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 Post subject: Re: DreamcastHDMI github by chriz2600
PostPosted: Wed Jan 31, 2018 11:12 pm 


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Location: USA, California
This is fantastic, and happy to see this is still being worked on. :mrgreen:


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 Post subject: Re: DreamcastHDMI github by chriz2600
PostPosted: Thu Feb 01, 2018 12:06 am 


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I don't get what people are saying about the dreamcast being in a 720x480 frame. At what stage is this supposed to be the case? The VGA signal does not specify a horizontal dimension in pixels, so that distinction is only a product of the dot clock rate and sync timings. If that quoted 720 pixel width includes the blanking and sync periods, then that's not far off from the typical 768 / 800.
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 Post subject: Re: DreamcastHDMI github by chriz2600
PostPosted: Fri Feb 02, 2018 3:21 pm 



Joined: 07 Feb 2016
Posts: 15
Location: Cologne, Germany
mikejmoffitt wrote:
I don't get what people are saying about the dreamcast being in a 720x480 frame. At what stage is this supposed to be the case? The VGA signal does not specify a horizontal dimension in pixels, so that distinction is only a product of the dot clock rate and sync timings. If that quoted 720 pixel width includes the blanking and sync periods, then that's not far off from the typical 768 / 800.


You are absolutely right regarding analog domain. The dreamcasts sync signal placement will create a 640x480 image on screen with a pixel aspect ratio of 1:1.

For the digital domain there is EIA-CEA-861 standard:
There are two relevant formats here:

- Format 1:
640x480p @59.94/60 Hz (4:3 only) based on VESA Monitor Timings Specification, version 1.0 revision 10 [10]
- Format 2:
720x480p @59.94/60 Hz (4:3 aspect ratio) based on CEA-770.2-C [19]

The dreamcast uses a field rate (vertical sync frequency) of 59.94Hz with 525 horizontal lines with a pixel clock rate of 27Mhz, which results in 858px per line.
-> 59.94Hz * 525px = 31,4685kHz
-> 27Mhz / 31,4685kHz = 858px

So a modern display will internally convert the dreamcast "VGA" singal to format 2
The problem is, that Format 2 is 720x480 with a picture aspect ratio of 4:3, which results in a pixel aspect ratio of 8:9, which will result in a visibly squashed image.


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 Post subject: Re: DreamcastHDMI github by chriz2600
PostPosted: Fri Feb 02, 2018 11:46 pm 


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I think this misunderstanding stems from mid-2000s era televisions that will accept VGA, but sometimes have a "square peg in a round hole" method of trying to make everything "just work", and the first thing they probably did was try to guess the intended image resolution from the video timings.
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 Post subject: Re: DreamcastHDMI github by chriz2600
PostPosted: Sun Feb 18, 2018 9:31 am 


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Joined: 15 Dec 2012
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Speaking of modes, are the any plans to support higher than 480p? I understand that 1080p is not feasible with the current board, but 1280x960 would probably be possible with just firmware changes.


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 Post subject: Re: DreamcastHDMI github by chriz2600
PostPosted: Mon Feb 19, 2018 5:49 pm 



Joined: 07 Feb 2016
Posts: 15
Location: Cologne, Germany
marqs wrote:
Speaking of modes, are the any plans to support higher than 480p? I understand that 1080p is not feasible with the current board, but 1280x960 would probably be possible with just firmware changes.


Yes! I did some math yesterday, and it's definitely possible to support 1280x960 and even 1080p in "pixel exact" mode, meaning 1280x960 pixels inside a 1920x1080 frame.
I will give this a try the next days.


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 Post subject: Re: DreamcastHDMI github by chriz2600
PostPosted: Mon Feb 19, 2018 9:16 pm 


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chriz2600 wrote:
Yes! I did some math yesterday, and it's definitely possible to support 1280x960 and even 1080p in "pixel exact" mode, meaning 1280x960 pixels inside a 1920x1080 frame.
I will give this a try the next days.
Wouldn't you need larger FPGA than EP4CE6E22C8 or external RAM for line buffers to compensate the difference between linedoubled DC output (2x525=1050 lines) and 1125 lines of 1080p?


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 Post subject: Re: DreamcastHDMI github by chriz2600
PostPosted: Mon Feb 19, 2018 9:48 pm 



Joined: 07 Feb 2016
Posts: 15
Location: Cologne, Germany
marqs wrote:
chriz2600 wrote:
Yes! I did some math yesterday, and it's definitely possible to support 1280x960 and even 1080p in "pixel exact" mode, meaning 1280x960 pixels inside a 1920x1080 frame.
I will give this a try the next days.
Wouldn't you need larger FPGA than EP4CE6E22C8 or external RAM for line buffers to compensate the difference between linedoubled DC output (2x525=1050 lines) and 1125 lines of 1080p?


Actually I don't need a full frame buffer, because I can display lines while they are read.
The horizontal frequency of 1080p is 67.5kHz -> 33.75kHz line doubled.
The horizontal frequency of VGA is 31.5kHz.
In the time 480 line doubled lines in 1080p are put out, 448 lines of VGA are displayed.
So I only need 32 lines of buffer (31.5kHz / 33.75kHz * 480 = 448)
The required memory size is: 32 lines * 24 bit * 640 pixels = 491.520 bits. This fits well inside the FPGA.


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 Post subject: Re: DreamcastHDMI github by chriz2600
PostPosted: Tue Feb 20, 2018 5:14 pm 


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chriz2600 wrote:
Actually I don't need a full frame buffer, because I can display lines while they are read.
The horizontal frequency of 1080p is 67.5kHz -> 33.75kHz line doubled.
The horizontal frequency of VGA is 31.5kHz.
In the time 480 line doubled lines in 1080p are put out, 448 lines of VGA are displayed.
So I only need 32 lines of buffer (31.5kHz / 33.75kHz * 480 = 448)
The required memory size is: 32 lines * 24 bit * 640 pixels = 491.520 bits. This fits well inside the FPGA.
I made similar calculations for cps2 digital AV mod and ended up selecting 10CL025YE144 (largest non-BGA FPGA in Cyclone 10 LP series) which has enough block RAM for line buffers but only barely. I assume you refer to different FPGA than EP4CE6E22 which only has ~270 kbits of block RAM.


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 Post subject: Re: DreamcastHDMI github by chriz2600
PostPosted: Tue Feb 20, 2018 8:54 pm 



Joined: 07 Feb 2016
Posts: 15
Location: Cologne, Germany
marqs wrote:
chriz2600 wrote:
Actually I don't need a full frame buffer, because I can display lines while they are read.
The horizontal frequency of 1080p is 67.5kHz -> 33.75kHz line doubled.
The horizontal frequency of VGA is 31.5kHz.
In the time 480 line doubled lines in 1080p are put out, 448 lines of VGA are displayed.
So I only need 32 lines of buffer (31.5kHz / 33.75kHz * 480 = 448)
The required memory size is: 32 lines * 24 bit * 640 pixels = 491.520 bits. This fits well inside the FPGA.
I made similar calculations for cps2 digital AV mod and ended up selecting 10CL025YE144 (largest non-BGA FPGA in Cyclone 10 LP series) which has enough block RAM for line buffers but only barely. I assume you refer to different FPGA than EP4CE6E22 which only has ~270 kbits of block RAM.

Yes you are right, I messed things up. I will definitely need more memory than available on the EP4CE6E22. The altsyncram megafunction lets you create memory larger than available on the device, which let me to believe this was possible.


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 Post subject: Re: DreamcastHDMI github by chriz2600
PostPosted: Mon Mar 05, 2018 4:07 pm 


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Joined: 05 Mar 2018
Posts: 664
joined the forum just for this thread! excited to FINALLY have a reasonable way to correct DC aspect on a digital display


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 Post subject: Re: DreamcastHDMI github by chriz2600
PostPosted: Wed Mar 28, 2018 1:58 pm 


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Joined: 25 Dec 2013
Posts: 582
Location: Indiana
Finally got video output the other night. I accidentally have the ADV IC flipped 180 :oops:

https://www.youtube.com/watch?v=kOAO_-zbwp4


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 Post subject: Re: DreamcastHDMI github by chriz2600
PostPosted: Wed Mar 28, 2018 3:53 pm 


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citrus3000psi wrote:
Finally got video output the other night. I accidentally have the ADV IC flipped 180 :oops:

https://www.youtube.com/watch?v=kOAO_-zbwp4

I want this soo bad lol, I know you don't typically sell premade boards - but you should for this one :mrgreen:


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 Post subject: Re: DreamcastHDMI github by chriz2600
PostPosted: Wed Aug 22, 2018 5:40 pm 



Joined: 19 Jul 2017
Posts: 1146
chriz2600 wrote:
Wolf_ wrote:
So does this mean that to play every game you would need to use analog output for the 49 games that won't run in vga mode as well as a hdmi connection for everything else?


No, the current implementation supports line doubling of 480i content to 480p. You only need HDMI.

How does the DreamcastHDMI handle the handful of games that aren't compatible with RGB?


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 Post subject: Re: DreamcastHDMI github by chriz2600
PostPosted: Wed Aug 22, 2018 6:33 pm 


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nmalinoski wrote:
How does the DreamcastHDMI handle the handful of games that aren't compatible with RGB?


240p & 480i RGB and Composite games are handled the same way. Digital video is grabbed before the DAC.

If you are not using VGA mode (480p) all games will have RGB quality via HDMI, even composite only games.


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 Post subject: Re: DreamcastHDMI github by chriz2600
PostPosted: Wed Aug 22, 2018 9:06 pm 



Joined: 13 Dec 2015
Posts: 71
citrus3000psi wrote:
nmalinoski wrote:
How does the DreamcastHDMI handle the handful of games that aren't compatible with RGB?


240p & 480i RGB and Composite games are handled the same way. Digital video is grabbed before the DAC.

If you are not using VGA mode (480p) all games will have RGB quality via HDMI, even composite only games.
Forgive me but I’m not clear on this. Are you saying games which support VGA mode will automatically use it as if a VGA box is connected while games which don’t will still load and display without producing the VGA unsupported error? So this will be completely seamless?


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 Post subject: Re: DreamcastHDMI github by chriz2600
PostPosted: Thu Aug 23, 2018 2:47 pm 


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mario64 wrote:
Forgive me but I’m not clear on this. Are you saying games which support VGA mode will automatically use it as if a VGA box is connected while games which don’t will still load and display without producing the VGA unsupported error? So this will be completely seamless?


Yes in a way.

We have designed the Pin6/Pin7 to work in a bi-directional fashion. The FPGA will have three modes (planned):

1:VGA Mode - FPGA will force Pin6 and Pin7 low thus putting the dreamcast into VGA mode with no box connected.
2:VGA Trick Mode - FPGA will allow the game to boot and swap to VGA mode after a determined time. (This is still in the works, but should be possible)
3:Detect Mode - FPGA will read the status of Pin6.
---3a:If you insert a VGA box, FPGA will go into VGA mode.
---3b:If you insert an RGB cable, FPGA will go into 15Khz Mode with RGB in the analog port
---3c:If you do not insert nothing OR insert composite/S-Video cable, FPGA will go into 15Khz.

I'm also considering designing a little addon board, which will xor the syncs. So we can get 480p over scart. Will be helpful to GSCART users etc.


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 Post subject: Re: DreamcastHDMI github by chriz2600
PostPosted: Thu Aug 23, 2018 5:50 pm 



Joined: 13 Dec 2015
Posts: 71
citrus3000psi wrote:
mario64 wrote:
Forgive me but I’m not clear on this. Are you saying games which support VGA mode will automatically use it as if a VGA box is connected while games which don’t will still load and display without producing the VGA unsupported error? So this will be completely seamless?


Yes in a way.

We have designed the Pin6/Pin7 to work in a bi-directional fashion. The FPGA will have three modes (planned):

1:VGA Mode - FPGA will force Pin6 and Pin7 low thus putting the dreamcast into VGA mode with no box connected.
2:VGA Trick Mode - FPGA will allow the game to boot and swap to VGA mode after a determined time. (This is still in the works, but should be possible)
3:Detect Mode - FPGA will read the status of Pin6.
---3a:If you insert a VGA box, FPGA will go into VGA mode.
---3b:If you insert an RGB cable, FPGA will go into 15Khz Mode with RGB in the analog port
---3c:If you do not insert nothing OR insert composite/S-Video cable, FPGA will go into 15Khz.

I'm also considering designing a little addon board, which will xor the syncs. So we can get 480p over scart. Will be helpful to GSCART users etc.
Thanks Citrus. I’m curious as to what would be the need for VGA boxes, Scart, etc if you already have HDMI. I assume those are just extras in case someone doesn’t want to use HDMI?


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 Post subject: Re: DreamcastHDMI github by chriz2600
PostPosted: Thu Aug 23, 2018 6:02 pm 


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Location: Indiana
mario64 wrote:
Thanks Citrus. I’m curious as to what would be the need for VGA boxes, Scart, etc if you already have HDMI. I assume those are just extras in case someone doesn’t want to use HDMI?


Dual output for streamers, also someone may have a mutliformat monitor they still might like to hookup occasionally. The goal was add features but not hinder at the same time :D


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 Post subject: Re: DreamcastHDMI github by chriz2600
PostPosted: Thu Aug 23, 2018 6:29 pm 



Joined: 13 Dec 2015
Posts: 71
citrus3000psi wrote:
mario64 wrote:
Thanks Citrus. I’m curious as to what would be the need for VGA boxes, Scart, etc if you already have HDMI. I assume those are just extras in case someone doesn’t want to use HDMI?


Dual output for streamers, also someone may have a mutliformat monitor they still might like to hookup occasionally. The goal was add features but not hinder at the same time :D
Very cool. Thanks again. Can’t wait for availability! :D


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 Post subject: Re: DreamcastHDMI github by chriz2600
PostPosted: Thu Oct 11, 2018 8:41 pm 



Joined: 19 Jul 2017
Posts: 1146
Has it been decided where the HDMI port/board will be mounted?


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 Post subject: Re: DreamcastHDMI github by chriz2600
PostPosted: Mon Apr 15, 2019 8:15 pm 



Joined: 19 Jul 2017
Posts: 1146
For the handful of games that support it, how is Dolby ProLogic/surround sound handled by the DCHDMI?


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 Post subject: Re: DreamcastHDMI github by chriz2600
PostPosted: Mon Apr 15, 2019 9:16 pm 


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nmalinoski wrote:
For the handful of games that support it, how is Dolby ProLogic/surround sound handled by the DCHDMI?

I think it's safe to assume that he is transmitting all audio over HDMI as 2 channel PCM

matrixed surround (i.e. prologic 1/2 and dolby surround) would be fully supported in that case as long as you switch your receiver over to dolby PL mode when playing an appropriate game


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