Recommended accelerator options for ST

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jamesfmackenzie
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Re: Recommended accelerator options for ST

Postby jamesfmackenzie » Thu May 24, 2018 11:09 am

Greenious wrote:While the FPGA clones certainly got the potential to have the ST/STE replicated 100% hardwarewise, they are not there yet.

There is still work to be done on the custom IC's. A while back someone discovered old schematics of some of the IC's, and I'm sure these findings eventually will find it's way into the FPGA code.

Also, I know that 8-bit clone guys ditched dram in favour of sram in their FPGA clones since these timing issues were made even harder when they also had to take dram refresh into consideration.


Got it. I guess there aren't that many VHDL experts out there either! Hopefully one day we can reach 100% compatibility - really the only way we can preserve the ST the long term once these old machines die on us! :,-(

jamesfmackenzie
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Re: Recommended accelerator options for ST

Postby jamesfmackenzie » Thu May 24, 2018 11:10 am

joska wrote:
jamesfmackenzie wrote:Thanks! Off topic question, but related. If FPGA clones exactly replicate the original hardware, what is the source of incompatibility? The only thing that comes to mind is that they are functional hardware replicas (rather than mirroring the exact logic gate topology in original hardware). Do you know?


You are right. Cycle exact code is used to exploit the shifter to remove borders and/or scroll the display, or to display more colours by changing palette at very exact points. This does not work on the FPGA clones for two reasons:

1. The 68000 implementation is not cycle exact, which means that "synclock" code gets out of sync compared to a real 68000.
2. Even with a cycle exact 68000 it would not work, because border removal and sync scolling techniques depends on implementation details of the shifter which is not present in the FPGA implementation.


Thanks. Theoretically, is it possible to bring the shifter (and any other hardware that matters) into the FPGA implementation? (of course, you need a large enough FPGA ...)

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Re: Recommended accelerator options for ST

Postby joska » Thu May 24, 2018 11:22 am

I guess it's possible, but getting the timings *exactly* right would be very difficult I think.
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