DEVELOPMENTS IN THE FIELD OF VLSI

DEVELOPMENTS IN THE FIELD OF VLSI

There are a number of directions a person can take in VLSI, and they are all closely related to each other. Together, these developments are going to make possible the visions of embedded systems and ubiquitous computing.

1. Reconfigurable computing:
Reconfigurable computing is a very interesting and pretty recent development in microelectronics. It involves fabricating circuits that can be reprogrammed on the fly! And no, we are not talking about microcontrollers running with EEPROM inside. Reconfigurable computing involves specially fabricated devices called FPGA's, that when programmed act just like normal electronic circuits. They are so designed that by changing or "reprogramming" the connections between numerous sub modules, the FPGA's can be made to behave like any circuit we wish.

This fantastic ability to create modifiable circuits again opens up new possibilities in microelectronics. Consider for example, microprocessors which are partly reconfigurable. We know that running complex programs can benefit greatly if support was built into the hardware itself. We could have a microprocessor that could optimise itself for every task that it tackled! Or then consider a system that is too big to implement on hardware that may be limited by cost, or other constraints. If we use a reconfigurable platform, we could design the system so that parts of it are mapped onto the same hardware, at different times. One could think of many such applications, not the least of which is prototyping - using an FPGA to try out a new design before it is actually fabricated. This can drastically reduce development cycles, and also save some money that would have been spent in fabricating prototype IC's

2. Software Engineers taking over hardware design?:
ASIC's provide the path to creating miniature devices that can do a lot of diverse functions. But with the impending boom in this kind of technology, what we need is a large number of people who can design these IC's. This is where we realise that we cross the threshold between a chip designer and a systems designer at a higher level. Does a person designing a chip really need to know every minute detail of the IC manufacturing process? Can there be tools that allow a designer to simply create design specifications that get translated into hardware specifications?

The solution to this is rather simple - hardware compilers or silicon compilers as they are called. We know by now, that there exist languages like VHDL which can be used to specify the design of a chip. What if we had a compiler that converts a high level language into a VHDL specification? The potential of this technology is tremendous - in simple manner, we can convert all the software programmers into hardware designers!

3. The need for hardware compilers:
Before we go further let us look at why we need this kind of technology, that can convert high-level languages into hardware definitions. We see a set of needs which actually lead from one to the other in a series.

A. Rapid development cycles.
The traditional method of designing hardware is a long and winding process, going through many stages with special effort spent in design verification at every stage. This means that the time from drawing board to market, is very long. This proves to be rather undesirable in case of large expanding market, with many competitors trying to grab a share. We need alternatives to cut down on this time so that new ideas reach the market faster, where the first person to get in normally gains a large advantage.

B. Large number of designers.
With embedded systems becoming more and more popular, there is a need for a large number of chip designers, who can churn out chips designed for specific applications. Its impractical to think of training so many people in the intricacies of VLSI design.

C. Specialized training.
A person who wishes to design ASIC's will require extensive training in the field of VLSI design. But we cannot possibly expect to find a large number of people who would wish to undergo such training. Also, the process of training these people will itself entail large investments in time and money. This means there has to be system a which can abstract out all the details of VLSI, and which allows the user to think in simple system-level terms.

There are quite a few tools available for using high-level languages in circuit design. But this area has started showing fruits only recently. For example, there is a language called Handel-C, that looks just like good old C. But it has some special extensions that make it usable for defining circuits. A program written in Handel-C, can be represented block-by-block by hardware equivalents. And in doing all this, the compiler takes care of all low-level issues like clock-frequency, layout, etc. The biggest selling point is that the user does not really have to learn anything new, except for the few extensions made to C, so that it may be conveniently used for circuit design.

Another quite different language, that is still under development, is Lava. This is based on an esoteric branch of computer science, called "functional programming". FP itself is pretty old, and is radically different from the normal way we write programs. This is because it assumes parallel execution as a part of its structure - its not based on the normal idea of "sequence of instructions". This parallel nature is something very suitable for hardware since the logic circuits are is inherently parallel in nature. Preliminary studies have shown that Lava can actually create better circuits than VHDL itself, since it affords a high-level view of the system, without losing sight of low-level features.