NIOS II and Cyclone III Remote Update

Still not sure you got it; please excuse me if I'm wrong, but I'll try to explain better.

You CAN definitely select a different image for FPGA configuration with remote update core. What you can't do is selecting a Nios boot image independently from FPGA configuration, since Nios bootloader is embedded in the specific configurated logic.

Example:

In epcs you have a base FPGA configuration at address 0, another one at address 0x20000 and a third one at address 0x40000 and possibly others at higher addresses.

Upon power up the default base configuration at address 0 is loaded: this may or may not have a Nios system configurated inside it; if it does, the bootloader should also be implemented and will take care of loading Nios firmware.

Let's now assume you need to reconfigure with the image at address 0x40000; you set the remote update address to point there and trigger the reconfiguration. At this point the FPGA is configured from the image stored at 0x40000; but this is only the hardware part: whether a Nios firmware is bootloaded and WHERE it has to be loaded from it's a specific information hardcoded into the newly loaded image.

If you want the configuration at 0x40000 to be able to boot different Nios programs upon user request, or even select the Nios boot image position, you must provide a far more complex bootloader which test other system variables (for example input pins coming from dip switches) and proceed according to the user selection; remote update core is not involved in this part.