4 ms·

You're correct but I guess my thoughts are if we're going to wind up with a mess of extensions, why not just use x86-64?

whaleofatw2022 8mo ago
Because the ISA is not encumbered the way other ISAs are legally, and there are use cases where the minimal profile is fine for the sake of embedded whatever vs the cost to implement the extensions
computably 8mo ago
> why not just use x86-64? Uh, because you can't? It's not open in any meaningful sense.
- userbinator 8mo ago
  The original amd64 came out in 2003. Any patents on the original instruction set have long expired, and even more so for 32-bit x86.
  - panick21_ 8mo ago
    Its not about patents. Believe what you want but there is a reason nobody else is doing x86 or ARM chips unless they are allowed by the owner.
    - dbdr 8mo ago
      You're probably right. It would be helpful to say what the reason is, if it's not patents.
      - panick21_ 8mo ago
        I'm not a lawyer but I would assume its copyright. Kind of like API in software. In software somehow this does not apply most of the time. But it seems in hardware this is very real. But I would appreciate a lawyer jumping in. I know for example that Berkley when thinking pre-RISC-V that they had a deal with Intel about using x86-64 for research. But they were not able to share the designs.
        MarsIronPI 8mo ago
        I don't know why there aren't independent X86-64 manufacturers. Patents on the extensions maybe? But as I understand copyright, APIs can't be copyrighted so it's not that.
        panick21_ 8mo ago
        The original ARM 32 stuff is clearly out of patents and is not being copied. And it doesn't require new extensions to be commercially viable.
        userbinator 8mo ago
        and is not being copied Are you sure, especially considering China? I doubt there is any legal barrier, because there are a few existing projects with x86 cores on an FPGA, as well as some SoCs. Here's a 486: https://opencores.org/projects/ao486 https://opencores.org/projects/ao486
        panick21_ 8mo ago
        Ok if China is doing something only for China market that tells you something. As for opencores, yes you can design them, but do any companies making commercial products sell them?
        sidewndr46 7mo ago
        I'm reasonably certain at least one Chinese fab has a license for some of AMDs older product lines
LeFantome 8mo ago
First, x86-64 also has “extensions” such as avx, avx2, and avx512. Not all “x86-64” CPUs support the same ones. And you get things like svm on AMD and avx on Intel. Remember 3DNow? X86-64 also has “profiles” which tell you what extensions should be available. There is x86-64v1 and x86-64v4 with v2 and v3 in the middle. RVA23 offers a very similar feature-set to x86-64v4. You do not end up with a mess of extensions. You get RVA23. Yes, RVA23 represents a set of mandatory extensions. The important thing is that two RVA23 compliant chips will implement the same ones. But the most important point is that you cannot “just use x86-64”. Only Intel and AMD can do that. Anybody can build a RISC-V chip. You do not need permission.
- BoredomIsFun 8mo ago
  1. Yes, but most of the code would run on anything older than 2007. 20 years of stable ISA. 2. Also, fundamentally all modern CPUs are still 64-bit version of 80386. MMU, protection, low level details are all same.
  - sidewndr46 8mo ago
    This isn't really accurate, lots of commercial software is now compiled for newer x86 64 extensions. If you're using OSS it doesn't really matter as you can compile it for whatever you want.
    - NetMageSCW 8mo ago
      No, you really can’t. For some OSS, on hardware that has an OS supported by that software, with a compiler that supports that target and the options you want, and in some cases where the OSS has been written to support those options, you can compile it. Otherwise you are just out of luck.
      - sidewndr46 8mo ago
        I don't really understand your position here. Compiler availability isn't really that big of a deal, even on obscure or proprietary platforms. Why would there be "some cases where the OSS has been written to support those options"?

whaleofatw2022 8mo ago

Because the ISA is not encumbered the way other ISAs are legally, and there are use cases where the minimal profile is fine for the sake of embedded whatever vs the cost to implement the extensions

computably 8mo ago

> why not just use x86-64? Uh, because you can't? It's not open in any meaningful sense.

userbinator 8mo ago
The original amd64 came out in 2003. Any patents on the original instruction set have long expired, and even more so for 32-bit x86.
- panick21_ 8mo ago
  Its not about patents. Believe what you want but there is a reason nobody else is doing x86 or ARM chips unless they are allowed by the owner.
  - dbdr 8mo ago
    You're probably right. It would be helpful to say what the reason is, if it's not patents.
    - panick21_ 8mo ago
      I'm not a lawyer but I would assume its copyright. Kind of like API in software. In software somehow this does not apply most of the time. But it seems in hardware this is very real. But I would appreciate a lawyer jumping in. I know for example that Berkley when thinking pre-RISC-V that they had a deal with Intel about using x86-64 for research. But they were not able to share the designs.
      - MarsIronPI 8mo ago
        I don't know why there aren't independent X86-64 manufacturers. Patents on the extensions maybe? But as I understand copyright, APIs can't be copyrighted so it's not that.
        panick21_ 8mo ago
        The original ARM 32 stuff is clearly out of patents and is not being copied. And it doesn't require new extensions to be commercially viable.
        userbinator 8mo ago
        and is not being copied Are you sure, especially considering China? I doubt there is any legal barrier, because there are a few existing projects with x86 cores on an FPGA, as well as some SoCs. Here's a 486: https://opencores.org/projects/ao486 https://opencores.org/projects/ao486
        panick21_ 8mo ago
        Ok if China is doing something only for China market that tells you something. As for opencores, yes you can design them, but do any companies making commercial products sell them?
        sidewndr46 7mo ago
        I'm reasonably certain at least one Chinese fab has a license for some of AMDs older product lines

LeFantome 8mo ago

First, x86-64 also has “extensions” such as avx, avx2, and avx512. Not all “x86-64” CPUs support the same ones. And you get things like svm on AMD and avx on Intel. Remember 3DNow? X86-64 also has “profiles” which tell you what extensions should be available. There is x86-64v1 and x86-64v4 with v2 and v3 in the middle. RVA23 offers a very similar feature-set to x86-64v4. You do not end up with a mess of extensions. You get RVA23. Yes, RVA23 represents a set of mandatory extensions. The important thing is that two RVA23 compliant chips will implement the same ones. But the most important point is that you cannot “just use x86-64”. Only Intel and AMD can do that. Anybody can build a RISC-V chip. You do not need permission.

BoredomIsFun 8mo ago
1. Yes, but most of the code would run on anything older than 2007. 20 years of stable ISA. 2. Also, fundamentally all modern CPUs are still 64-bit version of 80386. MMU, protection, low level details are all same.
- sidewndr46 8mo ago
  This isn't really accurate, lots of commercial software is now compiled for newer x86 64 extensions. If you're using OSS it doesn't really matter as you can compile it for whatever you want.
  - NetMageSCW 8mo ago
    No, you really can’t. For some OSS, on hardware that has an OS supported by that software, with a compiler that supports that target and the options you want, and in some cases where the OSS has been written to support those options, you can compile it. Otherwise you are just out of luck.
    - sidewndr46 8mo ago
      I don't really understand your position here. Compiler availability isn't really that big of a deal, even on obscure or proprietary platforms. Why would there be "some cases where the OSS has been written to support those options"?