A Robust Asynchronous Interfacing Scheme with Four-Phase Dual-Rail Coding

This paper proposes new robust asynchronous interfaces for GALS-systems. A combination of delay-insensitive and error detecting/correcting codes is used to achieve two types of robustness: variation-tolerance and fault-tolerance. Concerning the delay-insensitive code this paper targets the well-known 4-phase dual rail code, frequently used in asynchronous circuit design. In order to enable an optimal choice of the used error detecting/correcting code, a precise fault model and a general classification of possible interconnect architectures is presented. The goal is to tolerate single-bit errors with maximum coding efficiency, i.e., with minimal overheads for interconnect resources. This is accomplished by fully utilizing the information redundancy provided by the combination of the delay-insensitive code and an appropriate error detecting/correcting code. Metastable upsets, however, cannot be handled with error correcting codes alone. Faults can occur at arbitrary times and thus compromise system timing. Even though metastability cannot be avoided, a metastability-tolerant implementation is presented, which waits for a metastable upset to resolve before processing a new data word. This guarantees correct data transmission regardless of the timing of erroneous inputs.