Bsnes smc files1/17/2024 ![]() NGEmu - Not many direct resources, but their forums are unbeatable.This is the absolute best resource you can possibly have. Zophar - This is where I got my start with emulation, first downloading emulators and eventually plundering their immense archives of documentation.I'm more than happy to help with any questions I've been very vague in most of this simply due to the immense complexity. I think I've given a pretty good intro here, but there are a ton of additional areas. If you have any specific questions here, feel free to ask and I'll add the info. I'd go into more detail, but there are a million ways you can go with it. For a hard-drive, you may have a memory mapped area where you place read commands, writes, etc, then read this data back. parts of memory that the device watches for changes to do signaling) and interrupts. This is generally some combination of memory mapped registers (e.g. The actual interface of the device is a bit more complex. This part is generally very straightforward. The functionality is emulated by creating the backing storage, read/write/format routines, etc. Emulating the functionality of the device.There are two sides to emulating a given hardware device: This is pretty straightforward - when your code throws a given interrupt, you look at the interrupt handler table and call the proper callback. Generally, your hardware components will tell the CPU what interrupts it cares about. Interrupts are the primary mechanism that the CPU communicates with hardware. If you use interpretation, you can easily count cycles and emulate proper timing with dynamic/static recompilation, things are a /lot/ more complex. With the NES, you have the PPU (pixel processing unit) which requires that the CPU put pixels into its memory at precise moments. This really has two sides:Ĭertain platforms - especially older consoles like the NES, SNES, etc - require your emulator to have strict timing to be completely compatible. The other side to processor emulation is the way in which you interact with hardware. For more information, Michael Steil has done some great research into static recompilation - the best I've seen. These combine to make static recompilation completely infeasible in 99% of cases. It's been proven that finding all the code in a given binary is equivalent to the Halting problem.compressed, encrypted, generated/modified at runtime, etc) won't be recompiled, so it won't run Code that isn't in the program to begin with (e.g. ![]() This would be a great mechanism if it weren't for the following problems: You end up building a chunk of code that represents all of the code in the program, which can then be executed with no further interference. With static recompilation, you do the same as in dynamic recompilation, but you follow branches. (BTW, most people don't actually make a list of instructions but compile them to machine code on the fly - this makes it more difficult to optimize, but that's out of the scope of this answer, unless enough people are interested) ![]() Then when you hit a given instruction group again, you only have to execute the code from the cache. Once you reach a branch instruction, you compile this list of operations to machine code for your host platform, then you cache this compiled code and execute it. With dynamic recompilation, you iterate over the code much like interpretation, but instead of just executing opcodes, you build up a list of operations. The core problem with interpretation is that it's very slow each time you handle a given instruction, you have to decode it and perform the requisite operation. Your code parses this instruction and uses this information to alter processor state as specified by your processor. With interpretation, you start at the IP (instruction pointer - also called PC, program counter) and read the instruction from memory. For the 6502, you'd have a number of 8-bit integers representing registers: A, X, Y, P, and S you'd also have a 16-bit PC register. Processor state is a conglomeration of the processor registers, interrupt handlers, etc for a given processor target. With all of these paths, you have the same overall goal: execute a piece of code to modify processor state and interact with 'hardware'. There are three ways of handling processor emulation: You build each individual piece of the system and then connect the pieces much like wires do in hardware. Basic idea:Įmulation works by handling the behavior of the processor and the individual components. If I'm a bit too vague on certain things, please ask questions so I can continue to improve this answer. ![]() Many of the things I'm going to describe will require knowledge of the inner workings of processors - assembly knowledge is necessary. I'm going to break it into pieces and then fill in the details via edits. Here are the basic ideas and functional components. ![]()
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