Friends for life?

Friends for life?The constant change and update of x86 processors and their chip sets means designing long-life embedded products can be a major headache. Leon Opit and Bob Bourne explain the problem
Moore’s law holds that computer chips double in power every 18 months.
The General Motors law holds that sales of any technology can be maximised through product variation.
The PC processor industry has taken both of these maxims to heart. Intel now offers a wide range of PC processors, at different speeds, for different sockets – and is about to add yet another family, the Pentium III.
Each individual product lasts for about six months and in some cases a whole section of a processor range can change direction in even less.
Driven by the cost savings wrought by the PC industry, x86 processor are coming to significance outside personal computers.
Mainframes and state-of-the-art supercomputers are being designed around Intel chips, and its products are also finding their way into the embedded systems market.
It is in embedded systems that the agile nature of the PC industry is beginning to pose some real problems, both for manufacturers and users.
There are some cases where using x86 processors and chipsets in embedded systems is fine. Such as where an embedded system is expected to have roughly the same price value and product life as the average high street PC. This kind of system has effectively become a throw-away item, much like calculators or mobile phones, just rather more expensive.
If, however, the embedded system is intended for a product with a long life cycle, then employing PC-based chips can present some major headaches.
Examples of long life cycle products include medical, manufacturing telecommunication and radar equipment. For instance, a telephone switching system or an x-ray machine can take over two years to bring to market and is then expected to last for ten years.
Employing PC-based architectures can leave manufacturers scrabbling about on the grey market to source the chips they have designed their systems around, even before the product has left the factory. Through-life support and maintenance can be impossible for such systems.
It is not the internal microprocessor architecture that is the problem. Ever since the early 1980s, x86 chips have had the same instruction set. This makes even the most advanced of today’s processors compatible with yesterdays software.
The problem stems from the electrical interface to the processor chips and the ‘chipsets’ that connect the processors to the outside world.
The main concern of PC-based chip manufacturers is product variation. New functionality and ever greater speeds can be wrung from chip families by product adaptations that, in turn, demand changes to the electrical and physical hardware interface. Socket One is an extreme case, a whole new interface to raise barriers to market entry against competitors.
Chip manufacturers are able to change the hardware interface because firmware BIOSs and device drivers hide the changes from higher level application software such as DOS or Windows.
One exception is the few chipset registers that are accessed directly by a higher level applications. These registers are maintained through all product families from one chip generation to the next.
The x86 processor bus has also been reconfigured over time for extra performance, tending to occur between different generations and becoming more frequent as the gaps between generations shorten.
PC peripheral devices, such as hard disk drives and graphic cards can present their own set of problems as peripheral manufacturers increase performance to reduce bottlenecks. At the same time, there has been move to distribute subsystem processing from the central processor to the peripheral device, again prompting alterations to the chipset registers on peripheral processors. Device driver software masks peripheral changes in the same way that a BIOS hides chipset changes.
All this constant change is causing major problems for the embedded device industry.
Embedded devices involve dedicated applications that directly access system hardware. Strategies, such as the loadable device drivers that are employed in PCs, are mostly inapplicable as embedded applications are frequently developed to access hardware directly.
Embedded systems also frequently operate under a tight regulatory regimes, making stable hardware essential.
For these reasons, any alterations to the physical or electrical properties of the processor’s hardware interface directly impact embedded applications.
Alterations to the processor bus pose an additional problem to embedded devices that have been developed around a particular chip family. Although this obsolescence tends to be over a longer time frame than alterations to the chipset registers, market conditions can make it much quicker – take Intel’s first Celeron chips.
Peripheral chipsets, if anything even more volatile than central processor chipsets, pose an additional headache since most embedded developers dispense with daughterboards and driver software, incorporating the peripheral processor directly onto the main board and interfacing directly with it.
PC-based processors and peripherals hold out a great attraction for many companies. Developing embedded software is a time consuming and expensive process. Being able to select one of the wide range of PC software development toolsets is seen as a major advantage of PC-based chips. Many companies believe that using PC-based chips will make it easier to integrate embedded devices directly into Windows-based corporate management systems.
Developers originally began to employ x86-based architectures when these were highly stable both in terms of software compatibility and hardware interface. This reputation for stability made them an obvious choice for embedded systems development. It is only recently, perhaps as a result of increased market competition between rival chip manufacturers, that the stability of PC-based architectures has yielded to a high degree of variability in the hardware interface.
Yet another strong reason for their ad option is that PC-based chips are available at commodity prices, thereby promising to slash the cost of the product.
However, with the commodity price comes commodity status. The result is that many companies are developing complex, long life cycle dedicated embedded systems around volatile, short life cycle commodity chips.
Many will find that it becomes increasingly impossible to source the chips at the heart of their embedded systems.
Leon Opit is director of software development & Bob Bourne is director of hardware development at embedded system company LocSof t


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