Asynchronous Chips

What Are The Potential Benefits Of Asynchronous Systems?

          First, asynchrony may speed up computers. In a synchronous chip, the clock’s rhythm must be slow enough to accommodate the slowest action in the chip’s circuits. If it takes a billionth of a second for one circuit to complete its operation, the chip cannot run faster than one gigahertz. Even though many other circuits on that chip may be able to complete their operations in less time, these circuits must wait until the clock ticks again before proceeding to the next logical step. In contrast each part of an asynchronous system takes as much or as little time for each action as it needs.

          Complex operations can take more time than average, and simple ones can take les. Actions can start as soon as the prerequisite actions are done, without waiting for the next tick of the clock. Thus the systems speed depends on the average action time rather than the slowest action time.

How Fast Is Your Personal Computer?

          When people ask this question, they are typically referring to the frequency of a minuscule clock inside the computer, a crystal oscillator that sets the basic rhythm used throughout the machine. In a computer with a speed of one Gigahertz, for example, the crystal “ticks” a billion times a second. Every action of he computer takes place in tiny step; complex calculations may take many steps. All operations, however, must begin and end according to the clock’s timing signals.

Asynchronous Logic

          Data-driven circuits design technique where, instead of the components sharing a common clock and exchanging data on clock edges, data is passed on as soon as it is available. This removes the need to distribute a common clock signal throughout the circuit with acceptable clock skew. It also helps to reduce power dissipation in CMOS circuits because gates only switch when they are doing useful work rather than on every clock edge.

About

          Computer chips of today are synchronous. They contain a main clock, which controls the timing of the entire chips. There are problems, however, involved with these clocked designs that are common today.

          One problem is speed. A chip can only work as fast as its slowest component. Therefore, if one part of the chip is especially slow, the other parts of the chip are forced to sit idle. This wasted computed time is obviously detrimental to the speed of the chip.

         The other major problem with c clocked design is power consumption. The clock consumes more power that any other component of the chip. The most disturbing thing about this is that the clock serves no direct computational use. A clock does not perform operations on information; it simply orchestrates the computational parts of the computer.

 Local Operation

          To describe how asynchronous systems work, we often use the metaphor of the bucket brigade. A clocked system is like a bucket brigade in which each person must pass and receive buckets according to the tick tock rhythm of the clock. When the clock ticks, each person pushes a bucket forward to the next person down the line. When the clock tocks, each person grasps the bucket pushed forward by the preceding person. The rhythm of this brigade cannot go faster than the time it takes the slowest person to move the heaviest bucket. Even if most of the buckets are light, everyone in the line must wait for the clock to tick before passing the next bucket.

Abstract

          Breaking the bounds of the clock on a processor may seem a daunting task to those brought up through a typical engineering program. Without the clock, how do you organize the chip and know when you have the correct data or instruction? We may have to take this task on very soon.

Today, we have the advanced manufacturing devices to make chips extremely accurate. Because of this, it is possible to create prototype processors without a clock. But will these chips catch on? A major hindrance to the development of clock less chips is the competitiveness of the computer industry. Presently, it is nearly impossible for companies to develop and manufacture a clock less chip while keeping the cost reasonable. Until this is possible, clock less chips will not be a major player in the market.

Conclusion

Clocks have served the electronics design industry very well for a long time, but there are insignificant difficulties looming for clocked design in future. These difficulties are most obvious in complex SOC development, where electrical noise, power and design costs threaten to render the potential of future process technologies inaccessible to clocked design.