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Excluding Cells from LVS Check (Calibre)

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unstablechimp

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I realize there is a way to exclude cells from DRC, by simple using "EXCLUDE CELL <cell name>" in the rules file.

I cannot find a equivalent rule for LVS, for hierarchical comparisons. In Herclues LVS, this was very easy to do, by placing the appropriate rule and list of cells in the rules file.

One might be wondering why this is necessary. In some cases RTL designers are using the verilog model prior to the deployment of any cdl/spice and/or gds. This means the cells exist in Verilog/Netlist, but have yet to exist in any other form. There are times in the design process, where a spice/cdl netlist exists, but a GDS does not for a custom cell. In these cases, it is beneficial to have a LVS rule which allows for the exclusion of certain cells in a LVS run.

There are other cases were one may want to exclude cells from LVS; decap cells, pad cells, etc.
 

dick_freebird

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I view this as potentially dangerous, because you will
have to apply a lot of care in eliminating all of these
"don't check" things from the final design. That introduces
human error. Far better to maintain clean matching from
bottom to top, stage by stage.

Parsing and rejecting LVS mismatches in the output is
better than hoaxing the input. Pads and decoupling, I like
to represent 1:1 also. Otherwise (depending on how your
LVS behaves) you could very well end up ignoring real
shorts.
 

unstablechimp

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I understand the risk, but this still doesn't answer my question.

This is an interim LVS check, and by no means the final LVS.

In an interim design, there are cases where one may not have all the necessary files from custom cells. In this case, it would be nice to have the ability to exclude these cells from an LVS check.
 

wpchan05

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unstablechimp said:
I understand the risk, but this still doesn't answer my question.

This is an interim LVS check, and by no means the final LVS.

In an interim design, there are cases where one may not have all the necessary files from custom cells. In this case, it would be nice to have the ability to exclude these cells from an LVS check.
I guess you can do calibre blackbox lvs. Basically, it will see the pin info of those cells which are in blackbox. Look for the doc or google this for further info.
 

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