The Case for Licensed Instruction Sets
Licensing Revenue Feeds Back to a Broad Ecosystem
This article is counterpoint to the recent UC Berkeley article (see MPR 8/18/14, “The Case for Open Instruction Sets).
In a world where over 50 billion chips have shipped using a licensable ISA from ARM, we’d like to spend a little time looking at why the choice of ISA is much more than just RISC versus CISC, or one RISC versus another architecture, and why in a world of choice, reducing risk matters.
As part of the research in gathering material to write this piece, we rewound the clock 20 years and accessed archives of Microprocessor Report. We found announcements including a youthful Mike Muller unveiling an ARMv4-based device focused on the set-top-box market (see MPR 11/14/94, “ARM Reaches Into Set-Top Boxes”), as well as others about the extension of instruction sets like UltraSparc (see MPR 12/5/94, “UltraSparc Adds Multimedia Instructions”) and the development of a new instruction set by Intel and PA-RISC (see MPR 6/20/94, “Intel, HP Ally on New Processor Architecture”). In short, we found a slew of announcements at the architecture level covering both open-source and proprietary instruction sets.
Let’s fast-forward 20 years. One conclusion can be drawn: namely, that the business model of the instruction-set architecture (ISA) is not a leading indicator of long-term success or failure of an instruction set. Instead, the value of an ISA is created through the multiplication of factors that include the following:
- The choice of instructions that make up an ISA
- The proven compatibility of the ISA implementations
- The innovation in, diversity of, and accessibility to implementations of the ISA
- The evolution of the ISA to solve the problems that customers are facing
- The support provided for the ISA and its implementation
- The vibrancy of the ecosystem that supports the ISA
The Choice Behind an ISA
We assert that the choice of actual instructions to be included in an instruction set cannot alone determine the success of a processor architecture. Our experience, however, is that incredible diligence is required to ensure that new features are added in the right way to simplify the support of new functions in software. Two years ago, ARM announced version 8 of the instruction set. The new features include instructions to accelerate cryptographic algorithms. The path to their inclusion involved rigorous discussions with a broad set of partners in our ecosystem (more about this later) to ensure we extended the instruction set in the right way.
As Figure 1 shows, ARM partners have shipped billions of ARM-based chips into one of the world’s most competitive and explosively growing markets—and they have done so on the basis that the software they develop is going to run on any ARM chip from any vendor. The critical importance of this choice is not just the ISA.
Figure 1. Shipments of ARM-based chips in mobile devices. As the market shifted from basic phones to feature phones to smartphones, designers moved from one ARM generation to the next with full code compatibility. (Source: ARM)
We believe compatibility across ISA implementations is critical. The key to ARM’s success has been empowering silicon partners to deliver innovative capabilities alongside a CPU core that can use a broad range of standard software building blocks. This task is not trivial. Accomplishing it requires an investment in comprehensive validation test suites. ARM partners rely on these tools to ensure that the investment they make in designing an SoC is a safe one.
The ARM licensing model provides an immense benefit to our partners. For significantly lower cost than that of designing and implementing their own CPU, they can license an ARM implementation that is validated, stable, and easy to implement in the standard EDA tool flows used to produce today’s modern SoCs. The value to the SoC vendor of being assured of correct CPU operation enables semiconductor companies to commit their engineering resources to the design of the other areas of the SoC, delivering vital differentiation to compete in the extremely competitive markets in which they operate. This analysis does not even include the additional costs that would be incurred by the tool chains that would have to be tuned to a specific ISA implementation, even if an open-source tool chain is present. The cost of alignment is quite significant and is often underestimated.
As Figure 2 shows, the challenges of SoC design continue to climb, regardless of the business model associated with the instruction set. The sheer cost of building an implementation based on an open ISA would actually exclude a number of innovative companies from the market. Furthermore, from a skill-set perspective, their products would be less competitive, as the resources deployed on the effort would be lost to the creative and innovative differentiation that is so essential to their success.
Figure 2. Design complexity per process node. In each new IC process, the number of design rules increases dramatically. (Source: ARM)
Innovation and Diverse Implementations
In a world where most innovation and design originality has a recognized value, the ISA certainly contains patented ideas that are the result of long years of intensive creative effort. An example is the introduction of the ARM Thumb concept, where the ability to improve code density with a 16-bit instruction set, or to drive performance benefits with a 32-bit instruction set in the same processor, was a significant contributor to the success of the ARM7 CPU. Just as in many creative industries today (for example, the music industry or Hollywood), the ability to monetize that idea was critical to our development, which in turn enabled many partners to participate and thrive as the mobile-phone market ramped from almost nothing to the multi-billion-unit industry it is today.
We think few would argue that in terms of a diversity metric, ARM wins in all categories, such as number of licensees, number of chip implementations, variety of price points, and number of application areas addressed. The ARM architecture has more than 350 customers that have collectively taken more than 1,000 individual licenses. Companies continue to take new licenses, including 121 new licenses in 2013 and more than 30 licenses for the newest ARMv8-A technology. Cortex-M processor technology has been licensed over 200 times to more than 160 companies. ARM partners put these licenses to use in hundreds of different SoC products. More than 10 billion ARM-based chips shipped in 2013 alone.
ARM focuses on improving in all of these areas. We are not a charity; we are a business. We take a small royalty from every ARM chip that ships into the marketplace. Inside ARM, companies that license our technology are referred to as “partners.” Without them, our technology would not make it to the market, so we have a partnership model focused on achieving mutual success. ARM-based devices like 32-bit MCU SoCs can sell for less than $0.50, and MPU SoCs sell for less than $4. The royalty is a small percentage of that sale price. These price points are roughly equivalent to that of processors using open-source CPUs.
ISAs Must Evolve to Solve Customer Problems
In the almost 20 years since the debut of the ARM7 CPU, the ISA has evolved as shown in Figure 3, with each architecture advance introducing additional features that the market critically needed, alongside continued performance and efficiency enhancements.
Figure 3. ARM ISA evolution. Over a 20-year span, ARM has introduced several versions of its instruction set, including a new 64-bit version. (Source: ARM)
Looking forward, the topic of security is critical in IoT. Indeed, it’s important for any connected system, whether it be a phone connected to a cellular network, an over-the-top (OTT) media platform, or a smart streetlight in a city. The bigger issue is more about control of data than hacking, and it has driven our development of TrustZone technology implementation “blueprints” and an ecosystem that enables secure services in the IoT world. To say that only open designs are immune from secret trapdoors is, frankly, incorrect, as the scrutiny to which the ARM architecture is subjected, by a geographically diverse set of highly capable partners through the ARB (Architecture Review Board), renders the idea that a government could exert enough influence to insert a backdoor virtually impossible.
ISA Ecosystem Needs Support to Flourish
We completely agree with the other article, which says the ecosystem for the ISA is an important part of its success. The ecosystem of design services, tools, operating systems, and middleware that arrives as part of the ARM value proposition drastically improves the time to market for companies at all levels of the value chain. Today, with over 1,000 companies taking part in a thriving ARM community, the software and tools optimized for use on ARM-based chips and platforms represent a huge investment and commitment by ARM and its ecosystem partners. It is a major responsibility and one ARM takes extremely seriously—namely, to protect and support that investment.
In building relationships with suppliers of open and closed operating systems and middleware vendors, ARM engineers work hard to ensure that the support and stability on which the ecosystem thrives is maintained. ARM has an entire business group focused on supporting our partners, providing training, offering educational qualification programs such as AAE (ARM Accredited Engineer), and providing essential support across all the IP, from implementation issues to software drivers.
This support is even more critical when working to develop an evolution of the ARM ISA, such as ARMv8-A, in ensuring that the goals of improved performance and efficiency are realized affordably. After all, the ISA provides the consistent baseline on which the vast ecosystem of open software can be run.
If the goal of an open ISA is to enable more innovative, differentiated products while reducing development cost, we think ARM has demonstrated that this goal can clearly be realized through its partnership approach based on an IP licensing model. We have now completed over 1,000 CPU licenses, and tens of thousands of ARM-based devices are in the market. Diversity and innovation are both alive and well. We clearly cannot and are not resting on our laurels. Our investment in developing an ecosystem around mbed (development platforms based on the Cortex-M CPU), the momentum of ARM technology in the Raspberry Pi and Arduino communities, and the standardization and application software focused on IoT highlight that our focus is on further shrinking system development and deployment cycles.
Licensed ISAs Meet Customer Needs
The ISA license is a consistent baseline that maintains compatibility, enabling an ecosystem to coalesce. Implementations of the ISA incorporate valuable and solution-differentiating capabilities to be woven into the SoC, spurring innovation while reducing validation cost and shortening time to market. The value of the software ecosystem is in the breadth of software partners that deliver commercial and open-source software and middleware based on the ISA’s consistency and stability. This breadth is crucial for the vibrancy and viability of the ecosystem. Finally, the commercial need for support, reliability, and constant cost reduction, along with the knowledge that you can’t just “patch” an SoC, leads us to say that only a market-driven, nimble, well-supported, licensable ISA can deliver on those demands.
Ian Ferguson is Vice President of Segment Marketing at ARM. Ian Smythe is a Director of Processor Marketing at ARM.
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