Hi, I'm new. I hope newbie questions about C64 emulation are okay here.

I want to try to write a C64 emulator as a learning exercise. I started with implementing the 6510, which passes all these tests, and bank switching code.

Now when I run the C64 ROMs, the machine keeps running the RAM test (FD6C - FD86) loop forever, when it should be done after ~560k instructions according to VICE.

I currently have no other emulated hardware except for very incomplete CIAs, which I suppose could be the reason for this issue, but I can't tell it's missing hardware, or a bug in the CPU, or in the memory access routines. Can anyone here tell whether an emu should be able to get past this loop with nothing but CPU and memory emulation? I've read the disassembly and from what I understand I think I should be able to pass this RAM test.

Hi,

Not sure about the C64 memory test, but maybe it would help to try swapping-in my MCL65+ 6502 emulator to see if you get the same results? This emulator works in the VIC-20 and Apple II+ actual hardware, so should be able to tell you if the problem is your CPU emulator or your emulated hardware.

https://github.com/MicroCoreLabs/Projec ... L65%2B.ino

-Ted

Welcome grumpy!

If you've narrowed it down to some 30-odd bytes, that should be a help. Please share the code you're running - everyone here knows 6502 but only a fraction know C64. Help us to help you!

Thanks guys, I found the issue. My indirect addressing modes were faulty and the bug wasn't caught by the functional tests. The emulated C64 now completes its entire boot sequence, yay

Good to hear!

It would be great if you could feed the details to Klaus, so he could improve the tests. (It would be enough to describe them here.)

Yeah, I'll try and make a test case for the missed bug. Maybe there should be tests for every addressing mode that fill and compare a couple of RAM pages, just like the C64 RAM test. With my bugged implementation, the same page was tested over and over instead of progressing to the next page. How an error like that could be detected is beyond me though.

withdrawn