There are two standards in use known as BT classic and BT low energy.

Anything other than BLE is considered obsolete now.

BT 3.0+HS utilises WiFi. BT 4.0 onward is BLE, anything prior is BDR/EDR.

See bluetooth for Linux Bluetooth devices and setup.

Development has two services dependencies, dbus and bluetoothd.

I normally disable dbus with systemd and here is how to enable this service with `runit' if preferred.

#!/bin/bash
sleep 1

#LOG
exec 2>&1
ulimit -aH

#RUN
export TZ="UTC"
rm -Rf /var/run/dbus
mkdir -p /var/run/dbus
exec dbus-daemon --syslog --syslog-only --nofork --config-file=/usr/share/dbus-1/system.conf

Install bluez and various tools if not already installed

apt install bluez bluez-tools bluez-test-tools bluez-hcidump

I prefer to run Bluetoothd from `runit'

This run file can work but it should wait until dbus is ready before starting.

See the wait method of runit to detect /var/run/dbus/pid.

#!/bin/bash
sleep 5

#LOG
exec 2>&1
ulimit -aH

#RUN
export TZ="UTC"
exec /usr/sbin/bluetoothd -n

Development in C is mostly about reading the code examples.

Install dev headers for the current installation of bluez

apt install libbluetooth-dev

Access source code for documentation of how to use bluez

git clone https://github.com/bluez/bluez

bluez source code demonstrates how to access BT devices via dbus in the src directory or the API in the attrib and tools directories.

Build the source to create tools

sudo apt-get install glib2.0-dev libdbus-1-dev libical-dev python3-docutils
./bootstrap
./configure --prefix=/opt/bt --enable-experimental --enable-deprecated

Test BLE device.

./tools/btgatt-client -d 00:80:E1:22:F9:7C
Connecting to device... Done
[GATT client]# Service Added - UUID: 00001801-0000-1000-8000-00805f9b34fb start: 0x0001 end: 0x0004
[GATT client]# Service Added - UUID: 00001800-0000-1000-8000-00805f9b34fb start: 0x0005 end: 0x000b
[GATT client]# Service Added - UUID: 0000fe40-cc7a-482a-984a-7f2ed5b3e58f start: 0x000c end: 0x0011
[GATT client]# GATT discovery procedures complete
[GATT client]#
service - start: 0x0001, end: 0x0004, type: primary, uuid: 00001801-0000-1000-8000-00805f9b34fb
          charac - start: 0x0002, value: 0x0003, props: 0x20, ext_props: 0x0000, uuid: 00002a05-0000-1000-8000-00805f9b34fb
                  descr - handle: 0x0004, uuid: 00002902-0000-1000-8000-00805f9b34fb

service - start: 0x0005, end: 0x000b, type: primary, uuid: 00001800-0000-1000-8000-00805f9b34fb
          charac - start: 0x0006, value: 0x0007, props: 0x0a, ext_props: 0x0000, uuid: 00002a00-0000-1000-8000-00805f9b34fb
          charac - start: 0x0008, value: 0x0009, props: 0x02, ext_props: 0x0000, uuid: 00002a01-0000-1000-8000-00805f9b34fb
          charac - start: 0x000a, value: 0x000b, props: 0x02, ext_props: 0x0000, uuid: 00002a04-0000-1000-8000-00805f9b34fb

service - start: 0x000c, end: 0x0011, type: primary, uuid: 0000fe40-cc7a-482a-984a-7f2ed5b3e58f
          charac - start: 0x000d, value: 0x000e, props: 0x06, ext_props: 0x0000, uuid: 0000fe41-8e22-4541-9d4c-21edae82ed19
          charac - start: 0x000f, value: 0x0010, props: 0x10, ext_props: 0x0000, uuid: 0000fe42-8e22-4541-9d4c-21edae82ed19
                  descr - handle: 0x0011, uuid: 00002902-0000-1000-8000-00805f9b34fb

[GATT client]# ^C

Shutting down...

apt install python3-gattlib

This doesn't appear to work with the STM32WB p2pServer demo so no further to make at this time.