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

[Fabio Ballanti]

Hello Karl,

Karl Ylvisaker said:

Please try to typecast it to utiny16_t, and see if the error persists.

Ok, typecast and run done, but as I wrote before

Fabio Ballanti said:

but no c_uint8_t or c_uint16_t

and the result is as follow:

- with uint16_t

- with c_uint16_t

Probably this is not the good way to go in heaven 

[Karl Ylvisaker]

Hello,

Fabio Ballanti said:

Ok, typecast and run done, but as I wrote before

My mistake, I should have been more explicit. Please try this using the uint16 type available in the ctypes library then. The added _t is C convention when creating new typedef's, the important part is the number representation and memory allocation.

Best regards,
Karl 

[Fabio Ballanti]

Karl,

tried writing uint16 but there's not uint16 in ctypes library:

In the meanwhile I'll search if there's another option...

[Karl Ylvisaker]

Fabio,

Fabio Ballanti said:

there's the ctypes library which seems to have only ctypes.c_uint8 and ctypes.c_uint16

It seems the uint16 type is called c_uint16  in the ctypes library.

Karl Ylvisaker said:

Please try this using the uint16 type available in the ctypes library

Looking forward to resolving this issue together.

Best regards,
Karl

[Fabio Ballanti]

Hello Karl,

Yes, I've seen it now (I was set on mind for uint16_t), sorry if didn't check before and I missed it...

Ok, tried on my script, here's the result:

Reading well the other screenshots, and seeing this last one, it seems that the real problem now is on formatting DEVICE_NAME.encode(encoding='utf_8')

[Karl Ylvisaker]

Hello again.

Fabio Ballanti said:

Yes, I've seen it now (I was set on mind for uint16_t), sorry if didn't check before and I missed it...

No problem at all Fabio, it happens to all of us sometimes :)

Fabio Ballanti said:

Reading well the other screenshots, and seeing this last one, it seems that the real problem now is on formatting DEVICE_NAME.encode(encoding='utf_8')

Yes, this again is a TypeError. What is the type of the DEVICE_NAME.encode(encoding='utf_8') argument you are supplying? 
As you see from the sd_ble_gap_device_name_set function documentation, and the error message, the argument needs to be a uint8_t const pointer.

As I understand it you are now using the pc-ble-driver-py in your python project, correct?
If so you should check out the advertising example and how they use the pc-ble-driver-py to configure the device name there.

Best regards,
Karl

[Fabio Ballanti]

Hi Karl,

thank you again for your support!

Karl Ylvisaker said:

What is the type of the DEVICE_NAME.encode(encoding='utf_8') argument you are supplying? 

The variable DEVICE_NAME is a string (intended as array of chars), and following the example in Bluetooth low energy Advertising, a beginner's tutorial I've named it in  the same way:

DEVICE_NAME = "HelloWorld"

in the example code (written in C), there's a point which is called this function:

    err_code = sd_ble_gap_device_name_set(&sec_mode,
                                          (const uint8_t *)DEVICE_NAME,
                                          strlen(DEVICE_NAME));

where is passed a pointer type cast (const uint8_t *);

so, thought was a best practice to pass in the Python function the string DEVICE_NAME encoded in utf_8:

>>>print(DEVICE_NAME.encode(encoding='utf_8'))
b'HelloWorld'

But, I have to find out how to convert a string in a uint8_t const pointer...

Karl Ylvisaker said:

As I understand it you are now using the pc-ble-driver-py in your python project, correct?

Yes, correct! I've made for the Python interpreter the pip install pc-ble-driver-py command.

Karl Ylvisaker said:

If so you should check out the advertising example and how they use the pc-ble-driver-py to configure the device name there.

PERFECT! I'll study it and let you know!

 

[Karl Ylvisaker]

Hello again,

Fabio Ballanti said:

thank you again for your support!

No problem at all Fabio, I am happy to help!

Fabio Ballanti said:

PERFECT! I'll study it and let you know!

Great, I am happy to hear that!
That sounds like a good plan - let me know if you should encounter any issues or questions while doing so!

Best regards,
Karl