BLE Examples generic gatt server

From Technologic Systems Manuals

The BlueZ example GATT server emulates a dummy device with a dummy battery. It demonstrates being able to do active reads of a BLE device as well as subscribing to push notifications from a device.


1 Prerequisites

  • The example was tested against a smartphone with BLE capabilities, using a simple BLE monitor tool.
  • The Bluetooth device must already be set up via the device's manual's instructions (without the use of the hciconfig command!) and bluetoothd started via system as noted above.
  • Be running as root user or a user with proper permissions.
  • Set up and run the Example Advertisement example. This is needed so that the BLE device can be advertised and discovered.
Note: Due to caching on some devices, it may be necessary to completely exit any BLE applications/tools, and potentially even power-cycling the BLE device itself on any devices connecting to the example GATT server below. This has been observed to be necessary on at least one specific smartphone that was used to connect to the unit's on-board BLE module running these examples.


2 Running

Run the example with:

root@tsimx28:~# /usr/local/lib/bluez/test/example-gatt-server
Registering GATT application...
GetManagedObjects
GATT application registered
# The following lines will not be printed until the device connects and does a read of the "Battery Level" service
Battery Level read: 100
Battery Level read: 100
Battery Level drained: 98
Battery Level drained: 96
Battery Level drained: 94
...
# The following lines will not be printed until the device connects and subscribes to the "Heart Rate Measurement" service
Update HR Measurement Simulation
Updating value: [dbus.Byte(14), dbus.Byte(93), dbus.Byte(0), dbus.Byte(0)]
Updating value: [dbus.Byte(6), dbus.Byte(127)]
Updating value: [dbus.Byte(6), dbus.Byte(108)]
Updating value: [dbus.Byte(6), dbus.Byte(128)]
...
# The following lines will not be printed until the device connects and interacts with the "characteristic for testing" services
TestCharacteristic Write: dbus.Array([dbus.Byte(192), dbus.Byte(255), dbus.Byte(238)], signature=dbus.Signature('y'))
TestSecureCharacteristic Write: dbus.Array([dbus.Byte(222), dbus.Byte(250), dbus.Byte(206)], signature=dbus.Signature('y'))
TestCharacteristic Read: dbus.Array([dbus.Byte(192), dbus.Byte(255), dbus.Byte(238)], signature=dbus.Signature('y'))
TestSecureCharacteristic Read: dbus.Array([dbus.Byte(222), dbus.Byte(250), dbus.Byte(206)], signature=dbus.Signature('y'))
...

With the connecting device, it is possible to read from or subscribe to the Battery Level service. The running example will print "Battery Level read: ..." each time the battery is manually read. When subscribed to, the connecting device will receive periodic updates of the battery level. When an update goes out, the running example will print "Battery Level drained: ..." with the value also being sent to any subscribed devices. The following screenshot is an example of what a connected device would see.

Ble batt level.png

With the connecting device, it is possible to subscribe to the Heart Rate Measurement service. The running example will print simulation values to the terminal once every second, with the same values being sent to any subscribed devices. The following screenshot is an example of what a connected device would see.

Ble heart mon.png

With the connecting device, it is possible to write and read multiple of the characteristic for testing services. Anything that is written to these services can be read back independently. In the example output above, the hex value 0xC0FFEE was written and read back from the first service, while 0xDEFACE was written and read back from the third service.

Ble test char.png

When done, press Ctrl+c to end the example and return to the command line, leaving the advertising example running in the background still.