ARM sets new bar for smartphone power efficiency

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ARM sets new bar for smartphone power efficiency

New Cortex-A7 'little dog' processor can be used alongside A15 for low power tasks, or alone in su-$100 smartphones

By CAROLINE GABRIEL

Published: 20 October, 2011

READ MORE: ARM | Processor | Handset

As application processors find their way into mass market handsets, ARM - whose architecture underpins over 90% of those processors - has unveiled its most energy efficient design yet, the Cortex-A7. The UK firm also announced a new flexible design approach, which it dubs big.Little processing.

According to ARM, a single Cortex-A7 processor delivers five times greater power efficiency than its smartphone stablemate, the Cortex-A8, and is only 20% of the size yet with greater performance. The A7 is targeted at the growing category of sub-$100 smartphones for emerging and prepaid markets, a price range in which there was, until recently, very little processing power.

While the A7 would be used standalone in such devices, in single- or dual-core configurations, it is also designed to be used alongside ARM's top end Cortex-A15 as part of a heterogeneous multicore strategy. This would apply to more complex gadgets, but ones in which cores could be switched on and off to conserve power. The smaller chip supports the same virtualization and extended addressing of the A15, allowing customers to adopt a "little dog, big dog" strategy, as ARM calls it, so that individual cores are selected to run different applications based on power efficiency needs.

ARM's CEO Warren East said he expected multicore chips, which could be dual-core A15 plus dual-core A7, to be powering smartphones in 2013, with systems-on-chip appearing in about a year's time. Basic and always-on tasks would run on one or more A7 cores, while processor intensive tasks would move to the A15 cores. This goes further than current designs which allocated activities to different cores, as these have been confined to offloading specific work such as graphics to specialist cores.

In ARM's system, the dynamic selection of generic cores would be invisible to the applications and middleware, and would be managed by ARM system IP. The transfer of tasks between cores would be triggered by the same mechanism which handles dynamic voltage and frequency scaling, now common in high end chips.

When manufactured in a 28nm process, the A7 is less than 20% of the size of the Cortex-A8 in a 45nm process, with about 70% power saving compared with a dual-core A9 processor implemented in 40nm.

Chipmakers lining up to use the A7 included Broadcom, Freescale, HiSilicon, Samsung, ST-Ericsson and Texas Instruments, while the London launch also saw support from members of the wide mobile ecosystem, such as Compal, LG, OK Labs, QNX, Redbend and Sprint.

"We took the A15 to market last year because we needed to push the performance envelope. But power efficiency is the most important thing for ARM. The A7 is the most efficient core yet," said Tom Cronk, deputy general manager of the processor division. This, of course, is the area where ARM most convincingly retains its lead over Intel's x86. Although the latter has driven down power consumption dramatically in Atom, it has not yet convinced the market that it can keep moving along that curve as effectively as ARM - and the A7 launch was clearly designed to drive that point home.

Another key challenge for ARM is to move beyond smartphones, into the wider world of connected devices, ahead of Intel and other rivals like MIPS. East said the A7 was aimed initially at low end smartphones but he believed power-driven resource allocation would be used in consumer and industrial electronics gadgets in future.