So, you’ve decided to write a Bluetooth driver for Linux in C++.

Either you’re incredibly brave, or you lost a bet.

Either way, welcome to the wild world of kernel development, where one wrong move can turn your computer into a glorified paperweight.

Step 1: Understanding What a Bluetooth Driver Actually Does

A Bluetooth driver is what lets your Linux system talk to Bluetooth hardware. Without it, your fancy Bluetooth headphones are just overpriced earmuffs.

Your driver will need to:

• Communicate with the Bluetooth hardware (usually via USB, PCI, or UART).
• Register itself with the Linux Bluetooth stack (BlueZ).
• Handle data transmission and reception.
• Not crash the entire system (easier said than done).

Step 2: Setting Up Your Development Environment

Before you dive into the code, make sure you have everything you need:

Required Tools:

• A Linux Machine (or a virtual machine, unless you like rebooting your main system every 5 minutes).
• Kernel Headers & Source Code (because drivers live in kernel space).
• A Bluetooth Device (USB dongle, embedded module, or built-in chip).
• Patience (you’ll need a lot of it).

Install Essential Packages:

Fire up your terminal and get the required dependencies:

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sudo apt-get install build-essential linux-headers-$(uname -r)
sudo apt-get install bluez bluez-tools

If you’re using a different distro, substitute apt-get for your package manager of choice (dnf, pacman, etc.).

Step 3: Writing the Bluetooth Driver

Now for the fun part—writing the actual driver. We’ll keep it simple and focus on a USB-based Bluetooth module.

Step 3.1: Include the Necessary Headers

A Linux driver is just a fancy kernel module. Start with:

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#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/usb.h>
#include <linux/init.h>

These headers give you access to kernel module functions, USB handling, and initialization routines.

Step 3.2: Define the USB Device ID Table

Every USB device has an ID. Your driver needs to know which devices it should work with:

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static struct usb_device_id bt_table [] = {
    { USB_DEVICE(0x0a12, 0x0001) }, // Example Bluetooth dongle
    { } /* Terminating entry */
};
MODULE_DEVICE_TABLE(usb, bt_table);

You can find your device’s actual Vendor ID (0x0a12) and Product ID (0x0001) with:

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lsusb

Step 3.3: Define Probe and Disconnect Functions

The probe function runs when your Bluetooth device is plugged in:

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static int bt_probe(struct usb_interface *interface, const struct usb_device_id *id)
{
    printk(KERN_INFO "Bluetooth device connected!\n");
    return 0;
}

The disconnect function runs when the device is removed:

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static void bt_disconnect(struct usb_interface *interface)
{
    printk(KERN_INFO "Bluetooth device disconnected!\n");
}

Step 3.4: Register the USB Driver

Now, we register our driver with the Linux kernel:

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static struct usb_driver bt_driver = {
    .name = "bt_driver",
    .id_table = bt_table,
    .probe = bt_probe,
    .disconnect = bt_disconnect,
};

static int __init bt_init(void)
{
    return usb_register(&bt_driver);
}

static void __exit bt_exit(void)
{
    usb_deregister(&bt_driver);
}

module_init(bt_init);
module_exit(bt_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Your Name");
MODULE_DESCRIPTION("A Simple Bluetooth Driver");

Step 4: Compiling and Loading the Driver

Now, let’s build and test it.

Step 4.1: Compile the Module

Create a Makefile:

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obj-m += bt_driver.o
all:
    make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
clean:
    make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

Run:

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make

Step 4.2: Load the Driver

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sudo insmod bt_driver.ko

Check if it loaded:

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dmesg | tail -n 10

Step 4.3: Unload the Driver

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sudo rmmod bt_driver

Step 5: Testing the Driver

Now, let’s see if your driver works.

1. Run:

   1	hcitool dev

   If you see a device, congratulations! You did it.

2. Try scanning for Bluetooth devices:

   1	hcitool scan

If things break (and they will), check the kernel logs:

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dmesg | grep bt_driver

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