Mad MACs
Who’s Got the Best DSP Accelerators?

Maybe you saw them in science fiction movies when you were a kid. Possibly your Hot Wheels toy car collection contained a few as well. You may have even drawn your own on your school book covers. They looked like normal race cars, but a single engine just would not do. Sometimes four, six, or eight huge power plants graced the foredeck, each with eight big straight pipes sticking out the sides like stocky legs on some steel-bodied spider, complete with a Roots blower abdomen and air scoop head. You were never able to understand quite how all those engines might work together to make the car go fast, but the message of plenteous performance was clearly conveyed by the visual impact of this plethora of pipes and plenums.

A few years later, you were in engineering school and the magic spell was broken. You learned that the complexities of coordinating so many motors for the task of moving a single vehicle caused too many problems, and the promised performance of parallel power plants fell forever into the chasm of misguided engineering fantasies.

Today, however, the process repeats itself. We all know that the performance bottleneck for most digital signal processing (DSP) algorithms is the multiply operation. The most recognized benchmark of DSP performance is, in fact, a measurement of the number of multiplies and accumulates per second such as MMACs (Million multiply accumulates per second) and GMACs (Giga Multiply Accumulates per second). DSP processors sometimes have several multiply accumulate (MAC) units attached to a high performance processor that runs the overall algorithm and sequences the expensive multiply operations out to the available MACs. [more]