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esp-idf/examples/bluetooth/bluedroid/classic_bt/bt_l2cap_client/README.md
gongyantao b4a62fb339 docs(examples/bluetooth): Add the sequence diagram of L2CAP connection and the discription for the sequence diagram 
1: add the sequence diagram for the bluetooth example projects,bt_l2cap_server and bt_l2cap_client, which implenment the L2CAP connection.
2: add the discription for the sequence diagram.
2023-07-08 12:39:35 +08:00

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Supported Targets ESP32

ESP-IDF BT-L2CAP-CLIENT EXAMPLE

This example is to show how to use the APIs of Logical Link Control and Adaptation Layer Protocol (L2CAP) to create an L2CAP client. We also provide demo bt_l2cap_server to create L2CAP server. In fact, you can create L2CAP clients and L2CAP servers on a single device at the same time.

How to use example

Hardware Required

This example is designed to run on commonly available ESP32 development board, e.g. ESP32-DevKitC. To operate the example, it is supposed to connect to bt_l2cap_server example in ESP-IDF.

Configure the project

  1. Open the project configuration menu:
idf.py menuconfig
  1. Enable the BT-L2CAP functionality by choosing the path as following:

Component config --> Bluetooth --> Bluedroid Options --> BT-L2CAP

  1. If you want to limit the number of connected devices, please make sure set the BT/BLE MAX ACL CONNECTIONS and BR/EDR ACL Max Connections with same value you want.

Component config --> Bluetooth --> Bluedroid Options --> BT/BLE MAX ACL CONNECTIONS(1~7) and Component config --> Bluetooth --> Bluetooth --> Bluetooth controller --> BR/EDR ACL Max Connections

Build and Flash

Build the project and flash it to the board, then run monitor tool to view serial output:

idf.py -p PORT flash monitor

(Replace PORT with the name of the serial port to use.)

(To exit the serial monitor, type Ctrl-].)

See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.

Example Output

For the first step, this example performs device discovery to search for a target device whose device name is "ESP_BT_L2CAP_SERVER". If a candidate target is found, the local device will initiate connection with it.

When you run this example, the explain prints the following at the very begining:

I (1383) L2CAP_TAG: ESP_BT_L2CAP_INIT_EVT: status:0

I (1393) SDP_TAG: ESP_SDP_INIT_EVT: status:0

I (1393) SDP_TAG: ESP_SDP_CREATE_RECORD_COMP_EVT: status:0

I (1403) L2CAP_TAG: event: 10
I (1413) L2CAP_TAG: event: 1
I (1403) L2CAP_TAG: Own address:[c4:dd:57:5b:e7:46]

Troubleshooting

  • This example just demonstrates how to use the SDP and L2CAP APIs. This example cannot establish an l2cap connection with other devices (smartphones, computers, etc.) because the UUID is unknown and does not conform to the Bluetooth protocol standard.
  • You can complete OBEX related profiles through SPP, SDP and L2CAP APIs.

Workflow of an L2CAP Connection