HDMI output for A1200?

[sigmason]

It's probably do-able.  Just consider however that while this eliminates the 'interface' quantizing data through A/D - D/A conversion, it means you need to not only keep up with the video bus of the Lisa (not impossible) but also feed the HDMI display and deal with those issues in a predictable manner.

Remember that the inputs to the Lisa you plan on tapping while digital and RGB are meant to drive the logic of the Lisa.  The software creating those signals expects things like palettes and 'copper' (not the metal!) and you are getting in before all that.  So you'll have to replicate that function on your end.  I suspect todays programmable logic and MCUs could keep up.  How cost effective it would be, that's another question.

You should also be aware there are companies that make SCART to HDMI converters like Cyp and while they do loose some quality in the conversion, they likely work without you spending a good deal of time and effort.

http://www.cypress.com.tw/

Sigmason

[sigmason]

Considering the Amiga must create all the signals it needs to produce the video output, I have no doubt that an analysis of the schematic after the Lisa chip should reveal all the logic that went into the production of the video signal.

Whether you replicate the logic or do it some other way is of course up to the person putting in the effort.

Here's a block diagram of the Amiga 1200:
http://www.amigahistory.co.uk/block.gif

Now consider that by taping the output side you are potentially creating yourself a new problem.  When you tap the input side you have to replicate the functionality to get output.  When you tap the output side, you still eliminate the A/D - D/A but then you have to consider that the Lisa chip will start to output all of the funky variations of video mode that make this so complicated.

As to whether it's better to simply 'replace' the Lisa or deal with the output modes I'll leave up to the person that  tackles this.

There's more information here:
http://www.amiga-hardware.com/showhardware.cgi?HARDID=13
(note the schematics file)

Sigmason

[sigmason]

AlexH:

1. Lisa can't make RGB without a synchronization.  It doesn't matter what makes the original H&VSync.  It must be possible from Lisa alone to determine sync (and obviously someone has.)

2. Scan doublers and flicker fixers yes.  If the intent is to effect that as the limit of the change.  In doing scan doubling you are limiting your ability to get anything better though.  Basically as I said, the limit of the advantage in this mode is that you don't do another extra conversion.  It's not allowing you to bypass any of the clocking issues or the side effects that can create.  Just because you have the original RGB data, that doesn't mean you can't inject problems into the output quality from the syncs being inappropriate for certain displays.  I don't know how much or how little a problem that can create in this particular system.  I do know from working with video equipment that it can create problems.

3. It's much more work, but yes it's possible to replace the Lisa.  The only thing stopping someone from doing that is the engineering and reverse engineering of the existing Lisa to replicate it's functionality.  It's way beyond what your average person should do, but it's hardly impossible.  Think about how many Intel compatible UARTs Asian countries spat out in the early days of the PC industry.  Many of them were basically created in a manner that could be used to reverse engineer any chip in the system.  More over, given the cost of FPGAs and their speed today it's more probable then ever that someone really bent on doing this, could do this.

Sigmason

Let me phrase it like this, I wouldn't waste my time replacing Lisa.  It's a lot of work for little return as the market probably isn't large enough to net a return on that scale (that's a business problem, that doesn't make it impossible at an engineering level.)

It's probably better to say, it would be much more practical to work with the existing Lisa outputs and whatever else you need to replicate the scan doubler function like AlexH is saying.  That said, be prepared that you'll have to make sure the video system your HDMI is connected to will tolerate the resulting output.

[sigmason]

Leirbag28:

I don't think making an HDMI output from the signals in the Amiga would slow it down.

If you truly only take the existing signals and ask nothing more of the Amiga hardware then to output them it would have no effect on the Amiga system itself.

Now if you were to somehow how ask the Amiga to put itself in a particular mode, or do something extra to accommodate said change that's a different story and I don't think that was what someone was suggesting.  In a way, would that not be exactly like installing a video card?

Sigmason

[sigmason]

Eriond:

You'll only get from the Amiga what the Amiga will give you unless you start messing with the drivers and everything else.

If you want a clock other then the 28MHz clock that is on the Lisa, you'll have to create the hardware to insure that the data you want is where you need for the HDMI transmitter's sampling.  So think basically a scan doubler like AlexH is saying, but extend that to creating a digital output instead of an analog one like most monitors and older products made.  The big difference is that everything you are doing is digital.  Which means that you won't loose in the A/D - D/A conversions but again, you must compensate for the timing differences and that's where you have your challenges.

This could actually be harder to do if you want to make the Amiga Lisa chips output conform via conversion to HDMI then to get the output of the Lisa to conform to something that 'will work' with an SVGA monitor.  The SVGA monitor will work with simple scan doubling because of it's wide sync ranges.  The HDMI specs, if you want them correct, will be harder to match and the process you use to match them, while constant for all HDMI inputs, could create issues that will be ever present.  As apposed to creating an output that is close enough for SVGA monitors and might work better on some displays and not as well on others.

Sigmason

[sigmason]

AlexH:

LOL, so show me where I'm wrong:

Alright here you go:
http://www.hdmi.org/pdf/HDMISpecInformationalVersion.pdf

Be sure to read the sections: "Pixel-Repetition" (IE digital scan doubler) and "Pixel Encodings".

Here's your modes:
http://writch.com/video.html

Here's some history on 'NTSC' video:
http://www.epanorama.net/documents/video/rs170.html

Here's 576i:
http://en.wikipedia.org/wiki/576i

Here's 480i (aka NTSC HiRes Interlaced):
http://en.wikipedia.org/wiki/Display_resolution

Now depending on how much of this that 'HDMI transmitter' does will really depend on how this will react to having the Amiga sending video to it.

Let's consider this: if the Amiga at NTSC HiRes interlaced (which is a fine mode and the Toaster and other genlocks should work at it) is spitting out 640x400x60Hz or 480i.  The digital data you are tapping at Lisa is pixel data for less pixels then the HDMI interface will require in a given frame or field because the HDMI display modes are all more data then you actually have (causing you to do pixel repetition on HDMI).  Even if the frequency of the digital data stream amounts to NTSC video at 50 or 60Hz what about the resolution?  You are transmitting in digital per pixel.  Usually most of the HDMI displays I've seen scale 480i to get it fullscreen because not only are they not 480i resolution, but even if they are actually 640x480 they are missing 80 lines of information so it's either scaling or black somewhere (which you as the transmitter can't really control.)  So even 480i is actually stretching the timing in HDMI standard because it doesn't match one of the standard transmission resolutions so they resort to pixel repetition.

Now that's just 480i.  The Amiga obviously can do more modes then that (even if he drops the modes you mention.)  I suppose he could repeat further if he's actually the HDMI transmitter, but in doing so he's only asking for more screen scaling he can't control and by the specification itself the sink is simply being told how much pixel data it can drop if it wishes without loosing a unique pixel.  Of course pixel repetition is handy if your modes are actually an equal division of 640x400 or 480i.  However, I see a problem.

If the RGB data coming out of Lisa is 320x200 interlaced for instance and you want to double it think about the timing difference going into something designed to take in 480i and getting something a division of 480i.  If they sample more then one pixel in digital RGB for that input timing how do they compensate for the timing difference?  I don't see inputs specified for chips from Silicon Image or Analogix that are lower then 480i.  I don't see RAM in there.  They appear to be 'just in time' transmitters with no compression.  So how would it compensate for this difference if you use them to produce HDMI from the Amiga and the Amiga is not in NTSC HiRes Interlaced or 480i?

Sigmason

If you think I'm wrong enlighten me.
If I'm wrong I'm a big boy I can accept that.