Slew margin in openlane flow

[akhilesh911]

Good morning everyone,
After completion of openlane flow, I noticed the rcx_sta.slew.rpt. It shows the slew limit 4.00 for every design.

report_check_types -max_slew -max_cap -max_fanout -violators

max slew

Pin Limit Slew Slack

48482/A1 4.00 8.01 -4.01 (VIOLATED)
54806/Q 4.00 8.01 -4.01 (VIOLATED)
hold92/Z 4.00 5.89 -1.89 (VIOLATED)
48476/A1 4.00 5.75 -1.75 (VIOLATED)
54803/Q 4.00 5.75 -1.75 (VIOLATED)
42824/A3 4.00 5.72 -1.72 (VIOLATED)
42823/ZN 4.00 5.72 -1.72 (VIOLATED)
48478/A1 4.00 5.34 -1.34 (VIOLATED)

Is there any way to increase or decrease that limit?
Kindly help.

[vijayank88]

set ::env(GLB_RESIZER_MAX_SLEW_MARGIN) 10 check default variable. you can increase or decrease as per need.

[akhilesh911]

Yes I tried by changing that value and also placement slew margin but still it's limit is 4.

[vijayank88]

@akhilesh911 is this built-in example or own design?
If own design mean need source files to check the issue.

[akhilesh911]

It is own design. The slew margin is dependent on clock period, isn't it? My clock period is 50.

[kareefardi]

GLB_RESIZER_MAX_SLEW_MARGIN has nothing to do with adjusting the constraint.

[kareefardi]

Can you share your config? Slew margin used to be a percentage of the clock period.

[kareefardi]

and the OpenLane version that you are using

[akhilesh911]

config (copy).txt
This is my config file.

I am using the version of OpenLane 90d369b

[vijayank88]

@akhilesh911 you're using last year December build.
Try to update to latest build and try again.

[kareefardi]

You are using gf180. The max transition set for pins in the PDK lib files is 4.0. If you want to overwrite it, you can update to latest OpenLane and use MAX_TRANSITION_CONSTRAINT. You can also provide a custom sdc file and keep using your old version of OpenLane

[akhilesh911]

I understood. Thank you @kareefardi @vijayank88