Building an Atari ST

[zerkman]

Hi,

I am currently working on implementing an Atari ST on a FPGA board. I know it is not the first project of this kind, but it is mostly for me to familiarize and improve my skills in FPGA development.

I am starting a series of articles on this project, and I will talk about both FPGAs and the internals of the ST.

You can find the first introductory article here:
http://zerkman.sector1.fr/index.php?pos ... n-Atari-ST

thanks

zerkman

[Cyprian]

nice one,
will it be cycle exact?

[slingshot]

It's a nice exercise.
For creating a cycle-exact replica, this is a bit naive:

The general idea on how I designed those custom chips is by trying to implement each of the functionalities in the simplest possible way. I guess by doing this I get as close as I can to the real way those things work. The Atari engineers would probably have done the same or similar way, to minimize the required logic.

What is simple today, wasn't that simple in the 80's. For example, using D-type flip-flops everywhere could use a lot of transistors. You can find the schematics of the STe chipset recovered by @zietz, also @ijor posted some schematics of the shifter. They're far from being intuitively designed (by today's point of view).

[zerkman]

What is simple today, wasn't that simple in the 80's. For example, using D-type flip-flops everywhere could use a lot of transistors. You can find the schematics of the STe chipset recovered by @zietz, also @ijor posted some schematics of the shifter. They're far from being intuitively designed (by today's point of view).

Yes I agree with that. I know some choices that I can make will be different than those taken in the 80’s. What matters is that the implemented chips behave the same than the original ones. It’s more about reverse engineering than perfect replication.

[zerkman]

nice one,
will it be cycle exact?

I’m trying to get as close as cycle exact as possible. All the project is centered around ijor’s fx68k cycle-exact 68000 core. Also the GLUE timings are based on troed’s scanlines description, in colour modes. For monochrome mode I based the timings from a book.

[BlankVector]

Congratulations, excellent project!

[jfl]

Indeed, good project. And once you've honed your skills don't forget the FireBee needs FPGA coders