Synthesis from multi-cycle atomic actions as a solution to the timing closure problem

One solution to the timing closure problem is to perform infrequent operations in more than one cycle. Despite simplicity of the solution statement, it is not easily considered because it requires changes in RTL, which, in turn, exacerbates the verification problem. We offer a timing closure solution guaranteed to preserve functional correctness of designs expressed using atomic actions or rules. We exploit the fact that the semantics of atomic actions are untimed, that is, the time to execute an action is not specified. The current hardware synthesis technique from atomic actions assumes that each rule takes one clock cycle to complete its computation. Consequently, the rule with the longest combinational path determines the clock cycle of the entire design, often leading to needlessly slow circuits. We present a synthesis procedure for a system where the combinational circuits embodied in a rule can take multiple cycles without changing the semantics of the original design. We also present preliminary results based on an experimental compiler which uses the Bluespec (BSV) compiler front end and generates Verilog. The results show that the clock speed and the performance of circuits can be improved substantially by allowing slow paths to complete over multiple cycles. Our technique is orthogonal to solutions based on multiple clock domains.