MiST VGA Compatibility

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Re: MiST VGA Compatibility

Postby Newsdee » Sun Aug 28, 2016 3:51 am

Sorgelig wrote:
Newsdee wrote:Perhaps the ZxUno might be a way.

How it can solve the problem? Do you mean GPIO to control the GBS board?


The ZxUno is a full FPGA SoC with RGB out via 9-pin molex connector, so I think it should be possible to write a core for it that takes input from GPIO and outputs stable video? It still has the audio mixing problem for HDMI, though.

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Re: MiST VGA Compatibility

Postby Sorgelig » Sun Aug 28, 2016 9:30 am

Newsdee wrote:The ZxUno is a full FPGA SoC with RGB out via 9-pin molex connector, so I think it should be possible to write a core for it that takes input from GPIO and outputs stable video? It still has the audio mixing problem for HDMI, though.


1) To input VGA you need ADC inputs, not digital logic. So, at least additional video digitizer chip is required.
2) ZxUno VGA output has only 3 bits per color. So, some cores (Amiga, C64, NES, etc..) will loose color resolution.
3) It has only 500KB RAM which is not enough to hold a full frame with at least 16bits per pixel (although 18bits required if we dont want to reduce colors).

So, ZxUno won't provide any meaningful solution. LKV362A scaler is cheaper than ZxUno and gives more than ZxUno is capable.

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Re: MiST VGA Compatibility

Postby Newsdee » Sun Aug 28, 2016 10:25 am

I suppose the LKV362A is better than a VGA->HDMI upscaler if it doesn't have the vertical artifacts.

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Re: MiST VGA Compatibility

Postby Sorgelig » Sun Aug 28, 2016 11:02 am

LKV362A outputs at fixed standard resolution (720p/1080p) and fixed frame rate (50/60) according chosen preset and doesn't depend on input video format. So, technically it always upscale and always frame convert - no matter what video is on its input. So, i think, you won't get frame pass-through on this scaler since output scan is completely independent from input scan. You can treat this as drawback, but it gives you support for any non-standard old TV resolutions like 320lines per field and 48Hz VSync which is impossible to achieve using simple direct VGA->HDMI digitizer.

I don't know what vertical artifacts you are talking about.

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Re: MiST VGA Compatibility

Postby Sorgelig » Sun Aug 28, 2016 11:15 am

LKV362A has HDMI input as well, which supports 31KHz inputs and it looks like also accepts quite wide range of resolutions and frame rate. Probably (need verify this!) it supports 15KHz video on HDMI input. The only problem - there is no VGA->HDMI simple converters. All VGA converters accept only 31KHz (and ~50+ Hz Vsync, so no scandoubler with 48Hz). So, i couldn't test this (till i got OSSC). In theory, OSSC could be such direct frame converter from VGA input to HDMI output. An then chained to HDMI input of LKV362A. Quick tests shown that LKV362A accepts even 320lines per field on its HDMI input, so i'm kind optimistic here. I only need to make add-on board for OSSC to insert audio into HDMI output. Then i will need to fix OSSC firmware to auto-detect RGBS/RGBHV (it cannot detect it now - i was surprised such easy feature is not implemented).
Since i had no much time to play with OSSC, i'm not sure if it pass 15KHz to HDMI output or has scandoubler like MiST cores. So i'm still not sure if LKV362A accepts 15KHz on its HDMI input.

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Re: MiST VGA Compatibility

Postby Newsdee » Sun Aug 28, 2016 1:57 pm

Not sure how to describe the vertical artifacts other than columns of pixels that are slightly wider. They're mostly noticeable with scrolling text. I suspect they appear due to the non-standard frequency; and some displays show it more than others.

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Re: MiST VGA Compatibility

Postby Sorgelig » Sun Aug 28, 2016 4:25 pm

It's due to difference in frequencies between video source and video digitizer. Unfortunately it's impossible to avoid because different retro machines have different pixel frequency. It's 5MHz, 6MHz, 7MHz, 8MHz and so on. Usually good scaler minimize this effect by adjusting the frequency of digitizer and use good scaling formula.
Cheap digitizers (usually based on MS9282) don't have any picture improvements and look ugly.
But anyway, it's hard to make it ideal when you digitize and scale the video.
In case of OSSC, it's possible to use some tricks. Like sending frequency by VSync/HSync signals from MiST core in retrace time, so OSSC won't need to guess and will use exact frequency. Also, it's possible to send sample of pixel frequency to let OSSC fine tune the phase.

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Re: MiST VGA Compatibility

Postby Newsdee » Mon Aug 29, 2016 1:28 am

I suppose that if we ignore conversion to 60hz, the OSSC could be adapted to match each MiST core a little better than the XRGB?

It kind of puts the price of the XRGB into perspective though. If a second revision was made with RAM, it will probably cost more than than 200+ EUR of the current one, and then the gap with the XRGB isn't that great considering the XRGB handles audio and framerate conversion.

Aside from the price the one annoying thing of the XRGB is the few seconds it takes to resync when video frequency changes. How does the OSSC compare in switching modes?

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Re: MiST VGA Compatibility

Postby skeezix » Mon Aug 29, 2016 1:34 am

Newsdee wrote:But it's not just a pass-through... so it's not that simple.

If you want to "clean" the signal to a solid 50hz or 60hz, either you change the source core to run at just the right speed or you add a framebuffer to the output. For the latter, you need memory to store the image and read it back at the right rate, or you get tearing. It adds latency which can become noticeable.

It's probably possible to make something designed specifically for the MiST that only needs to handle the frequencies it outputs; but then it will end up fiddly anyway. The XRGB does have a lot of flexibility but then is built specifically for that purpose. And is very expensive...

Now don't get me wrong. I'd love a cheap way to stabilize the output. Perhaps the ZxUno might be a way.


Yeah, I'm talking a framebuffer, and a circuit to spit out a new (yet cleaner) signal. It should be possible to fix the core in MiST (say), but its a more general problem where a number of devices have slightly goofy output signals, or don't want to handle PAL to NTSC (or vice versa) translation.

Adding a framebuffer would of course add in a frame or two of latency (which would be noticeable for some games, but not all .. but then, maybe having working video 'at all' would be better than none :) .. ie: In MiST case (and other products), I just get no video whatsoever on my commercial TVs. Annoying as heck :)

A mcu could pull itoff, but its a lot of bandwidth; running a video out on an STM32 works just fine to bit bang it even, but managing video _in_ and out would be infeasible .. they also tend not to have enough RAM for a VGA image without a lot of trickery, or a higher end BGA part with an external memory interface .. I don't much like to work with those, I prefer SMT that I can hand solder still (like quad flat-pack 200pin and less sort of arrangements) (or thru-hole of course, but not going to get that for these sorts of processing requirements.)

An FPGA could probably tie it all up pretty nicely, but I've less experience there. Still, capturing video (done that) and emitting video (done that), but doing both.. maybe something fun to do.

But my blind spot is .. I'm not sure why a lot of these devices are fiddly. I need to put the gbs-8220 on my o-scope and inspect its sync and payload channels, and the MiST too; why do a number of these devices have these gotchas .. can't just assume lazy coding on the gbs-8220 .. just too many kinds of TVS and varieties of signals? or just a hard time converting from signal to Y with as limited a framebuffer as possible? So having not done a converter board, I'm not seeing all the myriad problems they've had to over come..

.. but that's why I thought a 'cleaner' board; not do upscale or downscale, just a 'simpler' board whose job is to let something else do its job and then just fix up the signal, so I can see something.

.. but yeah, doing all that work, 'just for that', doesn't seem worth it ..

So, maybe I should look into building a new cheap upscaler; we all want something in the gbs-8220 price range, but with a few more features. Sadly, the day you make something like that, our friends in China will clone the hell out of it :)

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Re: MiST VGA Compatibility

Postby Newsdee » Mon Aug 29, 2016 1:41 am

I don't think a cheap uscaler is possible given the points Sorgelig is raising about the OSSC. XRGB is the only device in my experience that has no major "gotchas" and even so isn't perfect.

If you're curious about the gritty details I recommend reading this thread on a custom FW for the GBS8200:
http://shmups.system11.org/viewtopic.php?t=52172

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Re: MiST VGA Compatibility

Postby skeezix » Mon Aug 29, 2016 1:50 am

yeah, I need to read more .. the looking into it I did a year or two back suggested most guys just didn't want to have RAM framebuffer either for cost or latency issues, and wanted to do live translation .. which caused a lot of artifacting and other issues.

*Shrug* I've got a few other projects on the go but if I get some time I'll look into it .. since its an almost-common enough issue, and annoying enough to _me_ that I may have to solve it for myself at least :)

Or if someone solves it for the gbs-8220, it'll be moot for me :)
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Re: MiST VGA Compatibility

Postby Newsdee » Mon Aug 29, 2016 4:04 am

would it be possible to alter the pixel clock on the MiST cores to make it more compatible with standard VGA? I noticed Kevtris slightly overclocked the NES CPU for the HDMI Analogue NT, for example. But I suppose it would lead to software compatibility issues.

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Re: MiST VGA Compatibility

Postby Sorgelig » Mon Aug 29, 2016 9:10 am

Newsdee wrote:would it be possible to alter the pixel clock on the MiST cores to make it more compatible with standard VGA?

You can set any pixel clock to any core if you don't care about "cycle exact" compatibility with real hardware. I prefer to have 100% compatibility, than VGA compatible video.

Newsdee wrote:I suppose that if we ignore conversion to 60hz, the OSSC could be adapted to match each MiST core a little better than the XRGB?

OSSC output is HDMI (it uses DVI connector to solve HDMI license issue) which is much more strict than VGA. You cannot have 48Hz or 49Hz video. You cannot have 320 lines per field. etc, etc... You can transcode VGA to HDMI, but none of TV will show this video.
But some HDMI-HDMI scalers may accept it - that's what i'm planning to test when i will have free time.
So, at the end you will need to insert some scaler after OSSC to correct the video which will be compatible with TV. Thus you will need to convert 48/49Hz to 50Hz(or to 60Hz) anyway.

If someone will make newer OSSC with RAM for frame buffer and it will cost like 200+ EUR, it will be much better than XRGB because of open source. XRGB has good hardware, but no one (except manufacturer) can fix issues - so for me it's more or less useless expensive device with problems.

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Re: MiST VGA Compatibility

Postby Sorgelig » Mon Aug 29, 2016 9:20 am

OSSC with RAM will need to use BGA FPGA (due to not enough pins in TQFP), so it won't be DIY project. Actually, for me it would be acceptable since i'm not planing to solder such devices by myself.

Actually, it would be better to have MiST v2, with HDMI(DVI is also fine) output and additional RAM chip, so we can have scaler inside with its RAM. Two RAM chips with independent buses will give a great freedom. 32MB of SDRAM for frame buffer will cover all needs for scaler.

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Re: MiST VGA Compatibility

Postby Newsdee » Mon Aug 29, 2016 9:40 am

Yes, I'd prefer an open source solution but it looks like we'll have to invent it :D

For a MisT V2 the worry would be cost of adding another FPGA to the board... although maybe it doesn't need to be too big if the only purpose is to control video upscaling and compatibility with DVI/HDMI. Perhaps it could be used for other things if there are enough free pins and RAM, too.

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Re: MiST VGA Compatibility

Postby ericgus » Mon Aug 29, 2016 3:28 pm

For MiST 2, more basic, I'd love to see some kind of generic .. say 50 pin GPIO header that could be used for any sort of hardware interface that the core might need to connect to retro hardware, commodore IEC bus, Amiga/Atari serial/parallel ports, Speccy tape in/out .. etc.. just a bank of whatever "leftover" i/o pins not being used by the primary FPGA .. (or secondary)

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Re: MiST VGA Compatibility

Postby Newsdee » Mon Aug 29, 2016 9:33 pm

In any case I don't think we're done squeezing functionality out ot the current hardware. :D

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Re: MiST VGA Compatibility

Postby Sorgelig » Tue Aug 30, 2016 4:18 pm

No additional FPGA required. Only another SDRAM chip and HDMI/DVI output. But it will require BGA version FPGA due to amount of required pins.

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Re: MiST VGA Compatibility

Postby Newsdee » Wed Aug 31, 2016 3:33 am

Still concerned about costs; there's new dev boards like this one that seem extremely powerful and the price is not too bad compared to a MIST + a good upscaler:

https://www.terasic.com.tw/cgi-bin/page ... 6&PartNo=1

It's listed at USD 350... doesn't support USB but other than that this thing could probably run anything you can throw at it? Or am I missing something? Perhaps they require licensing IPs or some other hidden costs.

Of course the MiST is better in that it feels like a proper "end user" device rather than a digital breadboard.

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Re: MiST VGA Compatibility

Postby mahen » Fri Jan 06, 2017 9:33 am

Hey guys, I tried to check the compatibility list but it seems broken :-)
(got back to a 15 KHz screen but it destroys my eyes :)
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Re: MiST VGA Compatibility

Postby Newsdee » Fri Jan 06, 2017 11:45 am

which list? the spreadsheet?

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Re: MiST VGA Compatibility

Postby mahen » Fri Jan 06, 2017 12:28 pm

Hmm, this one : http://code.google.com/p/mist-board/wiki/Displays
Well, linebreaks are missing which is easily fixed but there are very few entries actually.
Or is there another list ?
Thanks :)
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Re: MiST VGA Compatibility

Postby DrOG » Fri Jan 06, 2017 4:10 pm

Look at this:

https://github.com/mist-devel/mist-boar ... CoreStatus

First link ('This spreadsheet') on the above page. More detailed, but still no perfect...

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Re: MiST VGA Compatibility

Postby mahen » Fri Jan 06, 2017 4:25 pm

Thanks :) Actually I was looking for the screens / monitors / TV compatibility list :-)
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Re: MiST VGA Compatibility

Postby DrOG » Wed May 17, 2017 8:16 am

Hi all!

Last week I purchased a BenQ BL912 monitor.

I tested it only shortly, but my first impressions are very positive!

Tried mainly the 'PAL only' cores from Sorgelig, and some NTSCs as well (NES and Genesis). The display is compatible with all of them! To my surprise it handles flawlessly the cores in 15kHz mode without special wiring, it seems that the devide accepts composite sync over VGA pin 13. I used the standard VGA cable shipped within the package. Moreover it supports even YPbPr over the same connector, you can select the desired color format from the menu (RGB/YUV) both in scandoulber enabled and disabled mode.
Tried the known-to-be-problematic PC Engine (TurboGrafx16) core also, and the picture is perfect, not trunctated and well-centered. The 'Info' says 720x240@59Hz in TV, and 640x500@59Hz in VGA mode).
You need to use 'Auto Adjustment' often after changing core, but it's customizable to one of the 'hot keys'.
I read somewhere that this monitor is compatible with 'Sync-on-green' signals as well, but didn't try that so far.

So I recommend it as a (near) perfect screen for the MIST!

ADVANTAGES:
-Available as a new product
-Relative big display (19"=48cm diagonal)
-5:4 aspect ratio (4:3 would be perfect, but still better than 16:9)
-Accepts all kinds of non-VGA standard signals (in respect of resolution, refresh rate, colour format, sync signal)
-Practical 'Auto Adjustment' function and customizable hot keys
-Also has a DVI-D connector, works well with a passive HDMI adaptor (tested with Raspberry Pi 3).
-Many fancy marketing features (Flicker-free LED backlight panel, Ultra-high dynamic contrast ratio of 12,000,000:1, Low Blue Light Mode)

DISADVANTAGES
-TN panel (IPS would be better)
-Lack of built-in speaker
-Relative high price (compared to Full HD monitors).
-Slow menu

If you are looking for similar, 15kHz compatible monitor, visit the website below:
http://15khz.wikidot.com/


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