ARM Cortex-A7 combines 5x better efficiency and higher performance for smartphones and tablets
The Cortex-A7 processor builds on the low-power Cortex-A8 processor that is at the heart of many of today’s most popular smartphones. A single Cortex-A7 processor delivers 5x the energy-efficiency and is one fifth the size of the Cortex-A8 processor, while providing significantly greater performance.
Big.LITTLE processing, enabled by Cortex-A7, balances the demand for high performance while significantly extending battery life by pairing the best of the high-performance Cortex-A15 MPCore and ultra-efficient Cortex-A7 processors. Big.LITTLE processing allows devices to seamlessly select the right processor for the right task, based on performance requirements. Importantly, this dynamic selection is transparent to the application software or middleware running on the processors.
By combining big.LITTLE processing and the Cortex-A7 processor, designers can deliver both high-performance, required for content creation and consumption, while also delivering extreme power efficiency for extended battery life. This is particularly pertinent as smartphones and tablets continue to evolve into the primary platforms that consumers use to interact with our increasingly connected world.
Big.LITTLE processing
Big.LITTLE processing combines two different, but compatible processors within the same SoC and allows the power management software to seamlessly select the right processor, or multiple processors, for the right task. The processors appear identical from an applications software perspective.
In the first big.LITTLE system from ARM a ‘big’ ARM® Cortex™-A15 processor is paired with a ‘LITTLE’ Cortex™-A7 processor to create a system that can accomplish both high intensity and low intensity tasks in the most energy efficient manner. By coherently connecting the Cortex-A15 and Cortex-A7 processors via the CCI-400 coherent interconnect the system is flexible enough to support a variety of big.LITTLE use models, which can be tailored to the processing requirements of the tasks.
In one such use model — the big.LITTLE task migration use model —
the ‘LITTLE’, lowest-power processor — in this case, the Cortex-A7 — runs the Operating System (OS) and applications for basic always-on, always connected tasks, such as social media and audio playback. The OS and apps can then be seamlessly migrated to the higher-performance processor as demands increase for high end tasks, such as navigation and gaming. The time for this migration is in the order of 20 microseconds. This flexible approach of choosing the right processor for the right job enables highly optimized processing which results in significant energy savings for common workloads.
In the big.LITTLE task migration use model the OS and applications only ever execute on Cortex-A15 or Cortex-A7 and never both processors at the same time. This use-model is a natural extension to the Dynamic Voltage and Frequency Scaling (DVFS), operating points provided by current mobile platforms with a single application processor to allow the OS to match the performance of the platform to the performance required by the application.
However, in a Cortex-A15-Cortex-A7 platform these operating points are applied both to Cortex-A15 and Cortex-A7. When Cortex-A7 is executing the OS can tune the operating points as it would for an existing platform with a single applications processor. Once Cortex-A7 is at its highest operating point if more performance is required a task migration can be invoked that picks up the OS and applications and moves them to Cortex-A15.
This allows low and medium intensity applications to be executed on Cortex-A7 with better energy efficiency than Cortex-A15 can achieve while the high intensity applications that characterize today’s smartphones can execute on Cortex-A15.
System IP and tools
The efficient and seamless switching of workloads between the two processors is supported by advanced ARM system IP, such as AMBA® 4 ACE Coherency Extensions. This ensures full cache, I/O and processor-to-processor coherency between the Cortex-A15 and Cortex-A7, and across the complete system. Software and applications can therefore continue to run unhindered, and unnoticed by the user, as the tasks are rebalanced to provide the optimum big.LITTLE user experience. By selecting to optimum processor for each task big.LITTLE can extend battery life by up to 70%.
Big.LITTLE power management software has been developed by ARM ecosystem partners months ahead of silicon availability using ARM DS-5 tools and Fast Model virtual prototyping technology. The virtual platform, available now to lead partners, contains the Cortex-A15 and Cortex-A7 processors, as well as cache coherent interconnect System IP, allowing full system software development.
Cortex-A7 processors
The architecure and feature set of the Cortex-A7 processor are identical to the Cortex-A15 processor, with differences in the Cortex-A7 processor’s microarchitecture focused on providing optimum energy efficiency, enabling the two processors to operate in tandem in a big.LITTLE configuration to provide the ultimate combination of high-performance with ultra low power consumption.
The Cortex-A7 processor occupies less than 0.5mm2, using 28nm process technology, and provides compelling performance 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. However, this processor will bring energy savings to many other devices as well such as femtocells, set-top boxes and residential gateways.
For further information: www.arm.com.
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