How can I notify a handle defined by myself in pc-ble-driver-py?

[zhaoyuan]

Hi,

I try to use nrf52840 dongle and pc-ble-driver-py to connect nrf5340 and get the data from it. The handle and uuid is obtained from nRF Connect for Desktop BLE and the data sent by nrf5340 also can be obtained by notifying the Nordic Uart Tx handle. However, I get an "NordicSemiException: CCCD not found" error when trying to notify the hanle in pc-ble-driver-py.

Here are my error logs:

BLE Connection:2619629865808:
  role: BLEGapRoles.central
  peer_addr: [238, 248, 228, 219, 104, 37] (1)
  services:
    Service uuid(0x1801) start handle(1) end handle(8)
    Service uuid(0x1800) start handle(9) end handle(15)
    Service uuid(0x0001) start handle(16) end handle(21)
<Standard.cccd: 10498>
Traceback (most recent call last):
  File "D:/zhaoyuan_data/dsp/brain_usb/pc-ble-driver-py-master/pc_ble_driver_py/examples/heart_rate_collector.py", line 119, in connect_and_discover
    self.adapter.enable_notification(
  File "D:\zhaoyuan_data\dsp\brain_usb\pc-ble-driver-py-master\pc_ble_driver_py\ble_driver.py", line 104, in wrapper
    err_code = wrapped(*args, **kwargs)
  File "D:\zhaoyuan_data\dsp\brain_usb\pc-ble-driver-py-master\pc_ble_driver_py\ble_adapter.py", line 415, in enable_notification
    raise NordicSemiException("CCCD not found")
pc_ble_driver_py.exceptions.NordicSemiException: CCCD not found
python-BaseException

Process finished with exit code 1

the error is occured in the command:

self.adapter.enable_notification(
    new_conn, BLEUUID(0x2902),4
)

[Sigurd]

Hi,

1) What version of pc-ble-driver-py are you using?

2) You hovered the mouse over the CCCD, and got the handle like this?

[zhaoyuan]

Hi，

Thanks for your relpy.

1) The pc-ble-driver-py I use is verision 0.17.0.

2) Yes, I get handle in this way.

[zhaoyuan]

I find that I get a wrong uuid and handle. What I need is the uuid and handle of UART Tx but I took CCCD's uuid and handle. I can get the data from enable_notification now. However, the speed is much lower than the speed by the desktop tool, which is 10kbps contrast to 100kbps. 

And the function "self.adapter.enable_notification" seems to get data and print it as log, but I want to store the data in a variable and process it in the future. I wonder if there is any other appropriate function or api in pc-ble-driver-py. Thank you.

[Sigurd]

zhaoyuan said:

I can get the data from enable_notification now.

Great!

zhaoyuan said:

However, the speed is much lower than the speed by the desktop tool, which is 10kbps contrast to 100kbps. 

Could be a difference in connection interval, and if ATT MTU, DLE, etc is used or not.

[zhaoyuan]

Thank you for your reply. I find that connection interval is defined in ble_driver.py. Can the parameter such as connection interval be directly modified in ble_driver.py or any other api?

[Sigurd]

Hi,

You have the function conn_param_update() you can use. Changing to 2MPY should help as well, 

phy_update(). And also  data_length_update() and att_mtu_exchange()

[zhaoyuan]

Hi Sigurd,

Thank you for your helpful advice. I have another problem that I wonder to know where I can get the data notified from nrf5340. I can't find the data in any variable provided by enable_notification such as result. Currently it seems to get data and print it as log.

[Sigurd]

If you have a look at e.g. the heart_rate_collector example, you get the data in 'data' in on_notification(self, ble_adapter, conn_handle, uuid, data)

https://github.com/NordicSemiconductor/pc-ble-driver-py/blob/master/pc_ble_driver_py/examples/heart_rate_collector.py#L162