Return data selector employing barrel-incrementer-based round-robin apparatus

摘要

A return data selector is disclosed. A pipelined microprocessor includes N functional units that request to return data to the pipeline. In a given selection cycle, some of the functional units may not be requesting to return data. The return data selector includes a circuit for selecting one of functional units in a round-robin fashion. The circuit 1-bit left rotatively increments a first addend by a second addend to generate a sum that is ANDed with the inverse of the first addend to generate a 1-hot vector indicating which of the functional units is selected next. The first addend is an N-bit vector where each bit is false if the corresponding functional unit is requesting to return a result to the pipeline. The second addend is a 1-hot vector indicating the last selected functional unit.