Develop Reference

Android and C++ socket communication over WiFi Direct

Overview: I'm currently working on an Android app which connects to a Linux system via WiFi Direct, with the final intent of streaming video over this established connection.
The raspi will be acting as a server in this scenario, with the Android being the client. I will be streaming from a camera attached to the pi, and receiving this video on the Android side to display in my app using ExoPlayer. The pi cannot start sending this video over a datagram socket without having the client's ip address. The Android device will also need to send out miscellaneous packets to the Pi which would be telling it what to do, thus the need for both devices having each others ip addresses.
The current Linux system I am working on is a Raspberry Pi running Raspian, with development taking place in C++. The Android runtime environment being a Samsung Galaxy Tab A.
Problem: I'm able to successfully establish a connection between the two devices, which I have setup so that the Raspberry Pi is always the group owner. With the Pi being group owner, it doesn't have immediate access to the Android's IP address; thus a temporary TCP socket connection must be made between the two so the Raspberry Pi can take note of the Android's IP address.
After a WiFi connection is established, this C++ code is ran on the Pi to open & accept a TCP socket connection from the Android:
#include<cstddef>
#include<iostream>
#include<string>
#include<sys/types.h>
#include<sys/socket.h>
#include<sys/un.h>
#include<unistd.h>
#include<netdb.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#define BACKLOG 2 //Allowed connection count.
#define PORT 8988 //The port we will be listening on.
//The static IP of p2p-dev-wlan0
const std::string MY_IP = "192.168.4.1";
bool listen_for_ip() {
//Buffer for receiving messages.
char buffer[256];
//Create Server Socket:
int sock_fd = socket(AF_INET, SOCK_STREAM, 0);
if (sock_fd < 0)
return false;
else
std::cout << "Created Server" << std::endl;
struct sockaddr_in my_addr, peer_addr;
//Recieve messages from IPv4 addresses.
my_addr.sin_family = AF_INET;
//Set our IP address of the socket to the value in "MY_IP"
my_addr.sin_addr.s_addr = inet_addr(MY_IP.c_str());
//my_addr.sin_addr.s_addr = INADDR_ANY; // Also tested with this, no luck.
//Set our in port to the value in "PORT"
my_addr.sin_port = htons(PORT);
//Attempt to bind to IP and port.
if (bind(sock_fd, (struct sockaddr*) &my_addr, sizeof(my_addr)) == 0)
std::cout << "Binded successfully" << std::endl;
else
return false;
//Listen on the socket
if (listen(sock_fd, BACKLOG) < 0)
return false;
//Accept a connection.
socklen_t peer_addr_size = sizeof(peer_addr);
std::cout << "Accepting connection ..." << std::endl;
int new_fd = accept(sock_fd, (struct sockaddr*) &peer_addr, &peer_addr_size);
if (new_fd == -1) {
std::cout << "Error accepting connect" << std::endl;
close(sock_fd);
return false;
}
else
std::cout << "Connection accept completed status = " << new_fd << std::endl;
//
char ip[INET_ADDRSTRLEN];
inet_ntop(AF_INET, &(peer_addr.sin_addr), ip, INET_ADDRSTRLEN);
if (recv(new_fd, buffer, 256, 0) < 0) {
close(new_fd);
close(sock_fd);
return false;
}
std::cout << "Client says " << buffer << std::endl;
//Do other stuff with connection ...
close(new_fd);
close(sock_fd);
return true;
}
This code runs successfully, and as should blocks on the accept() call to wait for the Android connect to the socket.
On the Android side this code is ran to connect to the Pi (Group owner) over a basic socket:
public static final int PORT = 8988;
private static final int TIMEOUT_MS = 10000;
private final String myIp;
private WifiP2pInfo mGroupInfo;
private final WifiDirectService mWifiDirectService;
public P2pClientSocket(WifiDirectService wifiDirectService, WifiP2pInfo groupInfo, String ourDeviceIP) {
mGroupInfo = groupInfo;
myIp = ourDeviceIP;
mWifiDirectService = wifiDirectService;
exchangeIP();
}
/**
* Utilizes a basic socket & TCP to ensure that the IP address of this machine is sent to the group owner of established P2P group.
* If there is an error with sending or writing this message, or the message times out,
* {#link WifiDirectService} will be notified to immediately dispose of its current connection.
*/
private void exchangeIP() {
Socket initSocket = new Socket();
Runnable r = () -> {
try {
String host = mGroupInfo.groupOwnerAddress.getHostAddress();
Log.d(TAG, "Opening socket to : " + host + ", " + PORT);
initSocket.connect(new InetSocketAddress(host, PORT), TIMEOUT_MS);
OutputStreamWriter outputStreamWriter = new OutputStreamWriter(initSocket.getOutputStream(), StandardCharsets.UTF_8);
outputStreamWriter.write(myIp, 0, myIp.length());
outputStreamWriter.close();
Log.d(TAG, "Successfully wrote IP.");
} catch (SocketTimeoutException e) {
String message = "Connection Timeout - Disconnecting.";
Log.e(TAG, message, e);
mWifiDirectService.socketError(message);
} catch (IOException e) {
String message = "IP Exchange Error - Disconnecting.";
Log.e(TAG, message, e);
mWifiDirectService.socketError(message);
} finally {
try {
initSocket.close();
} catch (IOException e) {
Log.e(TAG,"Error Closing Init Socket.");
}
}
};
new Thread(r).start();
}
The value of
String host = mGroupInfo.groupOwnerAddress.getHostAddress()
will always be the IP address of the raspberry pi. I have configured it so it runs as a DHCP server with a static IP using:
cat > /etc/systemd/network/12-p2p-wlan0.network <<EOF
[Match]
Name=p2p-wlan0-*
[Network]
Address=192.168.4.1/24
DHCPServer=yes
EOF
However, on the .connect() call, the timeout threshold is always reached. I'm a bit of a networking noob so I'm not entirely sure on what I'm doing wrong. Included is the timeout stack trace:
java.net.SocketTimeoutException: failed to connect to /192.168.4.1 (port 8988) from /192.168.4.163 (port 33122) after 10000ms
at libcore.io.IoBridge.connectErrno(IoBridge.java:191)
at libcore.io.IoBridge.connect(IoBridge.java:135)
at java.net.PlainSocketImpl.socketConnect(PlainSocketImpl.java:142)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:390)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:230)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:212)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:436)
at java.net.Socket.connect(Socket.java:621)
at com.nlos.networking.P2pClientSocket.lambda$exchangeIP$0$P2pClientSocket(P2pClientSocket.java:54)
at com.nlos.networking.-$$Lambda$P2pClientSocket$fxU2Z0Zg0gRF1Fyl1fNnqgO2m8I.run(Unknown Source:4)
at java.lang.Thread.run(Thread.java:919)
I've tried multiple different sockets, ensured that the pi is actually up and listening, and am honestly stumped at this point. Any help would be greatly appreciated!

Android app works with ESP8266 using router as WAP but ESP8266 doesn't work with soft access points

I have an Android app I made using MIT App Inventor which works with the following ino file in the Arduino IDE:
#include <ESP8266WiFi.h>
const char* ssid = "my ssid";
const char* password = "my password";
// Set web server port number to 80
WiFiServer server(80);
// Variable to store the HTTP request
String header;
// Auxiliar variables to store the current output state
// Assign output variables to GPIO pins
int tool_box_lights = 0;
int pass_side_lights = 0;
int drv_side_lights = 0;
int rear_lights = 0;
int winch = 0;
// Current time
unsigned long currentTime = millis();
// Previous time
unsigned long previousTime = 0;
// Define timeout time in milliseconds (example: 2000ms = 2s)
const long timeoutTime = 2000;
void setup() {
Serial.begin(115200);
// Connect to Wi-Fi network with SSID and password
Serial.print("Connecting to ");
Serial.println(ssid);
WiFi.begin(ssid, password);
while (WiFi.status() != WL_CONNECTED) {
delay(500);
Serial.print(".");
}
// Print local IP address and start web server
Serial.println("");
Serial.println("WiFi connected.");
Serial.println("IP address: ");
Serial.println(WiFi.localIP());
server.begin();
}
void loop(){
WiFiClient client = server.available(); // Listen for incoming clients
if (client) { // If a new client connects,
// Serial.println("New Client"); // print a message out in the serial port
String currentLine = ""; // make a String to hold incoming data from the client
currentTime = millis();
previousTime = currentTime;
while (client.connected() && currentTime - previousTime <= timeoutTime) { // loop while the client's connected
currentTime = millis();
if (client.available()) { // if there's bytes to read from the client,
char c = client.read(); // read a byte, then
// Serial.write(c); // print it out the serial monitor
header += c;
if (c == '\n') { // if the byte is a newline character
// if the current line is blank, you got two newline characters in a row.
// that's the end of the client HTTP request, so send a response:
if (currentLine.length() == 0) {
// HTTP headers always start with a response code (e.g. HTTP/1.1 200 OK)
// and a content-type so the client knows what's coming, then a blank line:
client.println("HTTP/1.1 200 OK");
client.println("Content-type:text/html");
client.println("Connection: close");
client.println();
//Serial.println(header);
// turns the GPIOs on and off
if (header.indexOf("/tb/on") >= 0)
{
Serial.println("toolbox on");
client.println("toolbox on");
tool_box_lights = 1;
} else if (header.indexOf("/tb/off") >= 0)
{
Serial.println("toolbox off");
client.println("toolbox off");
tool_box_lights = 0;
} else if (header.indexOf("/ps/on") >= 0)
{
Serial.println("pass side on");
client.println("pass side on");
pass_side_lights = 1;
} else if (header.indexOf("/ps/off") >= 0)
{
Serial.println("pass side off");
client.println("pass side off");
pass_side_lights = 0;
} else if (header.indexOf("/ds/on") >= 0)
{
Serial.println("drv side on");
client.println("drv side on");
drv_side_lights = 1;
} else if (header.indexOf("/ds/off") >= 0)
{
Serial.println("drv side off");
client.println("drv side off");
drv_side_lights = 0;
} else if (header.indexOf("/rr/on") >= 0)
{
Serial.println("rear lights on");
client.println("rear lights on");
rear_lights = 1;
} else if (header.indexOf("/rr/off") >= 0)
{
Serial.println("rear lights off");
client.println("rear lights off");
rear_lights = 0;
} else if (header.indexOf("/wc/in") >= 0)
{
Serial.println("winch in");
client.println("winch in");
winch = 1;
} else if (header.indexOf("/wc/out") >= 0)
{
Serial.println("winch out");
client.println("winch out");
winch = 2;
} else if (header.indexOf("/wc/off") >= 0)
{
Serial.println("winch off");
client.println("winch off");
winch = 0;
}
// Display the HTML web page
// The HTTP response ends with another blank line
client.println();
// Break out of the while loop
break;
} else { // if you got a newline, then clear currentLine
currentLine = "";
}
} else if (c != '\r') { // if you got anything else but a carriage return character,
currentLine += c; // add it to the end of the currentLine
}
}
}
// Clear the header variable
header = "";
// Close the connection
client.stop();
// Serial.println("Client disconnected.");
// Serial.println("");
}
}
but when I try to make it work with soft access points:
IPAddress local_IP1(192,168,0,22);
IPAddress gateway1(192,168,0,1);
IPAddress subnet(255,255,255,0);
...
Serial.print("\nSetting soft-AP configuration ... ");
Serial.println(WiFi.softAPConfig(local_IP1, gateway1, subnet) ? "Ready" : "Failed!");
Serial.println(WiFi.softAP(ssid, password, false, 4) ? "Ready" : "Failed!");
Serial.print("Soft-AP IP address = ");
Serial.println(WiFi.softAPIP());
// Connect to Wi-Fi network with SSID and password
Serial.print("Connecting to ");
Serial.println(ssid);
WiFi.begin(ssid, password);
/*
while (WiFi.status() != WL_CONNECTED) {
delay(500);
Serial.print(".");
}
*/
// Print local IP address and start web server
Serial.println("");
// Serial.println("WiFi connected.");
Serial.println("IP address: ");
Serial.println(WiFi.softAPIP());
server.begin();
}
void loop(){
WiFiClient client = server.available(); // Listen for incoming clients
if (client) { // If a new client connects,
Serial.println("New Client"); // print a message out in the serial port
...
It never connects. I tried leaving out where I was manually setting the IP address:
IPAddress local_IP1(192,168,0,22);
IPAddress gateway1(192,168,0,1);
IPAddress subnet(255,255,255,0);
and it came out to be 192.168.1.4, so I set that as the IP address in MIT App and I get an 1103 error. Here's part of the block code for that:
The only thing I change is the IP address. It works fine if I use the router's IP address, but I want to use this in my truck and don't want to have to carry a router around.

Reading data from Arduino UNO R3 kit

I'm trying to read the data already stored by me in the Arduino kit, I'm using the physicaloid library to achieve this. I tested the kit (reading data) by connecting it to my PC using the Type B USB cable provided by Arduino itself and using Tera Term. The data begins to transfer after I press '#' on the keyboard (specific to our implementation).
But when I connect it my Android tablet and use the test project by physicaloid to open a device and start communicating, every time I click 'open' it shows a Toast saying it cannot open. I give permission to access the USB device every time it prompts me. Here is the sample program which I had created to read the data:
if(mPhysicaloid.open()){
Toast.makeText(getBaseContext(), "communicating", Toast.LENGTH_SHORT).show();
String signalToStart = new String("#");
byte[] bufToWrite = signalToStart.getBytes();
mPhysicaloid.write(bufToWrite, bufToWrite.length);
byte[] buf = new byte[255];
mPhysicaloid.read(buf);
String data = new String(buf);
tvResult.setText(data);
mPhysicaloid.close();
}
else
Toast.makeText(getBaseContext(), "no communication with device", Toast.LENGTH_LONG).show();
Now here's what I want to know about the data coming from the Arduino USB cable: is it in the RS232 format where the Android device is not able to understand (I don't know, I may be making a blunder here by asking this data format) or is it in the USB data format that is suitable for the Android device to understand? Please help, I have searched over this the whole day. What can I do to open the device and communicate?

I finally got the idea of reading the data from serial USB device. So I thought I'd share it:
First, get all the USB devices attached (if more than one) and get a suitable interface and search for endpoints to communicate with. While initializing the USB device make sure you consider the USB device which you really want to communicate with. You can do that by considering product id and Vendor id.
The code for doing the above described..
private boolean searchEndPoint() {
usbInterface = null;//class level variables, declare these.
endpointOut = null;
endpointIn = null;
Log.d("USB","Searching device and endpoints...");
if (device == null) {
usbDevices = usbManager.getDeviceList();
Iterator<UsbDevice> deviceIterator = usbDevices.values().iterator();
while (deviceIterator.hasNext()) {
UsbDevice tempDevice = deviceIterator.next();
/**Search device for targetVendorID(class level variables[vendorId = SOME_NUMBER and productId=SOME_NUMBER] which u can find) and targetProductID.*/
if (tempDevice .getVendorId() == vendorId) {
if (tempDevice .getProductId() == productId) {
device = tempDevice ;
}
}
}
}
if (device == null){
Log.d("USB","The device with specified VendorId and ProductId not found");
return false;
}
else
Log.d("USB","device found");
/**Search for UsbInterface with Endpoint of USB_ENDPOINT_XFER_BULK,
*and direction USB_DIR_OUT and USB_DIR_IN
*/
try{
for (int i = 0; i < device.getInterfaceCount(); i++) {
UsbInterface usbif = device.getInterface(i);
UsbEndpoint tOut = null;
UsbEndpoint tIn = null;
int tEndpointCnt = usbif.getEndpointCount();
if (tEndpointCnt >= 2) {
for (int j = 0; j < tEndpointCnt; j++) {
if (usbif.getEndpoint(j).getType() == UsbConstants.USB_ENDPOINT_XFER_BULK) {
if (usbif.getEndpoint(j).getDirection() == UsbConstants.USB_DIR_OUT) {
tOut = usbif.getEndpoint(j);
} else if (usbif.getEndpoint(j).getDirection() == UsbConstants.USB_DIR_IN) {
tIn = usbif.getEndpoint(j);
}
}
}
if (tOut != null && tIn != null) {
/** This interface have both USB_DIR_OUT
* And USB_DIR_IN of USB_ENDPOINT_XFER_BULK
*/
usbInterface = usbif;
endpointOut = tOut;
endpointIn = tIn;
}
}
}
if (usbInterface == null) {
Log.d("USB","No suitable interface found!");
return false;
} else {
Log.d("USB","Suitable interface found!");
return true;
}
}catch(Exception ex){
ex.printStackTrace();
return false;
}
}
Now you have a device, USB interface, and endpoints ready for communication. Now it's time to establish a connection between your Android device and USB device.
Below is the code for this (and checking whether the connection is up and communicating):
private boolean checkUsbCOMM() {
/**Value for setting request, on the USB connection.*/
final int RQSID_SET_CONTROL_LINE_STATE = 0x22;
boolean success = false;
Log.d("USB","Checking USB Device for communication: ");
try{
Boolean permitToRead = SUSBS_usbManager.hasPermission(SUSBS_device);
if (permitToRead) {
//class level variable(connection, usbManager : declare it)
connection = usbManager.openDevice(device);
if (connection != null) {
connection.claimInterface(usbInterface, true);
int usbResult;
usbResult = connection.controlTransfer(0x21, //requestType
RQSID_SET_CONTROL_LINE_STATE, //SET_CONTROL_LINE_STATE(request)
0, //value
0, //index
null, //buffer
0, //length
500); //timeout = 500ms
Log.i("USB","controlTransfer(SET_CONTROL_LINE_STATE)[must be 0 or greater than 0]: "+usbResult);
if(usbResult >= 0)
success = true;
else
success = false;
}
}
else {
/**If permission is not there then ask for permission*/
usbManager.requestPermission(device, mPermissionIntent);
Log.d("USB","Requesting Permission to access USB Device: ");
}
return success;
}catch(Exception ex){
ex.printStackTrace();
return false;
}
}
Voila, the USB device is now able to communicate. So let's read using a separate thread:
if(device!=null){
Thread readerThread = new Thread(){
public void run(){
int usbResult = -1000;
int totalBytes = 0;
StringBuffer sb = new StringBuffer();
String usbReadResult=null;
byte[] bytesIn ;
try {
while(true){
/**Reading data until there is no more data to receive from USB device.*/
bytesIn = new byte[endpointIn.getMaxPacketSize()];
usbResult = connection.bulkTransfer(endpointIn,
bytesIn, bytesIn.length, 500);
/**The data read during each bulk transfer is logged*/
Log.i("USB","data-length/read: "+usbResult);
/**The USB result is negative when there is failure in reading or
* when there is no more data to be read[That is :
* The USB device stops transmitting data]*/
if(usbResult < 0){
Log.d("USB","Breaking out from while, usb result is -1");
break;
}
/**Total bytes read from the USB device*/
totalBytes = totalBytes+usbResult;
Log.i("USB","TotalBytes read: "+totalBytes);
for(byte b: bytesIn){
if(b == 0 )
break;
else{
sb.append((char) b);
}
}
}
/**Converting byte data into characters*/
usbReadResult = new String(sb);
Log.d("USB","The result: "+usbReadResult);
//usbResult holds the data read.
} catch (Exception ex) {
ex.printStackTrace();
}
}
};
/**Starting thread to read data from USB.*/
SUSBS_readerThread.start();
SUSBS_readerThread.join();
}
For permission, make sure you add a PendingIntent as well add the permission to your manifest.
AndroidManifest : <uses-feature android:name="android.hardware.usb.host" />
PendingIntent:
private PendingIntent mPermissionIntent;
private static final String ACTION_USB_PERMISSION = "com.android.example.USB_PERMISSION";
mPermissionIntent = PendingIntent.getBroadcast(MainActivity.this,
0, new Intent(ACTION_USB_PERMISSION), 0);
/**Setting up the Broadcast receiver to request a permission to allow the APP to access the USB device*/
IntentFilter filterPermission = new IntentFilter(ACTION_USB_PERMISSION);
registerReceiver(mUsbReceiver, filterPermission);

ADK: device gets stuck when reading from the ADK

I have problems when I when to send messages via USB from the board to the devicersa.
Hardware:
Arduino ADK 2011
Samsung Galaxy S3, Android 4.1.2
The problem is the read method in the Android app never terminates and makes the thread get stuck:
mFileDescriptor = mUsbManager.openAccessory(accessory);
if (mFileDescriptor != null) {
mAccessory = accessory;
FileDescriptor fd = mFileDescriptor.getFileDescriptor();
Log.d(TAG, "openAccessory(): FileDescriptor instanciated. valid " + fd.valid());
mInputStream = new FileInputStream(fd);
mOutputStream = new FileOutputStream(fd);
new Thread(null, new Runnable() {
#Override
public void run() {
int ret = 0;
byte[] buffer = new byte[255];
while (ret >= 0 && mInputStream != null) {
try {
// never terminates
ret = mInputStream.read(buffer);
} catch (IOException e) {
Log.e(TAG, "openAccessory(): Could not read inputStream: " + e);
e.printStackTrace();
break;
}
} ...
The connection works fine since I use the special USB-library. When I connect the device the app opens automatically very well. But with logs I see it never passes the read command. Also the Arduinio monitor says that:
Device addressed... Requesting device descriptor.
found possible device. swithcing to serial mode
device supports protcol 1 or above
found android acessory device
config desc
interface desc
interface desc
2
4
Sending message...
Done
disconnect
The ADK sends messages, to the device in the loop (once):
sntmsg[0] = COMMAND_TEXT;
sntmsg[1] = TARGET_DEFAULT;
sntmsg[2] = 25;
for (int i = 0; i < 25; i++) {
sntmsg[3 + i] = hello[i];
}
// schreiben (buffer, length)
Serial.println("Sending message...");
acc.write(sntmsg, 3 + 25);
Serial.println("Done");
done = true;
delay(250);

Now I figured out the problem might be the disconnect. Immedeately after running through the first loop in the Arduiino code it prints disconnect to the monitor. The code in the libraries of AndroidAccessory.cpp is:
bool AndroidAccessory::isConnected(void)
{
USB_DEVICE_DESCRIPTOR *devDesc = (USB_DEVICE_DESCRIPTOR *) descBuff;
byte err;
max.Task();
usb.Task();
if (!connected &&
usb.getUsbTaskState() >= USB_STATE_CONFIGURING &&
usb.getUsbTaskState() != USB_STATE_RUNNING) {
Serial.print("\nDevice addressed... ");
Serial.print("Requesting device descriptor.\n");
err = usb.getDevDescr(1, 0, 0x12, (char *) devDesc);
if (err) {
Serial.print("\nDevice descriptor cannot be retrieved. Trying again\n");
return false;
}
if (isAccessoryDevice(devDesc)) {
Serial.print("found android acessory device\n");
connected = configureAndroid();
} else {
Serial.print("found possible device. swithcing to serial mode\n");
switchDevice(1);
}
} else if (usb.getUsbTaskState() == USB_DETACHED_SUBSTATE_WAIT_FOR_DEVICE) {
if (connected)
Serial.println("disconnect\n");
connected = false;
}
return connected;
}
So in the second loop this method returns false, even though the smartphone is still connected via usb. Do you know why it thinks it is dosconnected after the first loop iteration?
Thanks,
FL

Using Android to Communicate with a USB HID Device

I am new to USB and to Android so please forgive me if I don't explain myself clearly.
I have a USB HID device that I can communicate with in Windows. I am trying to establish communication using an Acer Iconia A500 tablet running Android 3.1.
I am able to find the device, enumerate it, get its only available interface, get the only available endpoint (0), and determine what type of endpoint it is (transfer interrupt from device to host).
My understanding of the USB spec is that all HID devices are required at a munimum to have a control endpoint (Endpoint 0) and an interrupt IN endpoint. But it seems that endpoint 0 here is the interrupt In endpoint, not the control endpoint.
Yet in order for the device to enumerate it must successfully transfer its descriptor data across the control endpoint. I deduce that the control endpoint therefore must be getting found (and used) because the host does, in fact, enumerate the device.
This is as far as I am able to proceed, as stated above, the only interface/endpoint presented to me at the application level is an interrupt type going from device to host. No endpoint available to my app going from host to device, interrupt or control. So the device waits to be told what to do and the host waits for something to happen in the device. Not very stimulating.
Bear in mind that this device responds properly when connected to Windows, e.g. I am able to send a report containing 13 bytes of data that causes the device to light an LED. So it seems to be complying with the USB HID spec. As an act of desperation I have tried using this one endpoint as both a control endpoint and as a interrupt OUT endpoint, using controltransfer() and UsbRequest() to submit the data to the device, no response in either case.
So my question is: "The control transfer endpoint is (?) being used to set up the device, why am I not able to find & use it?"
Thanks for any insight, below is the relevant code, I can include the rest in its entirety if needed:
private UsbManager mUsbManager;
private UsbDevice mDevice;
private UsbDeviceConnection mConnectionRead;
private UsbDeviceConnection mConnectionWrite;
private UsbEndpoint mEndpointRead;
private UsbEndpoint mEndpointWrite;
// check for existing devices
for (UsbDevice device : mUsbManager.getDeviceList().values())
{
//Need to filter for my device when other HIDs are also connected, but for now...
String devName = device.getDeviceName();
if (DEBUG == 1){
Toast.makeText(UsbHidDeviceTesterActivity.this, "My device got connected: " + devName, Toast.LENGTH_LONG).show();
}
//mDevice = device;
setHIDDevice(device);
}
private boolean setHIDDevice(UsbDevice device)
{
UsbInterface usbInterfaceRead = null;
UsbInterface usbInterfaceWrite = null;
UsbEndpoint ep1 = null;
UsbEndpoint ep2 = null;
boolean UsingSingleInterface = true;
mDevice = device;
//This HID device is using a single interface
if (UsingSingleInterface)
{
//usbInterfaceRead = device.getInterface(0x00);//only 1 EP on this interface
usbInterfaceRead = findInterface(device);
//Try getting an interface at next index
//usbInterfaceWrite = device.getInterface(0x01);//throws exception
// Try using the same interface for reading and writing
usbInterfaceWrite = usbInterfaceRead;
int endPointCount = usbInterfaceWrite.getEndpointCount();
if (DEBUG == 2)
{
Toast.makeText(UsbHidDeviceTesterActivity.this, "Endpoints: " + endPointCount, Toast.LENGTH_LONG).show();
//Toast.makeText(UsbHidDeviceTesterActivity.this, "Interface: " + usbInterfaceRead, Toast.LENGTH_LONG).show();
}
if (endPointCount == 1)//only getting 1 endpoint
{
ep1 = usbInterfaceRead.getEndpoint(0);
//As an act of desperation try equating ep2 to this read EP, so that we can later attempt to write to it anyway
ep2 = usbInterfaceRead.getEndpoint(0);
}
else if (endPointCount == 2)
{
ep1 = usbInterfaceRead.getEndpoint(0);
ep2 = usbInterfaceRead.getEndpoint(1);
}
}
else // ! UsingSingleInterface
{
usbInterfaceRead = device.getInterface(0x00);
usbInterfaceWrite = device.getInterface(0x01);
if ((usbInterfaceRead.getEndpointCount() == 1) && (usbInterfaceWrite.getEndpointCount() == 1))
{
ep1 = usbInterfaceRead.getEndpoint(0);
ep2 = usbInterfaceWrite.getEndpoint(0);
}
if (DEBUG == 3)
{
Toast.makeText(UsbHidDeviceTesterActivity.this, "Using Dual Interface", Toast.LENGTH_LONG).show();
}
}
//because ep1 = ep2 this will now not cause a return unless no ep is found at all
if ((ep1 == null) || (ep2 == null))
{
if (DEBUG == 4)
{
Toast.makeText(UsbHidDeviceTesterActivity.this, "One EP is null", Toast.LENGTH_LONG).show();
}
return false;
}
// Determine which endpoint is the read, and which is the write
if (ep1.getType() == UsbConstants.USB_ENDPOINT_XFER_INT)//I am getting a return of 3, which is an interrupt transfer
{
if (ep1.getDirection() == UsbConstants.USB_DIR_IN)//I am getting a return of 128, which is a device-to-host endpoint
{
mEndpointRead = ep1;
if (DEBUG == 5)
{
Toast.makeText(UsbHidDeviceTesterActivity.this, "EP1 type: " + ep1.getType(), Toast.LENGTH_LONG).show();
}
}
if (ep1.getDirection() == UsbConstants.USB_DIR_OUT)//nope
{
mEndpointWrite = ep1;
if (DEBUG == 6)
{
Toast.makeText(UsbHidDeviceTesterActivity.this, "EP1 is a write", Toast.LENGTH_LONG).show();
}
}
}
if (ep2.getType() == UsbConstants.USB_ENDPOINT_XFER_INT)
{
if (ep2.getDirection() == UsbConstants.USB_DIR_IN)
{
//Try treating it as a write anyway
//mEndpointRead = ep2;
mEndpointWrite = ep2;
}
else if (ep2.getDirection() == UsbConstants.USB_DIR_OUT)
{
//usbEndpointWrite = ep2;
mEndpointWrite = ep2;
}
}
//check that we should be able to read and write
if ((mEndpointRead == null) || (mEndpointWrite == null))
{
return false;
}
if (device != null)
{
UsbDeviceConnection connection = mUsbManager.openDevice(device);
if (connection != null && connection.claimInterface(usbInterfaceRead, true))
{
Log.d(TAG, "open SUCCESS");
mConnectionRead = connection;
// Start the read thread
//Comment out while desperately attempting to write on this connection/interface
//Thread thread = new Thread(this);
//thread.start();
}
else
{
Log.d(TAG, "open FAIL");
mConnectionRead = null;
}
}
if (UsingSingleInterface)
{
mConnectionWrite = mConnectionRead;
}
else //! UsingSingleInterface
{
mConnectionWrite = mUsbManager.openDevice(device);
mConnectionWrite.claimInterface(usbInterfaceWrite, true);
}
return true;
}
// searches for an interface on the given USB device
private UsbInterface findInterface(UsbDevice device) {
Log.d(TAG, "findInterface " + device);
int count = device.getInterfaceCount();
if (DEBUG == 7)
{
Toast.makeText(UsbHidDeviceTesterActivity.this, "Interface count: " + count, Toast.LENGTH_LONG).show();
}
for (int i = 0; i < count; i++) {
UsbInterface intf = device.getInterface(i);
String InterfaceInfo = intf.toString();
Log.d(TAG, "Interface: " + InterfaceInfo);
//Class below is 3 for USB_HID
if (intf.getInterfaceClass() == 3 && intf.getInterfaceSubclass() == 0 &&
intf.getInterfaceProtocol() == 0) {
return intf;
}
//....try just returning the interface regardless of class/subclass
//return intf;
}
return null;
}
private boolean sendControlTransfer(byte[] dataToSend)
{
synchronized (this)
{
if (mConnectionRead != null)
{
//byte[] message = new byte[13]; // or 14?
byte[] message = dataToSend;
if (DEBUG == 9)
{
Toast.makeText(UsbHidDeviceTesterActivity.this, "Sending Control Transfer", Toast.LENGTH_LONG).show();
}
//first field ox21 is bin 00100001 which splits into 0 01 00001 for direction(1bit)/type(2b)/recipient(5b)
//To set direction as 'host to Device' we need 0, To set type to HID we need 11 (3), and for recipient we want 00001
//second field 0x09 is class specific request code, 0x09 is listed as 'reserved for future use'
//third field 0x200 is value
//int transfer = mConnectionRead.controlTransfer(0x21, 0x9, 0x200, 0, message, message.length, 0);
//try with type set to HID
int transfer = mConnectionRead.controlTransfer(0xC1, 0x9, 0x200, 0, message, message.length, 0);
if (DEBUG == 10)
{
Toast.makeText(UsbHidDeviceTesterActivity.this, "Transfer returned " + transfer, Toast.LENGTH_LONG).show();
}
}
}
return true;
}
private boolean sendInterruptTransfer(byte[] dataToSend)
{
int bufferDataLength = mEndpointWrite.getMaxPacketSize();//The write endpoint is null unless we just copy the read endpoint
if (DEBUG == 12)
{
Toast.makeText(UsbHidDeviceTesterActivity.this, "Max Packet Size: " + bufferDataLength, Toast.LENGTH_LONG).show();
}
ByteBuffer buffer = ByteBuffer.allocate(bufferDataLength + 1);
UsbRequest request = new UsbRequest();
buffer.put(dataToSend);
request.initialize(mConnectionWrite, mEndpointWrite);
request.queue(buffer, bufferDataLength);
try
{
/* only use requestwait on a read
if (request.equals(mConnectionWrite.requestWait()))
{
return true;
}
*/
}
catch (Exception ex)
{
// An exception has occurred
if (DEBUG == 13)
{
Toast.makeText(UsbHidDeviceTesterActivity.this, "Caught Write Exception", Toast.LENGTH_LONG).show();
}
}
return true;
}

So, I have been researching similar things. I cannot confirm, but what I believe is happening is:
Android does not list the control endpoint when it enumerates it's endpoints. It only lists other endpoints.
A connection to any endpoint can send control transfers to endpoint 0, through the controlTransfer method, which (quoting from the api) "Performs a control transaction on endpoint zero for this device."
So, in your above code, I would use the 0th endpoint as an interrupt input endpoint, but it will still allow for control transfers.
An example of someone using a HID device is the Missle Launcher demo, the device it uses is a HID device with an interrupt endpoint.

You can get a full list of the details of interfaces and endpoint by using the following:
UsbManager mManager = (UsbManager) getSystemService(Context.USB_SERVICE);
HashMap<String, UsbDevice> deviceList = mManager.getDeviceList();
Iterator<UsbDevice> deviceIterator = deviceList.values().iterator();
while (deviceIterator.hasNext())
{
UsbDevice device = deviceIterator.next();
Log.i(TAG,"Model: " + device.getDeviceName());
Log.i(TAG,"ID: " + device.getDeviceId());
Log.i(TAG,"Class: " + device.getDeviceClass());
Log.i(TAG,"Protocol: " + device.getDeviceProtocol());
Log.i(TAG,"Vendor ID " + device.getVendorId());
Log.i(TAG,"Product ID: " + device.getProductId());
Log.i(TAG,"Interface count: " + device.getInterfaceCount());
Log.i(TAG,"---------------------------------------");
// Get interface details
for (int index = 0; index < device.getInterfaceCount(); index++)
{
UsbInterface mUsbInterface = device.getInterface(index);
Log.i(TAG," ***** *****");
Log.i(TAG," Interface index: " + index);
Log.i(TAG," Interface ID: " + mUsbInterface.getId());
Log.i(TAG," Inteface class: " + mUsbInterface.getInterfaceClass());
Log.i(TAG," Interface protocol: " + mUsbInterface.getInterfaceProtocol());
Log.i(TAG," Endpoint count: " + mUsbInterface.getEndpointCount());
// Get endpoint details
for (int epi = 0; epi < mUsbInterface.getEndpointCount(); epi++)
{
UsbEndpoint mEndpoint = mUsbInterface.getEndpoint(epi);
Log.i(TAG," ++++ ++++ ++++");
Log.i(TAG," Endpoint index: " + epi);
Log.i(TAG," Attributes: " + mEndpoint.getAttributes());
Log.i(TAG," Direction: " + mEndpoint.getDirection());
Log.i(TAG," Number: " + mEndpoint.getEndpointNumber());
Log.i(TAG," Interval: " + mEndpoint.getInterval());
Log.i(TAG," Packet size: " + mEndpoint.getMaxPacketSize());
Log.i(TAG," Type: " + mEndpoint.getType());
}
}
}
Log.i(TAG," No more devices connected.");
}

Control transfer doesn't show any interface descriptor and its endpoint number is 0 by default, for both in and out transfer.
if you have other interfaces the index of those interfaces should start from 0 i.e. default control transfer interface does not count.
So your interface 0 holds the endpoint 1 descriptor. use the UsbEndpoint methods to find the attributes of the endpoint whether it is interrupt type or not. if it is then endpoint type by UsbEndpoint.getType() should return 0x03 and endpoint number by UsbEndpoint.getEndpointNumber() should return 0x81 which is usual value for endpoint 1.
below your code is wrong:
//first field ox21 is bin 00100001 which splits into 0 01 00001 for direction(1bit)/type(2b)/recipient(5b)
//To set direction as 'host to Device' we need 0, **To set type to HID we need 11 (3)**, and for recipient we want 00001
//second field 0x09 is class specific request code, **0x09 is listed as 'reserved for future use'**
//**third field 0x200 is value**
//int transfer = mConnectionRead.controlTransfer(0x21, 0x9, 0x200, 0, message, message.length, 0);
//try with type set to HID
int transfer = mConnectionRead.controlTransfer(0xC1, 0x9, 0x200, 0, message, message.length, 0);
Type 2 bits is used to indicate class specific request, i.e. its value is 01,
0x09 is Hid class specific request SET_REPORT, not reserved.
value is the wValue which is used as Report ID for Hid class, for your case it is probably 0, if you have only one report at you HID descriptor.
and the 4 th parameter is wIndex which should be used to indicate the recipient, for your case it should be 0x01 for interface as recipient.
So your code for control transfer for Read or receive data form device should be:
int transfer = mConnectionRead.controlTransfer(0xA1, 0x01, 0x00, 0x01, message, message.length, 0);
where 0x01 in second parameter is GET_REPORT is Hid calls specific request.
And your code for control transfer for Write or send data to device should be:
int transfer = mConnectionWrite.controlTransfer(0x21, 0x09, 0x00, 0x01, message, message.length, 0);
Since you only have Interrupt IN endpoint 1, Bulk or Interrupt transfer should be like:
int transfer = bulkTransfer (ep1, message, message.length, 0);
to have the interrupt Out endpoint there should be a endpoint descriptor for that at the interface descriptor of firmware of your device.

Maybe it is a late answer or off topic. However, I hope someone will one day find this answer useful.
Github now contains great Android libraries to communicate with custom HID devices:
Mine in Kotlin
in Java
The good thing is that if you are lucky, then you only need to know the device VID:PID and the commands it accepts. You don't need to worry about USB protocol or communication details.
If interested about how USB works, then you can have a closer look at library source code.