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Comment by max_ | Hacker News Reader

How do people design emulators? Is there a good resource on how you can learn to do this?

It is really depend on the hardware you want to make the emulator. Usually there are 2 kind:

1. Emulate the whole system. 2. Emulate the system API.

The first one you write the code to emulate the CPU of target system like OP code interpreter (e.g. NES). The second one you write the code to re-implement the API of the target system (e.g. Wine). For the second one you may need to write a JIT compiler if the target system use a different CPU architecture (e.g. PS3).

Most modern console emulator are the later one because how the modern console work is similar to how the PC work. It have an OS kernel and a user-mode libraries for applications.

For the latter one there are 2 kind of it. The first one is emulate the user-mode libraries and the second one is re-implement the console kernel and reuse the system libraries from the console itself.

> Most modern console emulator are the later one because how the modern console work is similar to how the PC work. It have an OS kernel and a user-mode libraries for applications.

And additionally because the past couple of console generations have had x86-64 CPUs, there's no need to do full instruction translation/emulation—something like Wine would suffice.

https://rylev.github.io/DMG-01/public/book/ this is a good read

Thanks. This looks beautiful

If you want to learn, I guess look for something well-documented and comparatively simple, like an old Game Boy emulator

I think if you're new to emulation it's generally a good idea to start with something even simpler - the chip-8 system

http://www.emulator101.com/introduction-to-chip-8.html

An average programmer can probably get an emulator for that running in a weekend, and there are lots of guides and documetnation out there for the opcodes and similar.

NES / Gameboy / GameGear / similar are probably well-documented, but they will be harder at least because the processors have more opcodes you have to care about.

Yeah CHIP8 is a simple enough system that i even made two emulators (one in DOS and one in Windows) and an assembler back in 1999-2000 or so when i was in highschool and could barely put eight bits together to form a byte.

Also somehow for some reason i was convinced back then that mobile phones in the future will have a CHIP8 emulator to play games :-P. Sadly(?) they got Java instead.

I would say this is a good place to start. I did a Game Gear emulator in a single night with a buddy, having never written one before, just for the lulz.

You are bound to have an awesome game you can find on an 8-bit system and it's really fun trying to get to the point where you can play the game: getting the logo to appear, getting the title screen up, getting the sprites working, adding controls etc.

javidx9 (aka OneLoneCoder) on youtube did a pretty good series on how to write a NES emulator from scratch: https://www.youtube.com/watch?v=nViZg02IMQo&list=PLrOv9FMX8x...

There are loads of resources online on how to write a gameboy emulator, these use a straightforward enough architecture that it's pretty easy to follow. I'd recommend starting there in your language of choice.

Have a data structure for CPU registers. Have a data structure for memory. Have a data structure for i/o. Read a series of instructions that are being emulated. Create a series of rules as to how those instructions interact with CPU, memory, i/o, in a mutable fashion. A long if/then/elif/elif/elif/elif/else type loop, or switch case type loop, if you will. Create bridges between particular pieces of memory and system output: video, sound, controllers. That's most of it in the classic case at least. Now you have an emulator.

The "big league" emulators work differently. They may be simple compilers. Instead of compiling C code or java code, they compile machine code from system A to system B. A transpiler. This affords speed beyond the simple case. Speed, however, is only necessary if the machine running the emulator is weak, or if the machine being emulated is strong.

The simplest emulator in the world by Oscar Toledo G.:

https://news.ycombinator.com/item?id=39774932

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