The USB communication to achieve two Android devices

Experimental environment is as follows:
1, two Android phones, red rice (as the host), millet Note (as accessory);
2, OTG line host, accessory connect usb cable, connect OTG again;


Refer to the article and reference code:
https://developer.android.com/guide/topics/connectivity/usb/host.html
https://developer.android.com/guide/topics/connectivity/usb/accessory.html
https://github.com/quandoo/android2android-accessory

current status:
Can be connected to the device, however,
The host side:
With the connection. BulkTransfer (EndPointIn,... ) don't get data, instead of through UsbRequest receive data can be received;
With the connection. BulkTransfer (EndPointOut,... Have been return 1) to send data, using UsbRequst send data is not an error;
The accessory end:
MOutStream. Write can send;
MInStream. Read block, not receive data, unknown reason, need more protocol communication process? How to do?

The Host code

 
Public class UsbHostActivity extends AppCompatActivity {
Private UsbManager mUsbManager; 
Private UsbDevice mDevice; 
Private List MSendMsgList;//send data list 
Private CommunicationThread mCommThread; 
Private PendingIntent mPermissionIntent; 
@ Override 
Protected void onCreate (Bundle savedInstanceState) {
. 
MUsbManager=(UsbManager) getSystemService (Context. USB_SERVICE); 
MPermissionIntent=PendingIntent. GetBroadcast (this, 0, new Intent (ACTION_USB_PERMISSION), 0). 
IntentFilter filter=new IntentFilter (ACTION_USB_PERMISSION); 
RegisterReceiver (mUsbReceiver, filter); 
//the initial control, click on the button calls checkDevice connected devices 
} 

Private void initStringControlTransfer (final UsbDeviceConnection deviceConnection, 
Final int index, 
Final String String) {
DeviceConnection. ControlTransfer (0 x40, 52, 0, index, string. GetBytes (), string. The length (), 100); 
} 

Private volatile Boolean mExit=false; 
Private class CommunicationThread extends Thread {
@ Override 
Public void the run () {
MExit=false; 
UsbEndpoint endpointIn=null; 
UsbEndpoint endpointOut=null; 
UsbInterface UsbInterface=mDevice. GetInterface (0); 
If (usbInterface==null) {
return; 
} 
UsbDeviceConnection connection=mUsbManager. OpenDevice (mDevice); 
If (connection==null) {
return; 
} 
if (! Connection. ClaimInterface (usbInterface, true)) {
Connection. The close (); 
return; 
} 
//send the control message 
InitStringControlTransfer (connection, 0, "UsbTest Example");//MANUFACTURER 
UsbTest initStringControlTransfer (connection, 1, "");//MODEL 
InitStringControlTransfer (connection, 2, "Test Usb Host and Accessory");//the DESCRIPTION 
InitStringControlTransfer (connection, 3, "0.1");//VERSION 
InitStringControlTransfer (connection, 4, "");//URI 
InitStringControlTransfer (connection, 5, "42");//SERIAL 
Connection. ControlTransfer (0 x40, 53, 0, 0, new byte [] {}, 0, 100); 

For (int I=0; i Final UsbEndpoint endpoint=usbInterface. GetEndpoint (I); 
If (the endpoint. GetDirection ()==UsbConstants. USB_DIR_IN) {
EndpointIn=the endpoint; 
} 
If (the endpoint. GetDirection ()==UsbConstants. USB_DIR_OUT) {
EndpointOut=the endpoint; 
} 
} 
Byte buff []=new byte [256]. 
while (! MExit) {
Final int bytesTransferred=connection. BulkTransfer (endpointIn, buff, buff. Length, 100); 
If (bytesTransferred & gt; 0 {
//TODO 
} else {
//process until you come here, receive data failure 
} 
//this way successfully received message 
//ByteBuffer buffer=ByteBuffer. The allocate (256); 
//UsbRequest request=new UsbRequest (); 
//request. The initialize (connection, endpointIn); 
//a Boolean ret=request queue (buffer, 256); 
//if (ret) {
//if (mConnection requestWait ()==request) {
//} 
//} 
Synchronized (mSendMsgList) {
if (! MSendMsgList. IsEmpty ()) {
. 
Int len=connection. BulkTransfer (endpointOut, sendBuff, sendBuff. Length, 100); 
If (len & gt;=0) {
//TODO 
} else {
//process until you come here, send failure 
} 
//this method can send, will not return an error 
//UsbRequest request=new UsbRequest (); 
//request. The initialize (mConnection, mEndOut); 
//ByteBuffer buffer=ByteBuffer. Wrap (text) getBytes ()); 
//a Boolean ret=request queue (buffer, text getBytes (.) length); 
//if (ret) {
//} 
} 
} 
} 
. 
} 
} 

Private void checkDevice () {
HashMap DeviceList=mUsbManager. The getDeviceList (); 
If (deviceList==null | | deviceList. IsEmpty ()) {
return; 
} 
Iterator DeviceIterator=deviceList. Values (). The iterator (); 
While (deviceIterator. HasNext ()) {
UsbDevice device=deviceIterator. Next (); 
MUsbManager. RequestPermission (device, mPermissionIntent); 
break; 
} 
} 

Private static final String ACTION_USB_PERMISSION="com. Mobilemerit. Usbhost. USB_PERMISSION"; 
Private final BroadcastReceiver mUsbReceiver=new BroadcastReceiver () {
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