Advantages of Dsp Processor over Risc

list some of the advantages of using dsp processor over risc processor for applications like mpe4 encoder.

what i feel is dsp processor executes more instructions in a single clockcycle. but this consumes more processing power.

can some body put much more strong reason for it.

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DSP processors are optimized for implementing algorithms that feature a mix of "regular algorithmic stuff" plus a large number of highly repetitive tasks, like vector dot products (a FIR filter implementation is essentially a vector dot product). All of the DSP chips in current production that I know of will do a vector dot product in one clock cycle per element in the vector; they scream at this.

As a consequence of this focus on vector dot products and other highly repetitive tasks, DSP processors are less able to do other things really well. Specifically, the ones that I have worked with have required large context switches to maintain the vector dot product state machine, or they will not execute an interrupt while they're performing a vector dot product, or they store their vector dot product state machine in registers that are inaccessible to to use code, which makes any kind of a normal 'RTOS-like' context switch impossible.

RISC processors are optimized for implementing just about any algorithm that comes down the pike, without emphasis on any one thing. Consequently, they don't scream through vector dot products the way a DSP chip will, but they are at least as good, or better, at performing other operations, and they don't have the nasty context switching difficulties that DSP chips do, so an RTOS is more efficient to implement (if you feel you need one).

I'm not sure how this applies to the efficiency of an MPEG4 encoder, particularly since there are a lot of different ways you can encode MPEG. It really boils down to whether you are doing the kinds of things that a DSP chip is good for -- if you are, it will be to your advantage to use one. If you're doing a lot of function calls, memory searches, indexing, and other related stuff, and not a lot of vector dot products, then a RISC chip will probably be just as good as any DSP, and cost you less in other ways.

Tim Wescott
Wescott Design Services
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Tim Wescott

List homework topic. Kthxbye pls.


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Pete Fenelon

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