BerryGPS uses the serial port on the Raspberry Pi. By default, the serial port is already assigned to the console. This can be confirmed by using;
pi@raspberrypi ~ $ dmesg | grep tty
[ 0.001609] console [tty1] enabled
[ 0.092061] 3f201000.uart: ttyAMA0 at MMIO 0x3f201000 (irq = 87, base_baud = 0) is a PL011 rev2
[ 0.594855] console [ttyAMA0] enabled
The last line above shows that the console is enabled for the serial port.
ttyS0 = Serial for Raspberry Pi 3
ttyAMA0 = Serial for all other Raspberry Pi
On new versions of Raspbian, 'serial0' is assigned as an alias to either of the above devices. This makes the device a lot easier to remember.
lrwxrwxrwx 1 root root 5 Aug 28 12:49 /dev/serial0 -> ttyS0
We now need to disable the console so we can use the serial device for BerryGPS.
Setup Serial for BerryGPS
1. Update software and OS
pi@raspberrypi ~ $ sudo apt-get upgrade
pi@raspberrypi ~ $ sudo reboot
2. Open raspi-config and disable serial console
The serial console needs to be disabled and then the serial port enabled.
interfacing options -> Serial -> No -> Yes
Yes to reboot
Test and View GPS data
We can now test to see if we can see the raw GPS data, which would be outputted in NMEA sentences .
NMEA sentences contain all the requered GPS data needed to get and acruate location reading. E.g longatute, latitude, number of statilites, etc..
There are a number of ways to do this, using cat, Minicom or Screen and specifying the serial device.
pi@raspberrypi ~ $ minicom -b 9600 -o -D /dev/serial0
-b = baurdrate. BerryGPS's default baurdrate is 9600
-d = Serial device
Here are some useful commands while using Minicom
Exit - Ctrl+A and then q
Help, - Ctrl+A and then z
Settings, - Ctrl+A and then o
pi@raspberrypi ~ $ screen /dev/serial0 9600
Below is two examples of what you would see.
The first image is when you GPS has been up and running for awhile and has a fix. If your GPS has a fix, you would also see the green fix LED flash.
The second image is when your GPS is trying to obtain a fix. As you can see, most of the NMEA data is empty. On first power up, it can take your GPS module awhile to get a fix. It could be longer than 10 minutes in some situations, it all depends on interference and if your GPS has clear access to the sky.
A summary of the default NMEA sentences that BerryGPS will output;
|$GPVTG||Vector track and Speed over the Ground|
|$GPGGA||GGA - essential fix data which provide 3D location and accuracy data.|
|$GPGLL||GLL - Geographic Latitude and Longitude|
|$GPGSA||GSA - details on the nature of the fix. It includes the numbers of the satellites|
|$GPGSV||Detailed satelite data|
|$GPRMC||RMC - The recommended minimum|
This link has some great information on how to read NMEA sentences.
Viewing Meaningful GPS Data
There are number of freely available tools which we can used to view meaningful information from BerryGPS, like longitude, latitude and ground speed.
First, we will install GPSD. gpsd is a daemon that receives data from a GPS receiver, and provides the data back to multiple applications such gpsmon and cgps.
Install, gpsd, gpsmon and cgps;
If you need to stop gpsd, you can use
Be default, gpsd is configured to stat at boot and run in the background. If you are fine with this, you will need to edit the config file so that gpsd uses the correct serial device.
and change it to
Reboot once you have updated the above file.
If you want to manually run gpsd, you will need to disable it from starting at boot;
pi@raspberrypi ~ $ sudo systemctl disable gpsd.socket
To force it to autostart again at boot;
pi@raspberrypi ~ $ sudo systemctl start gpsd.socket
If you have disabled gpsd from automatically started at boot, you will need to start if before running gpsmon or cgps
You can now use gpsmon or cgps to view GPS data.
When gpsd is running, you will not be able to see the raw NMEA data on /dev/serial0 as the serial device will show as busy.
You can use gpspipe to view this data while gpsd is running.
gpsprof performs accuracy, latency, and time drift profiling on a GPS. It emits to standard output a GNUPLOT scatter graph.
The command below will take 100 samples from BerryGPS and display them in a graph.