Asynchronous, or clock-free systems, promise extra speed, safety, security and miniaturisation. The new designs work well in the laboratory and are only awaiting the development of software tools so that they can be produced commercially, says Professor Alex Yakovlev and fellow researchers in the Department of Computing Science at Newcastle University, England.
This week (April 8-12) the Newcastle team will present two papers at the International Symposium on Advanced Research into Asynchronous Circuits and Systems, in Manchester, England (see web link). One paper explains the latest techniques the team has developed for synthesizing asynchronous systems, the other relates to measuring metastability — a problem which may sound the death knell of conventional computers.
Because computers of the 1950s were relatively simple, they could function without clocks. Since the advent of faster and more complex systems in the 1960s, all hardware design has been based on the principle of the clock — a microelectronic crystal which emits rapid pulses of electricity to synchronise the flow of data. In modern PCs, this is at the heart of the Pentium Processor.
But computer systems are now so complex that clocks are imposing limitations on performance. The electrical pulses, travelling at the speed of light, are not fast enough to keep accurate time as they visit tens of millions of transistors on a single chip.
The result is that errors begin to occur in data. The phenomenon is known as metastability, a fundamental and insoluble problem which is causing increasing difficulty for designers who have to balance the demand for speed and complexity of systems with the need for reliability.
‘In binary terms, incoming data has a metastable state in which it is neither true nor false,’ said Professor Yakovlev. ‘A resulting system failure would be inconvenient to a PC user and could result in a disaster in an industry where reliability is critical, such as aviation.’
Asynchronous systems rely on a protocol of data transmission and acknowledgement which is not regulated by time. This can happen locally within a computer or globally between computers. Before data is exchanged, there must first be a ‘handshake’, or agreement on the mutually acceptable protocol.
Computer clocks generate heat as well as high frequencies, since they consume large amounts of power. To abolish them would allow portable devices to run on less power, enabling further miniaturisation.
Hackers would also be troubled by asynchronous systems, since the irregular pattern of data transmission allows the information to be encrypted far more effectively than at present.
Professor Yakovlev believes that the clock-based system is nearing the end of its useful life, with designers facing increasing difficulties as systems become more complex.
‘One of the problems is that all graduates entering the industry are immediately taught to design systems with clocks. It will be difficult to persuade them to change their ways,’ he admits. ‘We have shown that asynchronous systems work but we need to develop simple tools for commercial design and testing purposes. In my opinion, this is the last piece of the jigsaw.’
One of the barriers is that designing asynchronous systems requires the use of a new computer language, called Petri Net. At Newcastle, scientists are developing a design system which overcomes this problem by automatically translating Petri Net into orthodox computer language as asynchronous circuit designs are mapped out.
Such innovations are making asynchronous technology a more attractive commercial proposition and there are signs that the world is now at the dawn of the transitional period. Scientists talk of an intermediate system developing, nicknamed GALS — Globally Asynchronous, Locally Synchronous.
It is no secret that electronics company Philips has produced an experimental pager built from asynchronous circuits and is developing other devices based on the same principle (see web links). It is also rumoured that a leading manufacturer is designing the next generation of computer processor with at least some asynchronous elements.
Just over a year ago, the New York Times reviewed the concept of asynchronous design in a business article and claimed that ‘most of the mainstream computer world is not convinced that a wholesale change of the way industry designs and manufacturers chips is practical’ (see web link). However, researchers have opened up new horizons over the past year and many experts believe that widespread introduction of this new technology is now only a matter of time.