riscv-profiles
riscv-bitmanip
riscv-profiles | riscv-bitmanip | |
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21 | 12 | |
87 | 206 | |
- | 2.9% | |
8.0 | 0.0 | |
19 days ago | about 2 months ago | |
Makefile | Makefile | |
Creative Commons Attribution 4.0 | Creative Commons Attribution 4.0 |
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riscv-profiles
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How to improve the RISC-V specification
Ssstrict is supposed to address the undefined behaviour problem, or at least it'll make undefined instructions actually trap.
https://github.com/riscv/riscv-profiles/blob/main/rva23-prof...
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Raspberry Pi receives strategic investment from Arm
>there are a lot of incompatible ISA implementations of RISC-V
This is common FUD.
In reality, most chips in the market, including all known application processors, follow the RVA profile[0] spec.
So do Linux distributions.
0. https://github.com/riscv/riscv-profiles/releases
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You Won’t Believe This One Weird CPU Instruction (2019)
The bit manipulation [0] extension has been ratified for a while now and is part of the RVA22 application extension profile [1].
You can already buy SOCs that support it, e.g. vision five 2 and star64.
Interestingly the risc-v vector has it's own popcount instructions for vector registers/register masks. This is needed, because the scalable architecture doesn't guarantee that a vector mask can fit into a 64 bit register, so vector masks are stored in a single LMUL=1 register. This works really well, because with LMUL=8 and SEW=8 you get 100% utilization of the single LMUL=1 vector register.
Another interesting thing is that the vector crypto extension will likely introduce a element wise popcount instruction.
[0] https://github.com/riscv/riscv-bitmanip/releases/download/1....
[1] https://github.com/riscv/riscv-profiles/blob/main/profiles.a...
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The legend of "x86 CPUs decode instructions into RISC form internally"
That's why we have RISC-V profiles.
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Why is std::hardware_destructive_interference_size a compile-time constant instead of a run-time value?
Yeah more or less. They now have RISC-V Application Profiles which are basically minimum requirements for "application processors" - essentially devices like phones where you might want to distribute binary apps.
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RISC-V Profiles: Defining sets of extensions for coherent ecosystems
The Profiles spec which includes RVA22 was finally ratified[0] last week.
0. https://github.com/riscv/riscv-profiles/releases/tag/v1.0
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RISC-V Profiles
Context: RISC-V profiles spec got ratified last week.
- Questions about standard extensions
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RISC-V Business: Testing StarFive's VisionFive 2 SBC
Yeah unfortunately there isn't really a great place that lists all the extensions with links and ratification status.
But anyway there is a sort of standard set of extensions that "application processors" (I guess CPUs that want to run precompiled code) should support:
https://github.com/riscv/riscv-profiles/blob/main/profiles.a...
The 22 indicates the year.
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TinyEMU – x86 and RISC-V emulator, small and simple while being complete
Ah, you're right: https://github.com/riscv/riscv-profiles/blob/main/profiles.a...
That's good to see. (Boy, it's really hard to find info about RISC-V profiles on Google. It just seems to ignore all the letters and numbers.)
riscv-bitmanip
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You Won’t Believe This One Weird CPU Instruction (2019)
The bit manipulation [0] extension has been ratified for a while now and is part of the RVA22 application extension profile [1].
You can already buy SOCs that support it, e.g. vision five 2 and star64.
Interestingly the risc-v vector has it's own popcount instructions for vector registers/register masks. This is needed, because the scalable architecture doesn't guarantee that a vector mask can fit into a 64 bit register, so vector masks are stored in a single LMUL=1 register. This works really well, because with LMUL=8 and SEW=8 you get 100% utilization of the single LMUL=1 vector register.
Another interesting thing is that the vector crypto extension will likely introduce a element wise popcount instruction.
[0] https://github.com/riscv/riscv-bitmanip/releases/download/1....
[1] https://github.com/riscv/riscv-profiles/blob/main/profiles.a...
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Is Bit Manipulation extension ratified?
According to latest version of spec on GitHub (https://github.com/riscv/riscv-bitmanip) Bit-manip is in frozen state. Is this ratified and not updated in the sepc document or is it actually frozen?
- Hand optimised RISC-V assembly language clz
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Testing for presence of _Zba and _Zbb
I guess 0x20a52533 is a specific _zba instruction? Which one? I searched for "001000" (the left 6 bits of 0x20) in https://github.com/riscv/riscv-bitmanip/releases/download/1.0.0/bitmanip-1.0.0-38-g865e7a7.pdf , but couldn't find a match? Might be PEBKAC.
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A Neat XOR Trick
RISC-V does have a proposed extension Zbb that includes the cpop and cpopw instructions. It doesn't seem to have much recent activity, though.
https://github.com/riscv/riscv-bitmanip/blob/main/bitmanip/i...
- Why aren't there any RISC-V cores with desktop level power?
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Cores with V-extension and Linux support
Enabling B use in dynamically linked libc code will improve every application, especially for example use of orc.b in the C string functions, which is what I invented it for https://github.com/riscv/riscv-bitmanip/issues/41 (using V is even better, but that's optional in RVA22)
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Bitmanip: Missing bit field extract / insert instructions?
[2] https://github.com/riscv/riscv-bitmanip/releases/tag/1.0.0
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gmp: "Risc V is a terrible architecture"
There was a pick instruction, literally named cmov, in an older version of the B (bitmanip) extension (all the good stuff is in extensions). But it seems like it got canned or something, it's not in it anymore (various other interesting instructions were also lost). Silly if you ask me, but I haven't kept up with any of the debate, maybe there's a decent reason..
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RISC-V Int. Ratifies 15 New Specs, Opening Up New RISC-V Design Possibilities
Yoe maybe interested in the just ratified "RISC-V Bit-Manipulation ISA-extensions" https://github.com/riscv/riscv-bitmanip/releases/download/1....
What are some alternatives?
riscv-platform-specs - RISC-V Profiles and Platform Specification
riscv-v-spec - Working draft of the proposed RISC-V V vector extension
xuantie-yocto - Yocto project for Xuantie RISC-V CPU
riscv-sbi-doc - Documentation for the RISC-V Supervisor Binary Interface
openc906 - OpenXuantie - OpenC906 Core
riscv-isa-manual - RISC-V Instruction Set Manual
riscv-crypto - RISC-V cryptography extensions standardisation work.
volk - The Vector Optimized Library of Kernels
nytm-spelling-bee - Generate anagram puzzles like Frank Longo's "Spelling Bee" as in New York Times Magazine
linux-on-litex-vexriscv - Linux on LiteX-VexRiscv
cpu_features - A cross platform C99 library to get cpu features at runtime.