Resynchronization of a superscalar processor

Abstract

Operations of a pipeline processor (110) are resynchronized under designated conditions. The processor updates a fetch program counter (210) and, as directed by the counter, fetches instructions from a memory (114). The processor concurrently dispatches, in the fetched order, multiple instructions to designated functional units (170, 171, 172, 173, 174 and 175). Dispatched instructions are queued in functional unit reservation stations. Result entries corresponding to the queued instructions are allocated in a reorder buffer 126 queue in their order of dispatch. Instructions are executed out of their fetched order and results are entered in the allocated result entries when execution is complete. Allocated result entries at the head of the reorder buffer queue are retired and an instruction pointer (620) is updated. The processor is resynchronized when it detects a resynchronization condition and acknowledges the resynchronization condition in the allocated result entry corresponding to the instruction that detected the condition. When the reorder buffer entry holding the resynchronization acknowledgement is retired, the processor flushes the reorder buffer and the reservation stations of the functional units and redirects the fetch program counter to the instruction addressed by the instruction pointer.