Let me assume that you just have a "few" peripheral devices that you want to memory-map. You only use the internal XRAM for program variables. You do not have conventional external RAM.

Then you just set and clear the EXTRAM bit whenever you access your peripherals. The compiler does not know or care which memory you are accessing. So your regular program is always set up for the internal XRAM.

It all really depends on how fast or often you need to access your peripherals. You may find it as easy to access via ordinary port lines. But whichever way you do it, you need to ensure that only one CPU accesses one peripheral at a time.

David.