[time-nuts] Beginners GPS locked frequency counter question

Chris Caudle chris at chriscaudle.org
Sat Oct 31 14:19:02 EDT 2015

On Sat, October 31, 2015 10:03 am, Graham / KE9H wrote:
> The sound card sampling clock is
> usually derived from some master clock in the computer, such that the
> sound card is running in the same clock domain as the rest of the
computer, so
> you more likely need to GPS lock the whole computer.

Generally never true.  Sometimes on integrated (on motherboard) converters
the sample clock may be derived from a system clock, but that is a
convenience factor, not consequential to the design, and every add in card
(PCI or PCI Express) has an independent oscillator providing the sample
clock.  The samples are buffered and delivered asynchronously to and from
the processor over PCI or PCI Express, with bus operation not related to
the sample clock.
USB is slightly more complicated because there are multiple ways clocking
is handled.  Asynchronous isochronous mode is essentially the same as
described above.  USB adaptive isochronous mode throws some wrinkles in
that are probably not worth discussing in this context (unless it turns
out the original poster is trying to modify a USB sound interface and not
a PCI or PCIe interface).

Chris Caudle

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