Android平板电脑和相机之间的USB bulkTransfer

I would like to exchange data/commands between a camera and an Android tablet device using the bulkTransfer function. I wrote this Activity, but the method bulkTransfer returns -1 (error status). Why does it return the error?

我想使用bulkTransfer功能在相机和Android平板电脑设备之间交换数据/命令。我写了这个Activity，但方法bulkTransfer返回-1（错误状态）。为什么会返回错误？

public class MainActivity extends Activity {

    private TextView text;
    private int TIMEOUT = 1000;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        text = (TextView) findViewById(R.id.txt);
        usbTest();
    }

    private void usbTest() {
        UsbDevice device = (UsbDevice) getIntent().getParcelableExtra(
                                                                      UsbManager.EXTRA_DEVICE);
        if (device == null)
            text.setText("device null");
        else
            text.setText("device not null");

        UsbManager manager = (UsbManager) getSystemService(Context.USB_SERVICE);
        HashMap<String, UsbDevice> deviceList = manager.getDeviceList();
        text.setText(text.getText() + "\nDevices connected: "
                     + deviceList.values().size());
        Iterator<UsbDevice> deviceIterator = deviceList.values().iterator();

        while (deviceIterator.hasNext()) {
            device = deviceIterator.next();
            text.setText(text.getText() + "\nDevice name: "
                         + device.getDeviceName());
            text.setText(text.getText() + "\nDevice protocol: "
                         + device.getDeviceProtocol());
            text.setText(text.getText() + "\nDevice id: "
                         + device.getDeviceId());
            text.setText(text.getText() + "\nDevice product id: "
                         + device.getProductId());
            text.setText(text.getText() + "\nDevice vendor id: "
                         + device.getVendorId());
            text.setText(text.getText() + "\nDevice class: "
                         + device.getDeviceClass());
            text.setText(text.getText() + "\nDevice subclass: "
                         + device.getDeviceSubclass());
            text.setText(text.getText() + "\nDevice interface count: "
                         + device.getInterfaceCount());
            text.setText(text.getText() + "\n\n");
        }

        // communicate with device
        UsbInterface intf = device.getInterface(0);
        UsbEndpoint endpoint = intf.getEndpoint(0);
        UsbDeviceConnection connection = manager.openDevice(device);
        connection.claimInterface(intf, true);

        for (int i = 0; i < intf.getEndpointCount(); i++) {
            UsbEndpoint ep = intf.getEndpoint(i);
            if (ep.getType() == UsbConstants.USB_ENDPOINT_XFER_BULK) {
                if (ep.getDirection() == UsbConstants.USB_DIR_OUT) {
                    endpoint = ep;
                    text.setText("Found: "+i);
                }
            }
        }


        // byte[] opensession = { 0x0C, 0x00, 0x00, 0x00, 0x01, 0x00, 0x02,
        // 0x10,
        // 0x00, 0x00, 0x00, 0x00 };
        // connection.bulkTransfer(endpoint, opensession, opensession.length,
        // TIMEOUT);

        byte[] getEvent = { 0x0C, 0x00, 0x00, 0x00, 0x01, 0x00, toByte(0xC7),
            toByte(0x90), 0x00, 0x00, 0x00, 0x00 };
        int status = connection.bulkTransfer(endpoint, getEvent,
                                             getEvent.length, TIMEOUT);
        //text.setText("Status: " + status);

        byte[] capture = { 0x14, 0x00, 0x00, 0x00, 0x10, 0x00, 0x0E, 0x10,
            0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
            0x00, 0x00 };
        connection.bulkTransfer(endpoint, capture, capture.length, TIMEOUT);

        // teminate communication
        BroadcastReceiver mUsbReceiver = new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                String action = intent.getAction();
                if (UsbManager.ACTION_USB_DEVICE_DETACHED.equals(action)) {
                    UsbDevice device = (UsbDevice) intent
                    .getParcelableExtra(UsbManager.EXTRA_DEVICE);
                    if (device != null) {
                        // call your method that cleans up and closes
                        // communication with the device
                    }
                }
            }
        };

    }

    public static byte toByte(int c) {
        return (byte) (c <= 0x7f ? c : ((c % 0x80) - 0x80));
    }

}

2 个解决方案

#1

I suspect you are not correctly searching for interface and endpoint.

我怀疑你没有正确搜索接口和端点。

see explanation below.

见下面的解释。

Suggestion: test if the endpoint if it is valid and try to match it with device descriptor.

建议：测试端点是否有效并尝试将其与设备描述符匹配。

a interface can have multiple setting.

一个界面可以有多个设置。

AFAIK, for camera, their should be three alternate setting for the camera interface.

AFAIK，对于相机，它们应该是相机界面的三个备用设置。

Zero Bandwidth -- no endpoints inside -- most possibly alternate setting 0
零带宽 - 内部没有端点 - 最可能是交替设置0
Isochronous (if the camera support it) -- isochronous endpoint inside
等时（如果摄像机支持它） - 内部的等时端点
Bulk -- bulk endpoint inside <-- place of you interest
批量 - 批量端点< - 你感兴趣的地方

(I dont know the actual USB camera specification but, this should be applicable to all streaming protocol over USB (as i see in Audio Class))

（我不知道实际的USB摄像头规格，但是这应该适用于USB上的所有流媒体协议（正如我在音频类中所见））

You need to search for the bulk alternate setting and then perform communication on the endpoint inside it.

您需要搜索批量备用设置，然后在其中的端点上执行通信。

#2

I think this function is not passing the correct endpoint

我认为这个函数没有传递正确的端点

int status = connection.bulkTransfer(endpoint, getEvent,
                                     getEvent.length, TIMEOUT);

which is coming from

这是来自

UsbInterface intf = device.getInterface(0);
UsbEndpoint endpoint = intf.getEndpoint(0);

maybe the USB interface is not correct. Please check if index 0 parameter is correct.

也许USB接口不正确。请检查索引0参数是否正确。

#1