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Add useful-skew flag to CTS script #4794

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4e875e4
add useful-skew flag to CTS script
luis201420 Nov 5, 2026
59442c1
defined CTS_USEFUL_SKEW variable
luis201420 Nov 5, 2026
cb24a81
Merge remote-tracking branch 'origin' into add-useful-skew-flag-cts
luis201420 Nov 6, 2026
3848a1b
add CTS_USEFUL_SKEW
luis201420 Nov 6, 2026
a5dac33
Merge remote-tracking branch 'origin' into add-useful-skew-flag-cts
luis201420 Nov 9, 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 @@ -131,6 +131,7 @@ configuration file.
| <a name="CTS_CLUSTER_SIZE"></a>CTS_CLUSTER_SIZE| Maximum number of sinks per cluster.| |
| <a name="CTS_LIB_NAME"></a>CTS_LIB_NAME| Name of the Liberty library to use in selecting the clock buffers.| |
| <a name="CTS_SNAPSHOTS"></a>CTS_SNAPSHOTS| Create ODB/SDC files at different stages of CTS.| 0|
| <a name="CTS_USEFUL_SKEW"></a>CTS_USEFUL_SKEW| Enable useful skew during the CTS balancing phase.| 0|
| <a name="DESIGN_NAME"></a>DESIGN_NAME| The name of the top-level module of the design.| |
| <a name="DESIGN_NICKNAME"></a>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 different design.| |
| <a name="DETAILED_METRICS"></a>DETAILED_METRICS| If set, then calls report_metrics prior to repair operations in the CTS and global route stages| 0|
Expand Down Expand Up @@ -543,6 +544,7 @@ configuration file.
- [CTS_CLUSTER_SIZE](#CTS_CLUSTER_SIZE)
- [CTS_LIB_NAME](#CTS_LIB_NAME)
- [CTS_SNAPSHOTS](#CTS_SNAPSHOTS)
- [CTS_USEFUL_SKEW](#CTS_USEFUL_SKEW)
- [DETAILED_METRICS](#DETAILED_METRICS)
- [DETAIL_PLACEMENT_ARGS](#DETAIL_PLACEMENT_ARGS)
- [HOLD_SLACK_MARGIN](#HOLD_SLACK_MARGIN)
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2 changes: 1 addition & 1 deletion flow/scripts/cts.tcl
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Expand Up @@ -25,7 +25,7 @@ append_env_var cts_args CTS_CLUSTER_SIZE -sink_clustering_size 1
append_env_var cts_args CTS_CLUSTER_DIAMETER -sink_clustering_max_diameter 1
append_env_var cts_args CTS_BUF_LIST -buf_list 1
append_env_var cts_args CTS_LIB_NAME -library 1

append_env_var cts_args CTS_USEFUL_SKEW -useful_skew 0

@gemini-code-assist gemini-code-assist Bot Nov 5, 2026

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medium

The newly introduced environment variable CTS_USEFUL_SKEW is not defined in flow/scripts/variables.json. All environment variables used in the flow scripts must be declared in variables.json (or variables.yaml) to ensure they are properly documented, typed, and validated within the OpenROAD Flow Scripts environment.


if { [env_var_exists_and_non_empty CTS_ARGS] } {
set cts_args $::env(CTS_ARGS)
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7 changes: 7 additions & 0 deletions flow/scripts/variables.json
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Expand Up @@ -257,6 +257,13 @@
"cts"
]
},
"CTS_USEFUL_SKEW": {
"default": 0,
"description": "Enable useful skew during the CTS balancing phase.\n",
"stages": [
"cts"
]
},
"DESIGN_NAME": {
"description": "The name of the top-level module of the design.\n",
"required": true
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6 changes: 6 additions & 0 deletions flow/scripts/variables.yaml
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Expand Up @@ -1276,6 +1276,12 @@ CTS_LIB_NAME:
Name of the Liberty library to use in selecting the clock buffers.
stages:
- cts
CTS_USEFUL_SKEW:
description: |
Enable useful skew during the CTS balancing phase.
stages:
- cts
default: 0
POST_CTS_TCL:
description: |
Specifies a Tcl script with commands to run after CTS is completed.
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