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Re: Project: HDMI/DVI out for STFM

Posted: Sat Jun 23, 2018 10:45 am
by troed
On ST the physical placement of pixels on the screen indeed shifts with 0-3 pixels depending on wakestate, with regular TV/composite/RGB output. All is good if your HDMI solution does the same ;)

Re: Project: HDMI/DVI out for STFM

Posted: Sat Jun 23, 2018 10:56 am
by Smonson
Yep, the position shift matters if you want to use fullscreen no-borders mode, because it'll move the image slightly off the screen.

It's relative to vsync now, but I think hsync and vsync are both generated from the same counters, so if I understand correctly the image is also moving around relative to hsync. It'll be down to the timing that the MMU is generating the DE/LOAD/etc signals.
troed wrote: Sat Jun 23, 2018 10:45 am On ST the physical placement of pixels on the screen indeed shifts with 0-3 pixels depending on wakestate, with regular TV/composite/RGB output. All is good if your HDMI solution does the same ;)
Can the wakestate be determined from the signal timing of LOAD, DE, etc? Right now I'm basically just zooming in on the centre of the screen.

It looks fantastic in 720x400 mode though (more close to a square pixel aspect ratio on a widescreen TV), and you've got 40 pixels of overscan on each side there so a couple of pixels can't be noticed.

Re: Project: HDMI/DVI out for STFM

Posted: Sat Jun 23, 2018 11:07 am
by Methanoid
Does this work for STE? other STs? If so would be great if someone could change the thread title to stop idiots like me asking what may well be obvious to others?

Re: Project: HDMI/DVI out for STFM

Posted: Sat Jun 23, 2018 11:50 am
by IngoQ
Methanoid wrote: Sat Jun 23, 2018 11:07 am Does this work for STE? other STs? If so would be great if someone could change the thread title to stop idiots like me asking what may well be obvious to others?
Actually this has been asked before, here ist the answer:
Smonson wrote: Fri Nov 10, 2017 10:08 pm It's only possible to do this when he ST has a separate, external shifter. The STE shifter is integrated into a great big chip that handles lots of other things as well, so although it seems possible to do the same thing in principle (replace the entire chip by an FPGA), I don't have what I would need to attempt it, such as an STE for starters.

Sorry about that!

Re: Project: HDMI/DVI out for STFM

Posted: Sat Jun 23, 2018 4:16 pm
by troed
Smonson wrote: Sat Jun 23, 2018 10:56 am Can the wakestate be determined from the signal timing of LOAD, DE, etc? Right now I'm basically just zooming in on the centre of the screen.
Yeah if you have cycle accuracy detection of DE and LOAD then you can. The cause of the pixel offset is that the wakestates have different DE-to-LOAD delays. 3,4,5 and 6 cycles respectively for WS2, WS4, WS3 and WS1.

Re: Project: HDMI/DVI out for STFM

Posted: Mon Jun 25, 2018 2:48 pm
by Smonson
troed wrote: Sat Jun 23, 2018 4:16 pm Yeah if you have cycle accuracy detection of DE and LOAD then you can. The cause of the pixel offset is that the wakestates have different DE-to-LOAD delays. 3,4,5 and 6 cycles respectively for WS2, WS4, WS3 and WS1.
I experimented with this and found a correlation. Measuring the latency from DE to LOAD, I observed the following four permutations:

Code: Select all

4 cycles delay => no shift
5 cycles delay => 1 pixel shift
6 cycles delay => 2 pixels shift
7 cycles delay => 3 pixels shift
It's one off from your measurements, so I reckon you're measuring the falling edge of LOAD while I'm measuring the rising edge. Anyway, that seems to have solved the problem! Thanks again Troed!

Re: Project: HDMI/DVI out for STFM

Posted: Wed Aug 29, 2018 9:58 am
by Cyprian
Would be possible to connect it to the ST main ram, or add ram to FPGA, in order to provide additional extended video modes?

Re: Project: HDMI/DVI out for STFM

Posted: Wed Aug 29, 2018 10:14 am
by troed
I have a prototype of this and have run it in a 520ST as well as currently trying to interface it in my accelerated doubleST. I do have issues with the latter, I'm currently delaying /DTACK but there are still some weird issues I'm figuring out atm.

The image quality is truly amazing.

Re: Project: HDMI/DVI out for STFM

Posted: Wed Aug 29, 2018 10:43 am
by Smonson
BTW, this is how it's situated inside the ST.
20171107_210215-2.jpg
20171107_210215-2.jpg (231.63 KiB) Viewed 3738 times
(those wires poking out the right-hand side are just my debug wires)
  • It plugs into the shifter socket, you have to remove the original shifter
  • It also needs one extra wire attached which must be connected to the VSYNC signal
I do want to start building these as soon as possible, but that's countered by wanting it to be as good as it can be.

I'm expecting them to cost about 90 EUR plus postage.

Re: Project: HDMI/DVI out for STFM

Posted: Wed Aug 29, 2018 11:21 am
by Cyprian
I would like to buy one.