Accessing GATT Services

In this example we want to connect with a LE device and explore its provided GATT services. The used LE device in this example provides a number of vendor specific GATT services but also the standard battery GATT service.

First, connect with the discovered LE device by using the bluetoothctl command

$ sudo bluetoothctl
[bluetooth]# connect 5C:31:3E:71:0C:E7
Attempting to connect to 5C:31:3E:71:0C:E7
[CHG] Device 5C:31:3E:71:0C:E7 Connected: yes
Connection successful

As soon as BlueZ has discovered which GATT services are available the bluetoothctl utility will print out the following:

[CHG] Device 5C:31:3E:71:0C:E7 UUIDs: 00001800-0000-1000-8000-00805f9b34fb
[CHG] Device 5C:31:3E:71:0C:E7 UUIDs: 00001801-0000-1000-8000-00805f9b34fb
[CHG] Device 5C:31:3E:71:0C:E7 UUIDs: 0000180f-0000-1000-8000-00805f9b34fb
[CHG] Device 5C:31:3E:71:0C:E7 UUIDs: 0d271100-f0d4-469d-afd3-605a6ebbdb13
[CHG] Device 5C:31:3E:71:0C:E7 UUIDs: 0d27fa01-f0d4-469d-afd3-605a6ebbdb13
[CHG] Device 5C:31:3E:71:0C:E7 UUIDs: 0d27fa60-f0d4-469d-afd3-605a6ebbdb13
[CHG] Device 5C:31:3E:71:0C:E7 UUIDs: 0d27ffc0-f0d4-469d-afd3-605a6ebbdb13
[NEW] Service /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0010 Vendor specific (Primary)
[NEW] Characteristic /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0010/char0011 Vendor specific
[NEW] Characteristic /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0010/char0013 Vendor specific
[NEW] Characteristic /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0010/char0015 Vendor specific
[NEW] Characteristic /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0010/char0017 Vendor specific
[NEW] Characteristic /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0010/char0019 Vendor specific
[NEW] Characteristic /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0010/char001b Vendor specific
[NEW] Characteristic /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0010/char001d Vendor specific
[NEW] Service /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service001f Vendor specific (Primary)
[NEW] Characteristic /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service001f/char0020 Vendor specific
[NEW] Characteristic /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service001f/char0022 Vendor specific
[NEW] Characteristic /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service001f/char0024 Vendor specific
[NEW] Characteristic /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service001f/char0026 Vendor specific
[NEW] Descriptor /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service001f/char0026/desc0028 Client Characteristic Configuration
[NEW] Service /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0029 Battery Service (Primary)
[NEW] Characteristic /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0029/char002a Battery Level
[NEW] Descriptor /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0029/char002a/desc002c Client Characteristic Configuration
[NEW] Service /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service002d Vendor specific (Primary)
[NEW] Characteristic /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service002d/char002e Vendor specific
[NEW] Descriptor /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service002d/char002e/desc0030 Client Characteristic Configuration
[NEW] Descriptor /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service002d/char002e/desc0031 Characteristic User Description
[NEW] Service /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0032 Vendor specific (Primary)
[NEW] Characteristic /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0032/char0033 Vendor specific
[NEW] Descriptor /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0032/char0033/desc0035 Client Characteristic Configuration
[NEW] Descriptor /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0032/char0033/desc0036 Characteristic User Description
[NEW] Characteristic /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0032/char0037 Vendor specific
[NEW] Descriptor /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0032/char0037/desc0039 Client Characteristic Configuration
[NEW] Descriptor /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0032/char0037/desc003a Characteristic User Description
[NEW] Characteristic /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0032/char003b Vendor specific
[NEW] Descriptor /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0032/char003b/desc003d Client Characteristic Configuration
[NEW] Descriptor /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0032/char003b/desc003e Characteristic User Description
[CHG] Device 5C:31:3E:71:0C:E7 GattServices: /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0010
[CHG] Device 5C:31:3E:71:0C:E7 GattServices: /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service001f
[CHG] Device 5C:31:3E:71:0C:E7 GattServices: /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0029
[CHG] Device 5C:31:3E:71:0C:E7 GattServices: /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service002d
[CHG] Device 5C:31:3E:71:0C:E7 GattServices: /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0032
[CHG] Device 5C:31:3E:71:0C:E7 Name: X4-LIFE Xmarty 2.0
[CHG] Device 5C:31:3E:71:0C:E7 Alias: X4-LIFE Xmarty 2.0

It is now possible to select specific characteristics and read their values or, if possible, also write them. This example focuses on the battery level characteristic from the battery GATT service.

[5C-31-3E-71-0C-E7]# select-attribute /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0029/char002a
[X4-LIFE Xmarty 2.0:/service0029/char002a]# read
Attempting to read /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0029/char002a
[CHG] Attribute /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0029/char002a Value: 0x49
49

It is also possible to receive notifications when the value of a characteristic changes.

[X4-LIFE Xmarty 2.0:/service0029/char002a]# notify on
[CHG] Attribute /org/bluez/hci0/dev_5C_31_3E_71_0C_E7/service0029/char002a Notifying: yes
Notify started

This will now notify whenever the value of the selected characteristic changes.

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