Subject: Re: High-resolution clcoks (time vultures on pmaxes)?
To: Chris G Demetriou <Chris_G_Demetriou@LAGAVULIN.PDL.CS.CMU.EDU>
From: Jonathan Stone <jonathan@DSG.Stanford.EDU>
List: port-pmax
Date: 01/28/1995 18:51:52
>Is this paper anywhere around, online?

The relevant details are in xntp-kernel.tar.Z on
I forget the exact path.

>Where's the "free-running counter" live?

It's an undocumented turbochannel bus-cycle counter on the IO asic.

>if it's a reasonably univeral register then the thing to do would be
>to use it for microtime() only -- at each clock interrupt, get its
>value, then when microtime is called, use the offset from that value,

3100s and 5k/200s don't have this register.  I think other decstations
do. In any case one wants to discipline the time sources to avoid
introducing cumulative roundoff errors.  Dave Mills makes a living
doing research in this kind of thing; if possible, I'd take his code
and use it.