[time-nuts] Msg to N.Z. time nuts
Lux, James P
james.p.lux at jpl.nasa.gov
Tue May 19 23:38:27 UTC 2009
On 5/19/09 1:15 PM, "Russell Rezaian" <rrezaian at motorola.com> wrote:
> At 12:58 PM -0700 2009/05/19, Hal Murray wrote:
>> USB has a bad reputation, but I think it's way way overblown. Yes, it's
>> polled, but that polling is done in hardware and the time scale is 1 ms. If
>> you are satisfied with an accuracy of a few 10s of ms, USB works fine. The
>> problem is the GPS unit.
> And I can confirm that for my very un-scientific experiments I do get
> a pretty consistent time sync around 1 MS plus or minus mark from a
> USB serial port adapter in best case conditions. That's with no
> special work on a pretty stock consumer grade computer with an off
> the shelf USB to serial port.
I would expect that the basic "frame" timing on USB (without actually
digging out my USB documents, because I'm lazy) is on the order of 125
microseconds (e.g. 8kHz, to support a 8ksps audio stream, just like IEEE1394
does), but that might just be a latency jitter bound.
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