Recently a friend was lamenting that so many new processors continue to be designed, but few achieve commercial success. "Why do people persist in designing new processors?" he asked. "Maybe because universities keep training processor designers," I speculated. On closer reflection, though, there's more to the story.

Historically, processor designers created highly specialized DSP-oriented architectures with the goal of achieving real-time signal-processing performance with a programmable device, at a low cost. For some applications, achieving sufficient speed at reasonable cost is still a motivator for architectural innovation. But for many others, current processors are sufficiently fast. In fact, many signal-processing applications can be run on general-purpose processors (GPPs).

With clock speed increases afforded by modern IC fabrication processes, even a simple, inexpensive 32-bit GPP with few, or no, DSP-oriented features can handle many real-time audio tasks, like MP3 decoding. These GPPs, with their simple architectures and strong development tools, are easier to work with than DSPs--or even DSP-enhanced GPPs. Given the ease-of- use advantage of simple processors and their adequate performance, why continue to design specialized, DSP-oriented processors?

The answer is battery life. Many embedded signal-processing applications are constrained in terms of energy consumption. By using specialized architectures, processors can meet the real-time computational requirements of the application while operating at lower clock frequencies than general-purpose architectures. That's why system designers still often put a spe- cialized DSP chip or core next to a GPP.

So, for processor designers, there's good news: Innovation in processor architecture is still valuable. But in many cases, the goal of that inno- vation has shifted: from maximum performance to minimum energy consumption. n

Jeff Bier is the president of Berkeley Design Technology Inc. (www.BDTI.com), a consulting firm providing analysis and advice on DSP technology. Prasad Hariharan of BDTI contributed to this column.