If it helps, the LCD I use is , though you can probably use any lcd with that driver IC.

Wow, that was fast

Keep up the good work!

Gotcha! A CD4020 counter to automatically generate the /CS for the LCD, plus some code to write in bursts instead of single words, increased the framerate dramatically. It still isn't too quick, but should work OK for static data.

Video: Xfbdef (framebuffer-based X server) running on the Carambola, prboom running on my workstation sending the graphics data to the Xserver on the Carambola:
http://www.youtube.com/watch?v=vBnvMY7t5KQ
It ain't the 'playing Doom on the Carambola' I promised, but it comes pretty close imo.

I'm working on an article for my site about it (the code mostly isn't architecture-specific, so non-Carambola-users may benefit from it too) and I'll put online patches when that's finished.

This is already pretty awesome. Is there any chance for further improvement on the framerate? It'd be really impressive to have a pocket Doom aöways with you.
Keep up the good work

Theoretically I could shave off 1/4th of the time it takes to upload a frame by using a counter that only counts to 24, but that still wouldn't bring the speed up to something that'd enable a playable Doom... sorry.

Hmm, just found out the SSD1289-driver I use isn't too well-written... it tries to continouously refresh the display, making the CPU-load go to 100% even when the image doesn't change... I may have to roll my own driver using a true virtual framebuffer after all :/

So for a decent framerate we'd have to use some kind of USB graphics card.
If I knew how to implement a Linux driver for that I'd eventually try it out, I still got an STM32F4 laying around, it's more than adequate for that task.

I did that once; I however used a Macintosh CRT as output instead of an LCD (and a different arm, iirc I used a LPC1343). You still may find the code of some use, though: you can download it at the last page of article.

Code is coming along nicely: it's shaping up to be a fairly neat framebuffer device. I've been implementing the touchscreen too, and I'm now 'testing' using a little game you all may or may not know:

It's actually not even half bad, playability-wise, though screen-scrolls bring down the framerate a fair bit.