FlowVariables.md

Environment Variables for the OpenROAD Flow Scripts

Environment variables are used in the OpenROAD flow to define various platform, design and tool specific variables to allow finer control and user overrides at various flow stages. These are defined in the config.mk file located in the platform and design specific directories.

General variables for all stages

Variable	Description
SKIP_REPORT_METRICS	If set to 1, then metrics, report_metrics does nothing. Useful to speed up builds.

Platform

These variables must be defined in the platform specific config file located in the OpenROAD-flow-scripts directory of ./flow/platforms/<PLATFORM>/config.mk

Note: The variable PLATFORM_DIR is set by default based on the PLATFORM variable. For OpenROAD Flow Scripts we have the following public platforms:

• sky130hd
• sky130hs
• nangate45
• asap7

Platform Specific Environment Variables

The table below lists the complete set of variables used in each of the public platforms supported by the OpenROAD flow.

Note:

• = indicates default definition assigned by the tool
• ?= indicates that the variable value may be reassigned with design config.mk

Configuration Variable	sky130hd	sky130hs	nangate45	asap7	gf180
Library Setup
PROCESS	=	=	=	=	=
TECH_LEF	=	=	=	=	=
SC_LEF	=	=	=	=	=
LIB_FILES	=	=	=	=	=
GDS_FILES	=	=	=	=	=
DONT_USE_CELLS	=	=	=	=	=
Synthesis
LATCH_MAP_FILE	=	=	=	=	=
CLKGATE_MAP_FILE	=	=	=	=	=
ADDER_MAP_FILE	?=	?=	?=	?=	?=
TIEHI_CELL_AND_PORT	=	=	=	=	=
TIELO_CELL_AND_PORT	=	=	=	=	=
MIN_BUF_CELL_AND_PORTS	=	=	=	=	=
ABC_CLOCK_PERIOD_IN_PS	?=	?=	?=	?=	?=
ABC_DRIVER_CELL	=	=	=	=	=
ABC_LOAD_IN_FF	=	=	=	=	=
Floorplan
PLACE_SITE	=	=	=	=	=
MAKE_TRACKS	=	=	=	=	=
TAPCELL_TCL	=	=	=	=	=
MACRO_PLACE_HALO	?=	?=	?=	?=	?=
MACRO_PLACE_CHANNEL	?=	?=	?=	?=	?=
PDN_TCL	?=	?=	?=	?=	?=
IO_PLACER_H	=	=	=	=	?=
IO_PLACER_V	=	=	=	=	?=
Placement
CELL_PAD_IN_SITES_GLOBAL_PLACEMENT	?=	?=	?=	?=	?=
CELL_PAD_IN_SITES_DETAIL_PLACEMENT	?=	?=	?=	?=	?=
PLACE_DENSITY	?=	?=	?=	?=	?=
WIRE_RC_LAYER	=	=	=	=	=
Clock Tree Synthesis
CTS_BUF_CELL	=	=	=	=	=
CTS_BUF_DISTANCE	N/A	N/A	N/A	=	=
FILL_CELLS	=	=	=	=	=
SKIP_GATE_CLONING	?=	?=	?=	?=	?=
SKIP_PIN_SWAP	?=	?=	?=	?=	?=
TNS_END_PERCENT	?=	?=		?=	?=
EQUIVALENCE_CHECK	?=	?=	?=	?=	?=
REMOVE_CELLS_FOR_EQY	?=	?=	?=	?=	?=
Routing
KLAYOUT_TECH_FILE	=	=	=	=	=
MAX_ROUTING_LAYER	=	=	=	=	?=
MIN_ROUTING_LAYER	=	=	=	=	?=
RCX_RULES	=	=	=	=	=
RECOVER_POWER	?=	?=	?=	?=	?=

Library Setup

Variable	Description
PROCESS	Technology node or process in use.
CORNER	Library to select based on corner BC/TC/WC.
TECH_LEF	A technology LEF file of the PDK that includes all relevant information regarding metal layers, vias, and spacing requirements.
SC_LEF	Path to technology standard cell LEF file.
GDS_FILES	Path to platform GDS files.
LIB_FILES	A Liberty file of the standard cell library with PVT characterization, input and output characteristics, timing and power definitions for each cell.
DONT_USE_CELLS	Dont use cells eases pin access in detailed routing.

Synthesis

Variable	Description
SYNTH_HIERARCHICAL	Enable to Synthesis hierarchically, otherwise considered flat synthesis.
LATCH_MAP_FILE	List of latches treated as a black box by Yosys.
CLKGATE_MAP_FILE	List of cells for gating clock treated as a black box by Yosys.
ADDER_MAP_FILE	List of adders treated as a black box by Yosys.
TIEHI_CELL_AND_PORT	Tie high cells used in Yosys synthesis to replace a logical 1 in the Netlist.
TIELO_CELL_AND_PORT	Tie low cells used in Yosys synthesis to replace a logical 0 in the Netlist.
MIN_BUF_CELL_AND_PORTS	Used to insert a buffer cell to pass through wires. Used in synthesis.
ABC_CLOCK_PERIOD_IN_PS	Clock period to be used by STA during synthesis. Default value read from constraint.sdc.
ABC_DRIVER_CELL	Default driver cell used during ABC synthesis.
ABC_LOAD_IN_FF	During synthesis set_load value used.
MAX_UNGROUP_SIZE	For hierarchical synthesis, we ungroup modules of size given by this variable.

Floorplan

Variable	Description
FLOORPLAN_DEF	Use the DEF file to initialize floorplan.
PLACE_SITE	Placement site for core cells defined in the technology LEF file.
TAPCELL_TCL	Path to Endcap and Welltie cells file.
RTLMP_FLOW	Enable the Hierarchical RTLMP flow. By default it is disabled.
MACRO_HALO	Specifies keep out distance from macro, in X and Y, to standard cell row.
MACRO_PLACEMENT	Specifies the path of a file on how to place certain macros manually using read_macro_placement.
MACRO_PLACEMENT_TCL	Specifies the path of a TCL file on how to place certain macros manually.
MACRO_PLACE_HALO	horizontal/vertical halo around macros (microns). Used by automatic macro placement.
MACRO_PLACE_CHANNEL	horizontal/vertical channel width between macros (microns). Used by automatic macro placement when RTLMP_FLOW is disabled. Imagine channel=10 and halo=5. Then macros must be 10 apart but standard cells must be 5 away from a macro.
MACRO_BLOCKAGE_HALO	Blockage width overridden from default calculation.
PDN_TCL	File path which has a set of power grid policies used by pdn to be applied to the design, such as layers to use, stripe width and spacing to generate the actual metal straps.
MAKE_TRACKS	Tcl file that defines add routing tracks to a floorplan.
IO_PLACER_H	The metal layer on which to place the I/O pins horizontally (top and bottom of the die).
IO_PLACER_V	The metal layer on which to place the I/O pins vertically (sides of the die).
GUI_NO_TIMING	Skip loading timing for a faster GUI load.

Placement

Variable	Description
HAS_IO_CONSTRAINTS	Skip the initial non-IO based global placement if IO constraints are present.
CELL_PAD_IN_SITES_GLOBAL_PLACEMENT	Cell padding on both sides in site widths to ease routability during global placement.
CELL_PAD_IN_SITES_DETAIL_PLACEMENT	Cell padding on both sides in site widths to ease routability in detail placement.
PLACE_DENSITY	The desired placement density of cells. It reflects how spread the cells would be on the core area. 1.0 = closely dense. 0.0 = widely spread.
PLACE_DENSITY_LB_ADDON	Check the lower boundary of the PLACE_DENSITY and add PLACE_DENSITY_LB_ADDON if it exists.
REPAIR_PDN_VIA_LAYER	Remove power grid vias which generate DRC violations after detailed routing.
GLOBAL_PLACEMENT_ARGS	Use additional tuning parameters during global placement other than default args defined in gloabl_place.tcl.
ENABLE_DPO	Enable detail placement with improve_placement feature.
DPO_MAX_DISPLACEMENT	Specifies how far an instance can be moved when optimizing.
GPL_TIMING_DRIVEN	Specifies whether the placer should use timing driven placement.
GPL_ROUTABILITY_DRIVEN	Specifies whether the placer should use routability driven placement.
CAP_MARGIN	Specifies a capacitance margin when fixing max capacitance violations. This option allow you to overfix.
SLEW_MARGIN	Specifies a slew margin when fixing max slew violations. This option allow you to overfix.

Clock Tree Synthesis (CTS)

Variable	Description
CTS_ARGS	Override clock_tree_synthesis arguments
CTS_BUF_CELL	The buffer cell used in the clock tree.
FILL_CELLS	Fill cells are used to fill empty sites.
HOLD_SLACK_MARGIN	Specifies a time margin for the slack when fixing hold violations. This option allow you to overfix.
SETUP_SLACK_MARGIN	Specifies a time margin for the slack when fixing setup violations.
SKIP_GATE_CLONING	Do not use gate cloning transform to fix timing violations (default: use gate cloning)
SKIP_PIN_SWAP	Do not use pin swapping as a transform to fix timing violations (default: use pin swapping)
TNS_END_PERCENT	Specifies how many percent of violating paths to fix [0-100]. Worst path will always be fixed
EQUIVALENCE_CHECK	Enable running equivalence checks with to verify logical correctness of repair_timing
REMOVE_CELLS_FOR_EQY	String patterns directly passed to write_verilog -remove_cells <> for equivalence checks
SKIP_CTS_REPAIR_TIMING	Skipping CTS repair, which can take a long time, can be useful in architectural exploration or when getting CI up and running

Routing

Variable	Description
MIN_ROUTING_LAYER	The lowest metal layer name to be used in routing.
MAX_ROUTING_LAYER	The highest metal layer name to be used in routing.
DETAILED_ROUTE_ARGS	Add additional arguments for debugging purpose during detail route.
MACRO_EXTENSION	Sets the number of GCells added to the blockages boundaries from macros.
RECOVER_POWER	Specifies how many percent of paths with positive slacks can be slowed for power savings [0-100].

Extraction

Variable	Description
RCX_RULES	RC Extraction rules file path.
SET_RC_TCL	Metal & Via RC definition file path.
FILL_CONFIG	JSON rule file for metal fill during chip finishing.
KLAYOUT_TECH_FILE	A mapping from LEF/DEF to GDS using the KLayout tool.
IR_DROP_LAYER	Default metal layer to report IR drop.

Design Specific Configuration Variables

Required Variables

Following minimum design variables must be defined in the design configuration file for each design located in the OpenROAD-flow-scripts directory of ./flow/designs/<PLATFORM>/<DESIGN_NAME>/config.mk

Variable	Description
PLATFORM	Specifies process design kit or technology node to be used.
DESIGN_NAME	The name of the top-level module of the design.
VERILOG_FILES	The path to the design Verilog files.
SDC_FILE	The path to design constraint (SDC) file.

Optional Variables

These are optional variables that may be over-ridden/appended with default value from the platform config.mk by defining in the design configuration file.

Synthesis

Variable	Description
ADDITIONAL_FILES	Additional files to be added to make issue archive
ADDITIONAL_LEFS	Hardened macro LEF view files listed here. The LEF information of the macros is immutable and used throughout all stages. Stored in the .odb file.
ADDITIONAL_LIBS	Hardened macro library files listed here. The library information is immutable and used throughout all stages. Not stored in the .odb file.
ADDITIONAL_GDS	Hardened macro GDS files listed here.
VERILOG_INCLUDE_DIRS	Specifies the include directories for the Verilog input files.
CORNER	PVT corner library selection. Only available for ASAP7 and GF180 PDK.
DESIGN_NICKNAME	DESIGN_NICKNAME just changes the directory name that ORFS outputs to be DESIGN_NICKNAME instead of DESIGN_NAME in case DESIGN_NAME is unwieldy or conflicts with a difference design.
ABC_AREA	Strategies for Yosys ABC synthesis: Area/Speed. Default ABC_SPEED.
PWR_NETS_VOLTAGES	Used for IR Drop calculation.
GND_NETS_VOLTAGES	Used for IR Drop calculation.
BLOCKS	Blocks used as hard macros in a hierarchical flow. Do note that you have to specify block-specific inputs file in the directory mentioned by Makefile
CDL_FILES	Insert additional Circuit Description Language (.cdl) netlist files.
DFF_LIB_FILES	Technology mapping liberty files for flip-flops.
DONT_USE_LIBS	Set liberty files as dont_use.
PRESERVE_CELLS	Mark modules to keep from getting removed in flattening.
SYNTH_ARGS	Optional synthesis variables for yosys.
VERILOG_TOP_PARAMS	Apply toplevel params (if exist).

Floorplan

Variable	Description
CORE_UTILIZATION	The core utilization percentage (0-100). Overrides DIE_AREA and CORE_AREA.
CORE_ASPECT_RATIO	The core aspect ratio (height / width). This values is ignored if CORE_UTILIZATION undefined.
CORE_MARGIN	The margin between the core area and die area, in multiples of SITE heights. The margin is applied to each side. This variable is ignored if CORE_UTILIZATION is undefined.
DIE_AREA	The die area specified as a list of lower-left and upper-right corners in microns (X1 Y1 X2 Y2). This variable is ignored if CORE_UTILIZATION and CORE_ASPECT_RATIO are defined.
CORE_AREA	The core area specified as a list of lower-left and upper-right corners in microns (X1 Y1 X2 Y2). This variable is ignored if CORE_UTILIZATION and CORE_ASPECT_RATIO are defined.
RESYNTH_AREA_RECOVER	Enable re-synthesis for area reclaim.
RESYNTH_TIMING_RECOVER	Enable re-synthesis for timing optimization.
MACRO_HALO_X	Set macro halo for x-direction. Only available for ASAP7 PDK.
MACRO_HALO_Y	Set macro halo for y-direction. Only available for ASAP7 PDK.

Placement

Variable	Description
MACRO_WRAPPERS	The wrapper file that replace existing macros with their wrapped version.

Clock Tree Synthesis

Variable	Description
CTS_BUF_DISTANCE	Distance (in microns) between buffers.
CTS_CLUSTER_DIAMETER	Maximum diameter (in microns) of sink cluster. Default 20.
CTS_CLUSTER_SIZE	Maximum number of sinks per cluster. Default 50.

Routing

Variable	Description
FASTROUTE_TCL	Specifies a Tcl scripts with commands to run before FastRoute.

GDS Streamout

Variable	Description
USE_FILL	Whether to perform metal density filling. Default 0 (=off).
SEAL_GDS	Seal macro to place around the design.