A Processor & DSP Selection Checklist

A Processor and DSP IP Selection Checklist

SOC designs are major, high-risk projects and most consist of many IP blocks-some developed in house and some purchased. Many of the most complex blocks are processors and DSPs. With their associated software-development tools, simulation models, and EDA flow scripts, these processor IP blocks affect more than just the hardware design; their influence permeates the entire SOC design project. Consequently, processor IP can literally make or break your project. Here is a list of questions to ask yourself, your team, and any processor IP providers you contact. This list will help you to avoid unhappy IP choices and will help you get exactly what your team needs to develop successful SOC designs on time, within budget, and with minimal hassle.

What on-chip tasks should be handled by the on-chip processor and DSP cores?

The answers to this question may not be as obvious as you think. There is a very wide performance range for processor and DSP IP. Intuitively, there's a big performance difference between a simple 8-bit controller core and a large 32-bit RISC processor core. Likewise, there's a large performance difference between a simple, general-purpose, 16-bit DSP and an advanced DSP with special hardware execution units designed for specific applications such as audio and video. Before you can select a processor or DSP core for a specific task or task set on your SOC, you must be able to list all of the tasks you want that core to handle. Then you'll have some idea of the amount of performance you need for each processor or DSP used in your SOC design.

There's yet another consideration as well. Many experienced SOC designers have a preconceived notion of what processor and DSP cores can and cannot do. These assumptions are based on years of experience with conventional fixed-ISA (instruction-set architecture) processors and DSPs. Almost universally, these preconceived performance expectations are too low with respect to customizable or configurable processor IP cores because the performance of customizable processor and DSP cores can be increased almost without limit for specific on-chip tasks. If you are not familiar with the greatly expanded performance envelope of customizable processor IP, ask a vendor of such IP for a quick seminar. There's no point in grossly underutilizing your silicon just because you didn't take a quick look at something new.

Which on-chip tasks assigned to processors and DSP cores are routine and not performance-limited and which will stretch the limits of available technology?

There are many on-chip housekeeping tasks and other simple tasks that just need to get done. Such tasks are routinely handled in firmware on a general-purpose processor core that acts as the SOC's CPU. The heavy lifting-the big data-processing tasks-are often handled by dedicated hardware because of the huge processing load. Audio, video, and network-packet processing are all examples of dataplane processing, which is the heavy lifting that takes place on every modern SOC in some form or another. There's often an automatic assumption that processors and DSPs cannot handle these heavier processing tasks on advanced SOCs-that only dedicated hardware can manage the problem-but you'll want to check any such assumptions with the processor IP core vendors you contact. Let them help you understand what the real limits are today.

How much I/O bandwidth do you need?