Project: HDMI/DVI out for STFM

Progress on our FPGA cores.
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exxos
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Re: Project: HDMI/DVI out for STFM

Post by exxos » Mon Sep 10, 2018 10:56 am

Smonson wrote:
Mon Sep 10, 2018 10:50 am
Yeah, I agree. It could also be bad grounding since my entire board is powered and grounded through a single pin each in an IC socket, which is probably not the best if it's going to draw hundreds of milliamps of current.

The fact that my machine is incredibly stable makes me think that whatever the problem is, it must be near some threshold where I'm just under it and you guys are just over it. It feels like an analogue problem.
Yeah, I see that type of issue all the time. Like with my boosters, can work perfect for days on one machine, then identical other MB and nothing but trouble :( It could be literally anything..

I mean if the ribbon cable is half the length that could make or break something for example. Running gnd through a thin cable isn't likely helping issues.. Might be something else Troed could try, is making the cable as short as possible..
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Re: Project: HDMI/DVI out for STFM

Post by troed » Mon Sep 10, 2018 1:07 pm

Yeah analogue is where I'm lacking all knowledge. Adding a fat ground wire is an immediate thing I can check of course.

Ringing backwards on VSYNC causing GLUE to trip up is actually the best explanation so far as to what can happen that causes _resets_ always ;)

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Re: Project: HDMI/DVI out for STFM

Post by alienkidmj12 » Fri Sep 14, 2018 9:09 pm

this is awesome stuff :) keep up the good work, id buy one for each ste/stfm :)

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Re: Project: HDMI/DVI out for STFM

Post by troed » Sun Sep 16, 2018 12:11 pm

I'm not less confused.

Fatter GND and resistor on VSYNC made no difference. So just to rule out the possibility that the FPGA is fine and _both_ my doubleST and 520ST are weird I pulled up a non-recapped pure stock-as-stock-can-be 1040 STF and put it in there.

Booting without a disk in the drive, or with the floppy disconnected, first gave me a similar impression to the 520. Reset pretty soon after boot, and the the VSYNC LED on the FPGA starts flashing.

But if I insert an original disk (Closure, is what I had close by) there are no resets. The demo runs fine (bar the bitplane and pixel errors in the FPGA emulation that I think can be fixed easily).

If I boot without the drive connected and get to the desktop then that has pixel errors compared to on the 520 where it's perfect, so it's not the case of the 1040STF being "better" at running the FPGA. Now I'll get back to the 520 and connect a floppy drive to it ... haven't tested with that at all before.

(Closure gets rid of TOS directly after the boot sector has loaded the first screen - so this problem might be due to something TOS does ... ??)

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Re: Project: HDMI/DVI out for STFM

Post by troed » Sun Sep 16, 2018 12:25 pm

Wow.

It absolutely is. Connected up an HxC slim to my beautiful internal floppy header in the 520ST and booted ... Closure. No resets at all.

So previously I had looked at /MONOMON with my LA to see if it triggered - since one of the few ways an ST resets cleanly is when TOS detects a mono monitor having been plugged into the monitor port. There's no way I know of for the Shifter to induce that, but hey ...

And of course, a boot sector demo like Closure disables TOS /MONOMON check. So I guess I'll have to think hard about that theory again.

(Removing power from the HxC slim is enough for the 520ST to then start with the spurious resets on the next boot again)

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Re: Project: HDMI/DVI out for STFM

Post by exxos » Sun Sep 16, 2018 12:29 pm

odd.. maybe the FPGA is really sensitive to power rail spikes from the floppy drive or something ?

EDIT:
If you can do a boot sector which would keep the floppy motor turned on right from power up.. maybe that would give some clues ?
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Re: Project: HDMI/DVI out for STFM

Post by Smonson » Sun Sep 16, 2018 1:54 pm

troed wrote:
Sun Sep 16, 2018 12:25 pm
Wow.

It absolutely is. Connected up an HxC slim to my beautiful internal floppy header in the 520ST and booted ... Closure. No resets at all.

So previously I had looked at /MONOMON with my LA to see if it triggered - since one of the few ways an ST resets cleanly is when TOS detects a mono monitor having been plugged into the monitor port. There's no way I know of for the Shifter to induce that, but hey ...

And of course, a boot sector demo like Closure disables TOS /MONOMON check. So I guess I'll have to think hard about that theory again.

(Removing power from the HxC slim is enough for the 520ST to then start with the spurious resets on the next boot again)
Is it possible that the difference is that when running with the FPGA connected, there was no plug in the video out socket, while when you were running an original shifter you always had one plugged in? Perhaps the MONOMON pin could be floating.

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Re: Project: HDMI/DVI out for STFM

Post by Smonson » Sun Sep 16, 2018 3:10 pm

Smonson wrote:
Sun Sep 16, 2018 1:54 pm
Is it possible that the difference is that when running with the FPGA connected, there was no plug in the video out socket, while when you were running an original shifter you always had one plugged in
Hmm, that doesn't make enough sense. I should have thought about it for longer. The plug only grounds the pin for mono, and you weren't using mono mode.

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Re: Project: HDMI/DVI out for STFM

Post by troed » Sun Sep 16, 2018 8:07 pm

Finally, this mystery has been solved. A clue was indeed in why sometimes after reset the videomode wasn't correct.

The resets were caused by TOS detecting a change to mono. A bootsector that immediately disables the TOS reset vector at $46e (resolution change vector) stops the 520ST (where I did the test just now) from resetting.

However, now I can see that if I boot to desktop (low) and then switch to medium I had an immediate "force resolution switch" back to low. That is, not a clean resolution switch by GEM but what you get if you poke at $ff8260 directly.

So, conclusion: The FPGA Shifter causes $ff8260 to respond with wrong values, or even, fluctuating values. At least the prototype I have :)

(... and this is where my own knowledge is a bit lacking, but I have seen this described as the Shifter "owning" that register, as in, holding its contents and being responsible for outputting that data when that memory address is accessed)

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Re: Project: HDMI/DVI out for STFM

Post by exxos » Sun Sep 16, 2018 9:40 pm

troed wrote:
Sun Sep 16, 2018 8:07 pm
(... and this is where my own knowledge is a bit lacking, but I have seen this described as the Shifter "owning" that register, as in, holding its contents and being responsible for outputting that data when that memory address is accessed)
I half recall it was a shadow register in the shifter ?, where the values is held in ram and the shifter ? I might be thinking of something in GLUE and shifter or something, can't exactly remember now .
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