Date   : Sun, 17 Sep 2000 23:57:12 "GMT"
From   : "mikef@..." <mikef@...>
Subject: 6845 and Beebem

It's more than a bug really. From what I've seen in the code the whole 6845/video
routines will require a rewrite to allow the screen redraw to work from the
character row and scanline counters of the 6845.
With my emulator, BeebIt, I got a lot of help on this from Stuart Mc. and 
while it was confusing to start with the final result, of the rewrite, is
easier to understand and works more logically then the way BeebEm, BeebInC
etc. do it. The problem shows up the most in Uridium where there are two
parts to the screen.

If you really have the time to attempt this rewrite, I or Stuart, if he's
willing, can provide you with some info.

Related to this question is an idea I've been thinking about for some time.
I would really like to see a central repository of information and data that
would help writers of BBC emulators to write them properly.
It would contain info, in easy to understand text, about how each of the
ICs in a BBC work and how they communicate with each other. I find the datasheets
lacking in many ways and experimentation on a real BBC takes too long.
Info on how the 6845/video works would be a prime candidate for this as 
well as *exactly* how the 6522 works. From what I've seen everyone has emulated
this chip in a different way but nobody has done it exactly right so that
all software works correctly.

What does everyone else think?

Mike.
---- original message ----
Sent: Sun, 17 Sep 2000 23:00:49 +0200
From: mu.list@...
To: BBC Mailing List <bbc-micro@...>
Cc: 
Subject: [BBC-Micro] 6845 and Beebem
As emulators and the 6845 have been of interest lately, I thought I'd bring
this up. There is an apparent bug in Beebem. It shows itself in games such
as Karate Combat and Qwak!

The screen isn't centered as it is on a BBC, but rather displayed from top
left. There is also some video garbage on the right of the screen.

Any ideas anyone ?

Mark


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