pts@watt.acc.Virginia.EDU (Paul T. Shannon) (10/11/89)
Noah Price, of the Mac IIci hardware design team, replied to a question
about the IIci video. I asked:
.. is there just one address in system RAM where the video hardware
always looks? Can I create animations by simply telling the video
hardware to look at a series of different addresses?
he replied:
The video hardware always gets its data starting at the base of Bank A
of DRAM. This is why you must have memory in Bank A in order to use built-in
video.
I tried to follow up with Noah by email, but the mail bounced. Because our
purchase (at $7000-$10,000) of the IIci hinges upon its ability to animate
gray scale images at sufficient speed, I'd like to take up more net bandwidth
and ask the following:
Since page-flipping animation cannot be achieved in the manner I described, can
it be achieved by wholesale copying of images from (non-video) ram to video ram,
synchronised to the vertical retrace? If, say, we loaded up a IIci with
sufficient ram, and then stored 10-20 images (640 x 480 x 8 bits, ~300k each),
is the memory-to-memory transfer rate sufficient to display these images
at 30 frames per second?
A helpful acquaintance of mine did some tests with highly optimised
assembly language, and found that he could get a 19 frames per second
transfer rate (RAM to RAM) on a 16 Mhz Mac IIx. Does anyone have any hard
data on what the 25 Mhz IIci will do? What is the transfer rate if you
have to move the data over the nuBus (spelling?) to a 3rd party video card?
It seems unlikely (maybe impossible is a better word) to complete the transfer
during the vertical blanking interval, but wouldn't it be possible to do
the transfer so that new data is inserted into video ram just ahead of the
video hardware reading that data?
I've received a lot of good information over the last few months, from readers
of comp.sys.mac, comp.graphics, and comp.sys.amiga. My thanks to all of you.
I'll be grateful for any answers to the above questions.
- Paul Shannon
pts@virginia.edu