Method and apparatus for a high efficiency two-stage rotating priority arbiter with predictable arbitration latency

A scalable, two-stage rotating priority arbiter with re-circulation and bounded latency for use in multi-threaded, multi-processing devices. An apparatus implementing the two-stage arbiter includes a plurality of masters configured in a plurality of clusters, a plurality of targets, and an chassis interconnect that may be controlled to selectively connects a given master to a given target. The chassis interconnect includes multiple sets of bus lines connected between the plurality of clusters and the plurality of targets forming a cross-bar interconnect, including sets of bus lines corresponding to a command bus. A two-stage arbitration scheme is employed to arbitrate access to the command bus. The first arbitration stage is used to arbitrate between target requests issued by masters in a given cluster. The second arbitration stage is used to arbitrate between winning first-stage target requests. One embodiment of the arbitration scheme employs a rotating priority arbitration scheme at the first stage. Another embodiment employs a complementary rotating priority arbitration scheme at the second stage.