在Qt Android上使用NDK级别的低级USB API

Question

我需要在Android上与HID设备进行交互。问题是我正在使用Qt Android，并且没有使用Java UsbManager类。

是否有任何C库可以链接，以便在Android上与HID设备通信，而无需使用Java API？

我找到了这个：

http://source.android.com/devices/reference/bt__hh_8h_source.html

这似乎是定义HID通信的标头，但我找不到相关的库。有什么想法吗？

提前致谢。

- Nuno Santos

---

除非您打算对设备进行root，否则这是不可能的。 - László Papp

Answer 1

我已经找到了一种方法来实现这个。在我的情况下，我正在为一个设备开发控制面板，并且需要使其在没有root的情况下在每个设备上运行。

基本上，我使用UsbManager来查找并抓取设备。然后我打开设备并从UsbDeviceConnection调用getFileDescriptor()方法。然后我将该整数传递到本地代码端。从那里，我可以轻松地使用任何类型的请求从设备中获取数据，而无需通过JNI在本地代码和Java之间传递数据，这是缓慢而繁琐的工作。

最棘手的部分实际上是执行ioctl调用，这需要有特殊的格式。

部分代码已经在libusb源代码中很好地说明了，因为这是他们实现对Linux内核的libsub调用的方式。

如果有人知道更好的解决方案，请让我知道。

带有USBManager钩子的Android活动代码：

public class MyActivity extends QtActivity
{
    private static MyActivity m_instance;
    private UsbAccessory accessory;
    private String TAG = "TAG";
    private static final String ACTION_USB_PERMISSION = "com.android.example.USB_PERMISSION";
    private PendingIntent mPermissionIntent;
    private UsbManager manager;
    private UsbDeviceConnection connection;
    private HashMap<Integer, Integer> connectedDevices;

    public MyActivity()
    {
        m_instance = this;

        connectedDevices = new HashMap<Integer, Integer>();
    }

    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);

        manager = (UsbManager) getSystemService(Context.USB_SERVICE);

        registerReceiver(usbManagerBroadcastReceiver, new IntentFilter(UsbManager.ACTION_USB_DEVICE_ATTACHED));
        registerReceiver(usbManagerBroadcastReceiver, new IntentFilter(UsbManager.ACTION_USB_DEVICE_DETACHED));
        registerReceiver(usbManagerBroadcastReceiver, new IntentFilter(ACTION_USB_PERMISSION));

        mPermissionIntent = PendingIntent.getBroadcast(this, 0, new Intent(ACTION_USB_PERMISSION), 0);

        final Handler handler = new Handler();

        handler.postDelayed(new Runnable()
        {
            @Override
            public void run()
            {
                checkForDevices();
            }
        }, 1000);
    }

    @Override
    public void onDestroy()
    {
        super.onDestroy();
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data)
    {
        super.onActivityResult(requestCode, resultCode, data);
    }

    private static native void notifyDeviceAttached(int fd);
    private static native void notifyDeviceDetached(int fd);

    private final BroadcastReceiver usbManagerBroadcastReceiver = new BroadcastReceiver()
    {
        public void onReceive(Context context, Intent intent)
        {
            try
            {
                String action = intent.getAction();

                Log.d(TAG, "INTENT ACTION: " + action);

                if (ACTION_USB_PERMISSION.equals(action))
                {
                    Log.d(TAG, "onUsbPermission");

                    synchronized (this)
                    {
                        UsbDevice device = (UsbDevice)intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);

                        if (intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false))
                        {
                            if(device != null)
                            {
                                int fd = connectToDevice(device);
                                Log.d(TAG,"device file descriptor: " + fd);
                                notifyDeviceAttached(fd);
                            }
                        }
                        else
                        {
                            Log.d(TAG, "permission denied for device " + device);
                        }
                    }
                }

                if (UsbManager.ACTION_USB_DEVICE_ATTACHED.equals(action))
                {
                    Log.d(TAG, "onDeviceConnected");

                    synchronized(this)
                    {
                        UsbDevice device = (UsbDevice)intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);

                        if (device != null)
                        {
                            manager.requestPermission(device, mPermissionIntent);
                        }
                    }
                }

                if (UsbManager.ACTION_USB_DEVICE_DETACHED.equals(action))
                {
                    Log.d(TAG, "onDeviceDisconnected");

                    synchronized(this)
                    {
                        UsbDevice device = (UsbDevice)intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);

                        int fd = connectedDevices.get(device.getDeviceId());

                        Log.d(TAG, "device: " + device.getDeviceId() + " disconnected. fd: " + fd);

                        notifyDeviceDetached(fd);

                        connectedDevices.remove(device.getDeviceId());
                    }
                }
            }
            catch(Exception e)
            {
                Log.d(TAG, "Exception: " + e);
            }
        }
    };

    private int connectToDevice(UsbDevice device)
    {
        connection = manager.openDevice(device);
        // if we make this, kernel driver will be disconnected
        connection.claimInterface(device.getInterface(0), true);

        Log.d(TAG, "inserting device with id: " + device.getDeviceId() + " and file descriptor: " + connection.getFileDescriptor());
        connectedDevices.put(device.getDeviceId(), connection.getFileDescriptor());

        return connection.getFileDescriptor();
    }

    private void checkForDevices()
    {
        HashMap<String, UsbDevice> deviceList = manager.getDeviceList();
        Iterator<UsbDevice> deviceIterator = deviceList.values().iterator();

        while(deviceIterator.hasNext())
        {
            UsbDevice device = deviceIterator.next();

            if (device.getVendorId()==VID && device.getProductId()==PID)
            {
                Log.d(TAG, "Found a device: " + device);

                manager.requestPermission(device, mPermissionIntent);
            }
        }
    }
}

当连接或断开具有所需VID和PID的设备时，将调用原生调用notifyDeviceAttached（int fd）和notifyDeviceDetached（int fd），并发送设备的文件描述符到本机端。 在我的案例中，我实例化了一个类型为Device的类。此时设备已经打开，您可以开始对其进行调用。在Linux中，您可以像libusb一样进行ioctl调用。 您可以查看下面的代码以获取getFeature和setFeature。如果您需要比这更多的内容，则可以查看libusb源代码。

C++本地端代码：

#include <sys/ioctl.h>
#include <unistd.h>
#include <errno.h>

#include <QDebug>
#include <QElapsedTimer>

static inline uint16_t cpu_to_le16(const uint16_t x)
{
    union
    {
        uint8_t  b8[2];
        uint16_t b16;
    } _tmp;

    _tmp.b8[1] = (uint8_t) (x >> 8);
    _tmp.b8[0] = (uint8_t) (x & 0xff);

    return _tmp.b16;
}

struct usbdevfs_ctrltransfer
{
    unsigned char bRequestType;
    unsigned char bRequest;
    unsigned short wValue;
    unsigned short wIndex;
    unsigned short wLength;
    unsigned int timeout;
    void *data;
};

Device::Device(int fileDescriptor, QObject *parent) :
    fd(fileDescriptor)
{
}

int Device::getFeature(unsigned char reportId, unsigned char *buffer, int length)
{
    struct usbdevfs_ctrltransfer data;

    data.bRequestType = (0x01 << 5)|0x01|0x80;
    data.bRequest = 0x01;
    data.wValue = cpu_to_le16((3 << 8) | reportId);
    data.wIndex = cpu_to_le16(0);
    data.wLength = cpu_to_le16(length);
    data.data = buffer;
    data.timeout = 1000;

    int res = ioctl(fd, _IOWR('U', 0, struct usbdevfs_ctrltransfer), &data);

    if (res<0)
    {
        qDebug() << "error: " << strerror(errno);
    }

    return res;
}

int Device::setFeature(unsigned char reportId, unsigned char *buffer, int length)
{
    struct usbdevfs_ctrltransfer data;

    data.bRequestType = (0x01 << 5)|0x01|0x00;
    data.bRequest = 0x09;
    data.wValue = cpu_to_le16((3 << 8) | reportId);
    data.wIndex = cpu_to_le16(0);
    data.wLength = cpu_to_le16(length);
    data.data = buffer;
    data.timeout = 1000;

    int res = ioctl(fd, _IOWR('U', 0, struct usbdevfs_ctrltransfer), &data);

    if (res<0)
    {
        qDebug() << "error: " << strerror(errno);
    }

    return res;
}

敬礼，

Nuno Santos

- Nuno Santos

---

@LennartRolland，好的。我已经在我的答案中添加了代码。希望能有所帮助。问候 - Nuno Santos

你好。我正在为我的草图做相同的事情（但是在Xamarin下）。我从UsbManager中获取了文件描述符，并将其传递给我的C库（使用swig进行绑定）。但是，在使用读/写调用时，它们返回错误（无效参数）。我检查了FD，它是有效的> 0。我将尝试ioctl调用。 - Selso Liberado

+1，如何使用读/写C函数？调用ioctl（）不起作用。@SelsoLiberado，你成功了吗？ - François

我5年前做过这个，从那以后就再也没有尝试过。也许API已经改变了，不确定。 - Nuno Santos

@François 是的，我做到了！我使用了libusb库，请看我在这个主题上创建的stackoflow话题：https://stackoverflow.com/questions/65233959/android-with-native-library-interface-a-cdc-usb-device-cant-use-fd-in-nativ - Selso Liberado