From: strat@matt.ksu.ksu.edu (Steve Davis)
Newsgroups: comp.sys.amiga.graphics
Subject: Re: OpalVision
Date: 23 Jul 1992 17:01:32 -0500
Organization: Kansas State University
NNTP-Posting-Host: matt.ksu.ksu.edu

ab@nova.cc.purdue.edu (Allen B) writes:

|>In article <14mulcINNnbj@matt.ksu.ksu.edu> strat@matt.ksu.ksu.edu (Steve Davis)  
|>writes:
|>> ab@nova.cc.purdue.edu (Allen B) writes:
|>> >The device can run a 24 bit buffer at 768
|>> >x 480 from just the data available on the RGB port?  I'm not
|>> >contesting the video slot version, but the RGB port? 
|>> 
|>> No, it is a real frame buffer.  The 24-bit image is created and
|>> held internally, but the external device is *CONTROLLED* through
|>> the RGB port in this case, and the data appears either above or
|>> below the video data coming over the port.  It works just like an
|>> external GENLOCK in this sense.

|>It's got to get all its data from the RGB port if that's the
|>only connection to it.  I'm aware it has its own memory, but
|>it's got to be filled via the RGB port if that's where it's
|>connected.

I am not sure about Opalvision, but Colorburst also had a couple
other wires, I believe.  In any event, this is the main vision
between an Opalvision and a CDTV:  Once the image is IN the
Opalvision, the device can continue displaying it from its own RAM.
DCTV requires a constant presence of the codes.

|>> >784 * 482 * 30 * 4 = 45346560 bits per second
|>> 
|>> But, unfortunately, the video bus would be unable to cope with a
|>> continuous stream of raw data at this speed.  :-(

>Your RGB port does it all day long.  Scary, isn't it?  

The RGB port is analog.  This is 5.535 mega BYTES per second.  You
couldn't swap that much into chip ram each second and still
multitask.  In fact, I doubt that you could do it.  The fastest
I've ever seen a 7Mhz Amiga move data from Fast Ram is a little
over 1 meg a second!  

Once the data is there, you can display it ... but GETTING IT THERE
at that speed is impossible.  With the Colorburst, it took quite a
bit of time to get the image from Amiga's RAM into the card.

|>So, I'm asking, how fast can expect to
|>push data to OpalVision? 

|>I ask because they claim the Amiga 500/600 version hangs
|>from the RGB port instead of being a card inside the
|>machine.  If there's another connection to the unit, my
|>questions are answered. 

I would not be surprised if you could fill the Opalvision's card in
two or three seconds... maybe a little less.  But animations would
be impossible.  And you wouldn't be able to get much else done
since the processor would be accessing Fast RAM as fast as it could
to achieve this.

|>> >So what's the scoop?  Tell me tell me tell me.  I think the
|>> >makers of OpalVision are not telling us the whole truth.  I
|>> >want numbers and I want explanations that match with
|>> >reality.
|>> 
|>> Like I said, the image data is created in the device.  They don't
|>> advertise 30fps animation in 24 bits, so don't expect to get it! :-)

|>My "image data" is most certainly not >created< in the
|>device!  If I load an image from disk, it's got to go out my
|>RGB port to get into the buffer.  

Yes, you have to fill the thing's RAM, but the data does not reside
in Amiga's RAM.  The encoder is inside the box, and any software
you run manipulates data inside the box.  As far as the electronics
of the Amiga are concerned, you have a Genlock plugged in.

|>That's what I'm talking
|>about.  I question the throughput of this connection.  

One megabyte per second TOPS on a stock Amiga.  A little more if
you have something faster.

>I especially want to know how I can change OpalVision's
>buffer while I'm displaying useful stuff on the Amiga's
>screen. 

The first, last, and only time I ever saw a Colorburst was at the
Amiga Expo in Orlando Fl. last summer.  If I recall, the Amiga's
display was blanked while the transfer took place.

Stratocaster
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