Ben + UBB + a few components = "VGA"

Werner Almesberger werner at
Sun Apr 24 08:58:41 EDT 2011

David Kuehling wrote:
> Hey, this looks good.  Time to give my next powerpoint presentation with
> my nanonote :)

Yeah, I wonder how much we can strecth those timings. At least in
theory, a digital display doesn't really need a lower bound for
pixel frequency and such. So maybe even a better approximation of
full QVGA resolution is possible.

Another line of investigation would be to raise PCLK. I tried
changing it (up and down), and this always resulted in an
unresponsive system. But that doesn't have to mean that it's
impossible :)

> I guess that rules out playing back movies via your VGA?  Hmm, just had
> a look at the Jz47xx datasheet, unfortunately we can't make the hw
> scaler write all pixels to the same address (else that'd give us a
> dma-driven vga output :)

I actually looked at DMA, but it would be quite complicated
because you'd need to write to two registers, the set and the
clear register. The complexity would also mean that it's probably
slower and more jittery than just banging things from the CPU.

Another approach could be to abduct the LCD signals. There, it
would probably be possible to generate the right timing, even
for resolutions like full VGA. The problems: 1) finding a
suitable FPC and 2) the limited number of insertions this sort
of connection supports.

- Werner

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