Re: SecondSight FPS

[ballweb@PEAK.ORG (Brian Ballweber)]

Matt Portune (mportune@telerama.lm.com) wrote:
: Ok, so assuming the application has extremely well-written code, and is 
: designed to push the SS to it's max... Theoretically, how fast could the 
: card go?

Hmm, lets do the math:

If the Z80 works at 20 Mhz and takes 6 cycles <I think> to move a byte of
data, then it can move:

20e6 * (1 byte / 6 cycles) = 3.333 meg/s

Now figure the size of the screen is 320 x 200 x 1 byte:

320 * 200 * 1 byte = 64000 bytes 

Now divide the two:

(3.333 meg/s) / (64000 bytes) = 52.08 1/s = 52 Hz

So assuming you do nothing but move memory you could do it at 52 Hz.

However, typical games/animations/etc usually do not move the entire screen
continuously.  On the other hand, you usually also dont just move data,
somewhere along the line you gotta loop or toss in some control code.

One thing I do think people are overlooking is the fact that your 816 isnt
just sitting idle while the z180 pushes memory around.  The z180 should
<if im not mistaken> act along the lines of a coprocessor.  The VGA chip should
also act in a similar manner I would think.  The effect is the same as using
the DOC for doing sound, once you get the tedious job of moving graphics off
of the CPU you can use it for more useful stuff.

Everyone <well at least programmers> know the difference between MOD and
Soundsmith music players.  One uses the CPU to swap large chunks of DOC ram
and the other one dosent.  One has a huge CPU speed impact and the other one
dosent.  If your not aware of this get a copy of DOCVu <sorry blatant plug>
and check it out.

I think the effect of using a z180 to swap graphics memory and using the CPU
to do it is much along the lines of using the DOC to play music on its own
and using the CPU to swap DOC ram.  In fact the z180 is a much more capable
processor than a DOC as far as operating on its own.  The DOC requires that
the CPU do all of the intelligence work behind making it go.  The z180 is
capable of running on its own.


- Brian
  Digital Exodus