Multimedia round-robin arbitration with phantom slots for super-priority

Abstract

Low-latency arbitration is provided for a super-priority communications device such as modems and ISDN/DSL routers, LAN switches and routers. Phantom arbitration slots are inserted between each pair of permanent slots. When a request from the super-priority agent is received, the next phantom slot is used to service the request. The initial latency is just one slot period rather than the whole arbitration loop. Other phantom slots are skipped until the same phantom slot is again activated at the same point in the arbitration loop during subsequent rounds of arbitration. Thus only the initial latency is reduced; subsequent requests from the super-priority agent are handled just once for each arbitration cycle. The low initial latency allows the communications device to quickly respond to an incoming call. Other real-time agents are assigned a fixed slot in a round-robin arbitration. The last arbitration slot is used by all non-real-time agents. The last time slot uses a priority arbiter to grant access in a priority order to the non-real-time agents. A timer is used to limit the time that the last arbitration slot services non-real-time agents. The next arbitration loop then begins with the first real-time agent or a phantom slot. The amount of access time given the non-real-time agents is maximized while the real-time agents are ensured access within the maximum loop period.