USB bulkTransfer between Android tablet and cameraThe question about USB bulkTransfer between Android tablet and camera 

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?

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));
}
}

USB bulkTransfer between Android tablet and camera3 avaliable solutions to USB bulkTransfer between Android tablet and camera 

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

see explanation below.

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


a interface can have multiple setting.

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

  • Zero Bandwidth — no endpoints inside — most possibly alternate setting 0
  • Isochronous (if the camera support it) — isochronous endpoint inside
  • Bulk — bulk endpoint inside <– place of you interest

(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))

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

USB bulkTransfer between Android tablet and camera

I think this function is not passing the correct endpoint

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

which is coming from

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.

USB bulkTransfer between Android tablet and camera

Check usb endpoint direction. I’ve encountered some devices where USB_DIR_OUT was USB_DIR_IN and USB_DIR_IN was USB_DIR_OUT and it was causing some issues.