Emulating USB Protocol over BLE for Data Transfer

Hoshino Aoi

— 3 min read

As the Internet of Things (IoT) continues to grow, the need for efficient and reliable data transfer between devices has become increasingly important. One approach to achieve this is by emulating the Universal Serial Bus (USB) protocol over Bluetooth Low Energy (BLE) technology. In this blog, we will explore the concept of emulating USB protocol over BLE and provide a detailed implementation guide for computer enthusiasts.

Introduction to BLE and USB

BLE is a wireless personal area network technology that allows devices to communicate with each other over short distances. It is commonly used in IoT devices, wearables, and other low-power applications. USB, on the other hand, is a widely used interface standard for connecting devices to a computer.

Emulating USB Protocol over BLE

To emulate the USB protocol over BLE, we need to create a virtual USB device on the BLE device and configure it to communicate with the computer as if it were a physical USB device. This involves creating a BLE service that mimics the USB device's behavior, including its interface, endpoints, and device class.

Hardware and Software Requirements

To implement this project, you will need the following hardware and software components:

A BLE module (e.g., nRF52832 or CC2541)
A microcontroller (e.g., STM32 or Arduino)
A USB device (e.g., USB storage device or USB serial device)
BLE module's SDK (e.g., nRF5 SDK or CC2541 SDK)
Microcontroller's development environment (e.g., Keil µVision or Arduino IDE)
USB device's driver program (e.g., USB storage device driver or USB serial device driver)

Implementation Steps
Step 1: Create a BLE Service

Create a BLE service on the BLE module that mimics the USB device's behavior. This service should include characteristics that emulate the USB device's interface, endpoints, and device class.

Using the nRF5 SDK, you can create a BLE service as follows:

#include <ble_gap.h>
#include <ble_gatts.h>

#define SERVICE_UUID 0x180F // USB device service UUID
#define CHARACTERISTIC_UUID 0x2902 // USB device characteristic UUID

void create_service(void)
{
    uint16_t service_handle;
    uint16_t characteristic_handle;

    // Create a BLE service
    ble_gap_service_add(&service_handle, &SERVICE_UUID);

    // Create a BLE characteristic
    ble_gatts_characteristic_add(&characteristic_handle, &CHARACTERISTIC_UUID, BLE_GATT_CHAR_PROPERTIES_READ | BLE_GATT_CHAR_PROPERTIES_WRITE, &service_handle);
}

Step 2: Implement a Virtual USB Device Class

Implement a virtual USB device class on the microcontroller that emulates the behavior of a physical USB device. This class should provide a virtual USB interface and endpoints for data transfer.

Using the Arduino IDE, you can implement a virtual USB storage device class as follows:

#include <USB.h>

class USBStorageDevice {
public:
    USBStorageDevice() {
        // Initialize the USB device
        USB.begin();
    }

    void write_data(uint8_t* data, uint16_t length) {
        // Write data to the virtual USB storage device
        USB.write(data, length);
    }

    uint16_t read_data(uint8_t* data) {
        // Read data from the virtual USB storage device
        return USB.read(data);
    }
};

Step 3: Implement Data Transfer Mechanism

Implement a data transfer mechanism on the BLE module that allows data to be transferred between the BLE device and the computer. This mechanism should use the GATT protocol's write and read operations to transfer data.

Using the nRF5 SDK, you can implement a data transfer mechanism as follows:

void write_data(uint8_t* data, uint16_t length) {
    // Write data to the BLE characteristic
    ble_gatts_characteristic_write(&characteristic_handle, data, length);
}

uint16_t read_data(uint8_t* data) {
    // Read data from the BLE characteristic
    return ble_gatts_characteristic_read(&characteristic_handle, data);
}

Step 4: Connect to the Computer

Connect the BLE device to the computer and use the virtual USB device class and data transfer mechanism to transfer data between the devices.

Using the Arduino IDE, you can connect to the computer as follows:

#include <USB.h>

USBStorageDevice usb_device;

void setup() {
    // Initialize the USB device
    usb_device.begin();
}

void loop() {
    // Wait for the computer to connect
    if (usb_device.isConnected()) {
        // Read data from the computer
        uint8_t data[256];
        uint16_t length = usb_device.read_data(data);

        // Write data to the BLE device
        write_data(data, length);
    }
}

Step 5: Test Data Transfer

Test the data transfer mechanism by writing data to the BLE device and reading data from the computer.

Using the serial terminal, you can test the data transfer as follows:

# Write data to the BLE device
echo "Hello, world!" > /dev/ttyUSB0

# Read data from the BLE device
cat /dev/ttyUSB0

If everything is working correctly, you should see the data being transferred between the devices.

Conclusion

Emulating the USB protocol over BLE provides a convenient and efficient way to transfer data between devices. By following the implementation guide outlined in this blog, you can create a BLE device that communicates with a computer as if it were a physical USB device. This technology has numerous applications in IoT, wearables, and other low-power devices, and can enable new use cases and possibilities in the field of computer engineering.

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