Connecting an 8-bit peripheral to a 32-bit avalon bus

It is really best to make your slave 32bits and to ignore the high bits (set to zero on reads).

You probably still want to verify that the byte enable for D0..7 is asserted.

Note that the nios cpu always does 32bit reads (all byte enables asserted), discarding the unwanted bits internally.

The additional logic for the mux is almost certainly less than that for the bus width adapter!