Device Name changing with nRF52840 using sd_ble_gap_device_name_set in Python

[Fabio Ballanti]

Hi,

I'm trying to make a script in Python using the nRF52840 dongle, to make some BLE advertising.

I'm using:

- Python 3.7.2 (32 bit)

- pc_ble_driver_py library

- Windows 10

- Visual Code

- nRF52840 dongle with USB CDC ACM FW

Now I would like to set a name to my device as I can see it through nRF APP on my mobile phone.

Searching through similar issues in other posts, I've found this function sd_ble_gap_device_name_set, which defined as follow:

def sd_ble_gap_device_name_set(adapter, p_write_perm, p_dev_name, len):
 return _nrf_ble_driver_sd_api_v2.sd_ble_gap_device_name_set(adapter, p_write_perm, p_dev_name, len)

To figure out how to use it, I've searched in some tutorials and found Bluetooth low energy Advertising, a beginner's tutorial which are written in C;

The function in C is declared as follow:

uint32_t sd_ble_gap_device_name_set	(	ble_gap_conn_sec_mode_t const * 	p_write_perm,
                                        uint8_t const * 	p_dev_name,
                                        uint16_t 	len 
                                    )	

In my script, the function is used as follow:

    # Device Name Change
    device_name = split_str(DEVICE_NAME)
    gap_device_name = [hex(ord(x)) for x in device_name]
    str_length = len(DEVICE_NAME.encode(encoding='utf_8'))
    driver.sd_ble_gap_device_name_set(
            peripheral.adapter.driver.rpc_adapter,
            None,
            DEVICE_NAME.encode(encoding='utf_8'),
            str_length
            )

when in Debug mode with Visual Code, I receive this message:

Can anyone help me to solve this issue?

Thanx,

Fabio

[Karl Ylvisaker]

Hello Fabio,

What is the type of your passed str_length variable?
As you see in the sd_ble_gap_device_name_set the len parameter needs to be of type uint16_t, while then python len functions returns an int ( represented by 4 bytes ).
I assume this is why you have got your type error.
Please try to typecast the len variable to uint16_t, and see if this resolves your issue.

Best regards,
Karl

[Fabio Ballanti]

Hello Karl,

Yes, the str_length variable is of course an int. 

The variable DEVICE_NAME is a string "HelloWorld", which is converted and stored in device_name as ['H','e','l','l','o','W','o','r','l','d']

Googling around there's the ctypes library which seems to have only ctypes.c_uint8 and ctypes.c_uint16, but no c_uint8_t or c_uint16_t. Trying to import ctypes library and using c_uint8 or c_uint16 it in my code, the answer is the same:

Is there a better way to make a change name on the device?

Thanx

[Karl Ylvisaker]

Hello,

Fabio Ballanti said:

Googling around there's the ctypes library which seems to have only ctypes.c_uint8 and ctypes.c_uint16, but no c_uint8_t or c_uint16_t. Trying to import ctypes library and using c_uint8 or c_uint16 it in my code, the answer is the same:

I do not have any personal experience with the ctypes library you reference, but I see that you are typecasting it to an uint8_t, while the length argument needs to be of type uint16_t. Please try to typecast it to uint16_t, and see if the error persists.

Fabio Ballanti said:

Is there a better way to make a change name on the device?

I suppose you could create your own function to do this, in which you mask out the particular bytes from the int and place them over in a two byte structure - making sure to account for the potentially signed value bit of the int.
I would guess this is what they are doing behind the scenes of the ctypes library anyways - you could check their source code, and if they are doing exactly this then there is no reason to implement your own function to do the same.

Best regards,
Karl