.rwdata

The difficulty may be getting the exceptions to work for both the boot code (in on-chip memory) and subsequently getting the nios2 to vector to the program handler in SDRAM?

The exception setting appears to be set within the NIOS FPGA build, and is bound to a particular section(address)

I guess I can locate the exception handler part of the boot ROM actually in a small block RAM, and part of my boot copier will load the applications handler on-top of the boot-RAM one (which is initialised via initial FPGA bitstream) ?

However - this presents a problem upon nios_reset since the original exception handler for the boot RAM will now be lost (overwriting by the boot-copier)

Thanks for your efforts anyway!