riscv-asm-manual
riscv-isa-manual
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riscv-asm-manual
- RISC-V Assembler: Arithmetic
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RISC-V assembler input file format
This document has most of the explanations about the input format: https://github.com/riscv-non-isa/riscv-asm-manual/blob/master/riscv-asm.md. There are some small missing bits but all the directives like .text are there.
- If you were to start your coding journey from zero, what would be your plan?
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Question about RISC-V development
The is a C and C++ toolchain available https://github.com/riscv-collab/riscv-gnu-toolchain If you feeling brave, https://github.com/riscv-non-isa/riscv-asm-manual/blob/master/riscv-asm.md
- Is there any documentation relates to the riscv-gnu-toolchain ?
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Examples of RISC-V Assembly Programs
> Note: "jalr zero, 1b" can also be written as "j 1b", "jalr zero, 0(ra)" can be written as "ret"
`j` and `ret` are so-called "pseudo instructions" [1], not compressed instructions.
Pseudo instructions are just shortcuts used in assembly language to pretend that some common operations really "exist" with the need to type (or display) the real, more complex instructions. `nop` is a common pseudo instruction. RISC-V has `nop` instructions, but, instead, the "do nothing instruction" is canonically encoded as `addi x0, x0, 0`.
The compressed instruction set (a.k.a "extension C") is a subset of the full [2] instruction set, in which a restricted combinations of operands are possible. The assembly (human readable) code of the compressed instruction set looks similar to that of the full instruction set (including pseudo instructions), but they are encoded as completely different binary sequences.
[1] https://github.com/riscv/riscv-asm-manual/blob/master/riscv-...
[2] https://riscv.org/wp-content/uploads/2019/06/riscv-spec.pdf#...
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RISCV Assembly and absolute addressing ?
This should be helpful https://github.com/riscv/riscv-asm-manual/blob/master/riscv-asm.md
- Absolute beginner to RISC-V, where do I start?
riscv-isa-manual
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The Improved RISC-V Specification (latest WIP draft)
https://github.com/riscv/riscv-isa-manual/releases
Regarding the recent "How to improve the RISC-V specification" post [0], I just wanted to point out, that the latest draft manual is already a great improvement. (see link above)
It includes a lot of the newly ratified extensions: bitmanip,zicond,vector,vector crypto, ...
And there are a bunch of included SAIL definitions for bitmanip and zicond, but other instructions are still missing the SAIL code. Most notably, the SAIL definitions from the RV32I/RV64I base isa are also missing.
I asked for the further SAIL integration plans here: https://github.com/riscv/riscv-isa-manual/issues/1369
Here is an example SAIL snippet from cpopw:
let bitcount = 0;
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How to improve the RISC-V specification
I encourage you to look at the newest isa manual draft on github: https://github.com/riscv/riscv-isa-manual/releases
It includes the more recently extensions, and e.g. the bitmanip instructions all have associated pseudo code.
Here is e.g. the code for cpopw:
let bitcount = 0;
- Need help with designing a basic RISC V processor?
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The legend of “x86 CPUs decode instructions into RISC form internally”
I tried searching the spec [1] for "overflow" and here is what it says at page 17:
> We did not include special instruction-set support for overflow checks on integer arithmetic operations in the base instruction set, as many overflow checks can be cheaply implemented using RISC-V branches.
> For general signed addition, three additional instructions after the addition are required
Is this "cheap", replacing 1 instruction with four? According to some old mainframe era research (cannot find link now), addition is the most often used instruction and they suggest that we should replace each one with four?
Their "rationale" is not rational at all. It doesn't make sense.
Overflow check should be free (no additional instructions required), otherwise we will see the same story we have seen for last 50 years: compiler writers do not want to implement checks because they are expensive; language designers do not want to use proper arithmetic because it is expensive. As a result, there will be errors and vulnerabilities. A vicious circle.
[1] https://github.com/riscv/riscv-isa-manual/releases/download/...
- 64-bit Arm ∩ 64-bit RISC V
- Beginner question: F extension
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Riscv Ghidra Instruction Manual
Why not use the actual release PDF instead from their github? https://github.com/riscv/riscv-isa-manual
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How would I go about designing an 8-bit RISC-V CPU? Is it possible?
https://github.com/riscv/riscv-isa-manual/releases/download/Priv-v1.12/riscv-privileged-20211203.pdf Part 2
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Have to convert a C language code into RISC-V MIPS
If you don't want to cheat then read the RISC-V ISA manual: https://github.com/riscv/riscv-isa-manual/releases/download/Ratified-IMAFDQC/riscv-spec-20191213.pdf
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How does a computer understand machine language?
Yeah you are on the right track. Processors are designed on top of an Instruction Set Architecture (ISA). For an example you can look on top of the RISC-V specifications:https://github.com/riscv/riscv-isa-manual/releases/download/Ratified-IMAFDQC/riscv-spec-20191213.pdf (possible PDF download)
What are some alternatives?
riscv-elf-psabi-doc - A RISC-V ELF psABI Document
neorv32 - :rocket: A tiny, customizable and extensible MCU-class 32-bit RISC-V soft-core CPU and microcontroller-like SoC written in platform-independent VHDL.
riscv-emulator-docker-image
glibc - GNU Libc
amaranth - A modern hardware definition language and toolchain based on Python
riscv-gnu-toolchain - GNU toolchain for RISC-V, including GCC
riscv-v-spec - Working draft of the proposed RISC-V V vector extension
arduino-6502ctl - Arduino 6502 Controller
vroom - VRoom! RISC-V CPU
computer-science - :mortar_board: Path to a free self-taught education in Computer Science!
open-source-cs - Video discussing this curriculum: