[ntp:questions] high jitter on serial gps causes big time offsets

Uwe Klein uwe at klein-habertwedt.de
Sat Apr 13 20:01:21 UTC 2013


website.reader3 at gmail.com wrote:
> On Saturday, April 6, 2013 4:18:33 AM UTC-7, Charles Elliott wrote:
> 
>> I would test the local clock before relying on it for time.  In the bad old days, around year
>> 2000, when I first started processing SETI at Home (S at H) work units (WUs), I could actually see
>> that WUs were being processed faster in the cool early morning hours than they were in the hot
>> afternoons.  The caveat is that an Intel tech support rep denied that that was possible.  

There is lots of thermal throttling around.
But that does not have any connection to crystal precission.

Thermal throttling is about reducing the CPU clock by significant amounts ( 1/nth, n=1..10 ?
depending on clock multipliers for full speed.) when the on die temp sensor says CPU too hot.

>> In 
>> any case, many others have commented on this list that the timing crystals installed in typical
>> motherboards vary significantly with temperature.  If you price timing crystals with guaranteed
>> accuracy you may well believe that they don't install them in typical motherboards; they cost
>> at least as much.
> 
> 
> I can obtain some precision crystals (+/- 2ppm) for about $8 to $10, so why aren't they being
> added to the mid-level and up motherboards?
> 
"for about $8 to $10"
That is about the money motherboards sell for from the manufacturer, right ;-?

> It is disgusting to buy a motherboard, load it with graphics processors, and memory and then find
> that the whole thing cannot keep time.  I consider time keeping THE most neglected component in
> computer motherboards today.

Sure.
But the majority of users ( even those with perceived to be time critical applications )
don't think much about hardware features.
They tend to think in brand items ( hardware and software ).

uwe



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