Re: ISA Vector card already done...

On Wed, 25 Mar 1998 10:58:42 -0800, Clay Cowgill <ClayC@diamondmm.com> wrote:

>How did you calculate the speed required for the DACs for your Asteroids
>example?
>
>Off the top of my head I'd say:
>
> Resolution of "screen" = 1024x1024 (10 bits each direction
>significant)
> Max vectors = 2000 (decided by wild-ass-guess)
> Average Vector length = 100 clocks (about 1.5 inches on a 19"
>screen-- seems generous)
> Update Speed = 60Hz (16.67ms per frame)
>so...
> 2000 * 100 = 200,000 clocks total
> 16.67ms / 200,000 = 83ns per update ...
> ~12Mhz?

I didn't worry about the max number of vectors, refresh rate, etc. I looked at
it from the point of view of the monitor. I can't remember the slew rate off
the top of my head, but I took the slew rate in in/sec, used displayable screen
size in the horizontal direction (15 inches I think), divided by 1024, etc. and
ended up with 6.xx mhz. I then looked at the clock going into the DACs on an
asteroids and saw a 6 mhz clock.
>
>So that's about 2.5 DSP instructions per pixel, which if you need to
>update two DACs is probably pretty tight. I could go to the 40MIP part,
>or we can say that the above is "worst case" for 60Hz, and if you push
>it harder you'll just drop frame rate a little...

>Whatcha think?

I'm pretty sure it's a 6mhz update giving you 5 instructions per update.

This is the same problem I had with using software. I calculated that I would
be able to run around 20 instruction per update in the yet to be released 50mhz
PIC clone and it looked like I could write a line draw routine that would fit...

-Zonn

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Received on Wed Mar 25 12:20:17 1998