Change remote device name and class via HCI - linux

Question

I have a bluetooth audio interface which I want to change the name and the CoD (Class of Device) parameter. I have tried doing this using hcitool on Ubuntu, with: sudo hcitool cmd 0x03 0x0024 0x260420 which is supposed to set the CoD to 0x260420 (it's currently 0x260404), but I've had no luck. From what I now understand, I take id that you cannot use hcitool on a Linux computer to send cmd commands to a bluetooth device connected to that computer via bluetooth. Is there a way to achieve this?
Is it at all possible to change a bluetooth devices' configuration remotely in any way?

Answer 1

You can try it with a small C script. We will use these two methods you can find in the hci_lib.h header file.
int hci_read_class_of_dev(int dd, uint8_t *cls, int to);
int hci_write_class_of_dev(int dd, uint32_t cls, int to);
Be aware that a Class of Device (CoD) has strict requirements you can find in the official Bluetooth documentation (here). That's why you need sudo to execute.
// Simple program to read and write Class of Device.
// To compile: `gcc -o rw_cod rw_cod.c -lbluetooth`
// To install lbluetooth: `apt-get install libbluetooth-dev`
// Execute with `sudo ./rw_cod`
// Note the original CoD first because it has strict rules, you might need to write it back later.
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h> // for close()
#include <bluetooth/bluetooth.h>
#include <bluetooth/hci.h>
#include <bluetooth/hci_lib.h>
int main(void){
int dd = hci_open_dev(hci_devid("DC:A6:32:E4:9C:05"));
int timeout = 1000;
uint8_t cls[3] = {0};
int class;
int ret;
uint32_t new_class = 0x260404;
// Read CoD
ret = hci_read_class_of_dev(dd, cls, timeout);
class = cls[0] | cls[1] << 8 | cls[2] << 16;
printf("Class of Device = 0x%06x [%d]\n", class, ret);
// Set CoD
ret = hci_write_class_of_dev(dd, new_class, 2000);
printf("Required new Class of Device = 0x%06x [%d]\n", new_class, ret);
// Check read CoD
ret = hci_read_class_of_dev(dd, cls, timeout);
class = cls[0] | cls[1] << 8 | cls[2] << 16;
printf("Actual new Class of Device = 0x%06x [%d]\n", class, ret);
close(dd);
return 0;
}
Console returns:
pi#raspberrypi:~/Work_Bluetooth $ sudo ./rw_cod
Class of Device = 0x260404 [0]
Required new Class of Device = 0x260420 [0]
Actual new Class of Device = 0x260420 [0]
pi#raspberrypi:~/Work_Bluetooth $