Everything You Need to Know About Open Source CPU

Comparative Analysis Between Open Standards vs Open Source CPUs

Open standard processors and open source CPUs follow a similar principle of openness, but they differ in nature, while being available for free access. Open source CPUs allow for free licensing, which means the public can easily modify and distribute the source code or actual design files, such as netlists and HDLs. Examples of open source CPUs include OpenSPARC (initially developed by Sun Microsystems) and OpenRISC.

Whereas open standard processors are available to the public with specific specifications that enable compatibility and interoperability across various technological platforms. Examples for open standards include HTTP (IETF), Verilog (IEEE), and the C language (ISO).

Here is a brief comparison between Open Source CPUs and Open Standard Processors.

Understanding if RISC-V Processor is an Open Source CPU or an Open Standard Processor?

No, RISC-V is not an open source processor, but rather an open standard. It is an open source instruction set architecture (ISA) used for chip design. It enables the public to modify and distribute their own processors or designs based on the RISC-V specifications. A report from Deloitte Global predicts that the market for RISC-V processing cores will double in the upcoming years. It is projected that the revenue for RISC-V will increase from US$800 million in 2023 to approximately US$1 billion by 2024. It explains how rapidly RISC-V processors are gaining popularity.

RISC-V operates as an open standard processor. It has some established guidelines and technical specifications for processor development. It enables seamless compatibility and interchangeability of components across cross-implementations. This standardized approach drives technological advancement, ensures collaborative development, and innovation.

Although the RISC-V ISA (Instruction Set Architecture) adheres to open standard guidelines, individual processor implementations exhibit varying levels of transparency, with some RISC-V processors following open source principles. It means its source code is available for public access and modification. In comparison, others develop commercial processors that follow the RISC-V standards to ensure their specific designs and source code remain proprietary.

Licensing Models Explained

Traditional Commercial Licensing

Classic processor IP vendors like ARM, Cadence, or more typically compile several element distributions in their licenses, like:

• Rights to utilize the vendor’s instruction set architecture (ISA)
• Rights to use the vendor’s microarchitecture
• Warranty
• Vendor’s support in fixing bugs and troubleshooting
• Intellectual property indemnifications

These vendors do not readily offer their ISAs and microarchitectures. Even if they distribute the architecture licenses, it’s the instruction set architecture (ISA) without the microarchitecture, and rarely, that too at a premium price.

Comparing Traditional vs RISC-V Processors Licensing Modules

Traditional IP vendors have strict control over both the microarchitectures and ISAs. In conventional licensing, both ISA and microarchitecture come as a bundled package, without any modification rights for the licensee. There are specific scenarios where vendors provide architectural licenses that allow ISA use with tailored microarchitecture. These personalization are rarely available and come at premium pricing, making them out of reach for many projects.

RISC-V is not like traditional processors, which are designed by separating the instruction set from the internal architecture implementation. As ISA is available at no cost due to its open source architecture, businesses do not need to pay for expensive licenses. It gives developers the freedom to choose how they want to license their internal designs while taking full advantage of the RISC-V ISA.

Here is a brief comparison between Traditional IP Vendors and the RISC-V Model.

Choosing the Right Path

Now the question arises, “Is RISC-V actually an open source processor?” It is an apparent misunderstanding, as it is an open standard. However, it enables both open source and commercial implementations. The choice of licensing depends on the business requirements:

• Open Source: Ideal for projects that have a strong internal expertise and community support
• Commercial: It is recommended for projects that require support, warranties, and indemnification

Final Thoughts

Open source CPUs are not about replacing existing proprietary models, but rather to offer cost-effective options and flexibility. For developers and designers, it is essential to understand the differences between open source CPUs, open standards, and commercial IP, and to choose the right model to drive innovation and meet diverse market needs. RISC-V is a paradigm shift in processor architecture that offers free licensing and an open ISA while allowing flexibility in implementation and licensing approaches. Understanding the distinction between open standards and open source is essential for making informed decisions about processors, such as RISC-V, and their adoption.

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