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Consider power early in the design process

Posted: 17 Nov 2008 ?? ?Print Version ?Bookmark and Share

Keywords:power management? design? process? embedded system?

Portable system designers are very "power-aware." They look to save every milliwatt to increase battery life, and thereby runtime in their systems. But for embedded systems developers who plug their systems into an AC line, power management is not that important. Or is it?

Whether plugged or portable, all embedded systems must manage power wisely. Power management is becoming more important every day. There are many reasons designers need to care about power and the list is getting longer.

For example, the amount of data we store grows significantly larger every year. To handle all this data, we need newer, faster serversand more of them. More servers and server blades within each enclosure mean greater demand for power. Additional servers create more heat, requiring more cooling. Air conditioning can get expensive. And the cost of the power (electricity) itself is greater than ever before.

Just because your embedded system is line-powered doesn't mean you shouldn't be concerned with power management.

Performance over power
Why, then, isn't power a "front-of-mind" consideration for embedded systems developers? "It's starting to be," said Rob Oshana, an engineering manager at Freescale Semiconductor Inc. "Historically, embedded systems were all about allocation of scarce resources, like performance, memory and power. But performance was the key attribute, often at the expense of power."

Perhaps more apparent is how difficult it is to design for power management. Performance is usually easier to manage from a software-development and chip-design perspective. Although turning up the clock frequency may be an easy way to improve performance, it exacerbates the power problem.

System cost is another consideration. Lowering system power should result in fewer fans and heat sinks. A shorter BOM is a by-product of using less power.

Designers also need to be more power-aware as process technology evolves. As process technologies increase, 45nm in some cases, leakage is becoming the dominant power contributor to the overall power budget. The embedded systems developer needs to be acutely aware of the active part of the power equation.

Tim Morin, senior product development manager at Actel Corp., notes that needs change over time. "Your computing needs change. They always have. So how do you get more power/heat dissipated without having to change your environment or your power coming into the building? You do that by implementing power-use models, understanding how much power is available and how much you're actually consuming."

Value of power
Some industry members disagree with the contention that developers are ignoring power as a design factor. Jean Ann Booth of Luminary Micro Inc. said "Power frequently is considered early in the design process, and that frequency is increasing." Line-powered embedded segments that are increasingly power-sensitive include white goods like refrigerators, washing machines, dryers, HVAC etc."

Many of the power-efficiency improvements we've seen over the last few years in white goods are a result of government mandates and incentives. However, they are not enough.

According to Booth, "Every industrialized country except the United States has government mandates in place that require improvements in power efficiency for this class of systems. The U.S. chooses to encourage energy improvements through the power of consumer marketing and the coveted Energy Star ratings."

Design plan
The key to why it's so important to consider power early in the design process is consumption. The global consumption of power is increasing at an alarming rate. With much of that power generated from nonrenewable sources (oil or coal), the whole world will have to squeeze more "work" out of less available power. Engineers can do much to accomplish power savings by increasing an application's efficiency or lowering its total power requirement.

"Increased efficiency" comes by replacing older components with newer, more energy-efficient components. Because 70 percent of the world's total energy goes to motion applications, the improved efficiency can significantly contribute toward decreasing the world's overall power bill.

Don Shin, senior marketing analyst for networking and computing systems at Freescale said the term "power" is overused. "Whereas power for a designer is really a supply issue, related to FETs, capacitors, inductors and the like, energy is more complex and determines thermal strategies, system footprint and long-term consumption costs. Engineers frequently talk about reducing power, but what they're really talking about is lowering energy to support thermal, space and cost constraints."

Regardless of where our power-awareness level is at today, all designers understand that power management is and will be a high priority going forward.

- Richard Nass
Editorial Director, Embedded Systems Design

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