Complementary Synthesis for Encoder with Flow Control Mechanism

Abstract

Complementary synthesis automatically generates an encoder's decoder with the assumption that the encoder's all input variables can always be uniquely determined by its output symbol sequence. However, to prevent the faster encoder from overwhelming the slower decoder, many encoders employ flow control mechanism that fails this assumption. Such encoders, when their output symbol sequences are too fast to be processed by the decoders, will stop transmitting data symbols, but instead transmitting idle symbols that can only uniquely determine a subset of the encoder's input variables. And the decoder should recognize and discard these idle symbols. This mechanism fails the assumption of all complementary synthesis algorithms, because some input variables can't be uniquely determined by the idle symbol. A novel algorithm is proposed to handle such encoders. First, it identifies all input variables that can be uniquely determined, and takes them as flow control variables. Second, it infers a predicate over these flow control variables that enables all other input variables to be uniquely determined. Third, it characterizes the decoder's Boolean function with Craig interpolant. Experimental results on several complex encoders indicate that this algorithm can always correctly identify the flow control variables, infer the predicates and generate the decoder's Boolean functions.