Proposal to reduce confusion around small designs.

[armleo]

Prompt

People use OpenLane for small designs. However many small designs do not fit PDN grid properly and have some weird quirks and issues.

Proposal

Have a MIN_DIE_AREA defined in PDK and the DIE_AREA is compared to MIN_DIE_AREA and if the DIE_AREA is smaller then to error out with a clear message about the issue:

The die area is too small. PDK does not support cells smaller than $MIN_DIE_AREA.
If you are advanced user and want to disable this check than you can set DISABLE_MIN_DIE_AREA_CHECK, but this is NOT RECOMMENDED.

It is recommended to set the FP_SIZING to "absolute" and DIE_AREA to "0 0 300 300".

Then have DISABLE_MIN_DIE_AREA_CHECK configuration which can be used to turn off this check for users that specifically want to have small designs.