OpenRCX is an parasitics Extraction tool that works on OpenDB design APIs. It extracts routed designs based on the LEF/DEF model.
It extracts both Resistance and Capacitance for wires, based on coupling distance to the nearest wire and the context over and/or under and cell abstracts. The capacitance and resistance measurements are based on equations of coupling distance interpolated on exact measurements from a calibration file, called Extraction Rules File. The Extraction Rules file (RC technology file) is generated once for every process node and corner automatically.
OpenRCX stores resistance, coupling capacitance and ground capacitance on OpenDB objects with direct pointers to the associated wire and via db objects and optionally can generate a .spef file.
There is a set of regression tests in /test.
./test/regression
This flow generates an Extraction Rules file (RC tech file/RC Table) for OpenRCX. This file provides resistance and capacitance tables used for RC extraction for a specific process corner.
The Extraction Rules file (RC technology file) is generated once for every process node and corner automatically.
The detailed documentation can be found here
extract_parasitics
[-ext_model_file filename] pointer to The Extraction Rules file
[-corner_cnt count] process corner count
[-max_res ohms] combine resistors in series up to
<max_res> value in OHMS
[-coupling_threshold fF] coupling below the threshold is grounded
[-lef_res] use per-unit RC defined in LEF
[-cc_model track] calculate coupling within
<cc_model> distance
[-context_depth depth] caculate upper/lower coupling from
<depth> level away
The extract_parasitics command performs parastic extraction based on the
routed design. If there are no routed design information no parasitics are
added. Use ext_model_file to specify the Extraction Rules file used for the
extraction.
The cc_model is used to specify the maximium number of tracks on same routing level.
The default value is 10.
The context_depth option is used to specify the levels that OpenRCX needs to consider
The default value is 5.
for the over/under context overlap for capacitance calculation.
The max_res command combines resistors in series up to the threshold values.
The corner_cnt defines the number of corners used during the parastic
extractions.
write_spef
[-net_id net_id] output the parasitics info for spesific nets
[filename] the output filename
The write_spef command writes the .spef output of the parasitics stored in the
database. Use net_id command to write the output for spesific nets.
adjust_rc
[-res_factor res] scale the res value
[-cc_factor cc] scale the coupling capacitance value
[-gndc_factor gndc] scale the ground cap value
Use the adjust_rc command to scale the the resistance, ground, and coupling
capacitance. The res_factor specifies the scale factor for resistance. The
cc_factor specifies the scale factor for coupling cap. The gndc_factor
specifies the scale factor for ground cap.
diff_spef
[-file filename] specifies the input .spef filename
diff_spef command compares the parasitics in the database with the parasitic
information from <file>.spef. The output of this command is diff_spef.out and
contains the RC numbers from the parasitics in the databse and the <file>.spef,
and the percentage RC difference of the two data.
bench_wires
[-cnt count] specify the metal count
per pattern
[-len wire_len] specify the wire length
in the pattern
[-s_list space_multiplier_list] list of wire spacing multiplier
[-all] generate all patterns
bench_wires command produces a layout which contains various patterns that
are used to characterize per-unit RC. The generated patterns model the
lateral, vertical, and diagonal coupling capacitance, and the ground capacitance
effects. This command generates a .def file.
The cnt command determines the number of wires in each pattern, the default
values is 5. Use len command to change the wire length in the pattern. all
option is used to specify all diffrent pattern geometries (over, under,
over_under, and digonal). The option all is required.
The s_list option specifies the lists of wire spacing multipliers from the
minimum spacing defined in the LEF. The list will be the input index on the
OpenRCX RC table (Extraction Rules file).
This command is specifically intended for the Extraction Rules file generation only.
bench_verilog
[filename] the output verilog filename
bench_verilog is used after the bench_wires command. This command generates
verilog netlist of the generated pattern layout by the bench_wires
command.
This command is optional when running the Extraction Rules generation flow. This step is required if the favorite extraction tool (i.e., reference extractor) requires a netlist to extract parasitics of the pattern layout.
bench_read_spef
[filename] the input .spef filename
bench_read_spef command reads a <filename>.spef file and stores the
parasitics into the database.
write_rules
[-file filename] output file name
[-db] read parasitics from the databse
write_rules command writes the Extraction Rules file (RC technology file)
for OpenRCX. It processes the parasitics data from the pattern layout generated from
bench_wires command, and writes the Extraction Rules file with <file> as
the output file.
db command instructs OpenRCX to write the Extraction Rules file from
the parasitics stored in the database. This option is required.
This command is specifically intended for the Extraction Rules file generation purpose.
Example scripts demonstrating how to run OpenRCX in the OpenROAD environment on sample designs that can be found in /test. Flow tests taking sample designs from synthesis verilog to routed design in the open source technologies Sky130 is shown below.
gcd.tcl
Example scripts demonstrating how to run the Extraction Rules File generation can be found in this directory.
generate_patterns.tcl # generate patterns
generate_rules.tcl # generate the Extraction Rules
# file
ext_patterns.tcl # check the accuracy of OpenRCX