Data length update with pc-ble-driver-py library

[Imen]

Hi everyone,

I am trying to start a data length update procedure from a central that I am developing with python using the library pc-ble-driver-py.

However, I keep having the error 0x13 which corresponds to a timeout (generated in the function "ble_gap_data_length_update"). I had to add the event "on_gap_evt_data_length_updated" in the adapter.py file, but still nothing.

I saw on the github of the library that this event has been removed at a previous commit saying that only the API v3 supports this event.

Does this mean that I cannot start a data length from the central with API v5? why is the event "gap_evt_data_length_update = driver.BLE_GAP_EVT_DATA_LENGTH_UPDATE" still figure in the driver.py file? 

Can the central still receive and treat a data length update request from a peripheral?

Thanks in advance

Imen

[Imen]

More details about trying to get data_length_update to work

Peripheral flashed on a nrf52832 with  nRF5_SDK_15.3.0 ble_app_multirole_lesc exemple.

When I do a ble_gap_data_length_update() with all parameters set to BLE_GAP_DATA_LENGTH_AUTO “0”  (or any other value), none error is returned and I get the right event on_gap_evt_data_length but with strange values that  change after each try for on the pc-ble-driver-py:

 

Exemple with all parameter set to 0 (BLE_GAP_DATA_LENGTH_AUTO):

Result on the pc-ble-driver-py (nrf52832)

• Max tx octets = 27 (ok)
• Max rx octets = 483 (??)
• Max tx times us = 256 (??)
• Max rx time us = 0 (??)

 

Result on the JLink viewer connected to the peripheral nrf52832 with ble_app_multirole_lesc, I have the right parameters:

        BLE_GAP_EVT_DATA_LENGTH_UPDATE: Data length update to 27 on connection 0x1

• Max tx octets = 27 (ok)
• Max rx octets = 27 (ok)
• Max tx times us = 2120 (ok)
• Max rx time us = 2120 (ok)

 

I get the parameters with following lines:

  print("data_length_params max_tx_octets = " + str(data_length_params.max_tx_octets))

        print("data_length_params max_rx_octets = " + str(data_length_params.max_rx_octets))

        print("data_length_params max_tx_time_us = " + str (data_length_params.max_tx_time_us))

        print("data_length_params max_rx_time_us = " + str (data_length_params.max_rx_time_us))

 

 

Other exemples call ble_gap_data_length_update() with BLEGapDataLengthParams(max_tx_octets=100, max_rx_octets=100, max_tx_time_us=0, max_rx_time_us=0):

 

On the Central with pc-ble-driver:

• Max tx octets = 27 (ok)
• Max rx octets = 1000 (??)
• Max tx times us = 256 (??)
• Max rx time us = 0 (??)

 

Other try:

• Max tx octets = 27 (ok)
• Max rx octets = 20850 (??)
• Max tx times us = 0 (??)
• Max rx time us = 29184 (??)

 

Other try:

• Max tx octets = 14363 ((??))
• Max rx octets = 192 (??)
• Max tx times us = 0 (??)
• Max rx time us = 0 (??)

With the JLink viewer connected to the peripheral nrf52832 with ble_app_multirole_lesc I have the good parameters:

                BLE_GAP_EVT_DATA_LENGTH_UPDATE: Data length update to 27 on connection 0x1

• Max tx octets = 27 (ok)
• Max rx octets = 27 (ok)
• Max tx times us = 912 (ok)
• Max rx time us = 912 (ok)

 Do you have any idea what makes the event get me different values everytime with the same config asked? I believe the problem comes form pc-driver-ble-py knowing that the peripheral gets the right values

Thanks, Imen

[Vidar Berg]

Hello Imen,

I tried installing the latest 0.11.4 release to replicate this, but it appears to only support SD API v3 for the 52 series. Are you testing with a different branch? 

Regards,

Vidar 

[Imen]

I am testing with SD API v5, I thought that it could work with a more recent release. I added the event in the library and the peripheral I am using logs the new values but the central returns random corrupted data everytime as you can see above

[Vidar Berg]

Sorry, I thought v.0.11.4 was the latest, and I wasn't sure how you were able to use API v5 with that release. What I see now after updating to 0.14 is that the packet length gets correctly updated when receiving the request from the peer device, but the parameters reported to on_gap_evt_data_length_update() were still invalid like they were in your case.

I used the heart rate collector script for my test and only added on_gap_evt_data_length_update() function so I could log the DL parameters. 

    def on_gap_evt_data_length_update(
        self, ble_driver, conn_handle, data_length_params
    ):
        print("Max rx octets: {}".format(data_length_params.max_rx_octets))
        print("Max tx octets: {}".format(data_length_params.max_tx_octets))
        print("Max rx time: {}".format(data_length_params.max_rx_time_us))
        print("Max tx time: {}".format(data_length_params.max_tx_time_us))

Result from one of the tests I di:

Max rx octets: 400
Max tx octets: 151 
Max rx time: 0
Max tx time: 0

And the corresponding result from  the ble_app_hrs peripheral SDK example running on the other side:

<debug> nrf_ble_gatt: Data length updated to 151 on connection 0x0.
<debug> nrf_ble_gatt: max_rx_octets: 151
<debug> nrf_ble_gatt: max_tx_octets: 151
<debug> nrf_ble_gatt: max_rx_time: 1320
<debug> nrf_ble_gatt: max_tx_time: 1320

I have not been able to figure out why the event parameters are not correctly forwarded from the Softdevice, but it looks like it might be a bug in the driver implementation. I have reported this as a bug internally. 

Data Length Update Procedure 

[Imen]

Thank you for confirming the problem, I will be very happy to know when it is resolved, thank you

Imen