Is VIA emulation cycle-exact in VICE xvic?

[groepaz]

the datasheets are also often very vague, or plain wrong, and some aspects are not described at all. you really have to make test programs to verify how it really works.

i have not seen any correct emulation yet either... they are all broken in one way or another.

[lance.ewing]

Looking at the various 6522 implementations (HDL and software) they are all different. How sad.

Yeah, I've noticed that as well. I've had a look at various implementations to get inspiration.

P.S. peeking into JVic's source code but I could not find sound emulation

Yeah, didn't get that far. It is in sore need of some attention. Haven't looked at it in a while, in fact haven't looked at it since I started reversing the 6561 die shot, so there is probably quite a bit on the video side as well that could benefit from the analysis I've been doing. I think it's almost time to get back to it.

Those are the kinds of decisions I need to make from time to time: For example, embark on a new project to reverse the 6522, or switch back to my emulator to incorporate the things I've been learning over the past few years.

Just remembered that my Vectrex emulator also has 6522 emulation, and I think I took what I'd done for the Oric emulator and further enhanced it, because the Vectrex needed the shift register modes to be working properly, since it is involved in controlling the movement of the electron gun in the CRT. So the 6522 code in JVic has been through a couple of evolutions, firstly through work on the JOric emulator, and then the JVectrex emulator, but not yet incorporated back into JVic.

Anyway, take a look at both of these and see if anything can help:

https://github.com/lanceewing/joric/blo ... o/Via.java

https://github.com/lanceewing/jectrex/b ... a6522.java

yes, and there is no emulator that would not benefit from it.

...and maybe one day I'll start looking at the 6522 die shot.

[lance.ewing]

...and maybe one day I'll start looking at the 6522 die shot.

A few days ago, I discovered for the first time bwack's VIC II die shot reverse engineering video series on Youtube. I know its strange that I didn't previously know about it given my own interest in reversing die shots. Quite a task he's taking on because the VIC II die shots currently available are less "see-through" than the 6561 die shot.

In the case of the 6522, we're fortunate to have access to two die shots, one with the metal layer still on, and one with the metal removed. Makes it a lot easier. And it will be purely digital.