GBS 8200/8220 CFW Project

[Josh128]

Regarding the color handling of the GBS Control, I did a quick and dirty comparison of a PC Radeon VGA card out vs a Genesis model 2 via GBS Control out to a Compaq FS7600 CRT. I need to probably do more tests with locked down manual camera settings, but this is actually pretty representative of what I see. The black levels appear to be very different, with the PC giving much darker blacks yet still maintaining good color levels. The GBS Control image does still look good, but Im not sure which is more representative of what the image SHOULD look like.

PC on left, Genesis via GBS on right.

Thoughts?



Full Size:

Spoiler

[ldeveraux]

Regarding the color handling of the GBS Control, I did a quick and dirty comparison of a PC Radeon VGA card out vs a Genesis model 2 via GBS Control out to a Compaq FS7600 CRT. I need to probably do more tests with locked down manual camera settings, but this is actually pretty representative of what I see. The black levels appear to be very different, with the PC giving much darker blacks yet still maintaining good color levels. The GBS Control image does still look good, but Im not sure which is more representative of what the image SHOULD look like.

PC on left, Genesis via GBS on right.

Thoughts?



Full Size:

Spoiler

I can't speak for which it SHOULD look like, but the contrast is way too high for me on the Genesis. Compound that with your remarks on the blacks, we have a winner. Not sure if something within the settings needs to be tuned better though? I hope so.

[Josh128]

^^

So you feel the contrast looks too high on the right image? Cause to me it seems like the contrast looks higher on the left. The PC is ALMOST crushing blacks. If you look at the horizontal stripe under the "Pine Pot" sign, it looks almost totally black on the PC image, while you can see the detail/shading on the Genesis/GBS. Same goes for the back glass of the car at the bottom of the screen, the PC comes close to crushing the gray shading as you can see in the large spoiler image.

So you prefer the look of the image on the left? I guess the next thing to do would be to see how the colors on the Genesis look via composite on an NTSC TV, but we all know from FBX's NES RGB palette mania that trying to nail down true colors from composite video is not an exact science.

For reference, the GBS-C brightness control was set to auto-gain, scanlines set to 0 (full darkness). The monitor settings did not change between the two and are all default except for contrast, which is maxed out.

[Kez]

The one on the left looks too dark to me. Feels like detail is lost due to crushed blacks. Maybe check out some test patterns on 240p test suite?
This is how native Genesis looks on my CRT:

Spoiler

[Josh128]

^^

Yeah, I compared them side by side and that looks very much like the Genesis 2 through the GBS-C. Essentially identical I would say. So this is directly from the Gen into some sort of 15kHz monitor? From this comparison it appears that the color output from my GBS-C is pretty damned accurate.

The colorspace on my PC's VGA output may need to be adjusted or something, should be RGB 4:4:4 (I would imagine), but maybe its not, I need to check.

[Kez]

So this is directly from the Gen into some sort of 15kHz monitor?

Yeah, it's a Genesis 1 going into a BVM.

[ldeveraux]

^^

So you feel the contrast looks too high on the right image? Cause to me it seems like the contrast looks higher on the left. The PC is ALMOST crushing blacks. If you look at the horizontal stripe under the "Pine Pot" sign, it looks almost totally black on the PC image, while you can see the detail/shading on the Genesis/GBS. Same goes for the back glass of the car at the bottom of the screen, the PC comes close to crushing the gray shading as you can see in the large spoiler image.

So you prefer the look of the image on the left? I guess the next thing to do would be to see how the colors on the Genesis look via composite on an NTSC TV, but we all know from FBX's NES RGB palette mania that trying to nail down true colors from composite video is not an exact science.

For reference, the GBS-C brightness control was set to auto-gain, scanlines set to 0 (full darkness). The monitor settings did not change between the two and are all default except for contrast, which is maxed out.

I understand how it looked 30 years ago, but that didn't look good to me. Black was supposed to be black, not gray. The colors were supposed to be vibrant but not overpowering. So the VGA card looks best to me. Don't even get me started on scanlines...

[maxtherabbit]

^^

Yeah, I compared them side by side and that looks very much like the Genesis 2 through the GBS-C. Essentially identical I would say. So this is directly from the Gen into some sort of 15kHz monitor? From this comparison it appears that the color output from my GBS-C is pretty damned accurate.

The colorspace on my PC's VGA output may need to be adjusted or something, should be RGB 4:4:4 (I would imagine), but maybe its not, I need to check.

Yeah that picture on the right looks more like my unmodded genesis 2 going straight into an (uncalibrated) RGB TV

[Ryoandr]

I understand how it looked 30 years ago, but that didn't look good to me. Black was supposed to be black, not gray. The colors were supposed to be vibrant but not overpowering. So the VGA card looks best to me. Don't even get me started on scanlines...

Status bar is absolutely grey. On the emu version it's like, the darkest of dark greys, it nearly blends with the black scanlines.

Josh, judging by the FPS counter it's KEGA running, did you try to toggle the Brighten (ctrl+0) option ?

[Josh128]

Did another test with identical manual settings, position, camera mounted on a tripod. Same settings on monitor, just switched cable from GBS to PC. This one came out with better darks for the PC than the last one, not sure what was going on with the emulator the first go round. Again, the GBS-C and Genesis show very accurate colors vs the PC. There is a slight bit more contrast with the PC still, but this is just more confirmation that the GBS output is legit, at least with a Genesis. I wanted to make sure that the issue with the Gamecube discussed above is not a global GBS-C color issue across all systems. I have yet to try my GC on it. Curious as to what is causing the problem wiht the GC discussed above...

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Spoiler

[Guile]

I was trying to use the gbsc as a transcoder but the pass-through function isn't working for me. I have the vga out connected to an ossc but if I hit the pass-through button it never syncs and I get no image. It's fine if I go to 480p or even 15khz though I do get a glitch with color loss on 15khz that's fixed by toggling.

Is there some explanation for this? Is it possible to get 480i output on the vga from component 480i in?

[Josh128]

You hit the pass-through button but did you enable YPbPr output? Even so, that function is supposed to be preliminary/beta. I havent personally tested yet.

[awe444]

Is it possible to get 480i output on the vga from component 480i in?

I’ve never been able to output an interlaced signal of any kind from the GBSC under any circumstances, including passthrough mode. Earlier in this thread there are statements that it’s a hardware limitation of some kind.

[Guile]

You hit the pass-through button but did you enable YPbPr output? Even so, that function is supposed to be preliminary/beta. I havent personally tested yet.

No I didn't enable ypbpr, thanks for the tip, I will test it again. If it just passes ypbpr to ypbpr then it's not too helpful to me but I wonder if it could do vga to ypbpr.

Is it possible to get 480i output on the vga from component 480i in?

I’ve never been able to output an interlaced signal of any kind from the GBSC under any circumstances, including passthrough mode. Earlier in this thread there are statements that it’s a hardware limitation of some kind.

That's unfortunate, do you know of a good inexpensive transcoder that can output 480i? It seems like there are so few options.

[Ryoandr]

Do not forget that to use the component output option you need to mod the GBS, see 1st page. Else signal level is not high enough and even if it manages to sync it'll be too dark.
As far as I know, correct interlaced output is not possible. I got a very flickery output using passthrough on 480i, as if lines got spaced apart.

[Guile]

Do not forget that to use the component output option you need to mod the GBS, see 1st page. Else signal level is not high enough and even if it manages to sync it'll be too dark.
As far as I know, correct interlaced output is not possible. I got a very flickery output using passthrough on 480i, as if lines got spaced apart.

Oh well that's definitely not worth it for me then. I don't want to modify it any more and if it can't output 480i then there's no point in my case. Thanks for the tip, I probably would've wasted some time on that.

[Josh128]

I dont think the modification is necessary anymore. Per Rama:

Update:
This modification is not required anymore.
Gbscontrol now uses an undocumented clamping level bit to work well with the default capacitors.
It isn't necessary to do this modification anymore, but you can still do it and improve sync performance.

https://github.com/ramapcsx2/gbs-contro ... placements


Also, though the wiki says its essential to add a 100 ohm resistor across sync and ground when feeding from RGBs systems (like the Genesis 2 Ive been using), I DID NOT do that and the Genesis has been working fine with zero flickers or sync dropouts. Anyone know whats up with that?

[NoAffinity]

Both mods are all about correct voltages. Without them, theres potential risk to hardware over time (gbs and beyond).

That excerpt refers to ypbpr input and no longer needing input caps.

Sent from my SM-G955U using Tapatalk

[maxtherabbit]

Both mods are all about correct voltages. Without them, theres potential risk to hardware over time (gbs and beyond).

That excerpt refers to ypbpr input and no longer needing input caps.

Sent from my SM-G955U using Tapatalk

Not exactly. The 100R input sync mod actually RAISES the voltage seen at the TV5725 input. Not performing it is 100% safe, and performing it makes using TTL sync inputs a no-go

[NoAffinity]

Both mods are all about correct voltages. Without them, theres potential risk to hardware over time (gbs and beyond).

That excerpt refers to ypbpr input and no longer needing input caps.

Sent from my SM-G955U using Tapatalk

Not exactly. The 100R input sync mod actually RAISES the voltage seen at the TV5725 input. Not performing it is 100% safe, and performing it makes using TTL sync inputs a no-go

Raises it to a suitable level to compensate for typical console output voltages, correct?

Additional question - does the cfw in general affect the ability to input TTL signals (even without the 100R resistor)? I find that even without the 100R resistor, any arcade board is overly bright on GBS-C, and gain has to be cranked down to 0, and even then it's still a bit too bright.

[maxtherabbit]

Both mods are all about correct voltages. Without them, theres potential risk to hardware over time (gbs and beyond).

That excerpt refers to ypbpr input and no longer needing input caps.

Sent from my SM-G955U using Tapatalk

Not exactly. The 100R input sync mod actually RAISES the voltage seen at the TV5725 input. Not performing it is 100% safe, and performing it makes using TTL sync inputs a no-go

Raises it to a suitable level to compensate for typical console output voltages, correct?

Depends how you define typical output. Short answer is yes, but that's only because most factory RGB SCART cables include attenuation on sync. If you make custom cables you'd find that most consoles actually do output TTL level c-sync at the multiout

Additional question - does the cfw in general affect the ability to input TTL signals (even without the 100R resistor)? I find that even without the 100R resistor, any arcade board is overly bright on GBS-C, and gain has to be cranked down to 0, and even then it's still a bit too bright.

Sync amplitude has nothing to do with colour amplitude. I do not know if the CFW specifically affects usability with arcade boards, but removing the 3 trimmer pots on the GBS' input definitely hamstrings its ability to handle arcade PCB RGB. If you want to use GBS-control with arcade hardware it's best to not remove the 3 pots and use them to attenuate the brightness.

[AGC Retrogaming]

Joined: 18 Apr 2021
Posts: 1
Location: North Carolina
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Hi everyone, I'm new in this forum, so I'm sorry if this subject has been discussed before. but I could not find any information related.

does this firmware has any feature as:

- Rotate 90º for vertical games for example.
- Flip the imagine so show on screen the image inverted horizontal.

I'm not sure if it is possible, or requires to much effort to develop this code. but just let me know your thoughts about it.

Thanks in advance, and awesome improvement thought

[NoAffinity]

^the answer to both is no. And it is unlikely they will be added to development, as rama is focused on other efforts.

Sent from my SM-G955U using Tapatalk

[orange808]

Joined: 18 Apr 2021
Posts: 1
Location: North Carolina
Feedback: 0|0|0
Hi everyone, I'm new in this forum, so I'm sorry if this subject has been discussed before. but I could not find any information related.

does this firmware has any feature as:

- Rotate 90º for vertical games for example.
- Flip the imagine so show on screen the image inverted horizontal.

I'm not sure if it is possible, or requires to much effort to develop this code. but just let me know your thoughts about it.

Thanks in advance, and awesome improvement thought

^the answer to both is no. And it is unlikely they will be added to development, as rama is focused on other efforts.

Sent from my SM-G955U using Tapatalk

Rotation can't be done on these Gonbes boards. The hardware can't do it.

[TABYDACAT]

Just wanted to update on this OLED option. Currently still getting the logic down for the OLED itself, navigating menus, selecting options etc. So far, with other projects, I've been working on this at a slower pace. Also finished cleaning up the encoder signals via an efficient ISR and caps. Overall, its coming along and hopefully will be done for ppl to test out here. Also included a picture of the new boot logo I mentioned on the previous post. Anyways, thanks for reading, have a good day!

Spoiler

[SuperSpongo]

Great progress

[Guile]

I've been testing using the gbsc with an ossc but I'm noticing a large horizontal band of noisy diagonal lines in the top part of the image and some shimmering diagonal waves that move from the bottom right to the top left.

In a blog post I found they mentioned changing HTotal++ under developer mode. I tried this and it changes the noise but doesn't get rid of it. Either the waves get closer together or the noisy band splits.

So I tried connecting the gbsc to a different device and the noise was reduced a lot but is still there. I'm using 480p from the gbsc to line2x ossc to a scaler to get 1080p. It seems that the ossc greatly magnifies the noise when it line doubles the original. I also tried another power supply but it made no difference.

Has anyone else noticed this kind of noise? I saw a video of a guy putting copper tape on the bottom, maybe I will try that.

[Josh128]

Is your monitor by chance in close proximity to another monitor? My GBS-C output is absolutely rock solid with no waves, lines or interference on my VGA monitor-- unless I drive headphones with audio riding in the SCART cable feeding the input to the GBS-C OR I power on the 20" TV next to my monitor. Both induce very light waves/noise in the VGA monitor.

If I drive a high impedance audio input, such as an amplifier instead of the low impedance headphones, the audio does not disturb the picture (less current flowing in the audio wires of the SCART cable).

[NoAffinity]

I'm using 480p from the gbsc to line2x ossc to a scaler to get 1080p. It seems that the ossc greatly magnifies the noise when it line doubles the original. I also tried another power supply but it made no difference.

I'm not completely clear on what your chain is but why are you using anything other than gbsc to get 1080p?

Separate note: have you tried copper tape on the bottom, to stifle noise from the ram traces?

Sent from my SM-G955U using Tapatalk

[Guile]

Is your monitor by chance in close proximity to another monitor? My GBS-C output is absolutely rock solid with no waves, lines or interference on my VGA monitor-- unless I drive headphones with audio riding in the SCART cable feeding the input to the GBS-C OR I power on the 20" TV next to my monitor. Both induce very light waves/noise in the VGA monitor.

If I drive a high impedance audio input, such as an amplifier instead of the low impedance headphones, the audio does not disturb the picture (less current flowing in the audio wires of the SCART cable).

I'm going to make a case for it but it's just the bare board now. I do have it near some scalers and the ossc but no other monitors, it's going to a tv. I will test it on another environment and see if it changes the noise. I should have some ferrite wire clips somewhere I can try too.

I'm not completely clear on what your chain is but why are you using anything other than gbsc to get 1080p?

Separate note: have you tried copper tape on the bottom, to stifle noise from the ram traces?

Sent from my SM-G955U using Tapatalk

I tried the 1080p output from the gbsc but it looked a lot better to me going through the ossc line2x from 480p. I use a scaler to get the 960p to 1080p as the tv won't display 960p.

I was interested in the gbsc because it can switch 480i and 240p extremely fast and for its downscaling.

I mentioned the copper tape thing but I will definitely try that.