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 an error if the max
utilization is exceeded.
Commands¶
Set Wire RC¶
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 are 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.
Set Layer RC¶
The set_layer_rc command can be used to set the resistance and capacitance
for a layer or via. This is useful if these values 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, using 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¶
remove_buffers
Use the remove_buffers command to remove buffers inserted by synthesis. This
step is recommended before using repair_design so that there is more flexibility
in buffering nets.
Estimate Parasitics¶
estimate_parasitics -placement|-global_routing
Estimate RC parasitics based on placed component pin locations. If there are
no component locations, then no parasitics are added. The resistance and capacitance
values are per distance unit of a routing wire. Use the set_units command to check
units or set_cmd_units to change units. The goal is to represent “average”
routing layer resistance and capacitance. If the set_wire_rc command is not
called before resizing, then the default_wireload model specified in the first
Liberty file read 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 Don’t Use¶
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¶
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. The default behavior is -inputs and -outputs
if neither is specified.
Repair Design¶
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 and 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 wirelength defaults to
a value that minimizes the wire delay for the wire resistance/capacitance
values specified by set_wire_rc.
Set Max Fanout¶
Use the set_max_fanout SDC command to set the maximum fanout for the design.
set_max_fanout <fanout> [current_design]
Repair Tie Fanout¶
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¶
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 percentage of the number of instances in the design. The default value for
buffer_percent is 20, for 20%.
Report Design Area¶
report_design_area
The report_design_area command reports the area of the design’s components
and the utilization.
Report Floating Nets¶
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.
Example scripts¶
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
Regression tests¶
Limitations¶
FAQs¶
Check out GitHub discussion about this tool.
License¶
BSD 3-Clause License. See LICENSE file.