Date   : Mon, 02 Mar 2009 10:06:23 +0000
From   : robert@... (Rob)
Subject: Fwd: New Screen Modes with ARM7 Co-Processor?

2009/3/2 Ian Wolstenholme <bbcmailinglist@...>:

> So, with memory in abundance on the ARM7 co-processor, would there
> be a way of creating new screen modes, say an 8-colour mode at
> Mode 0 resolution, or even higher?
>

The memory for the display has to be accessible by the crt controller,
so has to be in the host machine, i.e. the Model B or Master. ?It
can't use memory on the co-processor (of any type). ?This means,
typically, that it needs to come out of the 32K RAM available. ?Mode 0
already takes 20K - to make it 8 colours would take 60K ...

It did cross my mind about paging in a SRAM bank, and using that to
give a few more contiguous KB upwards, but I think the circuitry is
set to hard-wire a wrap-around at the 32K boundary (so as to allow
hardware scrolling) which would preclude this, plus it'd keep getting
paged out for filing system access...

Rob

(apologies to Ian for duplicate, damn reply-to.. at least it gave me
the opportunity to correct a couple of typos!)