A Bumble application can interface with a local Bluetooth controller on a Linux host. The 3 main types of physical Bluetooth controllers are:
- Bluetooth USB Dongle
- HCI over UART (via a serial port)
- Kernel-managed Bluetooth HCI (HCI Sockets)
!!! tip "Conflicts with the kernel and BlueZ"
If your use a USB dongle that is recognized by your kernel as a supported Bluetooth device, it is
likely that the kernel driver will claim that USB device and attach it to the BlueZ stack.
If you want to claim ownership of it to use with Bumble, you will need to set the state of the corresponding HCI interface as DOWN.
HCI interfaces are numbered, starting from 0 (i.e hci0, hci1, ...).
For example, to bring `hci0` down:
```
$ sudo hciconfig hci0 down
```
You can use the `hciconfig` command with no arguments to get a list of HCI interfaces seen by
the kernel.
Also, if `bluetoothd` is running on your system, it will likely re-claim the interface after you
close it, so you may need to bring the interface back `UP` before using it again, or to disable
`bluetoothd` altogether (see the section further below about BlueZ and `bluetoothd`).
See the USB Transport page for general information on how to use HCI USB controllers.
!!! tip "USB Permissions"
By default, when running as a regular user, you won't have the permission to use
arbitrary USB devices.
You can change the permissions for a specific USB device based on its bus number and
device number (you can use lsusb to find the Bus and Device numbers for your Bluetooth
dongle).
Example:
```
$ sudo chmod o+w /dev/bus/usb/001/004
```
This will change the permissions for Device 4 on Bus 1.
Note that the USB Bus number and Device number may change depending on where you plug the USB
dongle and what other USB devices and hubs are also plugged in.
If you need to make the permission changes permanent across reboots, you can create a `udev`
rule for your specific Bluetooth dongle. Visit [this Arch Linux Wiki page](https://wiki.archlinux.org/title/udev) for a
good overview of how you may do that.
See the Serial Transport page for general information on how to use HCI over a UART (serial port).
HCI sockets provide a way to send/receive HCI packets to/from a Bluetooth controller managed by the kernel.
See the HCI Socket Transport page for details on the hci-socket tansport syntax.
The HCI device referenced by an hci-socket transport (hci<X>, where <X> is an integer, with hci0 being the first controller device, and so on) must be in the DOWN state before it can be opened as a transport.
You can bring a HCI controller UP or DOWN with hciconfig hci<X> up and hciconfig hci<X> up.
!!! tip "HCI Socket Permissions"
By default, when running as a regular user, you won't have the permission to use
an HCI socket to a Bluetooth controller (you may see an exception like PermissionError: [Errno 1] Operation not permitted).
If you want to run without using `sudo`, you need to manage the capabilities by adding the appropriate entries in `/etc/security/capability.conf` to grant a user or group the `cap_net_admin` capability.
See [this manpage](https://manpages.ubuntu.com/manpages/bionic/man5/capability.conf.5.html) for details.
Alternatively, if you are just experimenting temporarily, the `capsh` command may be useful in order
to execute a single command with enhanced permissions, as in this example:
```
$ sudo capsh --caps="cap_net_admin+eip cap_setpcap,cap_setuid,cap_setgid+ep" --keep=1 --user=$USER --addamb=cap_net_admin -- -c "<path/to/executable> <executable-args>"
```
Where `<path/to/executable>` is the path to your `python3` executable or to one of the Bumble bundled command-line applications.
!!! tip "List all available controllers"
The command
$ hciconfig
lists all available HCI controllers and their state.
Example:
```
pi@raspberrypi:~ $ hciconfig
hci1: Type: Primary Bus: USB
BD Address: 00:16:A4:5A:40:F2 ACL MTU: 1021:8 SCO MTU: 64:1
DOWN
RX bytes:84056 acl:0 sco:0 events:51 errors:0
TX bytes:1980 acl:0 sco:0 commands:90 errors:0
hci0: Type: Primary Bus: UART
BD Address: DC:A6:32:75:2C:97 ACL MTU: 1021:8 SCO MTU: 64:1
DOWN
RX bytes:68038 acl:0 sco:0 events:692 errors:0
TX bytes:20105 acl:0 sco:0 commands:843 errors:0
```
!!! tip "Disabling bluetoothd"
When the Bluetooth daemon, bluetoothd, is running, it will try to use any HCI controller attached to the BlueZ stack, automatically. This means that whenever an HCI socket transport is released, it is likely that bluetoothd will take it over, so you will get a "device busy" condition (ex: OSError: [Errno 16] Device or resource busy). If that happens, you can always use
$ hciconfig hci0 down
(or hci<X> with <X> being the index of the controller device you want to use), but a simpler solution is to just stop the bluetoothd daemon, with a command like:
$ sudo systemctl stop bluetooth.service
You can always re-start the daemon with
```
$ sudo systemctl start bluetooth.service
You can use the Bluetooth controller either via the kernel, or directly to the device.
Use an HCI Socket transport (see section above)
In order to use the Bluetooth controller directly on a Raspberry Pi 4 board, you need to ensure that it isn't being used by the BlueZ stack (which it probably is by default).
$ sudo systemctl stop hciuart
should detach the controller from the stack, after which you can use the HCI UART with Bumble.
!!! tip "Check the device name for the UART and at what speed it should be opened"
$ sudo systemctl status hciuart
should show the speed at which the UART should be opened.
For example:
$ sudo systemctl status hciuart hciuart.service - Configure Bluetooth Modems connected by UART Loaded: loaded (/lib/systemd/system/hciuart.service; enabled; vendor preset: enabled) Active: active (running) since Fri 2021-06-18 02:17:28 BST; 1min 10s ago Process: 357 ExecStart=/usr/bin/btuart (code=exited, status=0/SUCCESS) Main PID: 586 (hciattach) Tasks: 1 (limit: 4915) CGroup: /system.slice/hciuart.service └─586 /usr/bin/hciattach /dev/serial1 bcm43xx 3000000 flow -
When run before stopping the hciuart service, shows that on this board, the UART device is /dev/serial and the speed is 3000000
!!! example "Example: scanning"
python3 run_scanner.py serial:/dev/serial1,3000000
In addition to all the standard functionality available from the project by running the python tools and/or writing your own apps by leveraging the API, it is also possible on Linux hosts to interface the Bumble stack with the native BlueZ stack, and with Bluetooth controllers.
A Bumble virtual controller can be attached to the BlueZ stack. Attaching a controller to BlueZ can be done by either simulating a UART HCI interface, or by using the VHCI driver interface if available. In both cases, the controller can run locally on the Linux host, or remotely on a different host, with a bridge between the remote controller and the local BlueZ host, which may be useful when the BlueZ stack is running on an embedded system, or a host on which running the Bumble controller is not convenient.
With the VHCI transport you can attach a Bumble virtual controller to the BlueZ stack. Once attached, the controller will appear just like any other controller, and thus can be used with the standard BlueZ tools.
!!! example "Attaching a virtual controller"
With the example app run_controller.py:
python3 examples/run_controller.py F6:F7:F8:F9:FA:FB examples/device1.json vhci
You should see a 'Virtual Bus' controller. For example:
```
$ hciconfig
hci0: Type: Primary Bus: Virtual
BD Address: F6:F7:F8:F9:FA:FB ACL MTU: 27:64 SCO MTU: 0:0
UP RUNNING
RX bytes:0 acl:0 sco:0 events:43 errors:0
TX bytes:274 acl:0 sco:0 commands:43 errors:0
```
And scanning for devices should show the virtual 'Bumble' device that's running as part of the `run_controller.py` example app:
```
pi@raspberrypi:~ $ sudo hcitool -i hci2 lescan
LE Scan ...
F0:F1:F2:F3:F4:F5 Bumble
```
```