SAS: Source Asynchronous Signaling Protocol for Asynchronous Handshake Communication Free from Wire Delay Overhead

Asynchronous handshake protocol communication is accomplished by sending data down a communication link coupled with data validity information. Flow control is established by acknowledging the receipt of data, thereby enabling transmission of new data down the link. Handshake protocols operate at target cycle times based on system operational requirements. When the communication delay down wires increases beyond a certain point, the latency in sending the request and acknowledge signals across the link becomes longer than the target cycle time. This reduces the communication bandwidth below the desired value. This deleterious effect is particularly conspicuous on long links and network-on-chip communication. A method of enabling full communication bandwidth on wires with arbitrary delay when employing handshake communication is provided. This method supports end-to-end communication across links with arbitrarily large but finite latency without limiting the bandwidth, so long as line variation can be reliably controlled. This paper introduces the news AS protocol, provides an efficient implementation, and reports the resultant significant energy and bandwidth improvements over conventional handshaking methods.