[ntp:questions] drift modeling question

Hal Murray hal-usenet at ip-64-139-1-69.sjc.megapath.net
Mon Jul 14 21:58:02 UTC 2008


>Historically interrupts from the 32kHz clock have not been used, except,
>possibly, in powered down states to initiate a restart from suspend or
>hibernate.  It is possible that has changed very recently, but they
>certainly weren't used historically.

Well, at least one of us is confused.  Or maybe my history starts
long before yours.

I'm pretty sure that some of the systems I've worked on used
the interrupt from the 32 KHz clock chip to drive the scheduler.

Some/many systems have long had troubles keeping time if interrups
get lost.  That wouldn't make sense if something like the TSC was
used for timekeeping.

Here is the message from Dave Mills that got me thinking in the
right direction:
  Message-ID: <3CE6FB0C.C1A206 at udel.edu>
  http://groups.google.com/group/comp.protocols.time.ntp/msg/59d26948e56531d4

After that, I moved the temperature probe over to the 32 KHz crystal
and my temperature data looked much cleaner.  The 32 KHz crystal is
off in a corner of the board.  THe main CPU crystal is reasonably close
to the center of the board where all the heat is generated.

In the last year or two, the Linux timekeeping stuff has changed
a lot, partly in order to support laptops and such that go into
serious power down mode and don't want to waste a lot of battery
on each tick when there is nothing to do.

-- 
These are my opinions, not necessarily my employer's.  I hate spam.




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