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Re: [gpsd-users] [Gpsd-users] Availability of 1PPS for Laptop users

From: Dave Hart
Subject: Re: [gpsd-users] [Gpsd-users] Availability of 1PPS for Laptop users
Date: Tue, 17 Apr 2012 08:28:49 +0000

On Tue, Apr 17, 2012 at 07:48, Mihail Popa <address@hidden> wrote:
> Hi experts,
> I have to transition from my old desktop computer (with RS232 port) to a
> laptop computer (with no RS232 port)
> The GPS receiver I own connects using RS232 and provides good 1PPS signal
> (I’ve been using it already on my desktop computer…)
> As far as I know RS232 to USB Adapters do not propagate the 1PPS signal,
> therefore I need to find another way to provide RS232 connectivity to my
> new laptop.

Assuming the PPS signal is on the typical input (CD a.k.a. DCD carrier
detect) others' experience suggests some USB-serial chip/driver
combinations do relay the PPS properly:

The add-on expresscard serial port will give better performance (both
lower latency and lower jitter) compared to connecting via a USB to
serial adapter.  It will also likely enable PPSAPI support, though
that's not needed if you're using gpsd, which can watch for the CD
input change using traditional serial I/O interfaces.

At present, there are no known USB-connected GPSes which carry through
the PPS signal, though electronically they are essentially the same as
a 232-connected GPS plus a USB to serial adapter, the PPS signal isn't
wired into the serial/USB chip.  Eric Raymond, Dave Taht, and others
working on bufferbloat are trying to change that by enlightening USB
GPS suppliers regarding the utility and near-zero incremental cost.

Dave Hart

P.S.  The mailing list you sent to is no longer the correct list,
which I've cc'd.  After many years of hosting gpsd development, announced last fall their services were going away as soon
as the end of last year.  Please sign up to the new list and post
there going forward.

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