Combined time offsetN/A ┬Ás
Clock frequency offsetN/A PPM
Clock frequency wanderN/A PPM
Combined system jitterN/A
Clock jitterN/A
Total root dispersionN/A
Total roundtrip delay to the primary reference clockN/A
Time constant and poll exponentN/A
Minimum time constantN/A
Leap warning indicatorN/A
Poll messages sentN/A
No replyN/A
Bad date or timeN/A
Bad formatN/A

Raspberry Pi NTP server image

Connect the GPS module with these pins on the Raspberry Pi

A minimal SD-card image based on Raspberry Pi's Raspbian distribution featuring PPS-enabled kernel and ntpd.

It expects a gpsd-compatible GPS device connected to UART0 (P1-08/1-10, GPIO 14/15) and a PPS signal on P1-12 (GPIO 18).
Remember: The Pi's GPIO pins tolerate 3.3V levels only!

NTPi Adapter Board

This is a riser card with PPS-LED to fit the GPS module within the Raspberry Pi Case. I ordered the PCBs from OSH Park for $3.90 per 3 copies (plus $8 international shipping). Schematics and board layout in Eagle 6 format are available from GitHub.

The board provides an option to connect the PPS signal to GPIO 4, in case GPIO 18 is used otherwise (e.g. for PWM): Remove bridge R3 and wire the PPS line to "ALT PPS". This also requires changing "pps_gpio_info.gpio_pin" to 4 in arch/arm/mach-bcm2708/bcm2708.c in the kernel source and compiling a new kernel image.

NTPi PCB Top View