So, I want to have a GPS Receiver driving a PPS (pulse-per-second) signal to the NTP server for a highly accurate time reference service.

Introduction

There are at least a couple of ways to propagate the PPS signal to the ntpd (NTP daemon) service, plus some variants in each case. However, the GPS device must be seen as a device that sources two different types of data:

• the absolute date and time, and
• the 1Hz clock signal (PPS).

The first one provides the complete information (incl. date and time) about when now is, but with poor accuracy because data is sent over the serial port and then encoded using a specific protocol such as NMEA (National Marine Electronics Association). PPS provides instead a very accurate clock but without any reference to absolute time.