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OpenROAD

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|5.7|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, then the error is printed and no more commands are read from the file. If file_continue_on_error is 1 then OpenROAD will continue reading commands after the error.

If exit_on_error is 1 then 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 synthesizable RTL Verilog to detail-routed final layout in the open-source technologies Nangate45 and Sky130HD are shown below.

gcd_nangate45.tcl
aes_nangate45.tcl
tinyRocket_nangate45.tcl
gcd_sky130hd.tcl
aes_sky130hd.tcl
ibex_sky130hd.tcl

Each of these designs use the common script flow.tcl.

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.

write_abstract_lef (-bloat_factor bloat_factor|-bloat_occupied_layers) \
		   filename

Options

Switch Name Description
-bloat_factor Specifies the bloat factor used when bloating then merging shapes into LEF obstructions. The factor is measured in # of default metal pitches for the respective layer. A factor of 0 will result in detailed LEF obstructions
-bloat_occupied_layers Generates cover obstructions (obstructions over the entire layer) for each layer where shapes are present

Examples

read reg1.db

# Bloat metal shapes by 3 pitches (respectively for every layer) and then merge
write_abstract_lef -bloat_factor 3 reg1_abstract.lef

# Produce cover obstructions for each layer with shapes present
write_abstract_lef -bloat_occupied_layers reg1_abstract.lef

Global Connections

Add global connections

The add_global_connection command is used to specify how to connect power and ground pins on design instances to the appropriate supplies.

add_global_connection -net net_name \
                      [-inst_pattern inst_regular_expression] \
                      -pin_pattern pin_regular_expression \
                      (-power|-ground) \
                      [-reigon region_name]
Options
Switch Name Description
-net Specifies the name of the net in the design to which connections are to be added
-inst_pattern Optional specifies a regular expression to select a set of instances from the design. (Default: .*)
-pin_pattern Species a regular expression to select pins on the selected instances to connect to the specified net
-power Specifies that the net it a power net
-ground Specifies that the net is a ground net
-region Specifies the name of the region for this rule
Examples
# Stdcell power/ground pins
add_global_connection -net VDD -pin_pattern {^VDD$} -power
add_global_connection -net VSS -pin_pattern {^VSS$} -ground

# SRAM power ground pins
add_global_connection -net VDD -pin_pattern {^VDDPE$}
add_global_connection -net VDD -pin_pattern {^VDDCE$}
add_global_connection -net VSS -pin_pattern {^VSSE$}

Perform global connections

The global_connect command is used to connect power and ground pins on design instances to the appropriate supplies.

global_connect

Clear global connection rules

The clear_global_connect command is used remove all defined global connection rules.

clear_global_connect

Report global connection rules

The report_global_connect command is used print out the currently defined global connection rules.

report_global_connect

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.

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

FAQs

Check out GitHub discussion about this tool.

License

BSD 3-Clause License.