Feature Request: 15kHz "Direct Video" output over HDMI (PAL CRT support)

[MarkSpiru]

Hi! I’m looking for a way to use this core with a 15kHz PAL CRT using an HDMI-to-VGA adapter (similar to MiSTer’s "Direct Video" mode).
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Could you add an OSD option to output a raw 15kHz signal (240p/288p) over the HDMI port?

This would allow the use of a standard HDMI-to-VGA adapter to connect directly to a CRT/SCART setup without the lag of an external downscaler.

​​BIg thanks for all your hard work on this project :)

[harbaum]

That's actually more complex than it sounds as this requires to switch between different HDMI clocks. The HDMI clock is the base clock in most of our cores and all other clocks are derived from this. The HDMI clock needs to be five times the pixel clock which in turn is 28 MHz in our setup since we have a scan doubler integrated but would need to be 14mhz without scan doubling. This also affects the on screen display which is currently located behind the scan doubler and which would have to be rewritten to run in front or even without it.

I actually once tried that with the Atari ST core. The result was working but compatibility with my screens and the HDMI to VGA adapters own was pretty bad and those that coped failed to properly scale the image.

Are you sure your HDMI converter copes with 720x240@60p and 720x288@50p?

This is such a special use case that I'd actually suggest to build custom cores for this and not integrate this into the mainline cores. This may be a compile time option using some ifdef's.

Also switching between the modes at runtime IMHO doesn't make too much sense as the screens would not cope with "that other mode" at all.

[MarkSpiru]

Thanks for explaining the HDMI limitations..

Just an other option maybe it's. More feasible..

What about ..If one can sacrifice midi and DB9 joystick ports...Would it be possible instead to map the internal Amiga OCS/ECS color palette (which is 12-bit total: 4 bits for Red, 4 for Green, 4 for Blue) directly to 12 GPIO pins. So it can be used with a resistor ladder to output RGB and csync .. also is it possible to map audio ..

Keep up the good work ..

Thanks in Advance..

[harbaum]

Sure. That would be much easier. You'd also need hsync and vsxnc. The original MiST did this and you should easily get a few hints from its public schematic. And the 'lcd' variants already expose similar signals for the 40pin LCDs.

If you start with a scan doubled analogue signal you basically don't have to change anything and can test with an analogue VGA screen. Once that works you can try to remove the scan doubler.

[MarkSpiru]

Great thanks 😊