Why redefinition of MAX_ROUTING_LAYER is not possible for most platforms?

[jtremesay]

Hi,

I'm trying to create a hierarchical flow for a SoC design with nangate45.
For the sub-designs, I wanted to limit the routing to metal 6.

From what I see in the documentation, MAX_ROUTING_LAYER is the variable I should use.

But the documentation also says that the variable is already set for nangate45 and cannot be reassigned.

what is the reason for this choice?

Can I safely edit this line to export MAX_ROUTING_LAYER ?= metal10 ?

[maliberty]

I think that's fine. You can make a PR for the change if you wish.

[jtremesay]

I'm going to do some local tests and make a PR if thinks look ok

[maliberty]

Note that you may also need to look at PDN and the layers it uses for your sub-block.

[jtremesay]

PR available here