hbldh
Not reliable connection to BLE device on RPI4: different command being used LE Create Connection vs LE Extended Create Connection
Hi everyone I have been trying to use this library on a RPI4 to connect to a BLE device, but the connection is not reliable, as a lot of other issues have mentioned, it needs a lot of attempts to connect.
The thing is that when I use bluetoothctl command prompt and use the connect {MAC} command it always connects in the first attempt. So this lead me to believe that it is not a problem with the hardware but with the implementation.
I have captured with btmon the logs of the different ways a connection is stablished using this library and when a connection is stablished with bluetoothctl and I have seen that the commands used are different:
Connection with BLEAK it uses the LE Create Connection command. It fails and the device disconnects
< HCI Command: LE Create Connection (0x08|0x000d) plen 25
Scan interval: 60.000 msec (0x0060)
Scan window: 60.000 msec (0x0060)
Filter policy: Accept list is not used (0x00)
Peer address type: Public (0x00)
Peer address: FE:97:80:00:24:64 (OUI FE-97-80)
Own address type: Public (0x00)
Min connection interval: 30.00 msec (0x0018)
Max connection interval: 50.00 msec (0x0028)
Connection latency: 0 (0x0000)
Supervision timeout: 420 msec (0x002a)
Min connection length: 0.000 msec (0x0000)
Max connection length: 0.000 msec (0x0000)
> HCI Event: Command Status (0x0f) plen 4
LE Create Connection (0x08|0x000d) ncmd 1
Status: Success (0x00)
> HCI Event: LE Meta Event (0x3e) plen 19
LE Connection Complete (0x01)
Status: Success (0x00)
Handle: 64
Role: Central (0x00)
Peer address type: Public (0x00)
Peer address: FE:97:80:00:24:64 (OUI FE-97-80)
Connection interval: 48.75 msec (0x0027)
Connection latency: 0 (0x0000)
Supervision timeout: 420 msec (0x002a)
Central clock accuracy: 0x00
@ MGMT Event: Device Connected (0x000b) plen 44
LE Address: FE:97:80:00:24:64 (OUI FE-97-80)
Flags: 0x00000008
Connection Locally Initiated
Data length: 31
Flags: 0x06
LE General Discoverable Mode
BR/EDR Not Supported
16-bit Service UUIDs (partial): 1 entry
Health Thermometer (0x1809)
Service Data: Unknown (0xc1c4)
Data: fe97800024646c08bc05106c000003504607000a
@ RAW Open: btmon (privileged) version 2.22
@ RAW Close: btmon
< HCI Command: LE Read Remote Used Features (0x08|0x0016) plen 2
Handle: 64 Address: FE:97:80:00:24:64 (OUI FE-97-80)
> HCI Event: Command Status (0x0f) plen 4
LE Read Remote Used Features (0x08|0x0016) ncmd 1
Status: Success (0x00)
> HCI Event: LE Meta Event (0x3e) plen 12
LE Read Remote Used Features (0x04)
Status: Connection Failed to be Established (0x3e)
Handle: 64 Address: FE:97:80:00:24:64 (OUI FE-97-80)
Features: 0x3f 0x00 0x00 0x08 0x00 0x00 0x00 0x00
LE Encryption
Connection Parameter Request Procedure
Extended Reject Indication
Peripheral-initiated Features Exchange
LE Ping
LE Data Packet Length Extension
Remote Public Key Validation
> HCI Event: Disconnect Complete (0x05) plen 4
Status: Success (0x00)
Handle: 64 Address: FE:97:80:00:24:64 (OUI FE-97-80)
Reason: Connection Failed to be Established (0x3e)
@ MGMT Event: Device Disconnected (0x000c) plen 8
LE Address: FE:97:80:00:24:64 (OUI FE-97-80)
Reason: Unspecified (0x00)
Connection with bluetoothctl connect command it uses the LE Extended Create Connection command and it connects
< HCI Command: LE Extended Create Connection (0x08|0x0043) plen 58
Filter policy: Accept list is not used (0x00)
Own address type: Public (0x00)
Peer address type: Public (0x00)
Peer address: FE:97:80:00:24:64 (OUI FE-97-80)
Initiating PHYs: 0x07
Entry 0: LE 1M
Scan interval: 60.000 msec (0x0060)
Scan window: 60.000 msec (0x0060)
Min connection interval: 10.00 msec (0x0008)
Max connection interval: 10.00 msec (0x0008)
Connection latency: 0 (0x0000)
Supervision timeout: 4000 msec (0x0190)
Min connection length: 0.000 msec (0x0000)
Max connection length: 0.000 msec (0x0000)
Entry 1: LE 2M
Scan interval: 60.000 msec (0x0060)
Scan window: 60.000 msec (0x0060)
Min connection interval: 10.00 msec (0x0008)
Max connection interval: 10.00 msec (0x0008)
Connection latency: 0 (0x0000)
Supervision timeout: 4000 msec (0x0190)
Min connection length: 0.000 msec (0x0000)
Max connection length: 0.000 msec (0x0000)
Entry 2: LE Coded
Scan interval: 60.000 msec (0x0060)
Scan window: 60.000 msec (0x0060)
Min connection interval: 10.00 msec (0x0008)
Max connection interval: 10.00 msec (0x0008)
Connection latency: 0 (0x0000)
Supervision timeout: 4000 msec (0x0190)
Min connection length: 0.000 msec (0x0000)
Max connection length: 0.000 msec (0x0000)
> HCI Event: Command Status (0x0f) plen 4
LE Extended Create Connection (0x08|0x0043) ncmd 2
Status: Success (0x00)
> HCI Event: LE Meta Event (0x3e) plen 31
LE Enhanced Connection Complete (0x0a)
Status: Success (0x00)
Handle: 16
Role: Central (0x00)
Peer address type: Public (0x00)
Peer address: FE:97:80:00:24:64 (OUI FE-97-80)
Local resolvable private address: 00:00:00:00:00:00 (Non-Resolvable)
Peer resolvable private address: 00:00:00:00:00:00 (Non-Resolvable)
Connection interval: 10.00 msec (0x0008)
Connection latency: 0 (0x0000)
Supervision timeout: 4000 msec (0x0190)
Central clock accuracy: 0x00
@ MGMT Event: Device Connected (0x000b) plen 44
LE Address: FE:97:80:00:24:64 (OUI FE-97-80)
Flags: 0x00000008
Connection Locally Initiated
Data length: 31
Flags: 0x06
LE General Discoverable Mode
BR/EDR Not Supported
16-bit Service UUIDs (partial): 1 entry
Health Thermometer (0x1809)
Service Data: Unknown (0xc1c4)
Data: fe97800024646c08bc05146c000003505f07000a
@ RAW Open: btmon (privileged) version 2.22
@ RAW Close: btmon
> HCI Event: LE Meta Event (0x3e) plen 4
LE Channel Selection Algorithm (0x14)
Handle: 16 Address: FE:97:80:00:24:64 (OUI FE-97-80)
Algorithm: #1 (0x00)
< HCI Command: LE Read Remote Used Features (0x08|0x0016) plen 2
Handle: 16 Address: FE:97:80:00:24:64 (OUI FE-97-80)
> HCI Event: Command Status (0x0f) plen 4
LE Read Remote Used Features (0x08|0x0016) ncmd 2
Status: Success (0x00)
> HCI Event: LE Meta Event (0x3e) plen 12
LE Read Remote Used Features (0x04)
Status: Success (0x00)
Handle: 16 Address: FE:97:80:00:24:64 (OUI FE-97-80)
Features: 0x3d 0x00 0x00 0x00 0x00 0x00 0x00 0x00
LE Encryption
Extended Reject Indication
Peripheral-initiated Features Exchange
LE Ping
LE Data Packet Length Extension
Do you think this might be causing the connection fail issues?
Best regards
Interesting finding. Will have to look into it more. A quick web search comes up with some similar cases:
- https://github.com/bluez/bluez/issues/179
- https://stackoverflow.com/questions/71250571/how-to-send-le-extended-create-connection-in-ble-with-raspberry-pi
What commands do you use in bluetoothctl to initiate the connection?
In bluetoothctl console I do: [bluetooth]# scan on [bluetooth]# scan off (when I see my device) [bluetooth]# connect FE:97:80:00:24:64 (my MAC address)
Thanks. The difference in Bleak is that it does the equivalent of:
[bluetooth]# menu scan
[bluetooth]# transport le
[bluetooth]# back
before scan on. Does this also trigger the issue for you?
Apologies for the delayed response. I have been running more tests to reliably reproduce the issue, and I believe the problem was with my setup.
I have two Bluetooth interfaces, hci0 and hci1. In the bluetoothctl console, I set hci1 as the default interface, and all tests were conducted using that interface.
I thought the Bleak library used the default controller, but I believe I was mistaken and it was actually using the hci0 interface. If I set up the BleakScanner like this:
devices = await BleakScanner.discover(timeout=5, adapter='hci1')
and monitor the output it does use the LE Extended Create Connection command:
HCI Command: LE Extended Create Connection (0x08|0x0043) plen 58
Filter policy: Accept list is not used (0x00)
Own address type: Public (0x00)
Peer address type: Public (0x00)
Peer address: FE:97:80:00:24:64 (OUI FE-97-80)
Initiating PHYs: 0x07
Entry 0: LE 1M
Scan interval: 60.000 msec (0x0060)
Scan window: 60.000 msec (0x0060)
Min connection interval: 10.00 msec (0x0008)
Max connection interval: 10.00 msec (0x0008)
Connection latency: 0 (0x0000)
Supervision timeout: 4000 msec (0x0190)
Min connection length: 0.000 msec (0x0000)
Max connection length: 0.000 msec (0x0000)
Entry 1: LE 2M
Scan interval: 60.000 msec (0x0060)
Scan window: 60.000 msec (0x0060)
Min connection interval: 10.00 msec (0x0008)
Max connection interval: 10.00 msec (0x0008)
Connection latency: 0 (0x0000)
Supervision timeout: 4000 msec (0x0190)
Min connection length: 0.000 msec (0x0000)
Max connection length: 0.000 msec (0x0000)
Entry 2: LE Coded
Scan interval: 60.000 msec (0x0060)
Scan window: 60.000 msec (0x0060)
Min connection interval: 10.00 msec (0x0008)
Max connection interval: 10.00 msec (0x0008)
Connection latency: 0 (0x0000)
Supervision timeout: 4000 msec (0x0190)
Min connection length: 0.000 msec (0x0000)
Max connection length: 0.000 msec (0x0000)
> HCI Event: Command Status (0x0f) plen 4
LE Extended Create Connection (0x08|0x0043) ncmd 2
Status: Success (0x00)
> HCI Event: LE Meta Event (0x3e) plen 31
LE Enhanced Connection Complete (0x0a)
Status: Success (0x00)
Handle: 16
Role: Central (0x00)
Peer address type: Public (0x00)
Peer address: FE:97:80:00:24:64 (OUI FE-97-80)
Local resolvable private address: 00:00:00:00:00:00 (Non-Resolvable)
Peer resolvable private address: 00:00:00:00:00:00 (Non-Resolvable)
Connection interval: 10.00 msec (0x0008)
Connection latency: 0 (0x0000)
Supervision timeout: 4000 msec (0x0190)
Central clock accuracy: 0x00
@ MGMT Event: Device Connected (0x000b) plen 44
LE Address: FE:97:80:00:24:64 (OUI FE-97-80)
Flags: 0x00000008
Connection Locally Initiated
Data length: 31
Flags: 0x06
LE General Discoverable Mode
BR/EDR Not Supported
16-bit Service UUIDs (partial): 1 entry
Health Thermometer (0x1809)
Service Data: Unknown (0xc1c4)
Data: fe97800024646c08bc054f6c000003507807000a
@ RAW Open: btmon (privileged) version 2.22
@ RAW Close: btmon
It seems that BlueZ selects the command based on the characteristics of the controller. I'll continue testing to see if I can find anything else! Thank you for taking some time to look into this