ARM’s battery-saving technology debuts in tablet, smartphone prototypes
By Agam Shah
BARCELONA—ARM is promising close to 70 percent processor power savings with a new chip design called Big.Little, and mobile devices on display at the Mobile World Congress provided the first glimpse of how the technology works.
The concept of Big.Little revolves around off-loading mundane tasks like voice calls, SMS, and MP3 playback to low-power cores, leaving the high-performance cores to take on demanding workloads. The technology offers an alternative to today’s ARM processor designs in which the most mundane tasks are designated to high-performance CPUs, which could consume excess power while processing.
The benefits of the chip design were highlighted in a quad-core smartphone shown by chip maker Renesas and a prototype tablet with a Samsung eight-core chip shown in ARM’s booth. The Big.Little concept couples high performance with low-power cores in one chip, with tasks being assigned to specific cores based on their power requirements and priority.
Big.Little will provide longer battery life for mobile devices, according to ARM, which licenses its product designs to chip makers. Seven companies have licensed Big.Little.
How Big.Little works
The chip design pairs ARM’s latest Cortex-A15 core with the new low-power Cortex-A7 core for mobile devices, and the processors will start appearing together in mobile devices later this year. In the future, ARM is matching the high-power 64-bit Cortex-A57 processor with the low-power Cortex-A53 core.
Big.Little has been licensed by seven chip makers including Renesas and Samsung, and a glimpse of the technology was provided in devices containing chips from those companies.
ARM showed a prototype tablet with Samsung’s Exynos 5 Octa chip, which combined four Cortex-A15 performance cores with four Cortex-A7 cores. The tablet off-loaded some of the video tasks to the graphics core and sound and background tasks to the Cortex-A7 cores, leaving the four high-performance Cortex-A15 cores largely idle.
Eight cores is not overkill for a tablet, especially for users who need better performance and longer battery life, said Eric Gowland, senior engineer of applied system engineering at ARM.
The Android OS and programming tools will enable tablets to break up tasks effectively over the uniquely defined eight cores, Gowland said. Big.Little devices won’t face the same problems PCs had with the advent of multicore chips, in which programmers made the daunting move from writing single-threaded applications to producing code that could be effectively broken down over multiple cores.
The Cortex-A7 is a fast performer but uses very little power, Gowland said. He showed smartphones running on Cortex-A7 chips, but added that Cortex-A15 processors are better performers.
There is also no magic formula to mix and match the right number of performance and low-power cores, Gowland said. In the end, the implementation of Big.Little will depend on chip makers.
Nvidia not using Big.Little
One of ARM’s major licensees, Nvidia, has not adopted Big.Little, instead coming up with its own “4+1” design for its Tegra chips, which have four high-performance cores and one core for low-power tasks.
But Renesas showed how Big.Little could be used in smartphones with its upcoming MP6530 quad-core chip. The company coupled two Cortex-A15 cores with two Cortex-A7 cores in a prototype LTE smartphone, which was on display under glass at the company’s booth.
Economics drove the company’s decision to include two high-performance and two low-power cores in MP6530, said Ashley Wheeler, director of customer programs and support at Renesas Mobile Europe.
A quad-core chip is the right option for smartphones, so the best approach in the view of Renesas was to bring in two of each, Wheeler said. Any more would increase the size and cost of the chip, which Wheeler said was not an option, especially when smartphones are shrinking in size and consuming less power.
The Renesas chip will reach device makers by the end of the year and be in smartphones that become available next year.
The Big.Little design strikes the right mix of power consumption and performance on mobile devices, and seven customers licensing the technology is a good start, said Warren East, CEO of ARM, in an interview.
The technology has a lot of promise and there are many ways in which it could be implemented that ARM hasn’t yet envisioned, East said. Implementations could change as Big.Little is adapted for embedded devices, servers and other computing products.
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