pc_ble_driver_py.exceptions.NordicSemiException: Characteristic value handler not found

Question

Using the pc_ble_driver_py.ble_driver I'm able to subscribe to notifications, but unable to get the values upon connection. The error is: 
 "/home/marc/dev/src/<redacted>/v2/./gui.py", line 258, in connect_and_discover
status, data = self.adapter.read_req(new_conn, build_uuid('button'))
File "/home/marc/.local/lib/python3.9/site-packages/pc_ble_driver_py/ble_adapter.py", line 528, in read_req
raise NordicSemiException("Characteristic value handler not found")
pc_ble_driver_py.exceptions.NordicSemiException: Characteristic value handler not foundFile

I do not know how to install a value handler and could not find documentation about it. The code looks like: 
 
 new_conn = self.conn_q.get(timeout=scan_duration)
self.adapter.service_discovery(new_conn)
self.adapter.enable_notification(new_conn, build_uuid('button'))
def read_value(adapter, conn_handle, handle, offset):
 logging.debug(f"Readvalue({conn_handle} {handle} {offset}")
status, data = self.adapter.read_req(new_conn, build_uuid('button'))
logging.info('button_status: {} status: {}'.format(data, status)) 
 
 and fails in read_req(). 
 
 Any help would be helpful ; thanks. 
 
 Marc.

marto · Accepted Answer

In fact, the error message tricked me. It should probably be `value handle` and not `value handler`. 
 
 After realizing that value_handle could be specified and debugging the search for handles, I realized that I had to specify that my UUID is vendor specific. 
 
 The fix: 
 
 from pc_ble_driver_py.ble_driver import driver

[…]

UUIDS = {
 'base': "0000XXXX-1212-EFDE-1523-785FEABCD123",
 'led': 0x1525,
 'button': 0x1524,
}

def uuid(key):
 """Parse a string and returns a BLEUUID"""
 string = UUIDS[key]
 return list(bytearray.fromhex(string.replace('-', '').replace('X', '0')))

def build_uuid(key):
 """Build a nordic BLEUUID from a key (led, button)"""
 return BLEUUID(UUIDS[key], BLEUUIDBase(uuid('base'), uuid_type=driver.BLE_UUID_TYPE_VENDOR_BEGIN)) 
 
 What's strange is that googling for BLE_UUID_TYPE_VENDOR_BEGIN + python does not give a lot of answer. 
 
 Marc.

pc_ble_driver_py.exceptions.NordicSemiException: Characteristic value handler not found

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