Timekeeping oddities on MacMini G4s

[Achim Gratz]

Gary E. Miller writes:
> Then you have to take aging into account.  A 10 year old Mac may have
> difted a lot.  Or maybe the crystal got bumped.

The spec of most crystals take the aging across lifetime into account.
Unless you physically damage the crystal by bumping (which is nigh
impossible for SMD crystals due to their low mass), the worst that'll
happen is another retrace (you can expect a single-digit ppm event).

Metal can XO are more easily damaged, but if they're damaged during
manufacturing it's more likely to happen by a broken seal.  That would
trigger a drift to lower frequencies depending on how much moisture gets
onto the quartz slab.

> Also a lot of crystals are now surface mount.  The soldering process
> may have bend to crystal a lot.

There was a whitepaper from one of the crystal manufacturers about that
effect …now here:

http://www.axtal.com/cms/iwebs/download.aspx?id=71610

It generally only means that right after soldering you'll have a retrace
transient that may last several weeks.  Again, unless you use a
soldering temp profile that is far out of what the crystal manufacterer
prescribes/recommends, the spec is taking that into account.


Regards,
Achim.
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