Although many successful asynchronous control circuit synthesis methods are available, it is still unwieldy to conceive and describe the behaviors of a number of controllers which constitute a control unit of a target system manually. In this paper, an automatic and systematic method to derive an efficient asynchronous control unit from a system specification, a control data flow graph (CDFG), is suggested. In order to acquire an asynchronous control unit of acceptable quality, a new process-oriented method is proposed. In this method, the resulting asynchronous control unit has complete separation of 'execution controllers' and 'execution order controllers' according to the hierarchical decomposition of a given CDFG. This distributive feature leads to a significant improvement in area, performance, implementability and synthesis time for the derived asynchronous control units.

Asynchronous controllers effectively control high concurrence of datapath operations for high speed. Signal Transition Graphs (STGs) can effectively represent these concurrent events. However, highly concurrent STGs cause the state explosion problem in asynchronous synthesis tools. Many small but highly concurrent STGs cannot be synthesized to obtain control circuits. Moreover, STGs also lead to some control-time overhead of the four-phase handshake protocol. In this paper, we propose a method for deriving the serial control nodes from Control Data Flow Graphs (CDFGs) such that the concurrence of datapath operations is still preserved. The STGs derived from the serialized control nodes are serial STGs which are simpler for synthesis than the concurrent STGs. We also propose an implementation using these serialized controllers to generate local clocks at any necessary times. The implementation results in very small control-time overhead. The experimental results show that the number of synthesis states is proportional to the number of control signals, and the circuits with satisfiable small control-time overhead are obtained.