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Insight From ARM Panel: Low Power Is HW/SW Integration Problem

Comments(0)Filed under: Palladium, low power, Incisive, Industry Insights: ARM, HW/SW Integration

Most low-power panels and presentations I've attended talk only about hardware design techniques, like multiple supply voltages and power shutoff. I was thus very interested in a discussion about power-aware software that emerged at a panel at the March 25 EE Times "Designing with ARM" virtual conference.

It should be intuitively clear that if software doesn't take advantage of nifty hardware power management features, those features won't be very effective. For example, software needs to support power shutoff techniques by entering power-down modes at the right times. Embedded software can also be written in a power-efficient way - with limited memory accesses, for instance - or it can be a power hog, with inefficiently used registers and poorly managed I/Os. The least expensive pathway to system power optimization may actually be through the software.

At the 2009 Embedded Systems Conference, I went around talking to RTOS and software development companies asking one simple question -why isn't anybody here talking about low-power design? (You can read the answers here). At last week's panel Brian Carlson, OMAP platform marketing manager at Texas Instruments, spoke of attending a session of mobile OS providers at an ARM conference in 2008. "I was talking to these guys about how they support low power, and a lot of them didn't have good answers," he said.

Holistic approach

In the very first sentence uttered by a panelist at the ARM conference panel, Carlson said that low-power design in the mobile world must be "a holistic approach, all the way from the process to the SoC design and the methodology, even to the software level." Speaking more specifically later, he identified "energy-optimized software" as an area that has huge potential. "How do you manage what frequency you're at, how do you balance your load?" he asked, speaking of multicore designs. "These are huge issues, even at the driver level. We have to look at how drivers can be more intelligent."

"We don't have compiler technology that is power aware," said Rick Zarr, PowerWise technologist at National Semiconductor. "When software designers are designing blocks of code, they have no correlation to the [hardware] knobs and dials we can turn. It's disjointed and disconnected."

Pete Hardee, solutions marketing director at Cadence, noted that software developers in the mobile industry need to optimize their algorithms so less data is moved from place to place. Lower-level software should maximize cache efficiency. Moreover, he noted, software needs to have "system mode" knowledge about how long each part of the chip is going to be powered down. "All of that is in the software," he said.

EDA solutions

Cary Chin, director of technical marketing at Synopsys, said EDA vendors are considering power-aware software and are making progress. "We have been focused on putting together a connection between the hardware and software design worlds, so you can actually start to develop, as well as debug and verify, software environments early," he said.

Hardee, however, noted that "if you're waiting until you've got a prototype, it's too late." Virtual platforms make it possible to run a lot of software and do some optimization, but they don't provide enough accuracy for power estimation, he said. Design teams traditionally have to either wait until they can get the accuracy, or make an early decision when they don't have the accuracy. In the Cadence environment, he noted, many design teams are using the Incisive Palladium emulators to do software integration, and the Palladium Dynamic Power Analysis option lets users run software and get accurate power estimates.

Aha! moment

My conclusion from these discussions is that low-power design is a hardware/software integration problem. It would be great to have a power-aware compiler, but if software is written with no visibility into system hardware, you won't have an optimized low-power system. Software and hardware need to work hand-in-glove to enable cost-effective power management features. Decisions about power management need to involve both hardware and software, and should be made as early in the design process as possible.

To make all this possible, system design teams need to develop software in a virtual or emulated hardware environment that is fast enough for software developers, but also accurate enough to do some realistic power estimation and optimization. As Carlson said, "I think there is a huge opportunity for tools and a huge opportunity for developers to provide a what-if analysis for power estimation."

 

Richard Goering

 

 

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