SOPC builder - connect a custom component to tightly coupled i/f?

Insert a simple 'conduit' block with an avalon master and avalon slave interface between the nios data master and the actual code memory block.

I actually run a system that doesn't have data access to the code memory at all, this does require a non-standard linker script, and can't be done with the gcc4 compiled by altera (unless you code has no switch statement jump tables).

You probably want to move the .rodata (and strings) into tightly coupled data memory - especially if you have to real reason to enable the data cache.