android - UsbDeviceConnection.controlTransfer() 尝试与 Arduino UNO 通信时失败

Question

尽管有claimedInterfaced，有正确的权限等，当 controlTransfer() 被调用时，它返回 -1。Logcat显示没有什么有趣的。我使用此代码作为指南。

查看源代码，here和here，我知道设备已正确打开（getFileDescriptor() 返回正确的值）。这意味着 ioctl 调用失败。我无法访问 errno。

有任何想法吗？

private static UsbInterface getSerialInterface(UsbDevice device)
{
    for (int i = device.getInterfaceCount() - 1; i >= 0; i--)
    {
        UsbInterface iface = device.getInterface(i);
        if (iface.getInterfaceClass() == UsbConstants.USB_CLASS_CDC_DATA)
            return iface;
    }
    return null;
}

private byte[] getLineEncoding(int baudRate) {
    final byte[] lineEncodingRequest = { (byte) 0x80, 0x25, 0x00, 0x00, 0x00, 0x00, 0x08 };
    if (baudRate != 9600)
        throw new UnsupportedOperationException("Bad Baud rate.");
}


private boolean openSerialEndpoints(UsbDevice device)
{
    mConnection = mManager.openDevice(device);
    if (mConnection == null) return false;
    UsbInterface iface = getSerialInterface(device);
    if (iface == null) {
        closeSerialEndpoints();
        return false;
    }
    if (!mConnection.claimInterface(iface, true)) {
        Log.e(TAG, "Claiming interface failed!");
        closeSerialEndpoints();
        return false;
    }
    Log.d(TAG, "controlTransfer.");
    if (mConnection.getFileDescriptor() == -1)
        Log.d(TAG, "NOt Opened!!");
    // Arduino setup.
    if (mConnection.controlTransfer(0x21, 0x22, 0, 0, null, 0, 0) <= 0) {
        Log.d(TAG, "Control transfer 1 failed.");    // This fails
        return false;
    }
    if (mConnection.controlTransfer(0x21, 0x20, 0, 0, getLineEncoding(9600), 7, 0) <= 0) {
        Log.d(TAG, "Control transfer 2 failed.");
        return false;
    }
 }