Two NIOS2 sharing the same SDRAM for instruction/data master

I designed a similar 2 CPU / 1 SDRAM system (not Nios) a few years ago.

So, you can surely design a system with two Nios processors and a single shared sdram device, but you must be aware of these points:

- sdram accesses will be shared between the two processors, so the running applications could suffer great performance decrement; the actual performance will depend on several factors, i.e. number of sdram accesses, arbitration priorities and cache usage.

- you must carefully instruct the linker to place memory sections into proper sdram areas in order to avoid overlapping and consequent data/code corruption.

I think the first point is the major issure. I'd suggest you keep the more program code you can in onchip memory, along with stack and often-accessed data.

Move into sdram only non time-critical parts and bulk data or seldom accessed data.

Cris72 how can i move only part of my program to a sdram?

Just to remember, one of my NIOS2's program is a mmu-linux and the other is a simple elf application

Sorry, I don't know anything about mmu-linux, since I never used it.

For normal Nios application, a simple method is using the __attribute__ directive after the function/variable definition you want to place in a specific memory.

For example, if your code defaults to onchip_ram and you want function ext_function to be mapped to ext_sdram, you define it:

int ext_function(int param) __attribute__ ((section (".ext_sdram")));

This is convenient if you only need to move a few functions to the alternate memory device.

If you need something more advanced (i.e. remapping a whole library module or all symbols of a set of .c files), you'd better use a custom linker script file.

In your case you need to move symbols to sdram but you also need to specify where, in order to avoid overlap, as I said before. So I believe the linker script method is mandatory.