[WARNING] FastRoute cannot handle net user_clock2 due to large number of pins [WARNING] Net user_clock2 has 37130 pins It's a clock... It goes everywhere! Should I be concerned with this warning?

you might need to mark the clock as a clock in the config so that it's properly treated as a clock tree

The fact it can't distribute your clock ? Yeah, I'd be concerned.

It is already marked as a clock!

Apparently not. But as I told you I'm not sure multi clock works ...

Hmm.. The caravel SOC provides 2 clocks to for the user project.

yeah, for you to pick one ...

You'd need two clock tree generations.

I mean, you can also work out how to support multiple, but from what I've seen here, it's not "out of the box" ATM so if you want that ,you need to work it out.

Also, would STA handle asynchronous clocks?

you'd need custom constraint files to define relationships between clock or maximum delays, etc etc ... AFAIK OpenSTA supports analyzing those path but it's all up to you to call it correctly, I don't thin kanything in OpenLANE supports that.

Ok, I can handle the custom .sdc if I ever get to a 2 clock flow.