4 ms·

I used to contribute to the project back in v1 days. I'm not sure if the architecture has changed since then, but basically it worked by compiling the game logi

I used to contribute to the project back in v1 days. I'm not sure if the architecture has changed since then, but basically it worked by compiling the game logic as a kind of byte code that got interpreted at run time.

Waterluvian 3y ago
Like on top of the CPU’s opcodes? I imagine you mean the opcodes. That CPU probably can’t handle much abstraction. What impresses me the most is that to get performance out of these games, they’re often very carefully coded in the Sharp/Z80/8080 assembly. This compiler must be quite something.
- ehaliewicz2 3y ago
  It actually does interpret bytecode, you can see the opcode definitions here https://github.com/chrismaltby/gb-studio/blob/1f995a976bd3aa5579ed86678912f59ed3a42ddb/appData/src/gb/include/vm.i#L52 https://github.com/chrismaltby/gb-studio/blob/1f995a976bd3aa... The trick is that a lot of the heavier stuff is implemented in assembly and this is mostly used for scripting (from what I understand).
  - djxfade 3y ago
    Yes exactly. It's not a zero cost abstraction, but it's a very simple format, each byte code oppose maps directly to function and passes its args. So it's basically just a conditional jump
    - Waterluvian 3y ago
      Oh wow. So surprised this is viable on a 4 (1, really) MHz processor. Thanks for clarifying and sharing, you both!
      - kmill 3y ago
        You might also like the fact that the Apollo Guidance Computer (which ran at a similar speed) was also programmed using something like bytecodes. It didn't have to drive a graphical display though, only a spaceship.
        Waterluvian 3y ago
        “Only a space ship.” yawns Ahahaha. But my understanding was that they wanted it to be somewhat field programmable? You can tediously write in a program with all the VERB NOUN stuff?
        kmill 3y ago
        The verb/noun stuff I understand was the UI for the astronauts (the DSKY). There was also the native instruction set for the CPU as well as an interpreter with a richer instruction set built on top of that, and they used this to more easily write complex navigation programs. Wikipedia mentions some of this at https://en.wikipedia.org/wiki/Apollo_Guidance_Computer https://en.wikipedia.org/wiki/Apollo_Guidance_Computer around the phrase "virtual machine." I'm not sure it being interpreted code would aid in field reprogrammability, since it would have been woven into the rope memory just like the rest of the software.

Waterluvian 3y ago

Like on top of the CPU’s opcodes? I imagine you mean the opcodes. That CPU probably can’t handle much abstraction. What impresses me the most is that to get performance out of these games, they’re often very carefully coded in the Sharp/Z80/8080 assembly. This compiler must be quite something.

ehaliewicz2 3y ago
It actually does interpret bytecode, you can see the opcode definitions here https://github.com/chrismaltby/gb-studio/blob/1f995a976bd3aa5579ed86678912f59ed3a42ddb/appData/src/gb/include/vm.i#L52 https://github.com/chrismaltby/gb-studio/blob/1f995a976bd3aa... The trick is that a lot of the heavier stuff is implemented in assembly and this is mostly used for scripting (from what I understand).
- djxfade 3y ago
  Yes exactly. It's not a zero cost abstraction, but it's a very simple format, each byte code oppose maps directly to function and passes its args. So it's basically just a conditional jump
  - Waterluvian 3y ago
    Oh wow. So surprised this is viable on a 4 (1, really) MHz processor. Thanks for clarifying and sharing, you both!
    - kmill 3y ago
      You might also like the fact that the Apollo Guidance Computer (which ran at a similar speed) was also programmed using something like bytecodes. It didn't have to drive a graphical display though, only a spaceship.
      - Waterluvian 3y ago
        “Only a space ship.” yawns Ahahaha. But my understanding was that they wanted it to be somewhat field programmable? You can tediously write in a program with all the VERB NOUN stuff?
        kmill 3y ago
        The verb/noun stuff I understand was the UI for the astronauts (the DSKY). There was also the native instruction set for the CPU as well as an interpreter with a richer instruction set built on top of that, and they used this to more easily write complex navigation programs. Wikipedia mentions some of this at https://en.wikipedia.org/wiki/Apollo_Guidance_Computer https://en.wikipedia.org/wiki/Apollo_Guidance_Computer around the phrase "virtual machine." I'm not sure it being interpreted code would aid in field reprogrammability, since it would have been woven into the rope memory just like the rest of the software.