Date   : Mon, 02 Mar 2009 20:42:05 +0000 (GMT)
From   : tommowalker@... (Tom Walker)
Subject: Fwd: New Screen Modes with ARM7 Co-Processor?

> But that hardly constitutes 'hardware support'. And it is far more 
> complex and far more sensitive to timing than what I suggested. You 
> only need to switch banks every frame (in the vblank period) if you 
> leave the CRTC in 'interlace sync' mode.

But this method gives a more logical memory map. And gives no chance of getting
the fields the wrong way round - requiring user intervention is bad!

And it's not that sensitive to timing - unless you're insistant on not running
your beeb on a 50hz 312-line display.

> No, just insistent that you can't change the CRTC start address mid-
> frame (as in : the appropriate registers in the CRTC).

You need to read up on the vertical splitting or 'rupture' trick, which lets
you do exactly this.

> Using the wraparound instead is a neat trick, but it doesn't change the 
> CRTC's start address.

That's not needed for what we're talking about! Look at the sodding code
I posted earlier.

Tom