Problem with GPSD refclock

[Hal Murray]

richw at richw.org said:
> When I first wired up a GPS in 2009 for use as an NTP refclock, my
> understanding was that USB-based devices (including "serial port" PCIe cards
> which really used USB technology under the hood) were simply not capable of
> the exact timing necessary to handle a PPS signal from a GPS unit.

I've never seen a PCI serial card that used USB.  (But there is a lot of the 
world I haven't seen.)

It would require 2 chips rather than one: PCI-USB and USB-Serial vs 
PCI-Serial.

PPS over USB adds roughly 1 ms of noise/jitter.  It works, just not as well 
as a real serial port.


-- 
These are my opinions.  I hate spam.