Amiga HDMI output

[Jope]

Originally Posted by Staringlizard

Hi,

I made another video as demonstration. I have fixed some bugs and also changed the output to 50Hz as Jobe pointed out. I have also tried and highlight the current issues in this video.

Getting better all the time, great work! :-D

Photon's TV Tester may also be useful for your development work:
http://eab.abime.net/showpost.php?p=914581&postcount=49

The thread might be of interest otherwise as well.

[pandy71]

Originally Posted by Staringlizard

Hello,

I am done with my latest project

Be aware that this board has some state of the art, expensive as hell, parts.
Lets see what the interest is in this gadget and go from there.

Nice but:
- wrong assumption about pixel clock and horizontal resolution (not 720 pixels, no 13.5MHz clock)
- real 576i is only when LACE bit is active

As such for best results probably 1280x720p mode must be used as output mode with smaller video embedded inside.
Alternatively 1080p mode with pixel doubling can be (so efficiently 960x540p - Amiga window centered/cropped).
For 1080 pixel doubler maybe one of "pixel art resizers" can be implemented in FPGA https://en.wikipedia.org/wiki/Image_...ing_algorithms .
For correct phase acquisition external system clock source is recommended.

btw there is no such thing as 288p mode in Amiga - it can be 312p or 313p mode

[Mrs Beanbag]

Originally Posted by pandy71

For 1080 pixel doubler maybe one of "pixel art resizers" can be implemented in FPGA https://en.wikipedia.org/wiki/Image_...ing_algorithms .
For correct phase acquisition external system clock source is recommended.

Don't use pixel art resizers. They change the graphics and sometimes ruin things with their wrong assumptions. You could make it optional i suppose. But if you want to use your Amiga for actually making graphics it would really get annoying.

btw there is no such thing as 288p mode in Amiga - it can be 312p or 313p mode

Well technically maybe, but not all lines are visible, only 576 of the 625 lines are "active" according to the PAL standard. (some of these Inactive lines occur during the vertical blank, and were used to encode teletext signals)

[Supamax]

Originally Posted by Retro-Nerd

Sorry Supamax. This is nonsense. All computer/consoles from that time outputs a 240/288p signal for lores games. It's a non-standard PAL/NTSC signal, today also comparable with Low-definition television. Don't mix up the interlaced TV standard with this.

https://en.wikipedia.org/wiki/Low-definition_television

No, all PAL TVs could accept interlaced-only signals.
Via SCART/composite/RGB socket/RF (modulator), only 576i was possible.

Sinclair Spectrum, QL, C64, Amiga 500, game consoles, VCRs, ... all have video exits @ 15 KHz 50Hz interlaced.

Uhm, I see now that perhaps I didn't make myself clear: I'm not saying that the equipment above was "really" outputting a screen with 576 lines. What I'm saying is that the (lower) resolution was outputted in the form of a 576i (interlaced, always interlaced, never progressive) signal, so that it could be accepted by TVs, monitors (CM8833 class, not VGA 31 KHz of course), etc.

[Retro-Nerd]

Nope, still 240/288p. Hence the scanlines you can see due to half of the standard PAL/NTSC resolution. CRTs always supported progessive output.

http://scanlines.hazard-city.de/demystified.html

[Supamax]

Originally Posted by Retro-Nerd

Nope, still 240/288p. Hence the scanlines you can see due to half of the standard PAL/NTSC resolution. CRTs always supported progessive output.

http://scanlines.hazard-city.de/demystified.html

Nope, I'm sure, and even the website you linked proves me right.
Here are the most important phrases:

All the classic videogame system (Mega Drive, SNES in standard mode, PC Engine, etc) as well as almost all 2D arcade games over the past two decades put out 15kHz RGB signals. A 15kHz signal (well, actually 15.75kHz, but nobody really cares) is called a 15khz signal because the cathode ray in your classic tube TV will cross the screen 15750 times horizontally per second.

If you take a 60Hz refresh rate (standard for arcade games and NTSC videogame systems) you just divide 15750 by 60 you'll see that your TV is able to produce 262 lines per 1/60 second this way. (per 1/60 sec means "per pass"). Taking away some front porch & back porch, you'll get your 220 to 240 which most videogames and arcade game have as their vertical resolution.

The horizontal resolution isn't really limited by the TVs horizontal scanrate, but most games systems are going for a 4:3 pixel ratio, so you end up with something like 320x240 pixels for classic arcade games.

As you can imagine 320x240 pixels is a rather low resolution for a TV signal (or DVD if you like). This is why TV signals are transmitted interlaced. This means that first all odd lines are drawn across the screen and then all even lines are drawn. This means you'll get 480 lines onscreen (instead of 240), but you'll have to live with a little flicker since the two adjacent lines aren't drawn directly after each other, but only alternating (in other words you still only get 240 lines per 1/60 sec).

This mode is called 15 kHz interlaced (640x480i).

The above for NTSC signals. For PAL signals it's 576i (interlaced).

[hooverphonique]

a CRT is essentially a 50/60Hz progressive device with a vertical resolution somewhere in the ~260-290 lines range. interlace is achieved by the source signal delaying every other field by half a scanline, effectively causing it to display the lines in-between the lines of the previous/next field.

[demolition]

Originally Posted by Supamax

No. Normal RGB Amiga signal (15 KHz) is always outputting in *interlaced* 50Hz mode.
It never outputs a 288p progressive signal. Never.
So the assumption that the output signal is always 576i is correct.

In non-interlaced PAL, the Amiga outputs 50 frames per second as well as 50 fields per second. If it was indeed interlaced, it would be field rate = 2 x frame rate. Since all fields are on top of each other, it is a progressive mode, not interlaced.

This looks like a cool project, and we need to good converter between 288p@50Hz RGB and HDMI@50Hz for smooth motion. Perhaps 1920x1080 would be best suitable as 1080/4=270. With some scanline emulation, each input line could be made into two output lines and then two black lines (or light reduced lines), so to not require non-integer scaling.

[Mrs Beanbag]

Supamax what you just quoted proves nothing to do with what you're saying...

and it is FACT that Amiga outputs progressive (not interlaced) modes because i can SEE it with my EYES. If it were interlaced, it woud visibly flicker, even if even and odd frames were identical, as the image would still shake up and down by half a line.

additionally, i know that the signals are different because when i switch to an interlaced mode on my LCD monitor, it throws a hissy fit and i have to turn it off and on again.

[Retro-Nerd]

Supamax is still confused with TV broadcast, VHS/DVD video etc. First consoles that used a 480i/576i output regulary for games were Dreamcast and Playstation 2. Hopefully Staringlizard isn't get confused too now. Nice progess btw (second test clip).

[demolition]

Yes, you cannot broadcast an Amiga 288p signal without first converting it to interlaced (with quality loss).

[Retro-Nerd]

This could help him too. Actually the hazard city link was enough.

http://retrorgb.com/240p.html

[robinsonb5]

Originally Posted by Supamax

Nope, I'm sure, and even the website you linked proves me right.

None of what you posted is incorrect, but you're missing one important detail: in interlaced modes, all the even lines are transmitted in one field, and all the odd lines are transmitted in the other field, and the two types of field have a different sync pattern in the VBlank, which allows the TV to distinguish them and offset the odd lines, achieving the interlacing.

The mode people are calling 240p or 288p is output by almost all video game systems from the 80s and early 90s, and involves either only odd fields, or only even fields. The sync patterns don't alternate each frame - hence no interlacing occurs. The same 240 / 288 scanlines are drawn each time, and the normally-interlaced scanlines are left blank - hence the black scanline emulation you find in certain emulators. So while the display timings are basically the same as 480i / 576i, these modes are not the same as an interlaced signal with successive 50Hz frames assigned to alternating interlaced fields.

[Staringlizard]

Getting more and more confused here

The only thing I can say for sure is that the AD9984A asic that I am using as ADC does not alternate its field bit (e.g. it is fixed at odd or even field all the time) when receiving data from Amiga unless Amiga is explicitly set for interlaced graphic mode. Then the field bit will alternate.

This makes me believe that the output is indeed, normally, progressive from Amiga Video Connector.

Regards,
StaringL

[Doppelgaenger]

Wow, this looks really awesome! Go for it

[pandy71]

Originally Posted by Mrs Beanbag

Well technically maybe, but not all lines are visible, only 576 of the 625 lines are "active" according to the PAL standard. (some of these Inactive lines occur during the vertical blank, and were used to encode teletext signals)

My point was that Amiga may produce video that have different number of lines short/long fields and as such different vertical frequency which is important for such device as video converter.
288p is functional description for default video mode but in real life even OCS can produce almost 'ANY' amount of lines video - this is even more challenging as based on pixel clock rest of video acquisition need to be done in a smart way.
Only one thing is sure in Amiga - Sys clock and if you do video capture from Amiga you need to be perfectly in sync - best way to do this is provide own system clock.

Originally Posted by Supamax

No, all PAL TVs could accept interlaced-only signals.
Via SCART/composite/RGB socket/RF (modulator), only 576i was possible.

Sinclair Spectrum, QL, C64, Amiga 500, game consoles, VCRs, ... all have video exits @ 15 KHz 50Hz interlaced.

Nope and nope - Amiga is first interlace computer on market - rest is progressive generating 288p50 (and VCR recording frame that consisting two fields) - and so called interlace mode are nothing else than switching content between two fields however without interlace - interlace is strange concept of half line - old computer count always integer, Amiga also btw but two field can be different in length and as such after average half line is produced.
Second TV's can accept various video - trust i made lot of experiments - you are limited in CRT only by V and H deflection circuits - digital TV's are different story as they need to be programmed with tight tolerance and as such they support only official mode (even if they circuitry can accommodate more modes than regular CRT even multisync).

Originally Posted by demolition

Yes, you cannot broadcast an Amiga 288p signal without first converting it to interlaced (with quality loss).

Nope - you can perfectly broadcast 288p from Amiga without converting it to interlace - A520 modulator is clear example - analog circuitry in TV (and most digital) can deal with this kind of signal.

[Mrs Beanbag]

Originally Posted by pandy71

Nope and nope - Amiga is first interlace computer on market - rest is progressive generating 288p50

Enterprise 64/128 had real interlaced video modes. Not sure if released before Amiga or not, both released in 1985.

[john1979]

Originally Posted by Supamax

This is why TV signals are transmitted interlaced.

Old consoles transmit progressive not interlaced. To see an example of interlaced output from a console play a PlayStation 2 game. Most of them use 480i (ICO uses 240p).

[pandy71]

Originally Posted by Mrs Beanbag

Enterprise 64/128 had real interlaced video modes. Not sure if released before Amiga or not, both released in 1985.

Maybe - some rare machines or special purpose may have also interlace - in theory MC6845 used as CRTC in CGA was capable to produce interlace video, probably other CRTC also (not sure on Intel 8275 as this was realy weird CRTC).

[Mrs Beanbag]

Originally Posted by john1979

Old consoles transmit progressive not interlaced. To see an example of interlaced output from a console play a PlayStation 2 game. Most of them use 480i (ICO uses 240p).

Playstation 1 could also do 480i although not all games used it

interlace can also be seen on Sega Megadrive on Sonic 2 when the screen splits in 2 player race mode