Creating external SRAM pin assignment?

The top level file is the "main" file for your design, whose I/O signals will be mapped to actual pins.

Eventually, you will be instantiating your SOPC within your top level file.

I like to start by writing an empty top level file, which just lists the I/O signals so I can perform pin assign.

But using the pin planner to assign pins and then have the pin planner create an empty top level file also works fine.