Re: [gpsd-users] [gpsd-dev] SemPiTernal - Bounding PPS uncertainty

[Gary E. Miller]

Yo Hal!

On Fri, 22 Apr 2016 00:08:42 -0700
Hal Murray <address@hidden> wrote:

> Connecting a TTL signal directly to a RS-232 modem control input pin
> ends up with assert being the leading edge which is what ntpd uses by
> default.

Depends on the GPS.  Some vendors have inverted serial output since they
know you will use a TTL/RS-232 level converter that inverts.

> Aside from wrong-edge, the other problem you can get into is pulses
> too narrow for software to notice.  GPSDOs tend to have 10-20
> microsecond pulses.

If you use the latch mode in the UART your typical PC with a serial
port can detect those fine.  I have had timing GPS running for
years on short pulses just fine.  The KPPS just report one edge
in that case.

except the typical PC no has a serial port...

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        address@hidden  Tel:+1 541 382 8588

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