Configurable Application-Specific Signal Processors Speed Design and Development
Fixed-function chips tend to be the least costly, since their NRE is zero (assuming that you aren't the one making the chip). They also tend to be very efficient because they are designed to implement a specific set of functions. One caveat, though: their low cost and high efficiency are true only if the chip has the exact functionality you require. If it has excess functionality, you end up paying for features you don't need.
ASSPs are similar to fixed-function chips. In fact, if you could open the hood of a fixed-function chip, often you'd find an ASSP inside. Since you're programming the entire solution yourself, you gain a great deal of flexibility, but the cost is enormous, owing to the time and effort you need to spend designing and developing the software.
Configurable ASSPs are nearly as efficient and cost-effective as fixed-function chips without the same caveat about their functionality, but they're far more flexible because of their configurability and because they're software-based and can be readily modified and updated. At the same time, they don't require the time and resources typical of custom DSP programming. Thus configurable ASSPs help fulfill a need for flexible, efficient, cost-effective DSP solutions without jeopardizing the all-important time to market factor.
The first step in developing a configurable ASSP is to define the requirements. Let's assume that one of the goals is to create a chip that can be used in a variety of products within a given application. We start with a DSP, which clearly can be used in a variety of applications because of its programmability and therefore its flexibility. By turning a DSP into a configurable ASSP, we're limiting its use within a single type of application in return for a chip that doesn't need to be programmed.
FLEXIBILITY VS. PERFORMANCE
Thus we face the first trade-off: flexibility versus performance. At one extreme, we could try to create a solution that is everything to everyone but efficient enough for no one. At the other extreme lies a solution that is optimal but that is most likely limited to a single product. A good configurable ASSP is somewhere in the middle.
In other words, we must narrow the scope to a particular application, such as voice, video, audio, or wireless. From there, it might be necessary to narrow the scope even further before starting to architect a configurable ASSP.
Let's look at the process. We might start out thinking about a configurable ASSP that covers all telecommunications applications. Quickly we see that this is too broad and we therefore need to limit the scope. Let's say we focus on TDM-based telecom applications. Common functionality could be G.711/G.726 speech compression, echo cancellation, tone detection, tone generation, automatic level control, conferencing, and noise reduction.
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