Processor IP licensor ARM Holdings plc has revealed a power efficient Cortex-A7 processor core that it says is intended to be used alongside its top-of-the-range Cortex-A15 as part of a heterogeneous power-driven multicore strategy.
The A7 is a dual-issue, eight-stage pipeline core that has been heavily optimized for power efficiency, but supports the same virtualization and extended addressing of the A15. As a result ARM (Cambridge, England) expects partners to implement a "little dog, big dog" strategy so that cores are selected to run different applications based on power efficiency needs.
Alternatively, the A7 processor can be used in single- or dual-core instantiations stand-alone to power an entry-level smartphone for price sensitive markets, ARM said.
Warren East, speaking at the U.K. launch of the A7, said that he expected multicore chips, which could be dual-core A15 plus dual-core A7, to be in the market and powering smartphones in 2013.
The "big-little" strategy allows low-performance basic and always-on tasks to be run on one or more A7 cores, to maximize battery life, while tasks requiring greater performance would migrate to the A15 cores. This dynamic core selection can be made transparent to the application software and middleware running on the processors, supported by advanced ARM system IP, such as AMBA 4 ACE Coherency Extensions. The movement of tasks between paired A7 and A15 cores is triggered by the same system that drives the dynamic voltage and frequency scaling that has become traditional in leading-edge system chips, the company said.
A coherent "big-little" system based on dual core A7 and A15 processors
In a 28-nm process the A7 is less than one fifth the size of the Cortex-A8 in a 45-nm process, while providing greater performance and much greater power efficiency, the company said. A dual-core A7 processor in 28-nm would produce about a 70 percent power saving compared with a dual-core A9 processor implemented in 40-nm. In other words it will consume about one-third the power.
ARM had two or three lead partners on the development of the A7 and the associated big-little strategy, East said, but he declined to name them individually. ARM now has a wave of semiconductor licensees eager to use the A7 core. Broadcom, Freescale, HiSilicon, Samsung, ST-Ericsson and Texas Instruments are listed as supporting the technology along with system and software companies Compal, LG Electronics Linaro, 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." Power efficiency driven selection of resources has been used before, for example in the area of graphics, said Tom Cronk, deputy general manager of the processor division, but not for general purpose processor cores.
The Cortex-A7 processor occupies less than 0.5 square millimeters, using a 28-nm process technology, and provides useful performance at about 1.2-GHz clock frequency in both single and multicore configurations. Used as a stand-alone processor, the Cortex-A7 will deliver sub-$100 entry level smartphones in the 2013-2014 timeframe with an equivalent level of processing performance to today’s $500 high-end smartphones, ARM said.
While A7 is aimed initially at smartphones East said he was sure the big-little strategy was applicable in other areas. East said he expected power-driven resource allocation would subsequently be deployed in consumer electronics and any area where complex processing also met a need for power efficiency.
Tape-outs including the Cortex-A7 are expected in the first half of 2012 with SoCs and products based on them to follow in 2013, East said.