NIOS II Control Unit (CU)

I mean the following. Your NIOS master puts a coded instruction (or one already decoded, "one-hot" bit instruction code) in the PIO output port. This is a simple IOWR write in C code. The slave processors have each one a PIO input port (which is externally, HDL, connected to the master's PIO port). So, as soon as the master puts the instruction out, all the slaves see it. You can even implement an interrupt routine in the slaves processors, if you want. In any case, the input PIO can be read with a simple IORD in C. Then, the instruction will be decoded (if needed) in each slave and executed separately in each processor.