NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/sys/amiga/misc-part1/6057

Internet Message Format | 1996-08-05 | 5.3 KB

Path: bruce.cs.monash.edu.au!not-for-mail
From: [e-mail] (Bernd Meyer)
Newsgroups: comp.sys.amiga.advocacy,comp.sys.amiga.misc
Subject: Re: A1200 Flicker free?
Followup-To: comp.sys.amiga.advocacy,comp.sys.amiga.misc
Date: 16 Feb 1996 00:20:36 GMT
Organization: Computer Science, Monash University, Australia
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Paper Tiger ([e-mail]) wrote:
: Bernie,
:
: As you don't understand I will try to explain.  On
: a PC TV cards do exactly what you are saying.  They
: take a signal and convert it from NTSC <=> VGA.

Well, that's NTSC=>VGA, PAL=>VGA, SECAM=>VGA and so on.
Basically, everything that is at 15.625kHz => VGA. This
might not be true for the more expensive frame grabber cards,
but it certainly is for my el cheapo just-get-it-on-the-screen
card.

: When you and I are talking Amigas we are discussing a machine
: that has the ability to shift in many different scan rates
: which, contrary to what you might think, do not posses the
: same scan frequencies and timing.

But all those modes either have a horizontal frequency of 15.625 kHz
(or close to it), which something like my card will handle just fine,
or 30+kHz, which doesn't need to be adapted at all to run on the VGA.

The fact that the vertical refresh rates are different is completely
irrelevant, because unless I am very mistaken, your product doesn't
know or care about vertical refreshes. If it did, it could be a real
flicker fixer (aka deinterlacer).

: Underlying all this is also the problem that each one of these
: selections needs to be taught to the Gecko.  Anything from
: timing to screen positioning.  That is inturn stored onto a
: EPROM.

Now I wonder why you do that. The position of the image on a given
screen is completely dependent on the screen. Which means that,
storing the stuff into an EPROM (and thus not making it user configurable),
you gain absolutely nothing.
However, as you are going for the high quality monitors anyway (as
it really doesn't make sense to use a $400 product to connect to a
$200 monitor), almost all of those monitors are microporcessor controlled
and do a very good job of screen positioning.

Now as for timing --- I really don't see the problem here. You
probably got some memory in that product with interlaced accesses
from the incoming signal and the outgoing signal (with twice as many
accesses for the outgoing signal), enough to hold two scanlines of
display. Now you simply synchronize the reads and writes to the
Amiga's pixel clock (which is available at the video connector),
and you got the pixel timing right. Everytime the input signal sends
a HSYNC, you latch the value of the current input pixel counter, and
on the falling edge of that HSYNC signal, you latch the value into
a second latch and reset the counter to zero (and switch to the other
scanline). You also reset the output pixel counter to zero and switch
it to the scanline that you just finished reading from the input.

The output pixel counter is running at twice the speed of the input
one (that's trivial, a PLL will double the frequency), and you raise
the output HSYNC signal everytime its value is larger than what is
stored in the first latch. When its value is equal to the second latch,
you reset it to zero.

The VSYNC signal is passed on as is.

Now, if your gecko product does anything else, I'd be interested as
to the what and why. As you might see from the above, I am quite able
to understand digital technology and have worked with digital video
in and out in the past. So don't feel compelled to dumb anything down.

: This is the easy description of what is going on.  It doesn't
: even begin to discuss such ideas as screen buffering and
: equations for dropping lines, digital signal support
: or many other issues.

Which you do? Now, _if_ you do all that, I'd really like to know
why you didn't implement a deinterlacer as well.
:
: I hope this helps you decide if you want to stay in this market.

I am not even in the market. At the moment, I make my living by
being on a scholarship, which is rather nice.

All this started when you posted what I could only see as an ad in
a non-biz.* newsgroup (or two, actually), and I was particularly
amazed at your prizepoint. As you had posted the ad, I thought I
might as well point out that your product was, well, creatively
prized.

: Our cost has nothing to do with labor rates and has everything
: to do with costs.  If it cost me $10 to make I am not going to
: sell it to you for $7, just because you are making direct corr-
: elations to products on the PC market (in which there are none).

But if you manage to even put $200 worth of parts into that gecko
product, I'd like a word with the head of your R&D department.

Bernie