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CC2745P10-Q1: L2CAP Packet Size Limitation in car_node Example

Peisheng Yang
Intellectual 700 points
Part Number: CC2745P10-Q1


Tool/software:

Hi, Ti

How can I make BLE L2CAP send 255 bytes buffer data at a time in car_node example project? When we used the car_node example in SDK 9.10.0.83 for Bluetooth CCC3.0 data transmission on CC2745, we found that L2CAP has a length limit, packets longer than approximately 60 cannot be transmitted (using L2CAP_SendSDU() function). However, ti_ble_config.h shows that the value of MAX_PDU_SIZE is 255, and the L2CAP configuration in syscfg is as follows, which does not seem to impose a limit of approximately 60 bytes. Are there other configurations that may cause additional restrictions on L2CAP transmission length?

Best regards!

Preston

  • 0
    Intellectual 700 points

    Hi, Ti

    Is there any update? Or do you need me to supplement any information?

    The following figure shows some definitions about PDU_SIZE.

    Additionally, when I replaced the car_node example of CC2745 with Basic_ble, this limitation issue disappeared. It seems that there are differences between the examples. Could you please tell me if there are any other places in the car_node example that limit the data transmission length of L2CAP?

    Best regards!

    Preston

  • 0 in reply to Peisheng Yang
    Prodigy 30 points

    Hi TI , Could you give some feedback for this case?  after calling bellow API the status return pass, but other side of BLE could not recive L2CAP data.

    status = L2CAP_SendSDU(&pkt);
    What settings should we check? Does TI meet the same issue? Note: SDK 9.10.0.83 car node & key node project have this issue. but Base BLE project have not.

    Hoper
  • 0 in reply to Liu Hoper
    TI__Expert 3571 points

    Greetings,

    Can you please provide a sniffer log for this? The key node, and car node examples set the MAX_PDU_SIZE variable to be 255, so there doesn't look to be a difference in the configuration from BasicBLE. Checking through the sniffer log will enable better debugging.

    Best,
    Achyut Ray

  • 0 in reply to Achyut Ray
    Intellectual 700 points

    Hi, Ray

    In the car_node example, the default MAX_PDU_SIZE is 69. I've modified it to 255, but the issue persists. I'll use BLE Analyzer to capture sniffer logs (including normal communication cases under the basic_ble example) and will provide them before tomorrow.

    Best regards!

    Preston

  • 0 in reply to Peisheng Yang
    Intellectual 700 points

    Hi, Ray

    These are the sniffer logs I captured.

    sniffer_log.zip

    The file "basic_ble_send102byte.ble" contains logs from the Basic_BLE example, where the CC2745 sends 102 bytes of data via L2CAP, and the peer device successfully receives it.

    The file "car_node_send59byte.ble" contains logs from the car_node example, where the CC2745 sends 59 bytes of data via L2CAP, and the peer device successfully receives it.

    The file "car_node_send61byte.ble" contains logs from the car_node example, where the CC2745 sends 61 bytes of data via L2CAP, but the peer device failed to receive any data.

    Best regards!

    Preston

  • 0 in reply to Peisheng Yang
    Intellectual 700 points

    Hi, Ray

    Is the BLE sniffer log I captured valid? Do you need any additional information to analyze the issue?

    Best regards!

    Preston

  • 0 in reply to Peisheng Yang
    Intellectual 700 points

    Hi, Ray

    May I know when we can expect a response to this issue?

    Best regards!

    Preston

  • +1 in reply to Peisheng Yang
    Intellectual 700 points

    Fixed in simplelink_lowpower_f3_sdk_9_11_00_18 version