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adafruit-raspberrypi-linux-pps

Update: 2015/02/09

Please note that this kernel is woefully out of date. Don't use it.

Your Raspberry Pi B+ and RPi2 will shed tears (not work), and you'll just want to break things (and me).

I'll get a proper kernel going sooner or later, but consider this archived.

Intro

Kernel image and modules with PPS-GPIO added (this tracks Adafruit's current Occidentalis kernel version and will probably be rebuilt when they next update). This will allow you to use PPS with NTP on a Raspberry Pi.

This repository is used as a part of this article, so check that out for help.

For source modifications, please see this page, branch: ppsgpio for the source this is based on.

Installation

To install this kernel, copy kernel.img to boot:

$ sudo su
# mv /boot/kernel.img /boot/kernel.img.orig
# mv kernel.img /boot/

Copy the modules:

# mv modules/* /lib/modules

Add the pps-gpio module to /etc/modules:

# echo "pps-gpio" >> /etc/modules

Reboot:

# reboot

Once your system is back up, check to see that the kernel version has changed and that pps-gpio loaded:

$ uname -a
Linux raspberrypi 3.1.9adafruit-pps+ #21 PREEMPT Sun Sep 2 10:57:58 PDT 2012 armv6l GNU/Linux
$ dmesg | grep pps
[ .. snip .. ]
[   10.339448] pps pps0: new PPS source pps-gpio.-1
[   10.341591] pps pps0: Registered IRQ 108 as PPS source

PPS input will be available on pin 23 of the Raspberry Pi header.

Note: Ensure that your GPS unit's PPS output is 3.3v friendly!

If you're looking for a unit which fulfills this requirement, Adafruit's Ultimate GPS (all versions) has a 1PPS output which is around ~2.8V, and is compatible with the Raspberry Pi.

Once connected, install pps-tools to test:

$ sudo aptitude install pps-tools
[ .. snip .. ]
Unpacking pps-tools (from .../pps-tools_0.20120406+g0deb9c7e-2_armhf.deb) ...
Processing triggers for man-db ...
Setting up pps-tools (0.20120406+g0deb9c7e-2) ..

Assuming that the pps line is on /dev/pps0:

$ sudo ppstest /dev/pps0
trying PPS source "/dev/pps0"
found PPS source "/dev/pps0"
ok, found 1 source(s), now start fetching data...
source 0 - assert [....], sequence: [....] - clear  [....], sequence: [....]

If your output looks something like the above (brackets are numbers removed for clarity), you're all set. If not, verify that everything is connected and that the pps-gpio kernel module is loaded (along with the -pps kernel itself).

It may be helpful to scope the PPS line to see if the GPS module is actually sending a signal. On some units, the 1PPS output only becomes active after a fix.

Credits

All of these modifications were cobbled together by reading this thread and following its instructions.

See this repository, (branch: ppsgpio) for source code.

About

Deprecated: Compiled kernel image and modules with PPS over GPIO pin 23 added

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