ARM Community: Watt’s the Limit for Smart Mobile Devices? Meet the Cortex™-A15 - ARM Community

This year has been an exciting and transformative year in mobile. I can’t believe it was just a few years ago when we first introduced the Cortex-A8 and this year the Cortex-A8 has been featured from some of the most innovative smartphones, tablets, and connected DTVs. Software and hardware have come together to deliver a fully connected experience across multiple device platforms. The Cortex-A9 is already headed mainstream into mobile and smart connected devices, enabling multicore performance and flexibility. So here we are today celebrating the arrival of the Cortex-A15 MPcore processor. So why reflect on this short bit of history?

Your hands are not burn-resistant and the size of your pocket doesn’t change

Even though ARM processor technology has helped to propel the mobile industry forward over the last decade, the nature of hands and pockets really haven’t changed. A mobile phone still needs to fit in your pocket and can’t burn your hands when you hold it. That means that the size of the processor and the amount of energy it can consume are severely constrained. All ARM processors have been designed consistently with efficiency in mind – to deliver the maximum amount of performance within those tight budgets. The Cortex-A15 will take us even further with a 5x improvement in performance over today’s advanced mobile handset processors without compromising the energy footprint and significantly more performance for non-mobile platforms (more on that another day).

On the power front, Moore’s Law is providing no real relief. In the earlier part of this decade we saw benefits on all axes: power, area, and frequency as we progressed to 45nm process nodes. However as we continue to move down to 32nm, 22nm and below, the picture is starting to change. We still enjoy some benefit on area, but there is less and less of a power and frequency advantage from using a smaller process geometry. A topic recently highlighted by our CTO Mike Muller.

So how does the ARM Cortex-A15 deliver more within the same power and area constraints?

As they say in Texas – it’s a result of family and upbringing.

Speaking of family, the Cortex family – from the tiny Cortex-A5 to the now leading-edge Cortex-A15 has common DNA of excellent power-efficiency. Let’s look at some of the key components

• The ARM and Thumb instruction sets with their RISC roots that enable a simpler instruction decode.
• All architectural features such as ARM’s TrustZone security infrastructure are architected with a view of reducing hardware and software overhead for power-efficiency.
• ARM processors are very efficient at getting into and out of standby – which is why phones are so responsive “instantly”. Cortex-A15 gets even better, taking less than 10 micro-seconds to get into standby and similarly quick wakeup.

In terms of upbringing ARM engineers think power first whenever developing processor designs

• So Like most ARM processors, nearly the entire Cortex-A15 design is clock-gated meaning that in each cycle, if the part does need to do work or change state, it won’t – thereby saving power
• With the larger datapath structures that are required for better performance, the Cortex-A15 is designed to take advantage of and shut down large parts of the pipeline for further savings in specific cases.
• Another aspect of upbringing is how to share and work well in tandem. ARM processors are tightly integrated into systems-on-chip by our Partners. Partners add their own core competencies to save power not only in the CPU but also the rest of the system. Cortex-A15 enables more advanced implementation techniques, and ARM’s physical IP has been co-developed specifically for this mantra of power-efficient performance.

The Cortex-A15 leverages ARM’s low power advantages, yet takes ARM technology to a whole new level of performance with an advanced out-of-order super-scalar pipeline delivering greater parallelism. The Cortex-A15 can decode and dispatch up to 3 instructions per cycle (3X that of an ARM11) and can issue up to 8 instructions per cycle resulting in very high real-world performance. Cortex-A15 pays careful attention to power consumption and taking less than 10 micro-seconds to get into standby and similarly quick wakeup.

But why should energy efficient processing be limited to mobile devices?

As the world is becoming increasing connected so must our technology. The Cortex-A15 will spur a great deal of innovation on platforms that are not only handsets, but mobile computing and consumer devices. Yet these connected devices and cloud based demanding services will put even more burden on the delivery infrastructure – such as base stations for managing cellular traffic, routers to direct the traffic across the connected landscape and servers. Heat dissipation has become a critical factor in base stations and data centers, and the problem is getting worse, not better – a perfect opportunity for ARM’s low-power technology and design heritage with a few new twists.

The Cortex-A15 processor is the first ARM processor to incorporate support for multiple software environments that can operate simultaneously on a common hardware yet remain well isolated from each other. The result is the realization of devices that are robust enough to deliver seamless infrastructure support. Or alternatively in the client side, imagine your phone having a “work” personality and a “home” personality securely isolated on a single device – a perfect marriage.

The Cortex-A15 is the first ARM processor with the ability to access up to 1 TB of physical memory. The ability to access larger physical memory enables better performance for demanding systems and the ability to support complex SoCs with multiple cores, multiple tasks, and multiple virtual environments.

Cortex-A15 also extends reliability features by providing error correction for faults that may occur in devices. Reliability, once a bastion of enterprise platforms, is becoming a critical need in consumer devices too.

So what’s the limit for ARM and next generation Smart Mobile Devices??

Only our collective imagination. Watt’s not like about that.



Follow @ARMMobile on Twitter and join the ARM fan page on Facebook to stay up to date on the latest news and information on ARM Cortex-A15.

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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