simulieren-6502
W65C02 simulator, written in C/C++, and intended to be usable as an Arduino library.
This project is a result of my wanting to build a 65c02-based handheld. I did design a few iterations of hardware for the purpose, and that was fun, but very time-consuming, and I'd rather not do it again.
In the end, I decided to build a 6502 simulator, run it on an Arduino Due(it has the memory, and definitely the horsepower), and construct the hardware around that.
The /tests directory is no longer used. I have since switched to using Klaus2m5's test suite(here) to avoid writing my own and possibly getting it wrong. Simulieren-6502 passes nearly all the 6502 tests, and I am working on getting it to pass the 65C02 ones as well. The 6502 tests that it fails are:
- The decimal mode ADC/SBC test($2A). As it stands now, ADC and SBC should function correctly in decimal mode.
The 65C02 tests that it fails are:
- TRB/TSB zp/abs($10)
- anything that follows does not execute, for some reason.
Important: This project is intended to simulate the W65C02, as laid out in Programming the 65816, including the 6502, 65C02, and 65802 by David Eyes and Ron Lichty. However, this simulation is not perfect, and this is called out in the source files where relevant.
I am aware that there is at least one other 6502 simulator (on the Arduino forum), and I did take a look into that, but in my opinion, it makes a few design decisions that make it hard to call a library, as opposed to a straight-up program.
I have looked at its code, but not closely, and all of the code in this repository is my own work.
I would prefer to be able to include a library that just handles the 6502 simulation, allowing(and requiring) the user to provide memory, peripherals, etc. external to the simulation itself, and this is what I have built.
Criticisms aside, I did take a few design cues from that project. In particular, separating addressing modes from the actual operations.
For example, SBC Immediate is implemented as sbc(readByte(programCounter++);.
At one stage, I did try to decode the opcodes as a real 6502 would, but I found it too difficult to wrap my head around, so I just used a massive switch statement. I spread this switch across a few files in order to break it up, which may or may not have been a mistake.
A very nice side-effect of building this as a pure simulation is that it's not limited to the Arduino platform. This compiles with GCC under WSL perfectly fine, and should work just fine under a real Linux install(although this is not tested). Getting it to work under MSVC might take a bit of work, but I don't know, since I don't use it.