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RE: [Xen-devel] HPET/PIT timer accuracy

To: "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>, "Michael Hohnbaum" <hohnbaum@xxxxxxxxxx>
Subject: RE: [Xen-devel] HPET/PIT timer accuracy
From: "Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>
Date: Fri, 29 Jul 2005 19:29:47 +0100
Cc: xen-devel List <xen-devel@xxxxxxxxxxxxxxxxxxx>
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Thread-index: AcWUatXgGG7H8M2/RuqJOmc06syOkgAACLVA
Thread-topic: [Xen-devel] HPET/PIT timer accuracy
> We're not relying on TSC synchronisation between CPUs. They 
> can run at different frequencies, stop in deep sleep, and so 
> on. But we *do* want the frequency of each one to be as 
> stable as possible. I'd expect to get <1ppm stability from a 
> crystal source at constant temperature, no problem.

I'd wager the TSC is stable and it's the HPET that's wandering...

We'll probably just have to add more damping on the re-calibration.


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