Looking Back to the Future
First looking back, the Cortex-A15 launch event itself was eye-opening in terms of the level of interest in ARM’s low-power technology and the variety of discussions that have ensued on what’s possible with upcoming ARM Products. It more than validated the conclusion of my previous blog that the only limit to what’s possible with ARM technology is the imagination of the system designer, the software developer and the device manufacturer. At the event, a panel of industry experts, including stalwarts from Compal, Dell, HP and Nokia, weighed in on challenges facing the industry as well as on the applicability of ARM technology to address these challenges. The discussion encompassed smart mobile devices, consumer devices and as a natural extension, mobile infrastructure which is quite an integral part of the mobile user experience.
Cortex-A15 – Designed to Bring Power Efficiency to Smartphones...and Servers
But while the news of using the Cortex-A15 beyond mobile has caused a lot of excitement, in mobile there are very real limits. Not to imaginative solutions of course, but in terms of energy: mobile energy consumption must stay within the limits of the battery capacity for consumer usage requirements and thermal requirements of the chip package. This limit is reflected in the power (or more appropriately energy) efficiency of the processor and system and how well the overall system utilizes this energy to deliver the performance and work desired. The other thing is that the footprint (overall size) for the application processor complex stays pretty constant from generation to generation. Each generation, SoC designers use gains from new process technologies to cram more processors, more functionality and larger caches into the same footprint.
Power Efficiency and Battery Life is in ARM’s DNA
This may sound repetitive, but ARM processors since the company’s inception, have always been associated with devices that run on battery and products that are devoid of heat sinks . Building on what’s already established with ARM9, ARM11, Cortex-A8, A9 and A5, the Cortex-A15 is still designed to operate within the confines of the average mobile power envelope. The extensive clock-gating that is a signature of ARM products continues. It delivers more performance per cycle than prior generations and can finish the same task in a shorter period of time. Let’s compare a Cortex-A15 designed for mobile in 32/28nm to the ARM technology that today powers a number of great smartphones, the Cortex-A8 on 45nm technology. First the Cortex-A15 delivers more peak performance per core than Cortex-A8 solutions across all types of workloads for a typical mobile device.
But to measure true performance, the peak demands need to be addressed without compromising sustained workloads. The Cortex-A15 delivers a high-end “immediate” response for high-intensity activities. Today’s Cortex-A8s and tomorrow’s dual-Cortex-A9’s are very equipped to handle current mobile workloads such as rendering web-pages and gaming type workloads. But for 2013’s more complex activities, the Cortex-A15 provides the desired performance uplift even as a single-core with additional headroom available through dual-core solutions. Importantly, at the Cortex-A15 is still optimized for low-power mode – doing standard user interface activity, OS bookkeeping, twitter feed updates while consuming much lower active power for sustained smartphone workloads. As shown in the power graph below, the sustained workloads for all single-core processors are well below those of existing smartphones and comfortably within the average mobile envelope. This average (sustained) power draw is shown when the processor is actively crunching on what are today’s mid-range workloads . The dual-core can be used to boost performance even further than single-core and gives system and software designers lot of room for tuning performance and power draw with using all parameters including voltage and frequency scaling.
While running a lot of common lower end workloads, the processor will be able turn off parts of the pipeline elements even when active, based on workload requirements. Then, when it reaches an idle state, it can turn off most of the processor “instantaneously” in well under 10 micro-seconds. The key here is that the processor can recover and start working equally as fast – a key consideration in user response time. When taken together, these capabilities allow for additional system-level power savings that are not reflected in the above graph.
With our first Cortex-A9 dual-core systems expected to arrive in time for Christmas, and our leading smartphone platform providers Samsung, ST Ericsson and Texas Instruments already on board as Cortex-A15 licensees. The future of Smart Mobile Devices is looking very bright, and future devices won’t have to choose between being responsive or long-lasting – they will be optimized for both.
Nandan Nayampally, Director of CPU Product Marketing - Processor Division, ARM, He has long history with application processors having managed the ARM11 family and the Cortex-A8 before taking on the Cortex-A15. Having been a keen observer of the accelerating trend towards connected and differentiated devices and how they affect our everyday lives, this reluctant blogger intends to pitch in with a processor-centric viewpoint now and then.
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