RISC-V: The case for an open ISA standard for SoCs - Embedded.com

RISC-V: The case for an open ISA standard for SoCs

Systems-on-a-chip (SoCs), where the processors and caches are a small part of the chip, are becoming ubiquitous. Thus many more companies today are making chips that include processors than in the past. Given that the industry has been revolutionized by open standards and open-source software — like TCP/IP and Linux — why is one of the most important interfaces proprietary?

While instruction set architectures (ISAs) may be proprietary for historical or business reasons, there is no good technical reason for the lack of free, open ISAs.

It's not an error of omission. Companies with successful ISAs like ARM, IBM, Intel, and MIPS have patents on quirks of their ISAs, which prevent others from using them without licenses that academia and many small companies can't afford. Even IBM's OpenPower is an oxymoron; you must pay IBM to use its ISA.

An ARM license doesn't even let you design an ARM core; you just get to use its designs. (Only about 10 big companies have licenses that allow them to design custom versions of ARM cores.) While the business is sound, licenses stifle competition and innovation by stopping many from designing and sharing their ISA-compatible cores.

Nor is it because the companies do most of the software development. Despite the value of the software ecosystems that grow around popular ISAs, outsiders build almost all of their software.

Neither do companies exclusively have the experience needed to design a competent ISA. While it's a lot of work, many today can design ISAs.

Nor are the most popular ISAs wonderful ISAs. ARM and 80×86 aren't considered ISA exemplars.

Neither can only companies that design ISAs verify them. Long ago, open organizations developed mechanisms to ensure compatibility with hardware standards, such as floating point units (IEEE 754), networking chips and switches (Ethernet), and I/O buses (PCIe). If not for such organizations, open IT standards would not be so popular.

Finally, proprietary ISAs are not guaranteed to last. If a company dies, it takes its ISAs with it. Digital Equipment's demise also terminated the Alpha and VAX ISAs. Note that an ISA is really an interface specification, and not an implementation.

There are three types of ISA implementations:

  1. Private closed-source, analogous to Apple iOS
  2. Licensed open-source, like Wind River VxWorks
  3. Free, open-source that users can change and share, like Linux

Proprietary ISAs in practice allow the first two types of cores, but you need a free, open ISA to enable all three.

We conclude that the industry would benefit from viable, freely open ISAs just as it has benefited from freely open versions of the software stack. For example, it would enable a real, free, open market of processor designs, which patents on ISA quirks prevent. This could lead to:

  • Greater innovation via free-market competition from many more designers, including open vs. proprietary implementations of the ISA.
  • Shared, open core designs , which would mean shorter time to market, lower cost due reuse, fewer errors given many more eyeballs, and transparency that would make it hard, for example, for government agencies to add secret trap doors.
  • Affordable processors for more devices, which would help expand the Internet of Things, whose target cost could be only $1.

    To read more of this external content and to leave a comment, go to “The case for RISC-V.

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