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Contemplating Custom Instructions for RISC-V

July 7, 2023
By extending the instruction set, a processor can tackle an application more efficiently.

This article appeared in Microwaves & RF and has been published here with permission.

Check out our DAC 2023 coverage This article is also part of the TechXchange: RISC-V: The Instruction Set Alternative.

Most computer instruction sets include unutilized instructions that typically generate a fault or act as a no-op instruction. Sometimes this is by design, especially for architectures that are intended to be extended, such as RISC-V.

Thus, a chip designer can add instructions that will enhance the software developer’s repertoire. It allows an application to take advantage of these instructions that may perform special functions or operate more efficiently than what’s provided by default.

Custom instructions require additional logic to implement the desired functionality as well as enhancements to the compiler so that software can utilize them. The chip design cycle to address the inclusion of custom instructions is a relatively straightforward process (see figure).

If you have a chance to attend this year’s Design Automation Conference, you may want to attend the session “Extending RISC-V with Custom Instructions.” It’s presented by Imperas Software’s Jon Taylor.

In case you can’t make the session, Jon gave a similar talk earlier this year. You can download the presentation for some insights into the design process.

For more DAC 2023 coverage, visit our digital magazine.

About the Author

William G. Wong | Senior Content Director - Electronic Design and Microwaves & RF

I am Editor of Electronic Design focusing on embedded, software, and systems. As Senior Content Director, I also manage Microwaves & RF and I work with a great team of editors to provide engineers, programmers, developers and technical managers with interesting and useful articles and videos on a regular basis. Check out our free newsletters to see the latest content.

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Check out my blog, AltEmbedded on Electronic Design, as well as his latest articles on this site that are listed below. 

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I earned a Bachelor of Electrical Engineering at the Georgia Institute of Technology and a Masters in Computer Science from Rutgers University. I still do a bit of programming using everything from C and C++ to Rust and Ada/SPARK. I do a bit of PHP programming for Drupal websites. I have posted a few Drupal modules.  

I still get a hand on software and electronic hardware. Some of this can be found on our Kit Close-Up video series. You can also see me on many of our TechXchange Talk videos. I am interested in a range of projects from robotics to artificial intelligence. 

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