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#6502 emulator javascript how to#
#6502 emulator javascript code#
#6502 emulator javascript Pc#

The important things about this processor that we need to know in order to emulate it are: The 6502 was a popular CPU for its time, being used in the Atari 2600, Apple IIe, Commodore 64, BBC Micro, the original Nintendo Entertainment System (the CPU for the NES was actually a custom Ricoh chip, but it executed 6502 instructions), and many others. There’s a fair bit of ground to cover, so you might want to grab a cup of your favorite beverage before diving in! Enter: The 6502 I will also attach useful links at the end for those who are interested in doing further research on their own.

#6502 emulator javascript code#

Although the recompiler itself will be presented in C++, having a basic understanding of x86 assembly will be helpful.Īll of the source code shown here is attached to the end of this post, so you don’t need to worry about copying the code from this text.

#6502 emulator javascript how to#

I will show how to implement a recompiler for a very small subset of the 6502 CPU instruction set which will compile into 32-bit Intel x86 code, and then show how to execute the recompiled code in a Win32 application. Since describing how to write a complete emulator would easily fill a large book, I’ve decided to just start off with the minimal basics for this first part. The recompilation operation itself of course takes time to execute, but these recompiled blocks can be cached and reused next time the emulated CPU executes that specific area of memory, hence providing near real-time performance. This technique recompiles a group of CPU instructions - typically until a branch instruction is encountered - into exact or similar instructions for the native CPU, and then directly executes them. In order to get any kind of decent speed out of an emulator, a technique known as JIT (Just-In-Time compilation) or dynamic recompilation is used.

Repeat until the user quits your emulator because he’s tired of looking at a blank screen, and proceeds to send you hate mail complaining that the emulator doesn’t work.Īlthough this technique is fairly easy to implement, it doesn’t perform very well.

Decode the opcode, calling the appropriate function which implements that opcode’s functionality,.

Fetch the next CPU instruction (opcode) at the current instruction pointer,.

Basically, an interpreted emulator performs the following steps: Because the CPU emulation core I wrote used interpreted emulation, it was also horribly slow. Many many moons ago, I developed a Nintendo 64 emulator called Project UnReality. Regardless of the actual platform being emulated, the process of changing foreign machine code into native code is the same for every emulator. Since then, emulation techniques have improved drastically and emulators are now quite commonplace - executing Java byte code, for example, can be considered a form of emulation.

#6502 emulator javascript Pc#

The performance at the time was horribly slow, but seeing my favorite Nintendo games running on my PC was like magic to me. Emulation has been something I’ve been interested in for a very long time now, ever since I first fired up Pasofami after school that one day and saw Super Mario Brothers running in a window on my 486 PC.