6502 CPU仿真 [英] 6502 CPU Emulation

问题描述

今天是周末，所以我通过编写一个爱好项目来花整周的时间来放松自己。

It's the weekend, so I relax from spending all week programming by writing a hobby project.

昨天我写了一个MOS 6502 CPU仿真器的框架，寄存器，堆栈，内存和所有操作码均已实现。 （链接到下面的源代码）

I wrote the framework of a MOS 6502 CPU emulator yesterday, the registers, stack, memory and all the opcodes are implemented. (Link to source below)

我可以在编写的调试器中手动运行一系列操作，但是我想加载NES rom并仅指向程序

I can manually run a series of operations in the debugger I wrote, but I'd like to load a NES rom and just point the program counter at its instructions, I figured that this would be the fastest way to find flawed opcodes.

我写了一个快速的NES rom loader并将ROM bank加载到CPU内存中。

I wrote a quick NES rom loader and loaded the ROM banks into the CPU memory.

问题是我不知道操作码是如何编码的。我知道操作码本身遵循每个操作码一个字节的模式，可以唯一地标识操作码

The problem is that I don't know how the opcodes are encoded. I know that the opcodes themselves follow a pattern of one byte per opcode that uniquely identifies the opcode,

0 - BRK
1 - ORA (D,X)
2 - COP b

等

但是我不确定应该在哪里找到操作码参数。是紧随其后的字节吗？在绝对内存中，我想它可能不是字节，而是一个字节。

However I'm not sure where I'm supposed to find the opcode argument. Is it the the byte directly following? In absolute memory, I suppose it might not be a byte but a short.

是否有人熟悉此CPU的内存模型？

Is anyone familiar with this CPU's memory model?

编辑：我意识到这可能是在黑暗，但我希望这里有一些老派的苹果和准将黑客潜伏在这里。

I realize that this is probably shot in the dark, but I was hoping there were some oldschool Apple and Commodore hackers lurking here.

编辑：：谢谢大家的帮助。在执行适当的更改以对齐每个操作之后，CPU可以加载并运行Mario Brothers。它没有做任何事情，而是循环等待开始，但是它是一个好兆头：）

Thanks for your help everyone. After I implemented the proper changes to align each operation the CPU can load and run Mario Brothers. It doesn't do anything but loop waiting for Start, but its a good sign :)

我上传了源代码：

https://archive.codeplex.com/?p=cpu6502

如果有人想知道模拟器的工作方式，那么它很容易理解。至少没有进行优化，但是接下来，我要模拟一个在2.4ghz机器上以2mhz运行的CPU：）

If anyone has ever wondered how an emulator works, its pretty easy to follow. Not optimized in the least, but then again, I'm emulating a CPU that runs at 2mhz on a 2.4ghz machine :)

推荐答案

操作码占一个字节，而操作数位于以下字节中。例如，在此处中查看字节大小列。

The opcode takes one byte, and the operands are in the following bytes. Check out the byte size column here, for instance.

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