Project: HDMI/DVI out for STFM

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Smonson
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Re: Project: HDMI/DVI out for STFM

Post by Smonson » Wed Aug 29, 2018 12:26 pm

troed wrote:
Wed Aug 29, 2018 12:23 pm
So, since I have one (thanks Smonson for letting me beta test and play around with what it can do!) there's one thing I'd like to point out though. It runs off its own 32MHz clock, which means the ST CPU is running at 8.00MHz. That's no problem - most things will work just fine.

However, a real ST runs at 8.01MHz (old STF), 8.02MHz (PAL STFM, PAL STE) or 8.05MHz (NTSC STE). Since the motherboard has a separate clock for the MFP (the "timer chip") in the ST demo coders have for a long time known that they need to compensate for the difference between the timer clock and the CPU clock. This mostly affects the opening of the lower (and maybe top) border in demos.

A CPU clock of 8.00MHz is "unknown" and some demos will simply not work perfectly. I don't want to exaggerate this as an issue, just pointing it out for purists (like myself ;))
I wasn't aware of this until you mentioned it, but I've looked around on Mouser and those other clock values are easy to obtain. But what happens if you run a demo that was written for an 8.01MHz machine on an 8.05MHz one? Same problem?

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Smonson
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Re: Project: HDMI/DVI out for STFM

Post by Smonson » Wed Aug 29, 2018 12:48 pm

OK, they don't have exactly the right ones after all... These are the ST MHz values I found: 32.0424, 32.04245, 32.084988 (PAL), 32.215905.

Unfortunately Mouser's closest clocks in the right size are: 32, 32.11, 32.263.

If it's slightly out, will the top and bottom border openings develop a cumulative error, or will it be a stable error? If it's stable, it may be offscreen anyway - I'm only showing 20 extra lines on the top border and 20 on the bottom, so there are still quite a few lines that are outside the display area.

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IngoQ
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Re: Project: HDMI/DVI out for STFM

Post by IngoQ » Wed Aug 29, 2018 3:49 pm

sandord wrote:
Wed Aug 29, 2018 11:59 am
Apparently, it's my browser (I see only a small black icon with a cross). If I open the picture URL (http://smonson.com/unmanaged/atari/20171107_210215.jpg) on a separate tab, it works.
Don't see it either. Smonson, could you please upload it to the forum?
Ingo :geek:

“Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away.” - Antoine de Saint-Exupéry

troed
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Re: Project: HDMI/DVI out for STFM

Post by troed » Wed Aug 29, 2018 4:33 pm

Smonson wrote:
Wed Aug 29, 2018 12:26 pm
I wasn't aware of this until you mentioned it, but I've looked around on Mouser and those other clock values are easy to obtain. But what happens if you run a demo that was written for an 8.01MHz machine on an 8.05MHz one? Same problem?
Yes - and some ancient demos do have such problems. Most demo coders (European) learned to sort out 8.01 and 8.02 though, but that was done in ways that won't work with 8.00. What will happen is that the lower border (and maybe top) will either flicker or not be displayed at all. And yeah, it means the clocks you found at Mouser won't help either - too far off.

One solution would of course be to run the FPGA off the system clock - but I understand you need to rewrite all timing code for that to work. And also, I guess you would need different code in the FPGA depending on which motherboard clock it is ...

I just wanted to raise it so that no one gets caught out when their system suddenly doesn't show a particular demo correctly :)

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dhedberg
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Re: Project: HDMI/DVI out for STFM

Post by dhedberg » Wed Aug 29, 2018 9:15 pm

Awesome achievement! I'd be interested in buying one if the sync issues with opening the borders can be solved (I mostly use my ST to watch demos, so would hate to not have the possibility to watch old classics without switching back to the old Shifter).

Do you have any plans on doing something similar for the Falcon? Hijacking the RGB signals and bypassing the DAC?
Daniel, New Beat - http://newbeat.atari.org. Like demos? Have a look at our new Falcon030 demo MORE.

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exxos
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Re: Project: HDMI/DVI out for STFM

Post by exxos » Wed Aug 29, 2018 9:39 pm

I can donate a osc if needs be, not sure what they are, but got stacks of MB for breakers..
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

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Re: Project: HDMI/DVI out for STFM

Post by troed » Wed Aug 29, 2018 10:59 pm

I will discuss my interfacing of this into my doubleST here: viewtopic.php?f=18&t=283&p=8998#p8998

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Smonson
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Re: Project: HDMI/DVI out for STFM

Post by Smonson » Thu Aug 30, 2018 12:23 am

troed wrote:
Wed Aug 29, 2018 4:33 pm
One solution would of course be to run the FPGA off the system clock - but I understand you need to rewrite all timing code for that to work. And also, I guess you would need different code in the FPGA depending on which motherboard clock it is ...
exxos wrote:
Wed Aug 29, 2018 9:39 pm
I can donate a osc if needs be, not sure what they are, but got stacks of MB for breakers..
The problem is the FPGA needs a full digital clock signal, and the ST's board (mine, at least) only has the crystal, with part of the clock circuit completed inside the ST shifter. Maybe it's possible to add a clock generator circuit to the little PCB that plugs into the shifter socket. But it sounds like a bit of a pain.
dhedberg wrote:
Wed Aug 29, 2018 9:15 pm
Awesome achievement! I'd be interested in buying one if the sync issues with opening the borders can be solved (I mostly use my ST to watch demos, so would hate to not have the possibility to watch old classics without switching back to the old Shifter).
Right now most demos don't run properly because the shifter model doesn't behave exactly like the ST shifter that most machines had. I think it does behave like a real ST shifter - but an early, uncommon version (the one that Ijor reverse-engineered). Changing the model is no problem, but I need a demo coder's help to find out where the difference lies.

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Re: Project: HDMI/DVI out for STFM

Post by exxos » Thu Aug 30, 2018 8:15 am

Smonson wrote:
Thu Aug 30, 2018 12:23 am
The problem is the FPGA needs a full digital clock signal, and the ST's board (mine, at least) only has the crystal, with part of the clock circuit completed inside the ST shifter. Maybe it's possible to add a clock generator circuit to the little PCB that plugs into the shifter socket. But it sounds like a bit of a pain.
The ST generates 32Mhz signal, can't you use that then ? All the shifter does is convert that to 16mhz for the MMU.
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

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Smonson
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Re: Project: HDMI/DVI out for STFM

Post by Smonson » Thu Aug 30, 2018 8:24 am

exxos wrote:
Thu Aug 30, 2018 8:15 am
The ST generates 32Mhz signal, can't you use that then ? All the shifter does is convert that to 16mhz for the MMU.
On mine it doesn't, the crystal connects to 2 pins on the shifter to create the resonant circuit, the clean digital signal is only inside the shifter. If you measure one of the pins off the crystal, you get a low-voltage sinewave.

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