About how to connect a Bluetooth device with a 16-bit UUID

Hello, I have encountered a problem when using the Bluetooth master project of SDK. Hopefully you can give me answers to my mistakes or provide me with the correct code.

(https://github.com/Ai-Thinker-Open/Ai-Thinker-WB2/blob/main/applications/bluetooth/ble_master/ble_master/ble_central_api.c)

A brief description of my problems,

The core problem is that it cannot connect to the Bluetooth module DX-BT04-E whose uuid is TYPE_16. The code modification fails
There is no example when the uuid is TYPE_16 and 32, the former is slightly different from the given TYPE_128, hope to make a tutorial or solution
Do not understand the implementation of uuid conversion

It's about the file "ble_central_api.c" and the *bt_uuid_6/32/128 of"uuid.h" MY_UUID1_USER_TXD is char[16] for 128byte with the uint8_t uuid128[16]; which used at func ble_reverse_byte(); and memcmp(). My bluetooth device is DX-BT04-E"module. It's UUID identified as BT_UUID_TYPE_16. So I follow the code format of char MY_UUID1_USER_TXD[16]

const uint16_t MY_UUID_2_USER_TXD = 0x42001;
const char MY_UUID_2_USER_TXD[4] = { 0x42, 0x01, 0x9a, 0xac }; //42019AAC
 const char MY_UUID_2_USER_RXD[2] = { 0x66, 0x16 };

uuid16 = (uint16_t) (((struct bt_uuid_16*) (attr->uuid))->val);

debug: sprintf(buf1, "attr->uuid = uuid16_ori = %X\r\n", attr->uuid);bleuart_printf(buf1); output : 42019B40 debug: sprintf(buf1, "attr->uuid = uuid16_ori = %X\r\n", uuid16);bleuart_printf(buf1); output : 2800

Found in this val cannot be converted to uuid16 properly. Reading the source code for data type or casting type is also inavailable to find a solution. I was wondering if the recognition is TYPE16, why is the value before the conversion 4-bit hexadecimal instead of 2-bit hexadecimal. In the file gatt.h, const struct bt_uuid *uuid; how does the bt_uuid u8_t type convert to the bt_uuid_128

struct bt_uuid {
    u8_t type;
};

struct bt_uuid_16 {
    struct bt_uuid uuid;
    u16_t val;//
};

struct bt_uuid_128 {
    struct bt_uuid uuid;
    u8_t val[16];
};

The amount of data bytes is all different.It's not work when it come to the uuid16 and val use assign. Finally I change if (memcmp((char*) uuid16, MY_UUID_2_USER_TXD, 2) == 0) to if (uuid16 == MY_UUID_2_USER_TXD) because its about u16_t and char,not the char[] and uint8.

What should I do to solve if (attr->uuid->type == BT_UUID_TYPE_16)？ I hope I will not disturb you. This is the first time I have raised an issue. Look forward to your reply. Thank you.

Ai-Thinker-Open / Ai-Thinker-WB2

About how to connect a Bluetooth device with a 16-bit UUID #9