Mobile Building Blocks 2014: Mobile Cores

Each year after CES and Mobile World Congress, I ponder the shows' announcements and what they mean for the future of mobile application processors. We've certainly seen some interesting developments, including a set of 64-bit chip announcements, some of which are aimed more at mid-range phones, but new 32-bit chips seemed to be the most popular topic of conversation at the high end.

Almost every company that makes chips is talking about better graphics – with huge gains in performance – and all are talking about multiple cores, with 4- and even 8-core chips now becoming routine. What we haven't seen yet are any major applications processors built using 20nm technology (except those from Intel, which controls design and manufacturing for its chips), nor really new high-end 64-bit chips from most of the players. As a result, the changes we're likely to see in the chips for the highest-end phones over the next few months may not be huge, even as the mid-range and low-end phones catch up.

I'll discuss the details of the major chips later this week, but I'd like to start by talking about the basic building blocks that go into the creation of application processors. Unlike in the PC world, in general, makers of such processors tend to use at least some intellectual property (IP), either architectural licenses or full cores, in creating their products. Recall that a typical applications processor today includes a CPU, graphics core, often a baseband modem, and a raft of other features; and many makers license the CPU architecture, graphics, or potentially both. A typical processor maker will combine these features, both those they create themselves and those they license, to design a specific chip for a target market. In this post, I'll talk about CPU architecture, then follow tomorrow with one on graphics design.

The Many Flavors of ARM Designs
The vast majority of mobile application processors you see today run some variant of the ARM architecture. Indeed, across all markets, ARM claims that more than 50 billion processors using its technology have been sold, with more than 10 billion sold in 2013 alone. The phone and tablet markets are a significant part of that, with ARM claiming that 95 percent of the world's smartphones run some version of its architecture, but ARM processors are in a lot of other products as well.

But it's important to understand that ARM doesn't actually sell processors; instead it sells IP – including actual core designs and the basic underlying architecture, which several chip vendors including Apple and Qualcomm use to create unique cores. Using a common architecture – effectively the instruction set – allows for a degree of compatibility and thus makes it easier to get software to run on chips from multiple companies.

There are two basic ARM architectures that we see in mobile processors today – the 32-bit ARMv7 and the 64-bit ARMv8 version.

ARMv7 has been the standard in the phone market for years. This is a 32-bit design that is used in a variety of cores (including ARM's Cortex-A9, A7, and A15 designs, as well as Qualcomm's "Krait" architecture and the cores used in Apple processors before the A7). The Cortex-A9 has been incredibly popular, but its days seem numbered. This year, we're seeing more designs that include either a smaller, more power-efficient Cortex-A7; or a more powerful Cortex-A15, which offers higher performance; or a combination of the two in what ARM calls its "big.LITTLE" configuration. 

The Cortex-A7 is actually very small—less than half a square millimeter on a 28nm process—and was designed to use much less power; less than 100 milliwatts compared with a 200- to 300-milliwatt peak for an A9, and up to 500 milliwatts for an A15. Cortex-A15 adds support for a 40-bit physical address space, though individual applications can only access 32 bits. Last summer, ARM introduced the A12, meant to be a replacement for the A9, saying it was up to 40 percent faster than an A9 and would fit into the space between the A7 and the A15. Earlier this year, the company announced an upgraded version called Cortex-A17, which it says should offer better efficiency and 60 percent more performance than the Cortex-A9. (Thus far, only MediaTek has announced a phone processor and Realtek a TV processor using the A17.) ARM believes the A17 is the last of its 32-bit designs, and is meant to have a long life, in applications such as TVs and consumer products, while eventually the bulk of the mobile market switches to 64-bit designs.

A number of companies have combined A7s and A15s (or more recently A7s and A17s) into that big.LITTLE combination, which allows for a chip to have the lower-power cores running most of the time and the chip switching to the higher-power cores when it needs the additional performance, perhaps while running a complex calculation inside a game, or even complicated JavaScript in a webpage. In some of these designs, either the block of A7 cores or the one of A15 cores can be active at one time; in others, all the cores can work at once.

Again, it seems likely that most of the future mobile chips designed with ARM cores will move to the 64-bit architecture, although we seem to be in the early days of that migration. The ARMv8 instruction set seems to be used in Apple's A7 processor, which is found in the iPhone 5s and iPad Air, and is expected to be in a number of other proprietary designs as well. And of course, ARM has two cores it has announced using this architecture: a smaller Cortex-A53 and a more powerful Cortex-A57, again with the option of combining them in a big.LITTLE configuration. The 64-bit version is backward compatible, but includes larger registers for general purpose and media instructions (which could make it faster in some operations), support for memory beyond 4GB (particularly important in server applications); and new encryption and cryptography instructions.

The Cortex-A53 core is a bit further along, with companies such as MediaTek, Qualcomm, and Marvell all announcing chips with multiple A53 cores. ARM says it expects the first such chips will be out this summer. The A57 should be notably more powerful, and ARM expects mobile chips with that core to be out later in the year. (AMD has announced a server chip using the A57 architecture, due to enter full production toward the end of the year.)

ARM also offers a number of much smaller cores used in microcontrollers and other devices in its M series; these wouldn't run application processors on their own, but may get used in multiple other chips in the mobile ecosystem and are increasingly used to make mobile SoCs smarter. For example, Apple's A7 SoC has an M7 motion coprocessor reportedly based on the ARM Cortex-M3 and manufactured by NXP, and the Motorola X8 SoC in the Moto X combines a Snapdragon S4 Pro dual-core CPU with two low-power coprocessors based on Texas Instruments DSPs for natural-language processing and contextual computing.

As mentioned earlier, a number of companies have what is known as an "architectural license," which enables them to create their own cores using the instruction set, which they think allows them to make chips that stand out for the market through better performance, power management, or both. These include companies such as Qualcomm, Marvell, Nvidia, and Apple. On the other hand, offering standard cores allows companies to create designs more quickly and more easily; many of the companies that do have an architectural license use standard ARM cores in some products. Notably, Qualcomm now has some versions of its Snapdragon line of processors that use its Krait cores, while others use standard ARM cores.

Intel and MIPS Offer Alternatives
While ARM continues to dominate the mobile processor market, Intel has been making a big push as well, although with most of its successes coming in tablets running Windows and a few running Android. Intel's current offering seems more aimed at tablets than phones, although the company has two new processors that seem better suited to phones coming out later this year (which I'll discuss when I get into processors from specific companies in the next post). In the mobile arena, Intel is pushing its Atom line of processors, although there are some Windows tablets that use the larger Core family also used in laptops and desktops.   

Also within the x86 family, AMD has been showing some tablets running its lower-power x86 based CPUs. Again, I'll discuss details later when talking about the specific makers. In both cases, of course, the processors run the full version of Microsoft Windows, though both companies are now addressing Android as well. Intel in particular has made a big push to make Android run natively on its chips, while AMD has more focused on the BlueStacks emulator for its x86 products as it also prepares to launch ARM-compatible chips later this year.

Another option would be MIPS processors, a RISC based family of processors that was acquired by Imagination Technologies a little over a year ago. MIPS has offered a 64-bit architecture for some time, as part of its Aptiv line of cores. Earlier this year, the company announced its Series 5 "Warrior" CPU generation, which includes three classes of MIPS processors – the M-series for embedded markets, the I-class designed for high efficiency and very integrated devices; and the P-class designed for more performance, including applications processors. New features include integrated support for OpenCL graphics and improved security. Imagination says these chips use up to 40 percent less area than their competitors, with better multi-threading for multi-core use.

MIPS processors have been quite successful in a number of markets, including network processors and other real-time applications and set-top boxes, but to date, we haven't seen them in many traditional tablets or smartphones. A Chinese company called Ingenic has a line of processors running the Xburst architecture based on the earlier MIPS core, and this was used in some Android tablets. A while back, I did try one out, but the company that made it now seems to be focusing on ARM-based tablets. Still, it's possible that MIPS could be a competitor in the future, particularly with its new line of cores.