寻求帮助：Android端通过OTG读取FreeStyle Libre设备数据

Hey there, let's work through this issue together—you’ve already nailed device detection, so we’re close to getting this working! Here are targeted steps to figure out the right driver and access the device data:

• First, confirm the device’s actual USB interface class
  Many medical devices like FreeStyle Libre use HID (Human Interface Device) instead of CDC. You can verify this by checking the device’s USB descriptors:

  • Use a USB info app (or Android Studio’s Device File Explorer to inspect /sys/class/usb_device/[your-device-id]/ files) to find the bInterfaceClass value. HID corresponds to 0x03, while CDC is 0x02.
  • If it’s HID, the UsbSerial library won’t work here—you’ll need to use Android’s native UsbHidDevice API instead.

• If it’s an HID device, implement HID communication

  1. After detecting the UsbDevice, locate the HID interface and its input endpoint (used to receive data from the device).
  2. Request USB permission from the user, then open the device with UsbManager.openDevice().
  3. Use methods like transferIn() to read HID reports, or sendFeatureReport() to send commands to the device. Note that you’ll need to match the FreeStyle Libre’s specific report format—this is often reverse-engineered from official apps or community projects.

• Verify your USB device filter configuration
  Make sure your app’s manifest and filter XML correctly target the FreeStyle Libre’s VID and PID. If these are missing or incorrect, even detected devices might not be accessible:

  • Add this to your AndroidManifest.xml:

    <intent-filter>
        <action android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED" />
    </intent-filter>
    <meta-data
        android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED"
        android:resource="@xml/usb_device_filter" />
    

  • Create res/xml/usb_device_filter.xml with your device’s VID/PID (get these via UsbDevice.getVendorId() and UsbDevice.getProductId()):

    <?xml version="1.0" encoding="utf-8"?>
    <resources>
        <usb-device vendor-id="XXXX" product-id="YYYY" />
    </resources>
    

• Reverse-engineer communication via packet capture
  If you can’t find official documentation, capture USB traffic between the FreeStyle Libre and its official desktop app using tools like Wireshark (with USBPcap on Windows) or usbmon on Linux. This will show you the exact commands and data format the device expects, which you can replicate in your Android app.

• Leverage existing community work
  There are plenty of open-source projects focused on FreeStyle Libre data extraction. Many of these already handle the HID communication details—check out how they implement device access to skip the guesswork.

内容的提问来源于stack exchange，提问作者cyrille gate