Bulktransfer returns -1 <p>First let me state that I am brand new to Android Development so maybe USB is a bit complex for a first app but it is my only reason for wanting to write an app in the first place.</p> <p>I would like to communicate to a Garmin GPS over USB. I have done so in the past with success from the PC but it was via a driver supplied by Garmin.</p> <p>As far as I am aware there is no such driver for Android so I need to write directly to the USB.</p> <p>Garmin publishes this documentation:</p> <p><a href="http://www8.garmin.com/support/pdf/USBAddendum.pdf" rel="nofollow">http://www8.garmin.com/support/pdf/USBAddendum.pdf</a></p> <p>Basically it says you must transmit on bulk out: 00 00 00 00 05 00 00 00 00 00 00 00</p> <p>to tell the device to prepare for a transfer. When I do so, my bulktransfer fails with -1. If I have a 0 for the timeout then bulktransfer never returns. I assume becuase there is no response from the gps.</p> <p>I have included my code below. The code detects the GPS and opens it. But the first bulktransfer never completes. I am certain I am sending to the bulk out endpoint. Can anyone get me started?</p> <pre><code> public class MainActivity extends Activity { private static final String TAG = "TestGarmin"; private UsbManager mUsbManager; private UsbDevice mDevice; private UsbDeviceConnection mConnection; private UsbEndpoint mEndpointIntr; private UsbEndpoint mEndpointBulkOut; private UsbEndpoint mEndpointBulkIn; private static int TIMEOUT = 0; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); mUsbManager = (UsbManager)getSystemService(Context.USB_SERVICE); } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.main, menu); return true; } public void onResume() { super.onResume(); Intent intent = getIntent(); Log.d(TAG, "intent: " + intent); String action = intent.getAction(); String s = UsbManager.ACTION_USB_DEVICE_ATTACHED; UsbDevice device = (UsbDevice)intent.getParcelableExtra(UsbManager.EXTRA_DEVICE); if (UsbManager.ACTION_USB_DEVICE_ATTACHED.equals(action)) setDevice(device); } private void setDevice(UsbDevice device) { Log.d(TAG, "setDevice " + device); if (device.getInterfaceCount() != 1) { Log.e(TAG, "could not find interface"); return; } UsbInterface intf = device.getInterface(0); // device should have three endpoints if (intf.getEndpointCount() != 3) { Log.e(TAG, "could not find endpoint"); return; } // endpoint 0 should be of type interrupt UsbEndpoint ep0 = intf.getEndpoint(0); if (ep0.getType() != UsbConstants.USB_ENDPOINT_XFER_INT) { Log.e(TAG, "endpoint 0 is not interrupt type"); return; } if (ep0.getDirection() != UsbConstants.USB_DIR_IN) { Log.e(TAG, "endpoint 0 is not an input endpoint"); return; } mEndpointIntr = ep0; // endpoint 1 should be of type bulk UsbEndpoint ep1 = intf.getEndpoint(1); if (ep1.getType() != UsbConstants.USB_ENDPOINT_XFER_BULK) { Log.e(TAG, "endpoint 1 is not bulk type"); return; } if (ep1.getDirection() != UsbConstants.USB_DIR_OUT) { Log.e(TAG, "endpoint 1 is not an output endpoint"); return; } mEndpointBulkOut = ep1; // endpoint 2 should be of type bulk UsbEndpoint ep2 = intf.getEndpoint(2); if (ep2.getType() != UsbConstants.USB_ENDPOINT_XFER_BULK) { Log.e(TAG, "endpoint 2 is not bulk type"); return; } if (ep2.getDirection() != UsbConstants.USB_DIR_IN) { Log.e(TAG, "endpoint 2 is not an output endpoint"); return; } mEndpointBulkOut = ep2; mDevice = device; if (device != null) { UsbDeviceConnection connection = mUsbManager.openDevice(device); if (connection != null &amp;&amp; connection.claimInterface(intf, true)) { Log.d(TAG, "open SUCCESS"); mConnection = connection; byte[] init = {0x00,0x00,0x00,0x00,0x05,0x00,0x00,0x00,0x00,0x00,0x00,0x00}; //14 00 00 00 FE 00 00 00 00 00 00 00 int x = connection.bulkTransfer(mEndpointBulkOut,init, init.length, 100); Log.e(TAG, "BulTransfer returned " + x); } else { Log.d(TAG, "open FAIL"); mConnection = null; } } } } </code></pre>