Extending RISC-V ISA with Custom Instruction Set Extension

News & Docs, Whitepapers

RISC-V ISA (Instruction Set Architecture) is designed in a modular way. It means that the ISA has several groups of instructions (ISA extensions) that can be enabled or disabled as needed. This allows implementing precisely the instruction groups that the application needs, without having to pay for area or power that will not be used. One of the groups is special; it has no predefined instructions. Designers can add any instruction they need for the application that they want to accelerate. This is a powerful feature, as it does not break any software compatibility and leaves space for invention and differentiation at the same time. This whitepaper describes how to add application-specific instructions (custom ISA extension) and how to build all the needed tools in SDK, as well as implementing the custom ISA extension in HDL (e.g. Verilog).

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