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Unformatted text preview: Synchronization in Asynchronously Communicating Digital Systems Priyadharshini Shanmugasundaram Abstract – Two digital systems working in different clock domains require a protocol to communicate with each other in order to ensure validity of the data being shared between the two systems. Such systems are said to be asynchronous, and the protocol used for communication is said to synchronize the two systems. Asynchronous design techniques are not as widely used as synchronous design techniques are. This report points out the merits and demerits of asynchronous design techniques over synchronous techniques. It presents some of the commonly used asynchronous handshake protocols, and their implementation. Some common mistakes made in asynchronous design are also discussed. I. Introduction A synchronous circuit, as shown in Figure 1, consists of components that share a common and discrete notion of time, defined by a clock signal distributed throughout the circuit. In such circuits, the longest path in the com- binational logic determines the minimum clock period. However, during a typical clock cycle, all the components in the circuit may reach their steady states well before the next clock signal. Also, each register dissipates energy during every clock cycle. If dynamic logic is used, the combinational logic also dissipates clock power during each clock cycle. Since the clock modulates the overall supply current, peaks in power-supply noise and in elec- tromagnetic emission occur at the clock frequency leading to higher harmonics. Growing interconnect delays and the heterogeneous nature of systems-on-a-chip architecture place enormous constraints on the synchronous operation of components. Meanwhile, synchronous design techniques are well established. Hence, the design effort is lesser for such cir- cuits since the libraries and tools required for synchronous design are well developed. Also, tools for test vector generation are readily available making these circuits much easier to test than asynchronous circuits Asynchronous circuits  are fundamentally different from synchronous circuits in the sense that the compo- nents in the circuit do not share a common and dis- crete time. Such circuits use handshaking between their components to perform synchronization, communication, and sequencing of operations. This gives asynchronous Fig. 1. A synchronous circuit. design a number of advantages over synchronous design. Asynchronous circuits consume low power due to fine- grain clock gating and zero standby power consumption. They can operate at higher speeds since the operat- ing speed is determined by actual local latencies rather than global worst-case latency. The emission of electro- magnetic noise is less in these circuits since local clocks tend to tick at random points in time. They are robust towards variations in supply voltage, temperature, and fabrication process parameters since timing is based on matched delays. In fact, some of them can even bematched delays....
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This note was uploaded on 09/16/2011 for the course ELEC 7770 taught by Professor Agrawal,v during the Spring '08 term at Auburn University.
- Spring '08