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synth: ABC_LIBERTY_ARGS, extra arguments for ABC's read_lib #4730

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synth: ABC_LIBERTY_ARGS, extra arguments for ABC's read_lib #4730

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f421aff
synth: ABC_LIBERTY_ARGS, extra arguments for ABC's read_lib
Oct 24, 2026
c372b41
synth: ABC_LIBERTY_ARGS: American spelling in the description
Oct 27, 2026
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2 changes: 2 additions & 0 deletions docs/user/FlowVariables.md
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Original file line number Diff line number Diff line change
Expand Up @@ -92,6 +92,7 @@ configuration file.
| --- | --- | --- |
| <a name="ABC_AREA"></a>ABC_AREA| Strategies for Yosys ABC synthesis: Area/Speed. Default ABC_SPEED.| 0|
| <a name="ABC_DRIVER_CELL"></a>ABC_DRIVER_CELL| Default driver cell used during ABC synthesis.| |
| <a name="ABC_LIBERTY_ARGS"></a>ABC_LIBERTY_ARGS| Extra arguments for ABC's read_lib, passed with Yosys's abc -liberty_args. Without -S/-G, ABC's mapping library gives every cell a delay of 1, so mapping minimizes gate count, not delay. "-a -G 250" derives a delay for each cell from the liberty tables (all cells, gain 250). Ignored when SYNTH_WRAPPED_OPERATORS or SWAP_ARITH_OPERATORS is set: abc_new has no such option.| |
| <a name="ABC_LOAD_IN_FF"></a>ABC_LOAD_IN_FF| During synthesis set_load value used.| |
| <a name="ABC_SCRIPT"></a>ABC_SCRIPT| Replaces the ABC script synthesis runs, so that a design can vendor and change it. Ignored when SYNTH_WRAPPED_OPERATORS or SWAP_ARITH_OPERATORS is set: abc_new then maps each arithmetic operator with its own script.| |
| <a name="ABSTRACT_SOURCE"></a>ABSTRACT_SOURCE| Which .odb file to use to create abstract| |
Expand Down Expand Up @@ -343,6 +344,7 @@ configuration file.

- [ABC_AREA](#ABC_AREA)
- [ABC_DRIVER_CELL](#ABC_DRIVER_CELL)
- [ABC_LIBERTY_ARGS](#ABC_LIBERTY_ARGS)
- [ABC_LOAD_IN_FF](#ABC_LOAD_IN_FF)
- [ABC_SCRIPT](#ABC_SCRIPT)
- [ADDER_MAP_FILE](#ADDER_MAP_FILE)
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3 changes: 3 additions & 0 deletions flow/scripts/synth.tcl
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Expand Up @@ -282,6 +282,9 @@ if {
![env_var_equals SYNTH_WRAPPED_OPERATORS 1] &&
![env_var_equals SWAP_ARITH_OPERATORS 1]
} {
if { [env_var_exists_and_non_empty ABC_LIBERTY_ARGS] } {
lappend abc_args -liberty_args $::env(ABC_LIBERTY_ARGS)
}
log_cmd abc {*}$abc_args
} else {
# Not dead code: abc_new mistakes the "-script" in /OpenROAD-flow-scripts/...
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6 changes: 6 additions & 0 deletions flow/scripts/variables.json
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10 changes: 10 additions & 0 deletions flow/scripts/variables.yaml
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Expand Up @@ -1070,6 +1070,16 @@ ABC_AREA:
stages:
- synth
default: 0
ABC_LIBERTY_ARGS:
description: |
Extra arguments for ABC's read_lib, passed with Yosys's
abc -liberty_args. Without -S/-G, ABC's mapping library gives every
cell a delay of 1, so mapping minimizes gate count, not delay.
"-a -G 250" derives a delay for each cell from the liberty tables
(all cells, gain 250). Ignored when SYNTH_WRAPPED_OPERATORS or
SWAP_ARITH_OPERATORS is set: abc_new has no such option.
stages:
- synth
ABC_SCRIPT:
description: |
Replaces the ABC script synthesis runs, so that a design can vendor and
Expand Down