Reading and writing vendor-specific BLE characteristic values using bluetoothctl or gatttool

Question

I am able to connect to and read vendor-specific characteristic values from a BLE device using gatttool on a Raspberry Pi 4B terminal command line, but I have a couple of issues.

1. A dialog appears, "Connection successful", with an OK button. I do not think this will be acceptable in production code.

2. I am unable to "unpair" or "remove" the device using gatttool.

I am able to connect to a BLE device using bluetoothctl on a Raspberry Pi 4B terminal command line (interactive), and can read generic characteristic values, but I cannot read vendor-specific characteristic values. I can, however, remove (unpair) the device using bluetoothctl.

Using gatttool: gatttool -t random -b E0:0D:10:F1:D5:FC --char-read -a 0x0014 returns the value of the characteristic.

Using bluetoothctl: power on scan on pair E0:0D:10:F1:D5:FC connect E0:0D:10:F1:D5:FC /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0001 /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0010/char0027 /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0001/char0002 /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0010/char0029 /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0001/char0002/desc0004 /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0010/char002b /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0001/char0005 /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0010/char002d /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0001/char0007 /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0010/char002f /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0010 /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0010/char0031 /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0010/char0011 /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0010/char0033 /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0010/char0013 /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0010/char0035 /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0010/char0015 /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0010/char0037 /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0010/char0017 /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0010/char0039 /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0010/char0019 /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0010/char003b /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0010/char001b /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0010/char003d /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0010/char001d /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service003f /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0010/char001f /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service003f/char0040 /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0010/char0021 /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service003f/char0042 /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0010/char0023 /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service003f/char0042/desc0044 /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0010/char0025
[rSY?1T5WpDnQg==r#nRoZXaLm1Dc5_]# select-attribute /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service10/char0013 [rSY?1T5WpDnQg==r#nRoZXaLm1Dc5_]#

I thought perhaps the prompt would change to the selected attribute.

[rSY?1T5WpDnQg==r#nRoZXaLm1Dc5_]# read No attribute selected [rSY?1T5WpDnQg==r#nRoZXaLm1Dc5_]#

I thought maybe the read command would return the value of the characteristic, but that did not happen.

However, when I select a generic attribute,

[rSY?1T5WpDnQg==r#nRoZXaLm1Dc5_:/service0001/char0005]# select-attribute /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0001/char0007 [rSY?1T5WpDnQg==r#nRoZXaLm1Dc5_:/service0001/char0007]# read Attempting to read /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0001/char0007 [CHG] Attribute /org/bluez/hci0/dev_E0_0D_10_F1_D5_FC/service0001/char0007 Value: fd df 10 72 3e f3 f0 84 b5 df 9e f1 3a a8 85 44 ...r>.......:..D fd df 10 72 3e f3 f0 84 b5 df 9e f1 3a a8 85 44 ...r>.......:..D

the prompt changes and the characteristic value is returned.

I was hoping to find a good GATT tutorial on the internet. So far, all I seem to be able to find is the man pages (https://www.mankier.com/1/bluetoothctl).

Does anyone have suggestions on what BLE GATT tool to use and how to use it or references to online documentation?

Answer 1

Before using a technology, you should try to understand it. Each BLE characteristic is described by different attributes, which might define a Characteristic as write-only, for example. However, you might want to start with the material provided by the Bluetooth SIG, for example: Intro to Bluetooth Generic Attribute Profile (GATT)