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Start with the basics in feature-rich PMPs

Posted: 07 May 2007 ?? ?Print Version ?Bookmark and Share

Keywords:audio PMP? audio media player? PMP power consumption?

By Scot Robertson
Analog Devices Inc.

The steady march of features on portable media players (PMPs) is not only letting consumers strike up their favorite music wherever they go; it's also allowing them to watch video, shoot digital photos, play games and more. Wi-Fi connectivity is poised to be the next big thing, enabling direct-to-device downloads and peer-to-peer communication. That tightens the squeeze on processing and power requirements and raises concerns about digital rights management. How do you deliver features but keep fundamental design issues from getting in the way?

While great audio is the starting point for the design of any PMP, the processing and power consumption profile changes with the type of functionality you add. Some players hitting the street have the audio/video capacity to play full-length movies, for example.

Not only is more processing capacity required as functionality grows, but the same device also has to handle big swings in MIPS utilization. Using Analog Devices' Blackfin processor to show how different features affect the processing profile of a PMP, an example MP3 audio player would reasonably be expected to operate at around 30MIPS; a representative video-enabled media player would use around 175MIPS.

Now add Wi-Fi, which is how users on the go will download media directly to their players and stream media from one device to another. At up to 54Mbps, the high-speed data rate of 802.11g requires approximately 130 MIPS (peak) when handling video. That brings video streaming over Wi-Fi to the range of 300 MIPS or more.

While features like video and Wi-Fi multiply MIPS utilization by many times, music playback remains so important to consumers that a successful design cannot skimp on features such as postprocessing and graphic equalization.

Moving up from a 200MHz processor to perhaps a 400MHz processor is a straightforward route to more headroom. The more challenging obstacle is play time.

Bigger demand for MIPS ups the pressure on power efficiency-a persistent challenge for any device that depends on long battery life. The key measure is milliwatts per megahertz, which translates into battery life and play time.

The first video-enabled PMP designs supported play time of an hour or two-not enough for even the most ardent of early adopters. Current PMPs provide three or four hours of video on average and 10hrs of music. Similar improvements are being made in audio players, which once brought about eight hours of music to your ears; that play time is now closer to 20hrs.

Device designers have used a number of tactics to stretch battery life. The challenge is to create a PMP that has rich features while maintaining long play times for audio.

Some MP3 players reach play times of 50hrs or more by customizing the processing to match just the needs of the single function. This provides the most optimal power number but leaves no allowance for added features. Many video-centric devices have used dual-core processor approaches to provide capacity for video that is used when needed. But the more-complex dual-core processors inherently consume more power even during music-only operation.

A single-core approach with dynamic power management provides the optimal architecture to maximize power efficiency across a range of functions. Achieving extended play while packing in features calls for a power-conscious design that dynamically scales power with processing speed and that has the lowest power consumption possible during both low- and high-speed operation.

Analog Devices' Blackfin offers such power-management capabilities, opening the possibility for extending play times and battery life beyond the durations typical for most PMPs today.

DRM demands
Building in digital rights management (DRM) gets even more important as the PMP becomes networked. First, there is the sheer quantity of audio and video content for which content owners demand copy protection. Then there is the potential for new styles of use: e-commerce and sending content peer-to-peer. Enabling these models increases the security requirements for the portable device, because the PMP essentially replaces the PC in such interchanges.

And with Wi-Fi enabling opportunities for e-commerce and social-networking applications, the notion of DRM may well expand to include digital identity management on the PMP. Secure storage of digital keys and secure processing of key exchanges are foreseeable requirements, because those keys would safeguard the privacy of consumers and thwart fraud by allowing devices to be authenticated.

Skillful handling of such essentials as processing, power and DRM provides the basis for a feature-rich PMP that is able to lead the pack.

About the author
Scot Robertson
is director of networked media products at Analog Devices Inc. He holds an MSEE from Southern Methodist University. Comments may be sent to scot.robertson@analog.com.




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