我正在尝试从连接到主机模式的Android手机的USB设备中获取一些数据。我可以向它发送数据，但是读取失败。
我看了several examples并尽我所能，但我没有任何USB通讯经验，虽然现在我知道了一点，我一直坚持我想承认的这个时间越长。
我对端点配置不太熟悉，但我知道我的设备使用CDC类型的通信方法，并且输出（从手机到设备）和输入都已注册。
以下是使用连接到手机的唯一设备来管理USB连接的整个班级，它没有以任何方式完成，但我希望在我继续前进之前让阅读部分工作。
public class UsbCommunicationManager
{
static final String ACTION_USB_PERMISSION = "com.android.example.USB_PERMISSION";
UsbManager usbManager;
UsbDevice usbDevice;
UsbInterface intf = null;
UsbEndpoint input, output;
UsbDeviceConnection connection;
PendingIntent permissionIntent;
Context context;
byte[] readBytes = new byte[64];
public UsbCommunicationManager(Context context)
{
this.context = context;
usbManager = (UsbManager) context.getSystemService(Context.USB_SERVICE);
// ask permission from user to use the usb device
permissionIntent = PendingIntent.getBroadcast(context, 0, new Intent(ACTION_USB_PERMISSION), 0);
IntentFilter filter = new IntentFilter(ACTION_USB_PERMISSION);
context.registerReceiver(usbReceiver, filter);
}
public void connect()
{
// check if there's a connected usb device
if(usbManager.getDeviceList().isEmpty())
{
Log.d("trebla", "No connected devices");
return;
}
// get the first (only) connected device
usbDevice = usbManager.getDeviceList().values().iterator().next();
// user must approve of connection
usbManager.requestPermission(usbDevice, permissionIntent);
}
public void stop()
{
context.unregisterReceiver(usbReceiver);
}
public String send(String data)
{
if(usbDevice == null)
{
return "no usb device selected";
}
int sentBytes = 0;
if(!data.equals(""))
{
synchronized(this)
{
// send data to usb device
byte[] bytes = data.getBytes();
sentBytes = connection.bulkTransfer(output, bytes, bytes.length, 1000);
}
}
return Integer.toString(sentBytes);
}
public String read()
{
// reinitialize read value byte array
Arrays.fill(readBytes, (byte) 0);
// wait for some data from the mcu
int recvBytes = connection.bulkTransfer(input, readBytes, readBytes.length, 3000);
if(recvBytes > 0)
{
Log.d("trebla", "Got some data: " + new String(readBytes));
}
else
{
Log.d("trebla", "Did not get any data: " + recvBytes);
}
return Integer.toString(recvBytes);
}
public String listUsbDevices()
{
HashMap<String, UsbDevice> deviceList = usbManager.getDeviceList();
if(deviceList.size() == 0)
{
return "no usb devices found";
}
Iterator<UsbDevice> deviceIterator = deviceList.values().iterator();
String returnValue = "";
UsbInterface usbInterface;
while(deviceIterator.hasNext())
{
UsbDevice device = deviceIterator.next();
returnValue += "Name: " + device.getDeviceName();
returnValue += "\nID: " + device.getDeviceId();
returnValue += "\nProtocol: " + device.getDeviceProtocol();
returnValue += "\nClass: " + device.getDeviceClass();
returnValue += "\nSubclass: " + device.getDeviceSubclass();
returnValue += "\nProduct ID: " + device.getProductId();
returnValue += "\nVendor ID: " + device.getVendorId();
returnValue += "\nInterface count: " + device.getInterfaceCount();
for(int i = 0; i < device.getInterfaceCount(); i++)
{
usbInterface = device.getInterface(i);
returnValue += "\n Interface " + i;
returnValue += "\n\tInterface ID: " + usbInterface.getId();
returnValue += "\n\tClass: " + usbInterface.getInterfaceClass();
returnValue += "\n\tProtocol: " + usbInterface.getInterfaceProtocol();
returnValue += "\n\tSubclass: " + usbInterface.getInterfaceSubclass();
returnValue += "\n\tEndpoint count: " + usbInterface.getEndpointCount();
for(int j = 0; j < usbInterface.getEndpointCount(); j++)
{
returnValue += "\n\t Endpoint " + j;
returnValue += "\n\t\tAddress: " + usbInterface.getEndpoint(j).getAddress();
returnValue += "\n\t\tAttributes: " + usbInterface.getEndpoint(j).getAttributes();
returnValue += "\n\t\tDirection: " + usbInterface.getEndpoint(j).getDirection();
returnValue += "\n\t\tNumber: " + usbInterface.getEndpoint(j).getEndpointNumber();
returnValue += "\n\t\tInterval: " + usbInterface.getEndpoint(j).getInterval();
returnValue += "\n\t\tType: " + usbInterface.getEndpoint(j).getType();
returnValue += "\n\t\tMax packet size: " + usbInterface.getEndpoint(j).getMaxPacketSize();
}
}
}
return returnValue;
}
private void setupConnection()
{
// find the right interface
for(int i = 0; i < usbDevice.getInterfaceCount(); i++)
{
// communications device class (CDC) type device
if(usbDevice.getInterface(i).getInterfaceClass() == UsbConstants.USB_CLASS_CDC_DATA)
{
intf = usbDevice.getInterface(i);
// find the endpoints
for(int j = 0; j < intf.getEndpointCount(); j++)
{
if(intf.getEndpoint(j).getDirection() == UsbConstants.USB_DIR_OUT && intf.getEndpoint(j).getType() == UsbConstants.USB_ENDPOINT_XFER_BULK)
{
// from android to device
output = intf.getEndpoint(j);
}
if(intf.getEndpoint(j).getDirection() == UsbConstants.USB_DIR_IN && intf.getEndpoint(j).getType() == UsbConstants.USB_ENDPOINT_XFER_BULK)
{
// from device to android
input = intf.getEndpoint(j);
}
}
}
}
}
private final BroadcastReceiver usbReceiver = new BroadcastReceiver()
{
public void onReceive(Context context, Intent intent)
{
String action = intent.getAction();
if(ACTION_USB_PERMISSION.equals(action))
{
// broadcast is like an interrupt and works asynchronously with the class, it must be synced just in case
synchronized(this)
{
if(intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false))
{
setupConnection();
connection = usbManager.openDevice(usbDevice);
connection.claimInterface(intf, true);
// set flow control to 8N1 at 9600 baud
int baudRate = 9600;
byte stopBitsByte = 1;
byte parityBitesByte = 0;
byte dataBits = 8;
byte[] msg = {
(byte) (baudRate & 0xff),
(byte) ((baudRate >> 8) & 0xff),
(byte) ((baudRate >> 16) & 0xff),
(byte) ((baudRate >> 24) & 0xff),
stopBitsByte,
parityBitesByte,
(byte) dataBits
};
connection.controlTransfer(UsbConstants.USB_TYPE_CLASS | 0x01, 0x20, 0, 0, msg, msg.length, 5000);
}
else
{
Log.d("trebla", "Permission denied for USB device");
}
}
}
else if(UsbManager.ACTION_USB_DEVICE_DETACHED.equals(action))
{
Log.d("trebla", "USB device detached");
}
}
};
}
我一直从-1方法获得read()，这表示某种错误，它总是超时。也许问题来自连接配置，我已经尝试了几个（读取：试验和错误）并且没有工作，令人惊讶的是我不需要任何配置来向设备发送数据。
修改的
还必须注意的是，我使用的电缆是micro-USB到micro-USB，它只能以一种方式工作，那就是我的设备只有当插头A连接到手机和插头时才能通过我的手机供电B连接到设备，而不是相反...这似乎很奇怪。我能够发送数据而不是在插入正确方式时接收的事实仍然存在。
编辑2
我发现somebody else had the same problem，但似乎他无法解决它。
编辑3
我终于在this page找到了解决方案：
另一个主要的疏忽是主机没有机制通知设备主机端有数据接收器准备接受数据。这意味着设备可能在主机未侦听时尝试发送数据，从而导致传输例程中的冗长阻塞超时。因此，强烈建议尽可能使用虚拟串行线路DTR（数据终端就绪）信号，以确定主机应用程序是否已准备好接收数据。
因此DTR信号是强制性的，我所要做的就是将其添加到接口配置中：
connection.controlTransfer(0x21, 0x22, 0x1, 0, null, 0, 0);
编辑4
如果有人感兴趣我完成了项目，那就是open source and published on my GitHub account。虽然它一直不稳定（参见notes），我不打算继续工作，但它确实有效。随意将它用于您自己的项目。