INSTRUCTION DISPATCH SCHEDULER EMPLOYING ROUND-ROBIN APPARATUS SUPPORTING MULTIPLE THREAD PRIORITIES FOR USE IN MULTITHREADING MICROPROCESSOR

A dispatch scheduler in a multithreading microprocessor is disclosed. Each of N concurrently executing threads has one of P priorities. P N-bit round-robin vectors are generated, each being a 1-bit left-rotated and subsequently sign-extended version of an N-bit 1-hot input vector indicating the last thread selected for dispatching at the priority. N P-input muxes each receive a corresponding one of the N bits of each of the P round-robin vectors and selects the input specified by the thread priority. Selection logic selects an instruction for dispatching from the thread having a dispatch value greater than or equal to any of the threads left thereof in the N-bit input vectors. The dispatch value of each of the threads comprises a least-significant bit equal to the corresponding P-input mux output, a most-significant bit that is true if the instruction is dispatchable, and middle bits comprising the priority of the thread.