Bluetooth Communication

I. Experiment Objective

Learn the BLE (Bluetooth Low Energy) communication function of the MicroROS-V2 control board. Through this experiment, you will master how to initialize a BLE GATT server, create an SPP service with characteristic values, and implement data transmission and reception with a phone or other BLE devices.

II. Experiment Principle

1. Keywords

2. Technical Architecture

This example implements a BLE GATT server based on the ESP32 Bluedroid protocol stack. After startup, the program initializes NVS Flash, the Bluetooth controller, and the Bluedroid protocol stack, registers a GATT application, and creates an SPP service (UUID 0xFFE0) with 4 characteristic values for data transmission and reception. The device advertises under the name "YahBoom_BL" and waits for a phone or other BLE client to connect.

Main component files:

• main/main.c — Program entry, initializes BLE

• components/ble_server/ble_server.c — BLE GATT service implementation

• components/ble_server/ble_server.h — Characteristic index and constant definitions

III. Experiment Steps

1. Hardware Preparation

2. Prerequisites

1. Set up the ESP32-IDF development environment

2. Connect the MicroROS-V2 control board to the computer via USB

3. First, the Bluetooth feature is disabled by default in ESP-IDF, so you need to enable Bluetooth in the configuration file.

   cd ~/esp/base_samples/bluetooch
   idf.py menuconfig
   

   

   Because only the Bluetooth BLE 5.0 feature is enabled by default, to make the compilation pass, you need to manually enable the Bluetooth BLE 4.2 feature.

   

3. Compile and Flash

​x

cd ~/esp/base_samples/bluetooch
source ~/esp/esp-idf/export.sh
idf.py build flash monitor

4. Stopping Method

In the terminal, press Ctrl+] to exit the serial monitor.

IV. Experiment Result

After successful compilation and flashing, the Monitor will output:

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hello yahboom
I (xxx) MAIN: Nice to meet you!
I (xxx) BLE_SERVER: BLE_Init init bluetooth

Using a BLE debugging tool such as nRF Connect or LightBlue on your phone, you can scan for the BLE device named YahBoom_BL. After connecting, you can see the service with UUID 0xFFE0 and its 4 characteristic values underneath. You can write data to the 0xFFE1 characteristic, and the control board will print the received data in the log.

V. Program Analysis

Source code paths:

• Firmware source: ~/esp/base_samples/bluetooch/main/main.c

• BLE service: ~/esp/base_samples/bluetooch/components/ble_server/ble_server.h, ble_server.c

1. Main Program Logic

main/main.c is the program entry. After printing a welcome message, it calls BLE_Init() to initialize the BLE protocol stack:

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#include "ble_server.h"

void app_main(void)
{
    printf("hello yahboom\n");
    ESP_LOGI(TAG, "Nice to meet you!");
    BLE_Init();
}

2. BLE Service Initialization Flow

The BLE_Init() function in components/ble_server/ble_server.c completes the full initialization of the BLE protocol stack with the following steps:

1. Initialize NVS Flash — Call nvs_flash_init() to initialize non-volatile storage for saving Bluetooth configuration information. If the NVS partition is abnormal, erase it first and then initialize.

2. Release classic Bluetooth memory — Call esp_bt_controller_mem_release(ESP_BT_MODE_CLASSIC_BT) to release the memory occupied by classic Bluetooth, keeping only the BLE function.

3. Initialize the Bluetooth controller — Start the BLE controller through esp_bt_controller_init() and esp_bt_controller_enable(ESP_BT_MODE_BLE).

4. Initialize Bluedroid — Call esp_bluedroid_init() and esp_bluedroid_enable() to start the Bluedroid protocol stack.

5. Register callback functions — Register the GATT Server callback and the GAP callback.

6. Register the application — Call esp_ble_gatts_app_register(ESP_SPP_APP_ID) to register the SPP application, where ESP_SPP_APP_ID is defined as 0x56.

3. BLE Device Name and Advertising Data

The device advertising name is YahBoom_BL, and the advertising data packet format is as follows:

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static const uint8_t spp_adv_data[] = {
    0x02, 0x01, 0x06,                             /* Flags */
    0x03, 0x03, 0xF0, 0xAB,                       /* 16-bit Service Class UUIDs */
    0x0B, 0x09, 'Y', 'a', 'h', 'B', 'o', 'o', 'm', '_', 'B', 'L'  /* Complete Local Name */
};

Advertising parameter settings:

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static esp_ble_adv_params_t spp_adv_params = {
    .adv_int_min = 0x20,         // Minimum advertising interval
    .adv_int_max = 0x40,         // Maximum advertising interval
    .adv_type = ADV_TYPE_IND,    // Connectable advertising type
    .own_addr_type = BLE_ADDR_TYPE_PUBLIC,
    .channel_map = ADV_CHNL_ALL,
    .adv_filter_policy = ADV_FILTER_ALLOW_SCAN_ANY_CON_ANY,
};

4. SPP Service and Characteristic Values

This example implements a BLE service similar to SPP (Serial Port Profile). The service UUID is 0xFFE0 and it contains 4 characteristic values:

The data length limits of each characteristic (defined in ble_server.h):

• SPP_DATA_MAX_LEN = 512 bytes (maximum length of the data channel)

• SPP_CMD_MAX_LEN = 20 bytes (maximum length of the command channel)

• SPP_STATUS_MAX_LEN = 20 bytes (maximum length of the status channel)

5. Data Reception and Processing

The gatts_profile_event_handler handles the ESP_GATTS_WRITE_EVT event:

• When the write handle is SPP_IDX_SPP_DATA_RECV_VAL, call BLE_Parse_Rx_Data() to process the received data

• When the write handle is SPP_IDX_SPP_COMMAND_VAL, save the command data to the buffer

• When the write handle is SPP_IDX_SPP_DATA_NTF_CFG, enable or disable the notification function according to the CCCD value written by the client

6. Key Components

ble_server.h defines the characteristic index enum and key constants:

Parameter definition file: ~/esp/base_samples/bluetooch/components/ble_server/ble_server.h

7. Connection and Disconnection Events

• Connection event (ESP_GATTS_CONNECT_EVT): Save the connection ID and the GATT interface handle, and set is_connected = true

• Disconnection event (ESP_GATTS_DISCONNECT_EVT): Reset the connection state and restart advertising to wait for a new connection

• MTU negotiation (ESP_GATTS_MTU_EVT): Save the negotiated MTU size to spp_mtu_size, with an initial value of 23 bytes

VI. Common Problems