“Mobile processors are designed with the approach of doing more with less. This is one of the reasons why you do not see x86-based smartphones today,” quips James Bruce, lead mobile strategist at ARM. In the case of desktop processors, power ef-ficiency,size of the chip and thermal management are not limiting factors, though these are important design aspects. However, in the case of a mobile device, which needs to compete with a desktop in terms of functionality and at the same fitinto your pocket, working for long hours on battery, these ‘mobility’ factors are critical.

Bruce explains that desktop processors are ‘processors on chip.’ Many surrounding chips are needed to complete the compute sub-system. On the other hand, in the mobile world, the complete sub-system is on a single chip—a system-on-chip (SoC).

“For example, you may have a 3G (or even 4G) modem, processor, graphics, video unit, audio decoder, Wi-Fi, Bluetooth, geographical positioning system (GPS), dynamic random-access memory (DRAM) and Flash, all in one 14×14mm² package,” Bruce says.

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Praful Joshi, business development manager, WindRiver India, concurs, “The key challenge to an engineer designing a mobile processor is how to add more functionality while design-ing an SoC without compromising on low power consumption or low form factor. In fact, the processor chip size is a very important factor. You can see new very-large-scale integration (VLSI) technologies such as 30 nm or less being widely used in mobile processors as against desktop processors.”

“Today, consumers expect to have the same kind of computing experience on their mobile device as on their desktop or notebook PC—high-definition(HD) video playback, audio and video streaming, multitasking, Web browsing, 3D gaming and 3D interfaces. However, the power envelopes of a PC and a mobile device are radically different. Simply miniaturising a traditional x86 CPU, which you would find in vast majority of PCs, is not enough. The resulting processor might physically fitinto a mobile device but its power consumption would result in a device with a battery life of minutes,” says Vishal Dhupar, managing director, Asia-South, NVIDIA.

Dhupar recalls that when creating NVIDIA’s mobile solution Tegra, their engineers had started from the ground up with a strict power budget. The designers had to fightfor every milliwatt of power. All of this shows that a mobile being different from a desktop, its processor also needs to be different.

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War of the titans
Quite naturally, the repertoire of made-for-mobile microprocessors is also increasing, with many ARM-based offerings from Texas Instruments (TI), Qualcomm, NVIDIA, MediaTek, etc, and Intel Atom chips also catching up now.

“ARM is the most popular processor in the mobile device world. It is not a derivative of any desktop processor. It was designed specificallyfor low-power-consuming devices. Since then it has emerged as a mainstream mobile processor and added more computational capabilities and a software ecosystem. ARM licenses its core processors to SoC vendors such as TI, Qualcomm and others, who, in turn, add their own unique IP for different mobile markets,” says Joshi of WindRiver—an Open Source operating systems (Android, Linux and Tizen) commercialisation partner for mobile processor designers as well as mobile device manufacturers.

ARM has several processors for designers to choose from, including the latest Cortex-A9, which features 2GHz typical operation with the TSMC 40G hard macro implementation, low-power targeted single-core implementations into cost-sensitive devices, and an optional NEON media and floating-pointprocessing engine. It is also scalable up to four coherent cores with advanced MPCore technology.

ARM’s model of licensing its core processors to other vendors is a unique selling proposition. “Because desktop processors are really only available from two companies, there is limited innovation and diversity. Compare this to the ARM business model where any company can license an ARM processor and build its own unique intellectual property (IP) around its own unique configurationof ARM cores. This business model is very exciting as it provides opportunities for new companies in India to develop their own application processors for tablets or smartphones,” says Bruce.

Intel Atom processors are also emerging and gaining a market in mobile devices. These are derivatives of desktop processors like Pentium Core i5, i7, etc. The Intel Atom processor Z6xx combines 45nm Intel Atom processor core with 3D graphics, video encode and decode, as well as memory and display controllers into a single SoC design. Combined with the Intel SM35 Express chipset, it supports Windows, MeeGo and Android operating systems.

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While the processor appears more popular in the netbook space, a variety of smartphones and mobile Internet devices (MIDs) for cloud computing are also sporting the ‘Intel Inside’ logo these days. Joshi suggests that although ARM is a leader in the mobile space, Atom can benefitfrom the Intel’s experience in the desktop space as the current trend portrays a deep convergence of desktop and mobile worlds.

Multi-core magic
As mobiles race to beat the capabilities of computers, it is inevitable that some of the trends in the PC processor space will also spill over to the mobile world. One such trend is the magic of multi-cores.

“Due to the growth in the availability of high-speed mobile and WiFi networks, mobile devices will also be used for various performance-intensive tasks that were previously handled by traditional PCs. Single-core mobile processors are not designed to deal with this tidal wave of high-performance use cases,” explains Dhupar.

“On a mobile processor that has a multi-core CPU, multi-tasking can be shared between the distinct processing cores. Hence, as the performance requirements of mobile applications increase, SoC vendors are adopting multi-core processor architectures to deliver the increased performance and keep power consumption within mobile budgets,” he adds.

It is a common misconception that more cores mean higher power consumption. In fact, multi-core CPUs are able to distribute their workload across their cores so that each CPU core can run at a lower frequency and voltage. This means each core consumes significantlylower power and offers much higher performance per watt than single-core CPUs.

The performance of a smart phone has increased 40 times over the last ten years; and the increase in performance since 2008 alone has been eight times. One reason for this is the adoption of multi-core technology. Last year saw the launch of dual-core Cortex-A9 smartphones. This year, we are likely to see the launch of quad-core Cortex-A9 smartphones.

Bruce predicts that at the end of 2012, we will see the launch of Cortex-A15 handsets with a 50 per cent increase in performance. “Also in 2012 you will see the launch of Cortex-A15 based handsets at a $100 price point. The Cortex-A15 processor allows $100 smartphones to deliver the user experience of a $500 smartphone in 2010,” he says.

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NVIDIA is also focusing on multi-core architectures. Its latest Tegra 3 processor goes a step beyond quadcore by adding a fifth‘companion’ core. Its internal architecture is identical to the four main Cortex-A9 CPU cores but the fifthcore is built using a special low-power silicon process. Using a technology called variable symmetric multiprocessing, the fift core handles low-frequency tasks such as those common in active standby mode (Twitter and Facebook updates, e-mail synchronisation, etc) and applications that do not require significantCPU processing power, such as audio streaming, offline audio playback, an both online and offine video playback.

When more demanding tasks are required, the other four cores can be called upon. This approach allows Tegra 3 to deliver significantlylower power than competing mobile processors at all performance levels.

It is interesting to note that the popular low-cost, open mobile software development platform PandaBoard too is now available in a dual-core version, keeping pace with the current trend. In November 2011, the community announced the availability of the PandaBoard ES based on TI’s OMAP4460 processor, whose multi-core architecture includes two ARM Cortex-A9 cores running at up to 1.2 GHz each, delivering a 20 per cent increase in overall performance and a 25 per cent increase in graphics when compared to the OMAP4430 processor used by the earlier PandaBoard.

Looking ahead
Dhupar feels that with mobility becoming more sophisticated, the number of CPU cores in a mobile processor will continue to multiply. Quad-core CPUs will enable mobile devices to further push the performance envelope and allow application and game developers to deliver new mobile experiences, all while extending the battery life.

Dhupar expects Windows on ARM platform becoming a reality some time late this year or next year.

Joshi sums up, “The rapid increase in consumer demand for multimedia, gaming, etc on mobile devices will drive computing speed. Aside from that, low power consumptions, size and weight are key improvements to foresee.”


The author is a technically-qualified freelance writer, editor and hands-on mom based in Chennai

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