Asynchronous techniques for system-on-chip design

SoC design will require asynchronous techniques as the large parameter variations across the chip will make it impossible to control delays in clock networks and other global signals efficiently. Initially, SoCs will be globally asynchronous and locally synchronous (GALS). But the complexity of the numerous asynchronous/synchronous interfaces required in a GALS will eventually lead to entirely asynchronous solutions. This paper introduces the main design principles, methods, and building blocks for asynchronous VLSI systems, with an emphasis on communication and synchronization. Asynchronous circuits with the only delay assumption of isochronic forks are called quasi-delay-insensitive (QDI). QDI is used in the paper as the basis for asynchronous logic. The paper discusses asynchronous handshake protocols for communication and the notion of validity/neutrality tests, and completion tree. Basic building blocks for sequencing, storage, function evaluation, and buses are described, and two alternative methods for the implementation of an arbitrary computation are explained. Issues of arbitration, and synchronization play an important role in complex distributed systems and especially in GALS. The two main asynchronous/synchronous interfaces needed in GALS-one based on synchronizer, the other on stoppable clock-are described and analyzed

低電力非同期回路の面積高効率化設計

Tohoku University亀山充隆課

A new robust handshake for asymmetric asynchronous micro-pipelines

[[abstract]]In this paper, a new handshake methodology to enhance the performance of the asynchronous micro-pipeline systems is proposed. The proposed handshake methodology has more flexibilities to design an asymmetric asynchronous micro-pipeline system. The proposed handshake methodology also has some advantages, like latch free, robust, high throughput, very short pre-charge time, less transistors, and more flexibility in asymmetry data path. A technique that combines a single-rail dynamic circuit with a dual-rail dynamic circuit was proposed and used to design in the data path. In the critical delay data paths, the dual-rail dynamic circuits were used to improve the operating speed. Others, the single-rail dynamic circuits were used. It brings some advantages that reduce power consumption and die area while maintaining the calculation speed. An asynchronous micro-pipeline array multiplier was designed and implemented by the new robust handshake methodology. Based on the TSMC 0.35μm CMOS technology, the simulation results show that the proposed new handshake methodology has shortest latency and more robust property as compare with other handshake methodologies.[[conferencetype]]國際[[conferencedate]]20030525~20030528[[booktype]]紙本[[conferencelocation]]Bangkok, Thailan

Testing of Asynchronous NULL Conventional Logic (NCL) Circuits

Due to the absence of a global clock and presence of more state holding elements that synchronize the control and data paths, conventional automatic test pattern generation (ATPG) algorithms would fail when applied to asynchronous circuits, leading to poor fault coverage. This paper focuses on design for test (DFT) techniques aimed at making asynchronous NCL designs testable using existing DFT CAD tools with reasonable gate overhead, by enhancing controllability of feedback nets and observability for fault sites that are flagged unobservable. The proposed approach performs scan and test points insertion on NCL designs using custom ATPG library. The approach has been automated, which is essential for large systems; and are fully compatible with industry standard tools

Analysis of Parameter Tuning on Energy Efficiency in Asynchronous Circuits

Power and energy consumption are the primary concern of the digital integrated circuit (IC) industry. Asynchronous logic, in the past several years, has increased in popularity due to its low power nature. This thesis analyzes a collection of array multipliers with different parameters to compare two asynchronous design paradigms, NULL Convention Logic (NCL) and Multi-Threshold NULL Convention Logic (MTNCL). Several commercially available pieces of software and custom scripts are used to analyze the asynchronous circuits and their components to provide the energy consumption estimation on various parts of each circuit. The analysis of the software results revealed that MTNCL circuits are more energy efficient for any size provided the number of pipeline stages does not become too great. Otherwise NCL would consume less energy. A combinational logic gate count to register gate count ratio of 3 was given to help determine when an MTNCL circuit would have too many pipeline stages for circuits designed with IBM\u27s 130nm 8RF-DM design kit

CAD Tools for Synthesis of Sleep Convention Logic

This dissertation proposes an automated flow for the Sleep Convention Logic (SCL) asynchronous design style. The proposed flow synthesizes synchronous RTL into an SCL netlist. The flow utilizes commercial design tools, while supplementing missing functionality using custom tools. A method for determining the performance bottleneck in an SCL design is proposed. A constraint-driven method to increase the performance of linear SCL pipelines is proposed. Several enhancements to SCL are proposed, including techniques to reduce the number of registers and total sleep capacitance in an SCL design

Design and Analysis of an Asynchronous Microcontroller

This dissertation presents the design of the most complex MTNCL circuit to date. A fully functional MTNCL MSP430 microcontroller is designed and benchmarked against an open source synchronous MSP430. The designs are compared in terms of area, active energy, and leakage energy. Techniques to reduce MTNCL pipeline activity and improve MTNCL register file area and power consumption are introduced. The results show the MTNCL design to have superior leakage power characteristics. The area and active energy comparisons highlight the need for better MTNCL logic synthesis techniques