Getting GPS to work on Raspberry Pi 3 Model B

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Getting GPS to work on a Raspberry Pi 3 Model B

"My GPIO-connected UART device is broken on Pi 3, why?

The mini-uart is now routed to GPIO14/15 as the PL011 UART is now used for bluetooth communications. The mini-uart doesn't have a separate clock divisor and uses the core clock frequency. Changes in core clock (e.g. through throttling or idle/load frequency changes) will result in arbitrary modification of the effective baud rate. There's no easy way around this, but as a workaround there is a pi3-disable-bt devicetree overlay in latest rpi-update firmware which reverts this change."

We will show you the operations in the next steps.

Connection

Connect the LoRa/GPS HAT to Rpi, use built-in patch GPS antenna.



Enable the UART

First we need to download and install a new device tree overlay.

The Raspberry Pi Engineer PhillE (forum username) has kindly made a custom overlay called pi3-miniuart-bt-overlay.dtb to remap the UART ports and this needs to be copied into the /boot/overlays folder on the SD card and we also copied it into the root / pi3-miniuart-bt-overlay.dtb of the card as well.

We have made a copy of the new boot overlay available to download from here and it will also be included in a future Raspbian Linux release. We have archived the overlay in zip format and it will need to be uncompressed and copied to your SD card.

Next we need to edit the /boot/config.txt file, open the file either on your desktop computer or using the Raspberry Pi via SSH

sudo nano /boot/config.txt

You need to add the following lines:

dtparam=spi=on
dtoverlay=pi3-disable-bt-overlay
core_freq=250
enable_uart=1
force_turbo=1

Then use Ctrl+O to save changes and use Ctrl+X to exit.

edit /boot/config.txt

Now edit /boot/cmdline.txt.

sudo nano /boot/cmdline.txt

Change the file to the following:

dwc_otg.lpm_enable=0 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait

Exit and save your changes


If you have edited the cmdline.txt and config.txt files on your desktop put the SD card back in your Raspberry Pi 3 and boot to either a network SSH session or desktop and run the following in a shell window.

If you want to disable the built in bluetooth you need to stop hciattach trying to use the modem via uart0 which will disable the relevant systemd service

sudo systemctl disable hciuart

Now edit /lib/systemd/system/hciuart.server and replace ttyAMA0 with ttyS0 .

sudo nano /lib/systemd/system/hciuart.service

Replace "After=dev-serial1.device" with "After=dev-ttyS0.device"

Exit and save your changes

edit /lib/systemd/system/hciuart.server

You need to update the operating system with the latest patches with:

sudo apt-get update
sudo apt-get upgrade
sudo reboot

Once your Raspberry Pi 3 has rebooted you should now have access to the serial console via the GPIO header at 9600 baud.

If you just want to do a quick check to see what data is coming out of the GPS, you can enter the following command, following by CTRL+C to quit:

sudo cat /dev/ttyS0
cat /dev/ttyS0

Run the following two commands to stop and disable the tty service:

 sudo systemctl stop serial-getty@ttyS0.service
 sudo systemctl disable serial-getty@ttyS0.service



Reboot

 sudo shutdown -r now 



Install GPSD

You can always just read that raw data, but its much nicer if you can have some Linux software prettify it. We'll try out gpsd which is a GPS-handling Daemon (background-helper)

To install gpsd, make sure your Pi has an Internet connection and run the following commands from the console: 

 sudo apt-get install gpsd gpsd-clients python-gps 

Raspbian Jessie systemd service fix

Note if you're using the Raspbian Jessie or later release you'll need to disable a systemd service that gpsd installs.  This service has systemd listen on a local socket and run gpsd when clients connect to it, however it will also interfere with other gpsd instances that are manually run (like in this guide).  You will need to disable the gpsd systemd service by running the following commands:

 sudo systemctl stop gpsd.socket
 sudo systemctl disable gpsd.socket

Should you ever want to enable the default gpsd systemd service you can run these commands to restore it (but remember the rest of the steps in this guide won't work!):

 sudo systemctl enable gpsd.socket
 sudo systemctl start gpsd.socket

After disabling the gpsd systemd service above you're ready to try running gpsd manually.

Run gpsd

GPSD needs to be started up, using the following command: 

 sudo gpsd /dev/ttyS0 -F /var/run/gpsd.sock



Test gpsd

Now GPS doesn’t work indoors – as it needs a clear view of the sky so for this I’ve placed the PI on the window sill. Next I ssh into the pi and run cgps. There is a simple GPS client which you can run to test everything is working: 

 cgps -

The -s flag is there to tell the command not to write raw data to the screen as well as the processed data.

It may take a few seconds for data to come through, but you should see a screen like this: 

cgps-s

If you have any problems and cgps always displays 'NO FIX' under status and then aborts after a few seconds, you may need to restart the gpsd service. You can do that via the following commands:

 sudo killall gpsd
 sudo gpsd /dev/ttyS0 -F /var/run/gpsd.sock

If here still shows 'GPS timeout' or 'NO FIX',edit /etc/default/gpsd as below:

 sudo nano /etc/default/gpsd

change it to look like this

# Default settings for gpsd.
# Please do not edit this file directly - use `dpkg-reconfigure gpsd' to
# change the options.
START_DAEMON="true"
GPSD_OPTIONS="-n"
DEVICES="/dev/ttyS0"
USBAUTO="false"
GPSD_SOCKET="/var/run/gpsd.sock"

Then reboot. CGPS should work then.

NOTE:If the GPS receiver is new, or has not been used for some time, it may need a few minutes or so to receive a current almanac.You need 3 GPS satellites for a 2D fix (i.e. no height) or 4 satellites for a 3D fix. Once fixed,the LED '3D_FIX' will blink.


You can view http://www.catb.org/gpsd/ to get more info about gpsd.You can also try to use the following command:

* cgps

cgps and gpspipe should both just show curated data in the same way as your cat command did.

cgps


Try running gpsmon to get a live-streaming update of GPS data!

* gpsmon

The gpsmon real-time packet monitor and diagnostic tool. (This replaces the sirfmon tool in older versions.)

gpsmon