[ntp:questions] Thunderbolt at NTP ref clock.

Thomas Laus lausts at acm.org
Wed Jul 31 15:23:06 UTC 2013


On 2013-07-31, Thomas Laus <lausts at acm.org> wrote:
> The pulse width wasn't adjustable.  It was was just on the ragged edge
> of what the Soekris UART DCD was able to see for pps kernel
> discipline.  It occasonally missed a pulse and that caused some
> problems for ntp because it had the time solution from the serial
> port data, but not the pps timestamp that matched.
>
>From the Thunderbolt book:

1 PPS: BNC Connector TTL levels into 50 ohm 10 microseconds-wide
pulse with the leading edge synchronized to GPS or UTC within
20 nanoseconds (one sigma) in static, time-only mode. The rising
time is <20 nanoseconds and the pulse shape is affected by the
distributed capacitance of the interface cable/circuit.

My Soekris board could not handle something that narrow.

Tom


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