing_layers command sets the minimum and maximum routing layers for signal nets, with the -signal option, and the the minimum and maximum routing layers for clock nets, with the -clock option Example: set_routing_layers -signal Metal2-Metal10 -clock Metal6-Metal9

set_macro_extension extension

The set_macro_extension command sets the number of GCells added to the blocakges boundaries from macros Example: set_macro_extension 2

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 Metal4 0.5 reduces the routing resources of routing layer Metal4 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 Metal4-Metal8 0.3 reduces the routing resources of routing layers Metal4, Metal5, Metal6, Metal7 and Metal8 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 Metal6 1.34.

set_routing_alpha [-net net_name] alpha

By default the global router uses steiner trees to construct route guides. A steiner tree minimizes the total wire length. Prim/Dijkstra is an alternative net topology algorithm that supports a trade-off between total wire length and maximum path depth from the net driver to its loads. The set_routing_alpha command enables the Prim/Dijkstra algorithm and sets the alpha parameter used to trade-off wire length and path depth. Alpha is between 0.0 and 1.0. When alpha is 0.0 the net topology minimizes total wire length (i.e. capacitance). When alpha is 1.0 it minimizes longest path between the driver and loads (i.e., maximum resistance). Typical values are 0.4-0.8. 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_routing_alpha -net clk 0.3 sets the 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 Metal4 -adjustment 0.7

set_global_routing_random [-seed seed] \
                          [-capacities_perturbation_percentage percent] \
                          [-perturbation_amount value]

The set_global_routing_random command enables random global routing results. The random global routing shuffles the order of the nets and randomly subtracts or add the capacities of a random set of edges. The -seed option sets the random seed and is required to enable random mode. The -capacities_perturbation_percentage option sets the percentage of edges to perturb the capacities. By default, the edge capacities are perturbed by sum or subtract 1 from the original capacity. The -perturbation_amount option sets the perturbation value of the edge capacities. This option will only have effect when -capacities_perturbation_percentage is used. The random seed must be different from 0 to enable random global routing. Example: set_global_routing_random -seed 42 -capacities_perturbation_percentage 50 -perturbation_amount 2

repair_antennas diodeCellName/diodePinName [-iterations iterations]

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 and the number of iterations. By default, the command runs only one iteration to repair antennas. 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

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:

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

Options description:

• vsrc: (optional) file to set the location of the power C4 bumps/IO pins. Vsrc_aes.loc file for an example with a description specified here.
• dx,dy: (optional) these arguments set the bump pitch to decide the voltage source location in the absence of a vsrc file. Default bump pitch of 140um used in absence of these arguments and vsrc
• 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
• voltage: Sets the voltage on a specific net. If this command is not run, the voltage value is obtained from operating conditions in the liberty.

Note: See the file Vsrc_aes.loc file for an example with a description specified here.

TCL functions

Get the die and core areas as a list in microns: "llx lly urx ury"

ord::get_die_area
ord::get_core_area