Re: A couple of questions...

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Angus Dorbie (dorbie++at++sgi.com)
Fri, 17 Jul 1998 10:25:37 -0700


markc++at++io.com wrote:
>
> Hello,
>
> First off -- my configuration.
> --
> Onyx2, 6 195mhz r10's, 2 pipes, 6 rms.
> IRIX 6.4
> Performer 2.2.
> --
>
> My first question regards PFCHAN_SWAPBUFFERS_HW, is there any performance
> gain to be realized by genlocking two pipes ? I've gotten some
> conflicting info on this, and expect that my friend was really talking
> about PFPHASE_LOCK.

The real gain is for genlocking. You must genlock for good performance,
especially at high frame rates, and it looks better.

When on a single host there's a marginal benefit for genlocking the
pipes. The real win for genlock is when you have two separate machines,
and so the additional communications latency for the swap sync
eliminated

>
> Also, exactly how does one cable up a two (or n) pipe machine
> to SWBUFFERS_HW ? I've gone through the archives, Onyx hw docs,
> etc. And despite finding some info, even a recent thread on
> info-performer. I'm still uncertain...

Once you have daisychained the genlock you can wire all pipe swapreadys
on a single wire. Here,s a 3 pipe example:

 PIPE 0 PIPE 1 PIPE 2
[ ] []GEN IN []GEN OUT []GEN IN []GEN OUT
 \ / Video / \ / \/
  \ / out / \_________/ 75 Ohm
||\ / terminator
||\\___________/
|| \ H/C wire with
|| \ Composite Sync

Swapready Swapready Swapready
   [] [] []
    \ \ /
     \______________________\_____________________/
                           T Junction

Cheers,Angus.

-- 
"Only the mediocre are always at their best." -- Jean Giraudoux 

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