10 ms·

Virtualizing the 6502 on a 6502 with 6o6

189 points by goldenskye 2y ago

vertnerd 2y ago
> Here's the first of my bucket list projects I'm completing which I've intermittently worked on for literally two decades. This one hell of a bucket list you must have. Respect.
userbinator 2y ago
Despite how simple and limited the 6502 is, it's always interesting to see this almost 50-year-old architecture being stretched to new limits. 6502 cores are still found in some SoCs aimed at the ultra-low-cost high-volume market.
- dailykoder 2y ago
  > 6502 cores are still found in some SoCs aimed at the ultra-low-cost high-volume market. What's the reason behind that? Probably just keeping existing, working designs and thus saving R&D costs? Sounds like beating a 10 cent risc-v core would be hard. Edit: When I first read your comment I had to chuckle a bit, because I got the image of a multicore SoC with 6502 6502 cores. That would be a fun project for my FPGA hmmmmmmmm ...
  - themoonisachees 2y ago
    10c per part is incredibly high depending on how low-cost we're talking. If your chip needs very basic processing, and you're going to sell it for less than a cent per chip, you need your core to be basically free. Sure RISC-V is very inexpensive, but for parts like these risc is massive overkill and as a modern core, you'll be spending a lot of die area on a core that should really be an ASIC, but designing an ASIC is expensive so you can just slap a 6502 in that bad boy and call it a day. On the other end of the scale, you'd be surprised to learn that many chips you don't ever interface with as a user contain even ARM cores. These are usually ASICs in high-end products.
    - jeffgreco 2y ago
      Go on!
    - snvzz 2y ago
      >but for parts like these risc is massive overkill You seem to underestimate how small a RISC-V core can be. Take a look at SERV.
      - irdc 2y ago
        There’s also the cost of rewriting (yes, from assembler) all the existing code. And don’t forget QA.
      - monocasa 2y ago
        The area of just the register file (even for rv32e) is higher area than the survivors of the 8 bit ucontrollers.
        snvzz 2y ago
        Not true for SERV vs 6502. SERV is smaller.
        userbinator 2y ago
        16 registers * 32 bits * 4 transistors / cell = 2k transistors just for storing the bits alone, and that's not including the decoding and read/write circuitry.
        snvzz 2y ago
        There is no need to do weird math, as we know the actual numbers. 6502 has 3510 transistors. SERV at CMOS occupies 2.1kGE. SERV is smaller than 6502.
        monocasa 2y ago
        Gate Elements are multiple transistors. And that count doesn't include SERV's register file.
  - deleted 2y ago
    [deleted]
  - utensil4778 2y ago
    A lot of cheap USB1/2 widgets are actually a 6800 core. It's crazy how these old CPUs have stuck around for so long
- ddingus 2y ago
  There is a ton of code out there for pretty much any task you want. I have the 16 bit successor, the 65816, on a variable speed expansion card in my Apple 2. I run it in 8 bit mode most of the time mostly because it works and most library code is 8 bit. At those speeds, the chip is fast! Especially when one considers the simple model: ram clocked 1:1 with the cpu. In my case, I can run code over the 1Mhz bus, essentially turning most multi cycle ops into a single bus cycle per memory fetch. Or, the card has a megabyte of RAM and that runs at CPU speed. (0.15 to 16 Mhz) When doing that, it is fast enough to run large programs, written in higher level languages, at a useful speed. Of course Assembly language is crazy fast. It is a pretty fun environment to hack around in.
sitkack 2y ago
This post has been hanging out with no comments for ages. I was like, I'll skim it later. > It's almost burying the lede to announce that, though, because the real meat in this entry is how the Commodore 64 manages to emulate a very different 6502-based system. That piece is "6o6," for "6502-on-6502," and is a full virtualized software NMOS 6502 CPU that runs on a 6502 CPU — which I've open-sourced too. It has full control of guest code execution, including trapping undocumented and jam opcodes, and completely abstracts all memory access, making it possible to remap addresses, intercept illegal reads or writes, or even run entirely from virtual memory. On top of that, it's complete enough to not only pass a full functional test but also virtualize itself virtualizing itself: This is incredible! Not just from a 6502 perspective, but from an everything perspective! Amazing work. Also, it reminded me of this "The Zilog Z80 has a Protected Mode" https://www.youtube.com/watch?v=DLSUAVPKeYk https://www.youtube.com/watch?v=DLSUAVPKeYk posted to hn, but got no discussion.
- deleted 2y ago
  [deleted]
- FLT8 2y ago
  Also related: C64 booting Linux by emulating a RISC-V processor: https://hackaday.com/2023/08/27/linux-on-a-commodore-64/ https://hackaday.com/2023/08/27/linux-on-a-commodore-64/
  - sitkack 2y ago
    Wow! > There is a catch (rather: a couple) of course: It runs extremely slowly and it needs a RAM Expansion Unit (REU), as there is no chance to fit it all into just 64KiB. > It even emulates virtual memory with an MMU. https://github.com/onnokort/semu-c64 https://github.com/onnokort/semu-c64
  - userbinator 2y ago
    That reminds me of this similar project using an ARM emulator instead: https://news.ycombinator.com/item?id=5581851 https://news.ycombinator.com/item?id=5581851
- 2y ago
drpossum 2y ago
https://archive.fo/2u3Y8 https://archive.fo/2u3Y8
- aspenmayer 2y ago
  https://web.archive.org/web/20240512030623/http://oldvcr.blogspot.com/2024/04/virtualizing-6502-with-6o6-and.html https://web.archive.org/web/20240512030623/http://oldvcr.blo...
andrea76 2y ago
Can it run GEOS in a GEOS window?
varispeed 2y ago
I had goosebumps reading it. I will have to read again and again... Amazing!
cobbzilla 2y ago
This is amazing. It brings back memories of the first time I taught myself 6502 assembly, there was a book called “The Visual Computer” that came with an emulator on a floppy disk. It was very eye opening! I found a PDF of the book [1] but not sure if the software on the floppy survives anywhere. [1] https://files.commodore.software/reference-material/books/c64-books/c64-programming-books/assembly-and-machine-language/the-visible-computer-6502.pdf https://files.commodore.software/reference-material/books/c6...
- deleted 2y ago
  [deleted]
- pvg 2y ago
  Not sure about the C64 one but I've seen the Apple ][ one on the software archive sites before sites before. It's The Visible Computer, a reference to these educational models: https://americanhistory.si.edu/collections/nmah_214319 https://americanhistory.si.edu/collections/nmah_214319 'Visual 6502' is the name of the modern gate and transistor level 6502 simulators: http://visual6502.org/JSSim/index.html http://visual6502.org/JSSim/index.html
  - cobbzilla 2y ago
    Thank you, you’re right, I remembered the name wrong. It was The Visible Computer. I was learning on an Apple //c

189 points by goldenskye 2y ago

> Here's the first of my bucket list projects I'm completing which I've intermittently worked on for literally two decades. This one hell of a bucket list you must have. Respect.

userbinator 2y ago

Despite how simple and limited the 6502 is, it's always interesting to see this almost 50-year-old architecture being stretched to new limits. 6502 cores are still found in some SoCs aimed at the ultra-low-cost high-volume market.

dailykoder 2y ago
> 6502 cores are still found in some SoCs aimed at the ultra-low-cost high-volume market. What's the reason behind that? Probably just keeping existing, working designs and thus saving R&D costs? Sounds like beating a 10 cent risc-v core would be hard. Edit: When I first read your comment I had to chuckle a bit, because I got the image of a multicore SoC with 6502 6502 cores. That would be a fun project for my FPGA hmmmmmmmm ...
- themoonisachees 2y ago
  10c per part is incredibly high depending on how low-cost we're talking. If your chip needs very basic processing, and you're going to sell it for less than a cent per chip, you need your core to be basically free. Sure RISC-V is very inexpensive, but for parts like these risc is massive overkill and as a modern core, you'll be spending a lot of die area on a core that should really be an ASIC, but designing an ASIC is expensive so you can just slap a 6502 in that bad boy and call it a day. On the other end of the scale, you'd be surprised to learn that many chips you don't ever interface with as a user contain even ARM cores. These are usually ASICs in high-end products.
  - jeffgreco 2y ago
    Go on!
  - snvzz 2y ago
    >but for parts like these risc is massive overkill You seem to underestimate how small a RISC-V core can be. Take a look at SERV.
    - irdc 2y ago
      There’s also the cost of rewriting (yes, from assembler) all the existing code. And don’t forget QA.
    - monocasa 2y ago
      The area of just the register file (even for rv32e) is higher area than the survivors of the 8 bit ucontrollers.
      - snvzz 2y ago
        Not true for SERV vs 6502. SERV is smaller.
      - userbinator 2y ago
        16 registers * 32 bits * 4 transistors / cell = 2k transistors just for storing the bits alone, and that's not including the decoding and read/write circuitry.
        snvzz 2y ago
        There is no need to do weird math, as we know the actual numbers. 6502 has 3510 transistors. SERV at CMOS occupies 2.1kGE. SERV is smaller than 6502.
        monocasa 2y ago
        Gate Elements are multiple transistors. And that count doesn't include SERV's register file.
- deleted 2y ago
  [deleted]
- utensil4778 2y ago
  A lot of cheap USB1/2 widgets are actually a 6800 core. It's crazy how these old CPUs have stuck around for so long
ddingus 2y ago
There is a ton of code out there for pretty much any task you want. I have the 16 bit successor, the 65816, on a variable speed expansion card in my Apple 2. I run it in 8 bit mode most of the time mostly because it works and most library code is 8 bit. At those speeds, the chip is fast! Especially when one considers the simple model: ram clocked 1:1 with the cpu. In my case, I can run code over the 1Mhz bus, essentially turning most multi cycle ops into a single bus cycle per memory fetch. Or, the card has a megabyte of RAM and that runs at CPU speed. (0.15 to 16 Mhz) When doing that, it is fast enough to run large programs, written in higher level languages, at a useful speed. Of course Assembly language is crazy fast. It is a pretty fun environment to hack around in.

sitkack 2y ago

This post has been hanging out with no comments for ages. I was like, I'll skim it later. > It's almost burying the lede to announce that, though, because the real meat in this entry is how the Commodore 64 manages to emulate a very different 6502-based system. That piece is "6o6," for "6502-on-6502," and is a full virtualized software NMOS 6502 CPU that runs on a 6502 CPU — which I've open-sourced too. It has full control of guest code execution, including trapping undocumented and jam opcodes, and completely abstracts all memory access, making it possible to remap addresses, intercept illegal reads or writes, or even run entirely from virtual memory. On top of that, it's complete enough to not only pass a full functional test but also virtualize itself virtualizing itself: This is incredible! Not just from a 6502 perspective, but from an everything perspective! Amazing work. Also, it reminded me of this "The Zilog Z80 has a Protected Mode" https://www.youtube.com/watch?v=DLSUAVPKeYk https://www.youtube.com/watch?v=DLSUAVPKeYk posted to hn, but got no discussion.

deleted 2y ago
[deleted]
FLT8 2y ago
Also related: C64 booting Linux by emulating a RISC-V processor: https://hackaday.com/2023/08/27/linux-on-a-commodore-64/ https://hackaday.com/2023/08/27/linux-on-a-commodore-64/
- sitkack 2y ago
  Wow! > There is a catch (rather: a couple) of course: It runs extremely slowly and it needs a RAM Expansion Unit (REU), as there is no chance to fit it all into just 64KiB. > It even emulates virtual memory with an MMU. https://github.com/onnokort/semu-c64 https://github.com/onnokort/semu-c64
- userbinator 2y ago
  That reminds me of this similar project using an ARM emulator instead: https://news.ycombinator.com/item?id=5581851 https://news.ycombinator.com/item?id=5581851
2y ago

drpossum 2y ago

https://archive.fo/2u3Y8 https://archive.fo/2u3Y8

aspenmayer 2y ago
https://web.archive.org/web/20240512030623/http://oldvcr.blogspot.com/2024/04/virtualizing-6502-with-6o6-and.html https://web.archive.org/web/20240512030623/http://oldvcr.blo...

andrea76 2y ago

Can it run GEOS in a GEOS window?

varispeed 2y ago

I had goosebumps reading it. I will have to read again and again... Amazing!

cobbzilla 2y ago

This is amazing. It brings back memories of the first time I taught myself 6502 assembly, there was a book called “The Visual Computer” that came with an emulator on a floppy disk. It was very eye opening! I found a PDF of the book [1] but not sure if the software on the floppy survives anywhere. [1] https://files.commodore.software/reference-material/books/c64-books/c64-programming-books/assembly-and-machine-language/the-visible-computer-6502.pdf https://files.commodore.software/reference-material/books/c6...

deleted 2y ago
[deleted]
pvg 2y ago
Not sure about the C64 one but I've seen the Apple ][ one on the software archive sites before sites before. It's The Visible Computer, a reference to these educational models: https://americanhistory.si.edu/collections/nmah_214319 https://americanhistory.si.edu/collections/nmah_214319 'Visual 6502' is the name of the modern gate and transistor level 6502 simulators: http://visual6502.org/JSSim/index.html http://visual6502.org/JSSim/index.html
- cobbzilla 2y ago
  Thank you, you’re right, I remembered the name wrong. It was The Visible Computer. I was learning on an Apple //c