[time] GPS or CDMA Time servers

Koos van den Hout koos
Wed Apr 2 07:33:57 UTC 2008


On Tue 2008-04-01 at 18:15, Brandon West wrote:

> being. I did find something really cool though, if I wanted to move to  
> a low power dedicated box.
> 
> http://www.via.com.tw/en/products/embedded/artigo/index.jsp
> 
> AFAIK it lacks a serial port. I wonder if that would be detrimental to  
> combining it with a GPS-18LVC?

The specs mention

1 x COM Port Ribbon Cable

And the pictures too. So I guess it is included.

I would consider some sort of 'real' serial port (16550 or derived based)
on a timeserver important: the GPS-18LVC (and other timing devices) can
deliver a PPS (pulse per second) signal which will signal very accurately
to ntpd when the next second begins. The delay of that signal over a 16550
is minimal and predictable (given the right drivers).

Over usb it will cross more layers and drivers (gps -> usb convertor -> usb
bus -> host -> usb driver -> usbserial driver -> application).

.. but maybe I'm biased by a gut-feeling that multiple layers of drivers
and a shared medium (USB) for signalling with microsecond precision is
wrong.

                                                 Koos van den Hout

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