NIOS Custom Instruction with more than two input

A custom instruction is limited to two 32bit inputs (and one output) because of the design of the nios cpu - that can't change.

What you do with the values and the other other register fields is rather up to your imagination...

If you write a non-combinatorial instruction (and make sure that only one

thread uses the hardware at a time) you can save state between instructions.

So if 'writerc' is 0, you can use the 'C' bits as a sub-opcode (rather than a register number) - so maybe 'load first', 'load next', 'load last' ?

Similarly you can use 'readrb' of 0 to indicate other special actions.

However loading data via the nios is probably slow - if you really need a sort accelerator you probably need to give it an Avalom master interface so it can directly access the data in memory.