Asynchronous Pipeline Controller Based on Early Acknowledgement Protocol
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概要
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A new pipeline controller based on the Early Acknowledgement (EA) protocol is proposed for bundled-data asynchronous circuits. The EA protocol indicates acknowledgement by the falling edge of the acknowledgement signal in contrast to the 4-phase protocol, which indicates it on the rising edge. Thus, it can hide the overhead caused by the resetting period of the handshake cycle. Since we have designed our controller assuming several timing constraints, we first analyze the timing constraints under which our controller correctly works and then discuss their appropriateness. The performance of the controller is compared both analytically and experimentally with those of two other pipeline controllers, namely, a very high-speed 2-phase controller and an ordinary 4-phase controller. Our controller performs better than a 4-phase controller when pipeline has processing elements. We have obtained interesting results in the case of a non-linear pipeline with a Conditional Branch (CB) operation. Our controller has slightly better performance even compared to 2-phase controller in the case of a pipeline with processing elements. Its superiority lies in the EA protocol, which employs return-to-zero control signals like the 4-phase protocol. Hence, our controller for CB operation is simple in construction just like the 4-phase controller. A 2-phase controller for the same operation needs to have a slightly complicated mechanism to handle the 2-phase operation because of the non-return-to-zero control signals, and this results in a performance overhead.