Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!samsung!olivea!oliveb!amiga!boing!dale
From: dale@boing.UUCP (Dale Luck)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Simple Frame Buffer boards
Message-ID: <920@boing.UUCP>
Date: 5 Dec 90 18:04:32 GMT
References: <916@boing.UUCP> <23699@grebyn.com> <918@boing.UUCP> <1411@mpirbn.mpifr-bonn.mpg.de>
Reply-To: dale@boing.UUCP (Dale Luck)
Organization: Boing, Milpitas, Ca.
Lines: 45

In article <1411@mpirbn.mpifr-bonn.mpg.de> p554mve@mpirbn.UUCP (Michael van Elst) writes:
>In article <918@boing.UUCP> dale@boing.UUCP (Dale Luck) writes:
>>I think the benefit far out weighs the cost.
>>it is a very small price to pay. I just don't see that many
>>people unwilling to give up 1M-2M of memory. It still leaves
>>4-6 megs of memory for programs as well as the 1M of chip memory.
>
>Hmm, I can't see much benefit from this besides ease of programming.

This is a MAJOR benefit. Ease of programming.

>IMHO, it is sufficient to map a smaller rectangular part. The drawing
>routines can be adapted without much peformance loss.

If you can constrain most of your work to small regions then that is fine.
In a windowing environment we have little control over this. A driver
that needs to quickly access different portions of the display for moving
windows around, scrolling etc. the segment architecture means an
extra layer of complexity, over an above the complexity of overlapping
windows.

IMHO the benefits of a complete memory mapped frame buffer far outweigh
the costs giving up 1-2M of address space on the bus. The benefits of
of a mapped rectangular region just do not seem compare with the
large costs of much more complex code and slower speed.

I think Intel had the same thoughts regarding the 8088,8086, etc. line
of processors vs 68000 linear address space. Guess you know what most
Amiga people prefer.

It also seems to me that 100% mapped frame buffer compared to a portal
type frame buffer would be easier to design.

>
>Regards,
>-- 
>Michael van Elst
>UUCP:     universe!local-cluster!milky-way!sol!earth!uunet!unido!mpirbn!p554mve
>Internet: p554mve@mpirbn.mpifr-bonn.mpg.de
>                                "A potential Snark may lurk in every tree."


-- 
Dale Luck     GfxBase/Boing, Inc.
{uunet!cbmvax|pyramid}!amiga!boing!dale