NIOS II Structure Casting w/ Opt. (-O3)

Look at the assembler code generated for your code.

I had a case on an x86 where bit-field access resulted in byte-based assembly instructions, even though the bit-field is described using integers.

In your case, since each bit-field is actually a byte, it might be less ambiguous (in the sense of undefined compiler operation) to use an array of bytes. You can use a union to make the array accessible as either a single integer or four single byte fields.

Cheers,

Dave