Making sense of GBA RGB555 output signals

Discussion of programming and development for the original Game Boy and Game Boy Color.
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Verseus Tahl
Posts: 2
Joined: Fri Jan 10, 2020 10:40 pm

Making sense of GBA RGB555 output signals

Post by Verseus Tahl » Fri Jan 10, 2020 11:38 pm

Hello! I would like to understand more about how the GBA (specifically SP) constructs and outputs its video image.
My end goal is to attempt to process these signals and convert them to a standard RGB format using SNES hardware. Certainly very ambitious, and I have no illusions of it being simple or easy. My main interest at the moment, however, is learning more about how the GBA SP's RGB555 data could be processed, and less about the specifics of accomplishing that task on the SNES.

I am aware of the GBA TV Converter, which does part of what I am attempting to do and I have ordered one for my own reference, but I do not believe it can be repurposed for my ends. If you have any info on this I would be most appreciative!

lidnariq
Posts: 9491
Joined: Sun Apr 13, 2008 11:12 am
Location: Seattle

Re: Making sense of GBA RGB555 output signals

Post by lidnariq » Fri Jan 10, 2020 11:51 pm

Verseus Tahl wrote:
Fri Jan 10, 2020 11:38 pm
convert them to a standard RGB format using SNES hardware
... wut?

Are you trying to recreate the Super Game Boy, but GBA? Not going to happen: the SNES's already at its full bandwidth limit just relaying a full DMG screen and there's no room for any more pixels nor any more bits per pixel.
how the GBA SP's RGB555 data could be processed
It's basically standard low-resolution LCD timing. There's a bunch of digital signals corresponding to the individual bits, clock signals for pixel clock, line clock, frame clock, and there might also be one to indicate field.

It's also basically the same kind of structure as an old digital (CGA, &c) monitor but with a whole lot less overscan.

Verseus Tahl
Posts: 2
Joined: Fri Jan 10, 2020 10:40 pm

Re: Making sense of GBA RGB555 output signals

Post by Verseus Tahl » Sat Jan 11, 2020 12:07 am

Ah, (my) ignorance, we meet again...

Well, thanks for the info. And yes, you hit the nail on the head. I had brainstormed some alternative methods in the event that was the case. Not a complete project ender, if anything it makes things easier.

I’ll dive deeper into LCD timing in the mean time.

calima
Posts: 1149
Joined: Tue Oct 06, 2015 10:16 am

Re: Making sense of GBA RGB555 output signals

Post by calima » Sat Jan 11, 2020 2:58 am

There are already a couple "GBA on a SNES" solutions, they all have their own video output and just use SNES for the controller and power.

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