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From: andrew@teslab.lab.OZ (Andrew Phillips)
Newsgroups: comp.sys.amiga.emulations
Subject: Re: Bridgeboard Graphics Displays - are they as slow as I think?
Message-ID: <1189@teslab.lab.OZ>
Date: 22 Jan 91 00:39:29 GMT
References: <6474@munnari.oz.au>
Reply-To: andrew@teslab.lab.oz.au (Andrew Phillips)
Organization: Technology Evaluation Section, L.A.B., Sydney
Lines: 32

In article <6474@munnari.oz.au> ianr@mullian.ee.mu.OZ.AU (Ian ROWLANDS) writes:
> Since I got my bridgeboard, I've noticed that the display is rather
>slow when displaying graphics. This occurs even with the window
>having a priority of 10, and no other processes running. Has anybody
>else noticed this?

Yes, this is due to the fact that a task on the 68000 side has to
read the dual port RAM and write to the bit planes of the MSDOS
window.  This causes the only compatibility problem I have noticed
with my SideCar, which is not being able to run some games which
update the screen continually (not that MSDOS games are worth
playing).

The effect can be lessenned somewhat by using less colours in the
MSDOS window, thus reducing the number of bit planes that the task
has to write to.  Actually I find it surprising that it is as fast as
it is considering its done in software (with a bit of hardware help
to avoid bit fiddling).  This speed limitation is probably why there
has never been EGA emulation for SideCar/BridgeBoard.

>Also, how does the display perform with an accelerator in the system
>(the Amiga side, I mean)? Does the speed pick up or is the display
>still slow?

An Amiga accelerator would improve it somewhat but probably the
greatest limiting factor is the speed of writing to CHIP RAM.  Of
course, having an accelerator on the MSDOS side (such as a 386 card)
would not improve the display update speed at all.

Andrew.
-- 
Andrew Phillips (andrew@teslab.lab.oz.au) Phone +61 (Aust) 2 (Sydney) 289 8712