Building an Atari ST

Other FPGA systems, e.g. Turbo Chameleon.

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zerkman
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Building an Atari ST

Post by 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
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Cyprian
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Re: Building an Atari ST

Post by Cyprian »

nice one,
will it be cycle exact?
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slingshot
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Re: Building an Atari ST

Post by 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
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Re: Building an Atari ST

Post by zerkman »

slingshot wrote: Sat Oct 10, 2020 4:13 pm 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
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Re: Building an Atari ST

Post by zerkman »

Cyprian wrote: Sat Oct 10, 2020 3:49 pm 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
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Re: Building an Atari ST

Post by BlankVector »

Congratulations, excellent project!
Subscribe to my Vretrocomputing channel on YouTube and Facebook. Latest video: Replace Atari STE ROMs with EEPROMs.
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jfl
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Re: Building an Atari ST

Post by jfl »

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