Control over marco pdn layers

[kareefardi]

Prompt

This is how a macro's pdn is defined:

define_pdn_grid \
    -macro \
    -default \
    -name macro \
    -starts_with POWER \
    -halo "$::env(FP_PDN_HORIZONTAL_HALO) $::env(FP_PDN_VERTICAL_HALO)"

add_pdn_connect \
    -grid macro \
    -layers "$::env(FP_PDN_LOWER_LAYER) $::env(FP_PDN_UPPER_LAYER)"

A macro doesn't necessarily have it's own internal pdn on FP_PDN_LOWER_LAYER.

Proposal

Create a separate variable defining a macro's pdn layer.

[kareefardi]

Became relevant here https://github.com/The-OpenROAD-Project/OpenLane/issues/1768