Interacting with USB using Python

Ever wonder how your computer connects with all those USB gadgets? Well, it’s time to unravel the USB magic using Python, the friendly programming language. No fancy talk, just practical examples to kickstart your USB adventures.

What You’ll Need

Before we dive in, make sure you’ve got these things ready:

Python (3.6 or newer) installed on your computer.
A USB gadget you want to play with (like a USB flash drive or an Arduino board).
A sprinkle of Python knowledge.

Installing Required Libraries

Before we begin, we need to install the necessary libraries. In Python, the pyusb library is commonly used to interact with USB devices. Open your terminal and run the following command to install it using pip:

pip install pyusb

Finding USB Device Information

To interact with a USB device, we need to gather information about the device’s vendor ID (VID) and product ID (PID). These IDs uniquely identify the device. We can use Python to enumerate and retrieve the information.

import usb.core

def find_usb_device(vid, pid):
    device = usb.core.find(idVendor=vid, idProduct=pid)
    
    if device is None:
        raise ValueError("USB device not found.")
    
    return device

# Example usage
usb_device = find_usb_device(0x1234, 0x5678)
print(usb_device)

Replace 0x1234 and 0x5678 with your device’s VID and PID, respectively. This code snippet will print information about the USB device if it is found. If the device is not found, a ValueError will be raised.

Accessing USB Device Interfaces

USB devices can have one or more interfaces, each representing a distinct functionality. To interact with the device, we need to claim and open the desired interface.

def open_usb_interface(device, interface_number):
    device.set_configuration()
    usb.util.claim_interface(device, interface_number)
    endpoint = device[0][(0, 0)][0]
    
    return endpoint

# Example usage
interface_number = 0
endpoint = open_usb_interface(usb_device, interface_number)
print(endpoint)

In this example, we assume that the USB device has at least one interface, and we open the first interface by passing 0 as the interface_number. The code snippet will return the endpoint object for data transfer.

Reading and Writing Data

Once we have access to the USB interface, we can read and write data to the device.

def read_from_usb(endpoint, size):
    data = endpoint.read(size)
    return data

def write_to_usb(endpoint, data):
    bytes_written = endpoint.write(data)
    return bytes_written

# Example usage
data_to_write = b"Hello, USB!"
bytes_written = write_to_usb(endpoint, data_to_write)
print(f"Bytes written: {bytes_written}")

data_read = read_from_usb(endpoint, 64)
print(f"Data read: {data_read}")

In the above code snippet, read_from_usb reads size number of bytes from the USB device, while write_to_usb writes the data (as bytes) to the device. Modify the data_to_write variable to send custom data.

Interacting with USB Devices Using Vendor Commands

USB devices often have vendor-defined commands for accessing specific features or functionalities. Python’s pyusb library allows us to send vendor commands to USB devices.

# Assuming 'endpoint' is obtained from previous steps
# Sending a vendor command (example)
data = [0x01, 0x02, 0x03]  # Vendor command data
request_type = usb.util.build_request_type(
    usb.util.CTRL_OUT,
    usb.util.CTRL_TYPE_VENDOR,
    usb.util.CTRL_RECIPIENT_DEVICE
)

endpoint.ctrl_transfer(request_type, 0x42, 0x1234, 0x5678, data)

Working with USB HID (Human Interface Device)

USB HID devices include keyboards, mice, and game controllers. Python’s pyusb library allows interaction with USB HID devices.

import usb.core

# Finding a USB HID device
hid_device = usb.core.find(idVendor=0x1234, idProduct=0x5678, bInterfaceClass=3, bInterfaceSubClass=1)

# Interacting with the HID device (example)
endpoint = hid_device[0][(0, 0)][0]
data_to_send = b"\x00\x01\x02\x03"  # HID data
endpoint.write(data_to_send)

data_received = endpoint.read(64)
print(f"Data received: {data_received}")

Error Handling and Exception Management

During USB communication, errors and exceptions can occur. It is essential to handle them gracefully. For example:

import usb.core
import usb.util

try:
    device = usb.core.find(idVendor=0x1234, idProduct=0x5678)
    if device is None:
        raise ValueError("USB device not found.")
    
    # Rest of the code for interacting with the device
except usb.core.USBError as e:
    print(f"USB error occurred: {str(e)}")
except ValueError as ve:
    print(str(ve))

Advanced USB Functionality

Python’s pyusb library provides a foundation for interacting with USB devices, but it also supports advanced features and functionalities. Let’s explore some of the advanced USB functionality that you can leverage in your Python projects.

Isochronous Transfers

Isochronous transfers are used for real-time data streaming, where the timing of the data is critical. This transfer mode guarantees bandwidth but does not guarantee data integrity. To perform isochronous transfers with pyusb, you can utilize the isochronous_transfer method of the endpoint object.

# Assuming 'endpoint' is obtained from previous steps
data_to_send = b"\x01\x02\x03\x04"  # Data for isochronous transfer
result = endpoint.isochronous_transfer(data_to_send, timeout=1000)
print(f"Isochronous transfer result: {result}")

USB Descriptors

USB descriptors provide information about the USB device and its capabilities. The USB specification defines these descriptors and can be accessed using pyusb. You can retrieve various descriptors such as device, configuration, interface, and endpoint descriptors.

# Assuming 'usb_device' is obtained from previous steps
# Retrieving device descriptor
device_descriptor = usb_device.get_active_configuration().bConfigurationValue
print(f"Device descriptor: {device_descriptor}")

# Retrieving configuration descriptor
config_descriptor = usb_device.get_active_configuration().extra
print(f"Configuration descriptor: {config_descriptor}")

# Retrieving interface descriptor
interface_descriptor = usb_device.get_active_configuration()[(0, 0)]
print(f"Interface descriptor: {interface_descriptor}")

# Retrieving endpoint descriptor
endpoint_descriptor = usb_device.get_active_configuration()[(0, 0)][0]
print(f"Endpoint descriptor: {endpoint_descriptor}")

USB Device Classes

USB devices often belong to specific device classes, such as mass storage devices (USB MSC), audio devices (USB Audio), or human interface devices (USB HID). Python’s pyusb library provides class-specific methods and attributes for interacting with these devices.

# Example: Interacting with a USB MSC device
import usb.core
import usb.util

# Finding a USB MSC device
msc_device = usb.core.find(find_all=True, bInterfaceClass=usb.util.CLS_MASS_STORAGE)

# Interacting with the MSC device (example)
endpoint = msc_device[0][(0, 0)][0]
data_to_send = b"\x01\x02\x03\x04"  # Data for USB MSC
endpoint.write(data_to_send)

data_received = endpoint.read(64)
print(f"Data received: {data_received}")