le 13/06/04 22:21, Jeff Walther � [EMAIL PROTECTED] a �crit�:

>> From: "J Mood" <[EMAIL PROTECTED]>
>> Date: Sun, 13 Jun 2004 14:05:24 -0400
> 
> At 14:51 -0500 06/13/2004, Jeff Walther wrote:
>> From: Compact Macs [mailto:[EMAIL PROTECTED] Behalf Of
>>> Daniel Daplincourt
>>> Sent: Sunday, June 13, 2004 11:35 AM
> 
>>> On the site of Gamba is described the manner of giving 256 levels of gray to
>>> a SE30. There, I see the photo of the necessary piece in order to make it.
>>> This piece is very difficult to find. Is this possible of her to manufacture
>>> oneself? Does someone possess the schema in order to achieve the
>>> installation? Could someone draw this schematic drawing? Thank you
>>> beforehand.
>>> Daniel :-)
> 
>> The device your talking about involves a few dozen IC's.  I strongly doubt
>> that all of these parts are still available, some of them are likely
>> proprietary ICs and programmable logic manufactured exclusively by Micron.
> 
> I suspect that Daniel lacks a crucial piece of information.  It took
> me a little while to figure this out upon viewing Gamba's site.
> 
> The card which Gamba built is not sufficient to achieve 256 levels of gray.
> 
> His card is an accessory to the Micron Exceed video card which can be
> installed in the SE/30.   So, in order to achieve 256 levels of gray
> one would need both a Micron Exceed video card which is very
> expensive and rare, and one of the cards which Gamba built which is
> moderately expensive but available, assuming anyone ever hears from
> Gamba again.  Both cards are necessary.
> 
>> The schematic for this setup is not publicly available, you would need a
>> reverse-engineered schematic and knowledge of PC board layout tools to re-do
>> the board layout and have it manufactured.
> 
> There were/are schematics of the Micron card kicking around.
> Someone was selling them on Ebay.   A couple of the list members were
> kind enough to send me the copies which they obtained because I have
> some experience at designing and having built printed circuit boards.
> However, the schematics are not sufficient.
> 
> As James surmises, one of the chips is a custom integrated circuit
> designed by Micron and never available to the general public,
> although one of the list members seems to have obtained a handful of
> the left over chips.
> 
> Unfortunately, there are also a few other chips on board which are
> Programmable Logic Arrays (actually PALs) and these contain custom
> programming which can not be read out directly.   It might be
> possible to determine the contents by analyzing the behaviour.   But
> that would require obtaining a working copy of the card, removing the
> chips in question, without damaging them and then analyzing them.
> 
>> None of these tasks are impossible, but it may almost be easier to redesign
>> the unit from the ground up.  The SE/30 hardware is pretty simple if you
>> have a strong background in computer design and hardware.  The device driver
>> software would be the difficult part, unless you are intimately familiar
>> with programming device drivers for Mac OS.
> 
> It probably would be easier or at least cheaper to redesign from the
> ground up, especially considering that modern CPLDs/FPGAs, memory
> chips and video timing chips are so much cheaper and superior to what
> was used/available on the older Micron card.
> 
> I have made a very minor beginning by reading "Designing Cards and
> Drivers for the Macintosh" 3rd Edition and by having a lot of good
> intentions which are interfered with by life.    However, while this
> book covers what is needed to interface one's card to the SE/30 (and
> NuBus machines in general) it assumes that one is already an expert
> on the type of card one wishes to build.
> 
> I'm a fairly fresh EE.   I have never designed a video card.   I have
> looked around for references on the art and there don't seem to be
> any resources that cover the topic from a hardware designer's point
> of view.
> 
> The specific question that gives me the most  headache is how to
> handle the refresh of the screen data.    I believe that updates to
> the screen image (changes to the contents of the video RAM) may be
> coming from the host CPU at any time.   But if the video card is only
> halfway through drawing a screen image (the CRT has scanned half-way
> down the screen), one would not want to then implement an update on
> the second half of the screen which hasn't been drawn yet.   This
> could result in the top half of the screen showing one image and the
> bottom half showing a completely different image, though only for one
> screen refresh cycle.   In less extreme cases it just results in
> flickers and little starbursts here and there as on ancient CGA video
> systems.
> 
> There are various schemes for dealing with this.  One is to have two
> screen buffers--two sets of video RAM.    But this requires twice the
> memory on the card (not a big problem now days), and it seems to
> require moving a lot more data back and forth, though I'm not
> certain.    Another method is to only update the video RAM during the
> flyback period of the attached CRT.    This requires some kind of
> buffering of incoming data or lowers performance, as the video card
> tells the CPU to hold video updates until that short period.
> 
> Another method is to track where in the video RAM the screen scan is,
> and only update portions of the video RAM which are behind the
> current scan cycle, but this also requires some kind of buffering for
> updates to video RAM in front of the scan point.
> 
> I'm sure these methods have been worked out in detail better than I
> can reinvent them, and there is probably a comprehensive comparison
> of their relative merits discussed somewhere, but I have not been
> able to find such a reference.    Somehow the NuBus video cards we
> used to buy managed this without using twice the video RAM.
> 
> Another question that interests me, but is not critical, is how to
> implement QuickDraw accelleration.  If one is going to build a video
> card from scratch, one might as well consider providing some
> acceleration.   There's plenty of logic capacity  available in modern
> FPGAs at a low price and the things run at clock speeds that
> designers of ten years ago could only dream about. Was all the
> information on this topic proprietary to folks like Radius and Raster
> Ops, or did Apple ever publish guidelines or articles on building
> QuickDraw accelerators?
> 
> I'd appreciate any pointers or help.    For the optimistic, please
> don't expect any results--well anytime.  I'm puttering on this
> project, but there's a two-year-old in the house and similar things
> that distract me, so while I hope to produce something, I can't
> guarantee any results in any reasonable time frame.    It probably
> would go faster with collaboration though.
> 
> Jeff Walther

Thank you Jeff (and others) for your scientists information. It is very
precious of having of good and rich information. Unfortunately, I am not
capable of you help in order to continue your project. I can only benefit of
your work, of your acquaintances. I thought too merely that the card was
easy to reproduce, I had not imagined that on this map resides a specific
chips of MicronExeed.
I hope that some other greatly more qualified people that me, will construct
your project with you. and that I will be able to again benefit some fruits
of this constructive collaboration.
Daniel


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