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Success in complexity
Royalties and fees do vary depending on several factors. Newer and more complex IP—like, say, the Cortex-A15 CPU core used in high-end Android devices—tends to command a bit of a premium, although ARM has built in a number of provisions to ease the pain. Multiple copies of the same core on a chip usually don't cost any more, for instance. Discounts are applied to the royalties on chips that mix two different core types, so that the total royalty remains fairly modest. Some enabling IP, like ARM's AMBA interconnect and its memory controllers, are included as part of the package for no additional cost. I understand ARM has also been quite aggressive in discounting its Mali graphics IP for its CPU licensees in order to spur wider adoption.

Also not ARM's offices.

That's all quite complicated, but the thing to know about ARM's licensing model is that it works. In fact, licensed IP is arguably the lifeblood of today's semiconductor industry outside of a few traditional PC players. ARM's AMBA interconnect and its CPU cores are de facto standards in the world of SoCs, but a number of other players compete with ARM pretty directly. For instance, the graphics IP in all of Apple's iOS devices is supplied by Imagination Technologies, who abandoned the desktop PC market after the Kyro II. The success of this model has even prompted Nvidia to open up its current and future GPU portfolio for licensing by third-party device makers.

Thornton offered some numbers to illustrate the extent of ARM's, er, reach. (Yes, I did that.) Currently, the firm has roughly 1000 processor licenses active—that is, those licenses still have the potential to generate a royalty. A total of 320 companies are partnered with ARM via license agreements, and about half of those are currently shipping ARM-based chips. Each year, the firm adds 30 to 40 new licensees, and Thornton estimates that about 80% of those end up building a chip successfully. (The other 20% are start-ups that wind up being acquired.) All told, ARM's partners presently ship about 2.5 billion chips every quarter, and ARM estimates that its IP has shipped in a cumulative total of 45 billion chips over the years. Those are, obviously, some very big numbers. We're only three orders of magnitude shy of the scale of government debt.

So, this is... different
The fact that ARM (along with other IP houses) doesn't produce its own chips presents some difficulties for those of us well attuned to the traditional PC market. We're generally accustomed to a certain level of openness about things like future CPU roadmaps, die sizes and, transistor counts. ARM shared quite a bit with those of us who attended its recent event for the tech press, including juicy details of its current architectures that we'll be writing about in future articles. But the nature of the information ARM will disclose is limited by its business model, oftentimes because the answers to common questions depend on how and when ARM's partners choose to implement its technology.

For instance, ARM's engineers presented some compelling arguments about the merits of its big.LITTLE power-management scheme, which uses dual CPU architectures and intelligent thread scheduling to boost power efficiency. Trouble is, there isn't yet a really strong implementation of big.LITTLE in the wild, and ARM doesn't feel at liberty to disclose what it knows of its partners' plans. As a result, it's hard to gauge big.LITTLE's prospects for widespread adoption. By contrast, we know definitively that Intel's Bay Trail platform based on the Silvermont microarchitecture is slated for release later this year, and we can reasonably expect Silvermont's power-saving features be implemented uniformly at that time.

This one difference between ARM and Intel isn't a big deal in itself, but it illustrates a larger reality that permeates any discussion of ARM-based solutions. Because it's an upstream provider of technologies, ARM's control over how its creations are implemented is limited. That fact can be a strength, given the sheer diversity of its partners' products and how those products are tailored to specific applications. But it can also be a detriment, for example when ARM's partners choose to pursue higher core counts and clock speeds at the expense of architectural efficiency.

I expect this drawback will be something of a persistent challenge for ARM. On the PC, Intel addressed this problem years ago by delivering near-complete platforms to PC makers, as it did with Centrino and continues to do with ultrabooks. ARM has less leverage, so it must count on its licensees to do the right thing.

Then again, have you tried to find an ultrabook with a decent touchpad? Even Intel's clout doesn't solve every problem.

ARM tackles this challenge in part by offering a "lead licensing" program when it's ready to bring, say, a new CPU core to market in an SoC for the first time. The firm will choose several partners and work closely with them on the first few implementations of its new microarchitecture. These partners generally must serve different markets, and they must be able to dedicate substantial engineering resources to the project. Their reward, of course, is being one of the first to offer a new core, which seems like a pretty good incentive. This program helps ARM pass the hurdle of getting a new core etched into silicon, at least.

The issues created by the separation of ARM's R&D efforts from it partners' specific implementations come into sharper focus when the time comes to make performance assessments. Claims made about a microarchitecture's instruction throughput only mean so much without a chip to test. Also, the inherent complexity of the ARM ecosystem can make it difficult to eyeball a chip and estimate its performance.

For example, ARM reckons the performance of the ultra-popular Cortex-A9 CPU core more than tripled during its lifetime. Changes in the process technology and power envelopes used by ARM partners contributed some of those gains, but so did four separate revisions made to the Cortex-A9's RTL. We're talking fundamental architectural tuning here, such as tweaks to the branch prediction and cache pre-fetching algorithms. Similarly, the Cortex-A15 is already on its third rev. And we haven't even talked about the many possibilities for varying cache and uncore configurations in ARM-based SoCs. Knowing that your tablet has a Cortex-A9 at 800MHz inside of it doesn't provide much of a basis for comparison.

So, as the contest between Intel and ARM heats up and the performance claims are inevitably bandied about, we have much to consider. I expect we'll hear some hare-brained marketing claims from all sides of this contest.  As always, the ultimate verification will come from high-quality benchmarking that relies on real applications and takes the user's perceived experience into account. That we can do.

ARM presented us with a formidable amount of detailed info about its CPU and graphics cores, so we have lots more to say about these things. For now, though, I think we have a start on understanding how ARM's business works and why it's such a threat to the traditional dominance of x86 processors in high-end computing devices. That should be enough to chew on, since it pretty much changes everything.TR

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