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Nickson Jose

08/19/2020, 6:07 AM
I'm trying to plug in my custom inverter cell (inv_1) into picorv32a design and run the openlane flow..the runs are OK but placement of my cell isn't legalized (attached is a section of the post-routing layout & the inverter cell highlighted is my cell)..can anybody help?
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Ahmed Ghazy

08/19/2020, 12:20 PM
Looks like that your cell boundaries include the rails, is that correct? Does your cell height (as reported in the LEF file) match the site height?
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Nickson Jose

08/19/2020, 12:38 PM
That's something I am not able to figure out @Ahmed Ghazy.. I checked out the original inverter's .mag file..the total WIDTH x HEIGHT of the top cell (outer boundary) is 1.76 x 3.20 while the inner boundary is 1.38 x 2.72 (as shown in the attached pic)...when i do a lef write the SIZE (for original inverter) is 1.38 x 2.72......while for my custom inverter of same dimension (1.76 x 3.20) generates a SIZE of 1.76 x 3.20 while doing lef write....Im attaching both the layout and extracted lef for the standard as well as the custom inverter
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Ahmed Ghazy

08/19/2020, 12:50 PM
You can control the "inner" boundary with
property FIXED_BBOX x_ll y_ll x_ur y_ur
. Or more conveniently, adjust the box tool in magic on the inner boundary you'd like to set and use
property FIXED_BBOX [box values]
You want to adjust the width as well btw; both dimensions must be integer multiples of the HD site in the LEF file.
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Nickson Jose

08/19/2020, 1:09 PM
That would be really helpful..I will try and let you know👍
@Ahmed Ghazy..i did run the flow post bounding box inclusion..the lef file now were extracted correctly & I could see improvements but there are still some overlaps..hope its visible in snap attached..
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Ahmed Ghazy

08/19/2020, 3:25 PM
Could you share the LEF file?
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Nickson Jose

08/19/2020, 3:35 PM
Sure..
sharing with you merged.lef
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Ahmed Ghazy

08/19/2020, 3:45 PM
The issue that the rails you've drawn aren't of the same width as the other std cells nor are the upper/top boundaries perfectly centered at the rails they overlap with. For example, you want your rails to look like the following:
Instead they look like that:
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Nickson Jose

08/19/2020, 3:48 PM
Thanks for the analysis @Ahmed Ghazy..will work on it
Hi @Ahmed Ghazy..the final one has pretty great improvements..thanks !
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