This paper describes an asynchronous design tool flow known as phased logic that converts a clocked design into an asynchronous design implemented as a micropipeline using two-phase control and bundled data signaling. Example designs include variations of a double-precision floating-point clipping operation mapped to two commercial standard cell libraries (0.18/spl mu/ and 0.13/spl mu/) and a five-stage pipelined MIPs-compatible integer unit mapped to the 0.13/spl mu/ library. The design style includes a feature known as early evaluation, which is a generalized form of bypass that allows the self-timed design to recover some of the inherent latch delay penalty in micropipelines.

Data-dependent completion time is a well-known advantage of self-timed circuits, one that allows them to operate at average rather than worst-case execution rates. A technique called early evaluation (EE) that extends this advantage by allowing self-timed modules to produce results before all of their inputs have arrived is described here. The technique can be applied to any combinational function and is integrated into the phased logic (PL) design methodology that accepts synchronous design entry and produces delay-insensitive self-timed circuits. We describe an algorithm that ensures that the resulting delay-insensitive circuits are safe, and develop a generalized method for inserting EE gates into any PL netlist. We give performance results for several benchmark circuits, including a five-stage pipelined CPU and a microprogrammed floating-point unit. Comparisons are made among clocked circuits, PL circuits, and PL circuits with EE. Simulation results show a clear performance benefit for PL circuits that use EE.

A technique for automatic insertion of slack matching buffers for performance enhancement in the asynchronous design style known as Phased Logic (PL) is described. A description of how slack matching buffers can offer throughput increases in PL circuitry is presented and is supported through the use of a simulation tool developed for modeling the timing behavior of PL circuits. A description of the architecture of the simulator and its implementation is also discussed. Based on the analysis of results provided by the simulator and the topological characteristics of a PL circuit, an algorithm for automatic slack matching buffer placement is devised. Examples of the buffer insertion technique are given and the effectiveness of the technique is evaluated through a set of experimental results.

Phased logic has been proposed as a technique for realizing self-timed circuitry that is delay-insensitive and requires no global clock signals. Early evaluation techniques have been applied to asynchronous circuits in the past in order to achieve throughput increases. A general method for computing early evaluation functions is presented for this design style. Experimental results are given that show the increase in throughput of various benchmark circuits. The results show that as much as a 30% speedup can be achieved in some cases.

A logic style known as Phased Logic (PL) is applied to arithmetic circuits. Phased logic is a dual-rail LEDR logic style that allows automatic translation from a clocked netlist to a self-timed implementation. Bit level dataflow, early evaluation and automatic filtering of transient computations within PL circuits can lead to both increased performance and higher energy efficiency than the original clocked netlist. Simulation results for a 16/spl times/16 iterative multiplier based on a LUT4 design show a 23% speed improvement and 20% energy improvement over the clocked design. A Y=Y@1*a +b calculation using an array multiplier design shows a 15% performance decrease but is 2/spl times/ more energy efficient than the clocked counterpart.

Locally Clocked Modules (LCMs) allow asynchronous communication between synchronous computational elements. The concurrency workbench models concurrent systems in the CCS process algebra. We describe the use of the concurrency workbench to specify, simulate, and verify implementations of LCMs and discuss its application to the specification of asynchronous circuits.

The rapid prototyping of VLSI systems from an abstract specification is described. The high-assurance rapid-prototyping environment HARP is used. HARP is based on the translation of an abstract formal language with a formal semantics to a synchronous, communication-dominated finite state machine with data path implementation. The approach supports the specification, verification, synthesis, and VLSI level implementation of communicating sequential processes (CSP)-specified globally and locally clocked synchronous digital systems using existing tools for design and formal verification.>

This paper presents a comparison of asynchronous and synchronous standard cell implementations for finite state machine with data-path (FSMD) ASICs. The comparison is made through independent parallel designs of a 16-bit factoring ASIC. A common functional specification, standard cell library, and suite of EDA tools for layout and simulation are used to provide a common basis for comparison. To clarify design goals and provide more data for comparison each design is separately optimized for speed and for area. Timing and area information for each design is tabulated and discussed to illustrate the specific advantages and disadvantages of each approach.>