Date   : Tue, 20 Jan 2015 18:11:05 +0000
From   : jgh@... (J.G.Harston)
Subject: Compromises

Richard Broadhurst wrote:
> I would have rearranged the address lines on the video ULA which was
> custom anyway to view memory in columns of bytes, the the first scan

The video ULA had nothing to do with the screen memory addressing, that 
is entirely down to the CRTC. The video ULA merely takes whatever data 
byte happens to be on the data bus and serialises it into pixel data.

> line in mode 1 would have been &3000, &3100, &3200, ... This would
> have made gfx plotting routines faster, gfx text full speed when byte
> aligned and simplified sprite drawing, making it faster.

The video addressing was arranged to make text output faster, "drawing" 
a character in monochrome screen modes was a simple fast LDA (src),Y:STA 
(dst),Y:DEY:BPL loop. In MODE 7 the screen *is* addressed as base+0, 
base+1, base+2, etc.

> This would have helped in the BBC games department, which should have
> translated to improved sales.

I don't think Acorn or the BBC had any thoughts about the BBC being used 
for games, at least not to the extent that happened. It was conceived of 
primarily a learning, programming, experimentation and "office tasks" 
machine.

> Nice to have would have been:
...
> A border colour register.

One of my projects: http://mdfs.net/Info/Comp/BBC/Border
Just need to persuade emulator writers to support it. :)

-- 
J.G.Harston - jgh@...      - mdfs.net/jgh