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 Post subject: Re: OSSC Pro
PostPosted: Tue Feb 04, 2020 6:24 pm 


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Xyga wrote:
Yeah, some of the early flat panel TVs didn't have HDMI either.


Yup, I remember plasmas from the two premier (at the time) plasma producers Pioneer and Pansonic that didnt have HDMI inputs, but had component and VGA. Amazing when you think about it. Back when the Gamecube released with its digital video to analog component video in 2001, HDMI was not even a thing.


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 Post subject: Re: OSSC Pro
PostPosted: Wed Feb 05, 2020 1:21 am 



Joined: 28 Jan 2020
Posts: 3
XtraSmiley wrote:
the Goat wrote:
I'm not sure what makes something retro and I don't consider PS3 or xbox360 retro. But PS3 and xbox360 both featured analog outputs. HDMI was only added to the xbox360 later in life.


Well PS3 had HDMI out of the box, and the point I was making is that it's over a decade old, 50 lifetimes in electronic toy tech. You may not consider it retro, but it's old enough that I don't think anyone can consider HDMI 1.3 cutting edge or even modern.


Xbox360 is not retro. My coworkers continue to play it.

The issue arises when you have a console that was meant to be played on an sd crt, modernize it (analogue or mister), and cant play it on the monitor it was originally designed to be played on. Why would anyone restrict their outputs? Playing old games on an lcd is not fun, especially coming from some one with a house full of crt’s.


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 Post subject: Re: OSSC Pro
PostPosted: Wed Feb 05, 2020 1:42 am 



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keilmillerjr wrote:
Xbox360 is not retro. My coworkers continue to play it.

The issue arises when you have a console that was meant to be played on an sd crt, modernize it (analogue or mister), and cant play it on the monitor it was originally designed to be played on. Why would anyone restrict their outputs? Playing old games on an lcd is not fun, especially coming from some one with a house full of crt’s.

So, what is retro then? Released or discontinued so many years ago? Or two generations back? Or anything that requires adaptation to play nice with current AV equipment (analogue->digital conversion)? Do we include more recent consoles that have had their online infrastructure discontinued?


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 Post subject: Re: OSSC Pro
PostPosted: Wed Feb 05, 2020 1:47 am 



Joined: 19 Mar 2017
Posts: 242
nmalinoski wrote:
So, what is retro then?


The answer to that question doesn’t matter. It’s a silly question to begin with.


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 Post subject: Re: OSSC Pro
PostPosted: Wed Feb 05, 2020 2:55 pm 


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strayan wrote:
nmalinoski wrote:
So, what is retro then?


The answer to that question doesn’t matter. It’s a silly question to begin with.


It really doesnt matter, but its not a silly question. There are no silly questions, if asked out of sincerity. "Vintage" is a more accurate word to describe the systems which are the objects of our affection.


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 Post subject: Re: OSSC Pro
PostPosted: Sat Feb 08, 2020 6:54 pm 



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Just seeing this now. Pretty exciting stuff - it's crazy to think that the OSSC's been out for almost 4 years now.

Maybe I missed it, but are there plans to support gsync or freesync displays? In the case of arcade games with weird refresh rates, for example, it'd be nice to run those at the proper refresh rates on a modern display. Maybe there's a simpler way to do that, though.


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 Post subject: Re: OSSC Pro
PostPosted: Sat Feb 08, 2020 7:54 pm 



Joined: 19 Jul 2017
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Chacranajxy wrote:
Just seeing this now. Pretty exciting stuff - it's crazy to think that the OSSC's been out for almost 4 years now.

Maybe I missed it, but are there plans to support gsync or freesync displays? In the case of arcade games with weird refresh rates, for example, it'd be nice to run those at the proper refresh rates on a modern display. Maybe there's a simpler way to do that, though.

The HDMI TX chip is only 1.4, so no FreeSync; and, in either case, I think GSync would be prohibitively/unreasonably expensive to license or support.


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 Post subject: Re: OSSC Pro
PostPosted: Sat Feb 08, 2020 9:32 pm 



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Posts: 307
I doubt the HDMI version of the TX chip matters if Freesync/VRR is implemented on the FPGA.

Just like some HDMI 2.0 TVs that got the VRR feature which was introduced with 2.1


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 Post subject: Re: OSSC Pro
PostPosted: Sat Feb 08, 2020 11:32 pm 



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paulb_nl wrote:
I doubt the HDMI version of the TX chip matters if Freesync/VRR is implemented on the FPGA.

Just like some HDMI 2.0 TVs that got the VRR feature which was introduced with 2.1

My understanding is that VRR is an optional feature for HDMI 2.0 and a standard feature starting with 2.1; I've not seen anything that would suggest that VRR could be retrofitted to any versions prior to 2.0.


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 Post subject: Re: OSSC Pro
PostPosted: Sun Feb 09, 2020 11:00 am 



Joined: 20 Feb 2016
Posts: 307
I have not seen anything that would suggest it can't be implemented.

At least with Freesync AFAIK you just need to activate it in the AVI infoframe data and adjust the blanking time. It couldn't be done on the original OSSC because a framebuffer is needed but it should be possible with the OSSC Pro.


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 Post subject: Re: OSSC Pro
PostPosted: Mon Feb 10, 2020 12:03 am 



Joined: 27 Sep 2019
Posts: 4
Hello. I've been gradually familiarizing myself with analog video electronics over the past year, and I think I've learned enough to make a small suggestion: Make sure the capacitance of the AC coupling capacitors on the inputs is sufficient to minimize field tilt. This suggestion also applies to the current OSSC, and I will use it as an illustrative example below.

There are up to 3 AC coupling capacitors per channel in the video chain of a typical OSSC setup (at least the inputs that go to the THS7353, the SCART and RCA jacks), and each stage contributes some amount of field tilt.

Starting at the cable with a 220 uF coupling capacitor, this forms a High Pass Filter (HPF) with a cutoff frequency at 4.8 Hz with the two 75 ohm resistors in series with it. I guess you can include the input resistance at the video buffer in parallel with the 75 ohm termination resistor, but its contribution is negligible. The 4.8 Hz HPF causes an uneven top-to-bottom change in brightness across a frame, being brighter at the top and darker at the bottom. This is a problem external to the OSSC, and it relies on cable makers to install larger capacitors to deal with it.

At the second stage, there is more tilt caused by the HPF formed by the AC couple capacitor of the THS7353 input buffer in the OSSC. I'm assuming the buffer is set to "AC Bias" input mode of operation, which uses an AC coupling capacitor and DC levels are restored internally. According to the datasheet, the total parallel resistance of the DC offset resistors is 21 kohms, and it forms a 7.58 Hz HPF with a 1 uF capacitor. I think this is the biggest contributor to field tilt. The total parallel resistance contributed by the two 75 ohm resistors on the back end is negligible.

The 3rd stage is the output of the THS7353 to the TVP7002 ADC chip. The TVP7002 datasheet states that the input resistance of the analog pins is 500 kohms, which forms a 3.18 Hz HPF with a 0.1 uF AC coupling capacitor. Once more, the resistance contribution on the back end is negligible.

This tilt is easily measurable from quality video captures, even with a simple eyedropper tool. To handle this at the cable, I got a special order from Retro Access with no AC coupling capacitors (full DC coupling). This eliminates tilt produced from the cable, but it increases risk of hazards in the event of a short circuit. Plus, the video buffer must be able to drive a DC-coupled load, but modern video buffers can do it fine. It's up to the user to decide on full DC coupling or larger AC coupling capacitors to deal with it. 354 uF will bring the HPF cutoff down to 3 Hz (which is what I've seen TI recommend in some datasheets to minimize potential droop), so 360 uF is a good minimum value. Professional solutions apparently use 1000+ uF to push it down further.

At the THS7353, I added 10 uF ceramic caps in parallel with the stock 1 uF caps, which brought the tilt way down. I haven't changed the last set of caps to the TVP7002, but droop is now hard to measure from the 8-bit lossless video captures. As mentioned before, TI recommended 3 Hz to minimize droop, so 3.18 Hz at the TVP7002 is very close. Still, I may add a little more capacitance to see how much it changes.

I'm not sure what the new OSSC Pro will use for the LPF frontend (is it built into the fancy new chip?), but I hope that these considerations are made going forward.


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 Post subject: Re: OSSC Pro
PostPosted: Wed Feb 12, 2020 1:55 am 



Joined: 03 Dec 2015
Posts: 8
Good jobs. Do you know if OSSC pro have better compatibility in HDTV for res like 1080p...some of HDTV accept 480p only.


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 Post subject: Re: OSSC Pro
PostPosted: Wed Feb 12, 2020 2:14 am 


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@yoshiyukiblade The analysis for the first 2 stages is correct, but I think the view on AFE/ADC is too simplistic. It has a dynamic clamp, configurable bias currents and ALC which can affect line/field tilt and its effect on resulting brightness stability. The backporch clamp is enabled only for a short duration at the beginning of each line - the effective impedance should be much higher during active video than when clamp is active which should ideally minimize droop. Selected ADC/input bias current can also change the impedance value. Even if the clamp doesn't fully keep up with the droop, ALC can be used to negate the offset each line which could mitigate field tilt. This of course requires that ALC time constant is fast enough - since this is not ALC's primary purpose, the value is averaged over 1024 lines by default. There's now a test firmware for OSSC (see its own thread) where ALC filter options are exposed which enable reducing the time constant.

With OSSC Pro things are a bit different. THS7353 is not required for the video lines since the ADC chip has a configurable built-in LPF which makes things easier. However, there seems to be a design flaw in ISL51002's clamp. The clamp current probably is insufficient for (dis-)charging the default 0.1uF AC bypass caps which shows as smoothed transition when screen changes from black to white or vice versa. This can be mitigated by increasing the clamp width and/or enabling ALC, but the issue can be fully eliminated only by reducing the coupling caps to around 1nF. This does not seem to cause excessive droop as seen by eye (indicates very high input impedance), but I've not done thorough anylysis yet.


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 Post subject: Re: OSSC Pro
PostPosted: Wed Feb 12, 2020 2:53 am 



Joined: 27 Sep 2019
Posts: 4
Thank you for the detailed insight on what happens at the AFE (it's still black magic to me!). I've put together a comparison of the different changes I've tested: https://i.imgur.com/Ggu9pkX.png

I took a (132,132,132) grey screen average of 1024 frames, increased the contrast until the levels began to clip on the first image, and then I applied the same adjustment curve to the 2nd and 3rd images for consistency. Red channel only is shown. The 2nd and 3rd image is recent, but the first one was taken sometime last year before I soldered on the 10 uF ceramic caps, so it's not a perfect comparison.

It looks very good when the first 2 stages are dealt with. I wonder if the Datapath's AFE handles it differently because I saw a frame average from another user, who most likely had the 220 uF coupling caps on the cable, and the frame was pretty solid (besides the subtle vertical ripple seen on 1CHIP SNES consoles).


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 Post subject: Re: OSSC Pro
PostPosted: Thu Feb 13, 2020 3:20 am 


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OSSC Pro vs GBS Pro: The Final Scaling


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 Post subject: Re: OSSC Pro
PostPosted: Fri Feb 14, 2020 4:19 pm 



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Posts: 136
Will the OSSC Pro allow for automatic switching between optimized modes in a single profile? So for example with the Saturn automatically switching between 320x224p, 352x224p and 704x408i. Similar to the Mega SG switching between 256x224p and 320x224p games on the fly.

This would be an awesome feature and puts the Pro in OSSC Pro.


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 Post subject: Re: OSSC Pro
PostPosted: Fri Feb 14, 2020 4:27 pm 


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H6rdc0re wrote:
Will the OSSC Pro allow for automatic switching between optimized modes in a single profile? So for example with the Saturn automatically switching between 320x224p, 352x224p and 704x408i. Similar to the Mega SG switching between 256x224p and 320x224p games on the fly.

This would be an awesome feature and puts the Pro in OSSC Pro.


This would get me to use the optimized modes. It's way too much work right now, I just use generic 4:3 for everything.


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 Post subject: Re: OSSC Pro
PostPosted: Fri Feb 14, 2020 4:54 pm 


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The big advantage of the OSSC Pro using optimised sampling profiles should be the partial frame buffered hybrid line doubler mode. In plain language, the OSSC Pro is going to be able to correct the aspect ratio and add a touch of billinear filtering after line doubling--like an OSSC feeding a DVDO iScan with full uncompressed sampling and processing. :)
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 Post subject: Re: OSSC Pro
PostPosted: Fri Feb 14, 2020 7:44 pm 



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H6rdc0re wrote:
Will the OSSC Pro allow for automatic switching between optimized modes in a single profile? So for example with the Saturn automatically switching between 320x224p, 352x224p and 704x408i. Similar to the Mega SG switching between 256x224p and 320x224p games on the fly.

This would be an awesome feature and puts the Pro in OSSC Pro.

How would this work, though? As I understand it, the MegaSG's scaler, being part of the MegaSG itself, has direct access to all the information it needs to perform that switching, like pixel clock; but the OSSC [Pro], being downstream of analogue-encoded video (which does not contain pixel clock info), doesn't.


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 Post subject: Re: OSSC Pro
PostPosted: Fri Feb 14, 2020 7:51 pm 



Joined: 08 Mar 2017
Posts: 1324
Right.
If someone solves the issue of simply not knowing the source's pixel clock, that'd be huge!

I've heard some ideas, but all of them are too much for my scaler.
But maybe with a powerful compute core, it may be possible to do some FFT analysis to automatically figure out the ideal sample rate (and phase, too!).
Regardless of what the source shows, there should be a recognizable high frequency spike at the ideal sample rate, should it not?


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 Post subject: Re: OSSC Pro
PostPosted: Sat Feb 15, 2020 6:11 am 


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I'm really excitied about the OSSC Pro!
Have you considered going with HDMI 2.1? With 120hz slowly becoming a thing on new TVs, it could really help with platforms that go either slightly above 60hz or other cases like the Atari Lynx (75hz)
Even if there issues with licensing fees, have you considered going the route of crowdfunding? It could help!


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 Post subject: Re: OSSC Pro
PostPosted: Sat Feb 15, 2020 11:50 am 



Joined: 23 Jun 2016
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Not sure if any of these suggestions were covered. Just wanted to get these in even if they get completely ignored and/or cant be done for whatever reason.

- Automatic power on when signal detected and/or power on by remote
- All IO on the back (no side connections)
- Automatically selecting the best settings for the video source (no need for profiles)


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 Post subject: Re: OSSC Pro
PostPosted: Sat Feb 15, 2020 12:32 pm 


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Another feature request : horizontal & vertical flip please.
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 Post subject: Re: OSSC Pro
PostPosted: Sat Feb 15, 2020 2:54 pm 



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Posts: 128
parodius wrote:
Another feature request : horizontal & vertical flip please.


They have said it would have rotate, but flip can be useful too, if your setup uses mirrors for example.


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 Post subject: Re: OSSC Pro
PostPosted: Sat Feb 15, 2020 3:52 pm 



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Chris230291 wrote:
Not sure if any of these suggestions were covered. Just wanted to get these in even if they get completely ignored and/or cant be done for whatever reason.

- Automatic power on when signal detected and/or power on by remote
- All IO on the back (no side connections)
- Automatically selecting the best settings for the video source (no need for profiles)

All I/O is on the back, except for SCART, which I believe was done because most SCART connectors are angled; the way that the SCART input on the OSSC Pro is arranged, a SCART cable with an angled connector will exit towards the rear, rather than to the side, as with the existing, regular OSSC.

As for automatically selecting the best settings for the video source, I don't believe it's been explained how that would be possible, because information like pixel clock and phase are not transmitted over analogue video; the only thing that can handle that right now is an internal mod that would be able to tap and read the pixel clock, which would then negate the need for an OSSC Pro.

Personally, I think it might be possible to design per-console mods that could detect change in pixel clock (or anything else relevant to the OSSC) and transmit it downstream to the OSSC, either via a separate line or a signal/packet burst over the analogue sync line (maybe during v-blank?), which the OSSC [Pro] would then be looking for; but I've not the experience, knowledge, or capability to prototype anything, and of course that requires a hard mod applied to all consoles you want to use this functionality with.


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 Post subject: Re: OSSC Pro
PostPosted: Sat Feb 15, 2020 6:10 pm 


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XtraSmiley wrote:
parodius wrote:
Another feature request : horizontal & vertical flip please.


They have said it would have rotate, but flip can be useful too, if your setup uses mirrors for example.


It can also breathe new life into shmups and platformers that you are really familiar with.


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 Post subject: Re: OSSC Pro
PostPosted: Sat Feb 15, 2020 10:15 pm 



Joined: 20 Apr 2018
Posts: 128
Kez wrote:
XtraSmiley wrote:
parodius wrote:
Another feature request : horizontal & vertical flip please.


They have said it would have rotate, but flip can be useful too, if your setup uses mirrors for example.


It can also breathe new life into shmups and platformers that you are really familiar with.


Wow, hadn't considered that. Very interesting... I guess if you're a PRO like some of the guys here on the high scores, you could rotate AND flip and play a shooter going downwards.... super new game!


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 Post subject: Re: OSSC Pro
PostPosted: Sat Feb 15, 2020 10:53 pm 


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Yep. I think Fudoh was first suggesting mirrored games using the Datapath x4. It's a great idea. :)

There are warp processors that can do horizonal flipping faster, though. Don't need more than a few lines of buffering to stack and FILO each individual scanline.

I'm hoping the OSSC Pro eventually offers the horizonal mirroring as a feature in the partial frame buffered mode. :) With MiSTer, you won't (even) have to rewire a controller to play.

Fudoh already mentioned this: but, warp processing would be useful for creating warp effects to simulate the rounded edges of CRT. That's another option that currently requires specific (rather rare) warp processing machines--if you want it done with less than a full frame of lag. Probably a half a dozen of us (or less) have the option right now.
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 Post subject: Re: OSSC Pro
PostPosted: Sat Feb 15, 2020 11:17 pm 


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I have to admit that on horizontally scrolling games I found it very confusing, but it's absolutely great for vertically scrolling ones, since it keeps the basic gameplay and it's orientation intact. Of course you have to mod your controller as well, but it's worth it.

All the various video transformations should eventually be rather easy to implement, given that the FPGA has enough gates and there's enough RAM. Barrel effect warping while keeping the scanlines from totally falling apart is another topic though.


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 Post subject: Re: OSSC Pro
PostPosted: Sun Feb 16, 2020 1:56 am 


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XtraSmiley wrote:
parodius wrote:
Another feature request : horizontal & vertical flip please.


They have said it would have rotate, but flip can be useful too, if your setup uses mirrors for example.


Yes, I'm thinking Operarion Thunderbolt, which uses a flipped image (original cab used a mirror apparently) with no option to change it.
Positional gun will still be an issue though :mrgreen:
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