Why does the RISC-V ISA documentation *NOT* show encoding?

Mark Manning

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Jan 25, 2022, 10:04:11 AM1/25/22

to RISC-V ISA Dev

I will be writing a Forth compiler for RISC-V. Its kind of a hobby of mine but a useful one, it allows me to develop quality software and never have to go anywhere near any GNU development tools (horrible tools ick)

.

Stage one is to write a RISC-V assembler (in forth using an already existing forth compiler of mine). The instruction set is so tiny I should be able to do the entire assembler in a few short hours but nope, we have a major problem here with documentation from the RISC-V consortium.

Why is there absolutely no documentation giving the opcode encodings for ***ANY*** opcode? Yes.. the ISA documentation shows the opcode format for each opcode, it does NOT give the encoding... WNHY?????????

One clean table stating the opcode mnemonic its opcode type, its bit-field format, the binary content of each bit-field and a description of what said opcode does. Why is this so difficult to produce?

Rishiyur Nikhil

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Jan 25, 2022, 10:13:01 AM1/25/22

to Mark Manning, RISC-V ISA Dev

> Yes.. the ISA documentation shows the opcode format for each opcode, it does NOT give the encoding.

Not sure what you mean.

Chapter 25 (pages 129-136 of "Volume I: RISC-V Unprivileged ISA
V20190608-Base-Ratified" contains tables showing the bit-encondings of
the standard RV32I and RV64I ISAs, and standard extensions M, A, F, D.

Section 16.8 provides full bit-encondings of the C extension.

Or are you referring to some other issue?

Nikhil

Mark Manning

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Jan 25, 2022, 10:17:37 AM1/25/22

to RISC-V ISA Dev, nikhil, RISC-V ISA Dev, Mark Manning

aha i been up and down that docuement getting more and more frustrated by the minute looking for that lol

however, it would be nice if that table showd then opcode type specifer such as R, I, B, J, S etc

ty for the pointer :/

Neel Gala

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Jan 25, 2022, 10:52:43 AM1/25/22

to Mark Manning, RISC-V ISA Dev, nikhil

The riscv-opcodes repo : https://github.com/riscv/riscv-opcodes is also where the encodings could be found (for the ratified and unratified extensions). They are in a more parse-able format. Might be useful.

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