By , 3/14/2005
To create a successful digital video product, you need to choose the right processor. Sounds simple—but of course, it isn’t. A big part of the challenge is that there are so many types of processors from which to choose: general-purpose CPUs, FPGAs, DSPs, configurable processors, and fixed-function chips, among others.
A further complication is that digital video is a fast-moving field, with standards that are shifting and evolving. As a result, a processor’s ability to adapt to changes tends to be more important in digital video than in many other applications—but such flexibility usually comes at the cost of reduced efficiency.
Choosing a processor inevitably requires some compromises, but it’s crucial to know how to pick one that won’t compromise the success of your product.
One doesn’t fit all
Digital video technology is used in products ranging from cellular phones to personal video recorders (PVRs). While many video products share some common functionality—for example, most use video compression algorithms to compress and/or decompress video—they also have significant differences. Portable products place a high priority on energy efficiency; line-powered products typically don’t. Products designed for the living room usually have much higher video resolution than those designed for hand-held products.
In short, one processor won’t fit all. Even one type of processor won’t fit all. The key to success in processor selection lies in knowing what’s available, and understanding the strengths and weaknesses of each processor type.
A few of your favorite things
Because there are so many processor options, it isn’t practical to look at all—or even a significant subset—of them in detail. Instead, a hierarchical approach can make the process manageable: Use your most important criteria to weed out unsuitable candidates early on.
Criteria commonly used for making the first cut include:
- Speed. Digital video tasks, like many other types of signal processing tasks, place heavy computational loads on processors. Carefully analyze whether a processor has sufficient speed for the target application, preferably using video-oriented benchmarks such as the BDTI Video Benchmarks™.
- Price. Chip price is important, but cost per channel or overall system cost may be more important.
- Energy efficiency. In most cases, it’s more meaningful to evaluate energy efficiency than power consumption, since energy use governs battery life.
- Flexibility. Some classes of processors are more flexible than others and can accommodate late changes in product features or allow field upgrades, such as adding support for a new compression algorithm. In general, however, the more flexible the processor, the less efficient it is in cost and energy use.
- Quality of development tools. Whether the processor has tools that are designed to support development of signal processing applications (or better yet, video applications) can have a significant effect on development time, and hence on time to market.
- Compatibility with earlier processors. This is typically important if you expect to reuse software from an earlier product.
- Vendor roadmap. Does the vendor’s product roadmap line up well with your plans for follow-on products? Will the processor continue to be supported—or upgraded—over the life of your product?
- Availability as chip or licensable core. Some processors are sold as packaged off-the-shelf chips, and some as licensable intellectual property—often called licensable cores—for use in building custom chips. Most of the processor categories discussed here include both packaged chips and licensable cores.
As we will show, each class of processor makes different trade-offs in these areas.
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