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Catching a glimpse of ARM's next-gen high-end core

Posted: 28 Apr 2015 ?? ?Print Version ?Bookmark and Share

Keywords:ARM? smartphone? processor? big.LITTLE? core?

ARM has recently provided a sneak peek at its road map involving its next-generation high-end core that is yet to be announced. The company also announced its support for its big.LITTLE multiprocessing technology amid the lukewarm uptake.

"We've seen a big improvement in what phones can do, and I think we are about to see another improvement," said Brian Jeff, director of marketing for ARM's Cortex-A products, in a talk at the Linley Mobile event. Jeff described three functional units in the A72 taken from a design of an unannounced "high-end core which was a brand new redesign."

The A72 is the highest end member of ARM's 64bit V8 series the company has announced so far. Jeff described its design goals mainly in terms of power efficiency rather than raw performance.

"When we set the scope [for the A72], we had a little more than a year to take as much power out as possible and keep performance constant," he said.

Although he repeatedly described work optimising the A72 for mobile workloads, Jeff said the core is also configurable for enterprise applications that would benefit from its efficiency. For example, it can be used in SoCs with up to 48 cores, supports full ECC protection, accelerator interfaces and an AMBA 5 bus.

The description suggested the yet-to-be-announced core targets maximum performance, perhaps in an effort to leapfrog Intel's Broadwell design. However, Jeff would provide no details on the next-gen core except to say the A72 borrows three blocks from the design, a branch-predict unit, a load/store unit and a floating point unit.

Lowering power was clearly the top priority for the A72 on the heels of experiences with its A15 core. "The improvements in the A15 were a big jump up in performance, but you couldn't tap into it all because it got thermally throttled, so we've been focused on reining in power at the high end to fit in to an all-day performance of a smartphone," he said.

As a result the A72 is expected to hit a 2.5GHz maximum data rate in a 14/16nm process, up from 1.6GHz for the A15 in a 28nm process, a slight bump up from 2.3GHz for the A53 in a 14/16nm process. Individual A72 cores can draw up to 600mW to 750mW in SoCs that consume up to 2.5W, he added.

The figures translate to the A72 using 75 per cent less energy than an A15 or delivering 3.5x more performance, he said. However Jeff cautioned that ARM doesn't "have A72 silicon running at speed yet."


The Cortex-A72 shares branch prediction, load/store and floating point units with an unannounced high-end ARM core.

Jeff laid out a laundry list of power efficiency improvements in the three new blocks shared with the unannounced high-end core. For example the branch predictor eats more power but significantly reduces cache misses. "It more than pays for its increase in size," he said.

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