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It didn't occur to me until I was developing a Game Boy Color game to understand just how difficult it would be to create an accurate emulator. For Infinity (h

It didn't occur to me until I was developing a Game Boy Color game to understand just how difficult it would be to create an accurate emulator. For Infinity (https://news.ycombinator.com/item?id=12291850 https://news.ycombinator.com/item?id=12291850) we employed a number of tricks, notably changing video parameters mid-render. For example, when walking around on the overworld, the screen looks tilted. This was done by adjusting the camera's X offset after each scanline. Before this experience, I would have thought all an emulator needs to do is emulate the CPU, and render video frames as fast as possible based on video memory. Instead, the GPU needs to be fully emulated too, drawing pixels from top to bottom and left to right, at exactly the rate expected of real hardware and in sync with the CPU. Speaking of hardware tricks, one neat thing we discovered during development was that if a cartridge isn't present, then reading from the ROM memory area returned zeros. This was possible to do if your code was running from RAM and could survive a cartridge being taken out while it was running. This only worked with Game Boy Color (and not original Game Boy) because Nintendo removed the safety lock from the power switch. There is actually code in Infinity to do something with this, although it is unfinished. Just another ridiculous thing emulator authors would have to support somehow. :)

digi_owl 9y ago
The GBC is basically a handheld NES. And changing parameters mid-scanline was a trick on various microcomputers as well (i think it was used on the Amiga to push up the number of colors you could use by swapping the pallette). And i am not surprised that a non-cartridge would read zeros. I suspect the GB(C) was set up somewhat similar to the C64, where the cartridge connector on the back was basically wired to certain RAM pins on CPU.
- eru 9y ago
  > The GBC is basically a handheld NES. Do they just have roughly comparable computational power--or do they actually share some chips?
  - eropple 9y ago
    The GBC is a significantly more powerful machine than an NES, with some caveats around graphical rendering. The NES is a MOS 6502, the GBC has a weird chip by Sharp that hybridizes a Zilog Z80 and an Intel 8080 clocked about double in Game Boy mode and quadruple in GBC mode. The GBC also has sixteen times more RAM, eight times more VRAM, supports bigger carts (up to a megabit), and twice the palettized colors on screen, albeit with marginally fewer sprites. Huge difference in hardware--the primary reason the GBC is looked at as being "NES-like" is because of the lateness of its release and the comparative jump to the GBA, which is a recognizably modern ARM environment.
  - khedoros1 9y ago
    They don't share chips, and the GBC should be much more powerful than the NES. The NES had a CPU based on the MOS Technology 6502 running at around 1MHz, 2KB of RAM, 2 screens of video tile memory, and 2 sprite layers, with support for 64 sprites, max of 8 per line. The GBC had a CPU loosely based on a Z80 running at about 4 or 8MHz, 32KB of RAM, smaller resolution, more colors available (and more displayable on-screen at once), fewer sprites (40), but more displayable on one line (10).
    - eropple 9y ago
      > CPU loosely based on a Z80 Emphasis on "loosely". It's a weird thing. https://realboyemulator.wordpress.com/2013/01/01/the-nintendo-game-boy-1/ https://realboyemulator.wordpress.com/2013/01/01/the-nintend...
  - gens 9y ago
    Interesting talk: "The Ultimate Game Boy Talk" at CCC https://media.ccc.de/v/33c3-8029-the_ultimate_game_boy_talk https://media.ccc.de/v/33c3-8029-the_ultimate_game_boy_talk
  - digi_owl 9y ago
    Sorry, i didn't mean it in technical terms. But as best i understand it, the basic conceptual design of the GB/GBC and the NES is pretty much the same. Neither device do much if anything without a cartridge inserted. This unlike say a modern game console that have quite elaborate firmware that loads even without any game media present.
- jkarneges 9y ago
  What surprised me was that the GBC didn't abruptly crash. For something as critical as a memory chip going missing I would have expected either an abrupt halt due to inconsistent circuitry, or a halt on the next read to the ROM's addressable memory. That the CPU instructions would gracefully fall back to interpreting memory as zeros was unexpected to me. Although I don't know much about electronics. Do you think this would work on other consoles, such as the NES? Given how finicky the NES is about the cartridge loading mechanism, I would think that cart removal while a game is running would cause the system to go into that panic mode with the power light flashing.

digi_owl 9y ago

The GBC is basically a handheld NES. And changing parameters mid-scanline was a trick on various microcomputers as well (i think it was used on the Amiga to push up the number of colors you could use by swapping the pallette). And i am not surprised that a non-cartridge would read zeros. I suspect the GB(C) was set up somewhat similar to the C64, where the cartridge connector on the back was basically wired to certain RAM pins on CPU.

eru 9y ago
> The GBC is basically a handheld NES. Do they just have roughly comparable computational power--or do they actually share some chips?
- eropple 9y ago
  The GBC is a significantly more powerful machine than an NES, with some caveats around graphical rendering. The NES is a MOS 6502, the GBC has a weird chip by Sharp that hybridizes a Zilog Z80 and an Intel 8080 clocked about double in Game Boy mode and quadruple in GBC mode. The GBC also has sixteen times more RAM, eight times more VRAM, supports bigger carts (up to a megabit), and twice the palettized colors on screen, albeit with marginally fewer sprites. Huge difference in hardware--the primary reason the GBC is looked at as being "NES-like" is because of the lateness of its release and the comparative jump to the GBA, which is a recognizably modern ARM environment.
- khedoros1 9y ago
  They don't share chips, and the GBC should be much more powerful than the NES. The NES had a CPU based on the MOS Technology 6502 running at around 1MHz, 2KB of RAM, 2 screens of video tile memory, and 2 sprite layers, with support for 64 sprites, max of 8 per line. The GBC had a CPU loosely based on a Z80 running at about 4 or 8MHz, 32KB of RAM, smaller resolution, more colors available (and more displayable on-screen at once), fewer sprites (40), but more displayable on one line (10).
  - eropple 9y ago
    > CPU loosely based on a Z80 Emphasis on "loosely". It's a weird thing. https://realboyemulator.wordpress.com/2013/01/01/the-nintendo-game-boy-1/ https://realboyemulator.wordpress.com/2013/01/01/the-nintend...
- gens 9y ago
  Interesting talk: "The Ultimate Game Boy Talk" at CCC https://media.ccc.de/v/33c3-8029-the_ultimate_game_boy_talk https://media.ccc.de/v/33c3-8029-the_ultimate_game_boy_talk
- digi_owl 9y ago
  Sorry, i didn't mean it in technical terms. But as best i understand it, the basic conceptual design of the GB/GBC and the NES is pretty much the same. Neither device do much if anything without a cartridge inserted. This unlike say a modern game console that have quite elaborate firmware that loads even without any game media present.
jkarneges 9y ago
What surprised me was that the GBC didn't abruptly crash. For something as critical as a memory chip going missing I would have expected either an abrupt halt due to inconsistent circuitry, or a halt on the next read to the ROM's addressable memory. That the CPU instructions would gracefully fall back to interpreting memory as zeros was unexpected to me. Although I don't know much about electronics. Do you think this would work on other consoles, such as the NES? Given how finicky the NES is about the cartridge loading mechanism, I would think that cart removal while a game is running would cause the system to go into that panic mode with the power light flashing.