Bluetooth and `gpsd`

Bluetooth connections work with `gpsd` by leveraging the rfcomm serial port emulation. Rfcomm provides a serial port interface to a BT device and has been designed to allow for automated connect/disconnect operations over Bluetooth. The steps below will allow you to use your BT GPS device automatically whenever it is powered on and gpsd is running.

Note that you must be logged in as root for most of these steps.

## Installation

If your system comes with Bluetooth tools preinstalled (look for on your status bar) you can probably skip these steps.

1. First, the Bluez protocol stack must be installed. All the documentation can be found on http://bluez.sourceforge.net/.

2. Install bluetooth for your device with the "rfcomm" module to allow for serial port emulation.

3. Next, load the following modules:

       	# modprobe hci_xxx (xxx depend on your type of device)
       	# modprobe bluez
       	# modprobe l2cap
       	# modprobe rfcomm

4. If the modules have loaded successfully, type "hciconfig" and you should see your BT interface listed under the "hci0" name.

## Configuration

1. Turn on your BT GPS device and scan for remote BT devices:

       	# hciconfig hci0 up
       	# hcitool scan

2. Write down the address of your BT GPS receiver (xx:xx:xx:xx:xx:xx). At this point, it is quite likely that passing the address to gpsd will work.

3. If you're using a smartphone via Bluetooth, you will probably need to specify a channel other than 1. Start the GPS app on your phone, altering any settings needed to make it give NMEA strings over Bluetooth, and then do something like:

         sdptool browse xx:xx:xx:xx:xx:xx

   You should see something like this in the output:

         Service Name: GPS2BT
         Service RecHandle: 0x1000b
         Service Class ID List:
           UUID 128: 00001101-0000-1000-8000-00805f9b34fb
         Protocol Descriptor List:
           "L2CAP" (0x0100)
           "RFCOMM" (0x0003)
             Channel: 2

   The Service name will vary based on the app. Write down the channel number and use it in the next step instead of channel 1. The channel number will likely vary each time the app is started, so you will probably need some scripting or other additional configuration to fix that. If gpsd or gpsctl is reporting "connection refused" it is likely that you have the wrong channel number.

4. Set up rfcomm. Edit /etc/bluetooth/rfcomm.conf to reflect your BT GPS address and to enable binding.

       	#
       	# RFCOMM configuration file.
       	#
       	# $Id: rfcomm.conf,v 1.1 2002/10/07 05:58:18 maxk Exp $
       	#

       	rfcomm0 {
       	        # Automatically bind the device at startup
       	        bind yes;

       	        # Bluetooth address of the device
       	        device xx:xx:xx:xx:xx:xx;

       	        # RFCOMM channel for the connection
       	        channel 1;

       	        # Description of the connection
       	        comment "Your GPS Device Here";
       	}

5. Bind rfcomm0 (unless you are planning to reboot, in which case it will be automatically bound).

       	# rfcomm bind rfcomm0

6. Under most Linux distros, GPSD is by default configured to start gpsd on a hotplug event announcing a USB GPS. You need to reconfigure the GPSD installation so the daemon will be started at boot time listening to /dev/rfcomm0 (it will still work with hotplugged USB GPses after you do this).

   Under Debian and Ubuntu Linux, `"dpkg-reconfigure gpsd"` will start a dialog that will reconfigure the device for you. You will need to reboot for this change to take effect.

At this point, your system should be configured to use gpsd with your BT GPS device. You should test operation in the normal way described in the Troubleshooting Guide.

## Known Issues:

- On system startup, gpsd starts before rfcomm0 is bound by rfcomm and fails (at least on some systems) - a workaround for this is to add a symlink to the gpsd init.d script to a later runlevel.

      # cd /etc/rcS.d/
      # ln -s ../init.d/gpsd S89gpsd

- In February 2009 it was reported that there are some issues with the Bluetooth stack in Ubuntu Intrepid. This report advocates using a different Bluetooth device manager and describes some additional udev rules.

## Contributors:

- Jean-Michel Bouffard

- Joshua Layne

- Lukasz Stelmach

- Bertolt Loprets

- Rob Shinn

- Tomáš Ebenlendr