从Android App中的“USB GPS”获取PVT数据包

我尝试从Etrex 10 Garmin GPS读取PVT（位置，速度，时间）记录，其USB端口连接到Android平板电脑（三星Galaxy Tab S，型号SM-T705支持USB主机功能） . 首先我使用的是Windows应用程序为了模拟这种通信，我监控了USB发送/接收的数据包 . 根据Garmin文档（Garmin GPS接口规范，USB附录），这些数据包被成功发送和接收（所有数字都是十六进制的）：

（PC到GPS，启动会话包）00 00 00 00 05 00 00 00 00 00 00 00（GPS到PC，确认启动会话）00 00 00 00 06 00 00 00 04 00 00 00 0b ba aa e7

这是本文档第6部分的一部分，它显示了主机和设备（GPS）如何进行通信：..........................

6 - 示例通信会话

本节提供USB主机和Garmin USB GPS之间的示例通信会话 . 以下信息按时间顺序列出 . 所有数据均以HEX格式显示 . 批量输出（USB传输层 - 开始会话）主机首先将其发送到Garmin USB设备，告诉它准备传输 . 00 00 00 00 05 00 00 00 00 00 00 00中断输入（USB传输层 - 会话已启动）设备响应主机，让主机知道设备已准备好进行对话 . 00 00 00 00 06 00 00 00 04 00 00 00 37 C4 E4 AB

...........................

我尝试在Android应用程序中对此通信进行编码 . 在Android代码中，我可以在连接到平板电脑时识别GPS设备 . 有3个 endpoints . 一个Bulk_Out，另一个Bulk-in和第三个Interrupt-in . 当我发送开始时在Bulk-out endpoints 上的会话数据包，我没有收到中断（甚至是Bulk_in） endpoints 上的Acknowledge数据包.Xamarin Studio中的代码使用MONO库：

public class MainActivity : Activity
{
private UsbManager m_USBManager = null;
private UsbDevice m_GPS = null;
private UsbInterface m_USBInterface = null;
private UsbEndpoint m_BulkOut = null;
private UsbEndpoint m_BulkIn = null;
private UsbEndpoint m_InterruptIn = null;
private UsbDeviceConnection m_USBConnection = null;

public static string ACTION_USB_PERMISSION = "GarminEtrex10.USB_PERMISSION";

private TextView m_TxMsg;
private ListView m_LvTxRxRows;

private USBReceiver m_USBRx;
PendingIntent m_PermissionIntent;

public List<TxRxRow> m_TxRxRows = new List<TxRxRow> ();

protected override void OnCreate (Bundle bundle)
{
    base.OnCreate (bundle);

    SetContentView (Resource.Layout.Main);

    this.m_PermissionIntent = PendingIntent.GetBroadcast(this, 0, new Intent(ACTION_USB_PERMISSION), 0);

    Button button = FindViewById<Button> (Resource.Id.myButton);
    this.m_TxMsg = FindViewById<TextView> (Resource.Id.TxMsg);
    this.m_LvTxRxRows = FindViewById<ListView> (Resource.Id.LvTxRx);

    this.m_USBManager = (UsbManager) this.GetSystemService (Context.UsbService);
    this.m_USBRx = new USBReceiver (this, this.m_USBManager);
    IntentFilter filter = new IntentFilter (ACTION_USB_PERMISSION);
    RegisterReceiver (this.m_USBRx, filter);

    button.Click += new EventHandler (this.ButtonClicked);
}

protected override void OnResume ()
{
    base.OnResume ();

    bool bHasPermission = false;

    if (this.m_USBManager != null)
    {
        foreach (string strKey in this.m_USBManager.DeviceList.Keys)
        {
            UsbDevice usbd = this.m_USBManager.DeviceList [strKey];
            if (usbd.VendorId == 2334)//Garmin product Id
            {
                this.m_GPS = usbd;
                break;
            }
        }
    }
    else
        this.m_TxMsg.Text = "USB Manager is null";
    if (this.m_GPS != null) 
    {
        this.m_USBManager.RequestPermission (this.m_GPS, this.m_PermissionIntent);
        bHasPermission = this.m_USBManager.HasPermission (this.m_GPS);
        this.m_TxMsg.Text = "Garmin GPS found.";
        if (bHasPermission)
            this.m_TxMsg.Text += " and have permission to use it.";
        else
            this.m_TxMsg.Text += " but not have permission to use it.";
    }
    else
        this.m_TxMsg.Text = "No GPS found.";
    if (bHasPermission) 
    {
        this.m_USBInterface = this.m_GPS.GetInterface (0);
        if (this.m_USBInterface != null) 
        {

            for (int i = 0; i < this.m_USBInterface.EndpointCount; i++)
            {
                UsbEndpoint ep = this.m_USBInterface.GetEndpoint (i);
                if (ep.Type == UsbAddressing.XferBulk && ep.Direction == UsbAddressing.Out && this.m_BulkOut == null)
                    this.m_BulkOut = ep;
                if (ep.Type == UsbAddressing.XferBulk && ep.Direction == UsbAddressing.In && this.m_BulkIn == null)
                    this.m_BulkIn = ep;
                if (ep.Type == UsbAddressing.XferInterrupt && ep.Direction == UsbAddressing.DirMask && this.m_InterruptIn == null) 
                    this.m_InterruptIn = ep;
            }
        }
    }
}

public void PopulateListView(byte[] bytes, byte port)
{
    TxRxRow row = new TxRxRow (port, bytes);
    this.m_TxRxRows.Add (row);
    TxRxAdapter adp = new TxRxAdapter (this, this.m_TxRxRows);
    this.m_LvTxRxRows.Adapter = adp;
}

public void SetStatus(string strMsg)
{
    this.m_TxMsg.Text = strMsg;
}

public void SetDevice(UsbDevice gps, UsbInterface gpsInterface, UsbDeviceConnection gpsConnection, UsbEndpoint gpsBulkout,UsbEndpoint gpsBultIn,UsbEndpoint gpsInterruptIn)
{
    if (this.m_BulkIn != null)
        return;
    this.m_GPS = gps;
    this.m_USBConnection = gpsConnection;
    this.m_USBInterface = gpsInterface;
    this.m_InterruptIn = gpsInterruptIn;
    this.m_BulkIn = gpsBultIn;
    this.m_BulkOut = gpsBulkout;
}
private void ButtonClicked(object sender, EventArgs e)
{
    if (this.m_BulkOut == null || (this.m_BulkIn == null && this.m_InterruptIn == null)) 
    {
        Toast.MakeText (this, "Could not find right endpoints", ToastLength.Long).Show ();
        return;
    }
    if(this.m_USBConnection ==null)
        this.m_USBConnection = this.m_USBManager.OpenDevice (this.m_GPS);
    if (this.m_USBConnection == null) 
    {
        Toast.MakeText (this, "Can not open USB device", ToastLength.Long).Show ();
        return;
    }

    if (!this.m_USBConnection.ClaimInterface (this.m_USBInterface, true)) 
    {
        Toast.MakeText (this, "Can not claim interface", ToastLength.Long).Show ();
        return;
    }

    int sentBytesCount = 0;

    #region Send Start_Session Packet
    byte[] obuffer = new byte[12];
    for(int i = 0; i < 12; i++)
        obuffer[i] = 0;
    obuffer[4]=5;

    this.m_TxMsg.Text = "Sending Start session packet....";
    sentBytesCount += this.m_USBConnection.BulkTransfer (this.m_BulkOut, obuffer, 12, 100);

    if (sentBytesCount >= 0) 
    {
        this.m_TxMsg.Text = "Sent bytes = "+sentBytesCount.ToString();
        this.PopulateListView(obuffer,1);
        this.m_USBRx.ReceiveFlag = true;
        this.m_USBConnection.RequestWaitAsync();
    }
    else
    {
        Toast.MakeText (this, "Sent bytes for start session packet = 0.operation failed", ToastLength.Long).Show ();
    }
    #endregion
}
}

这是braodcast接收器类

public class USBReceiver : BroadcastReceiver
{
private UsbManager m_USBMngr = null;
private Context m_Activity = null;
private UsbEndpoint m_BulkIN = null;
private UsbEndpoint m_InterruptIN = null;
private UsbDeviceConnection m_USBConnection=null;

public bool ReceiveFlag = false;

public USBReceiver(Context activity, UsbManager mngr) 
{
    this.m_Activity = activity;
    this.m_USBMngr = mngr;
}
public override void OnReceive (Context context, Intent intent)
{
    String action = intent.Action;
    (this.m_Activity as MainActivity).SetStatus ("Receiving activity=" + intent.Action + "...");
    if (action.Equals (MainActivity.ACTION_USB_PERMISSION)) 
    {
        lock (this) 
        {
            UsbDevice device = (UsbDevice)intent.GetParcelableExtra (UsbManager.ExtraDevice);
            bool bHasPermission = intent.GetBooleanExtra (UsbManager.ExtraPermissionGranted, false);
            //For the first time initialize MainActivity local parameters
            if (this.m_USBConnection == null) 
            {
                if (device != null && bHasPermission) 
                {
                    if (device.VendorId != 2334)
                        return;
                    this.m_USBConnection = this.m_USBMngr.OpenDevice (device);
                    UsbInterface ui = device.GetInterface (0);
                    UsbEndpoint epBulkOut = null;
                    for (int i = 0; i < ui.EndpointCount; i++) 
                    {
                        UsbEndpoint ep = ui.GetEndpoint (i);
                        if (ep.Type == UsbAddressing.XferInterrupt && ep.Direction == UsbAddressing.In)
                            this.m_InterruptIN = ep;
                        if (ep.Type == UsbAddressing.XferBulk && ep.Direction == UsbAddressing.In)
                            this.m_BulkIN = ep;
                        if (ep.Type == UsbAddressing.XferBulk && ep.Direction == UsbAddressing.Out)
                            epBulkOut = ep;
                    }
                    (this.m_Activity as MainActivity).SetDevice (device, ui, this.m_USBConnection, epBulkOut, this.m_BulkIN, this.m_InterruptIN);
                }
            }
            if (this.m_BulkIN != null) 
            {
                int maxPacketSize = this.m_BulkIN.MaxPacketSize;
                byte[] buff = new byte[maxPacketSize];
                int bytesRead = this.m_USBConnection.BulkTransfer (this.m_BulkIN, buff, maxPacketSize, 4000);
                if (bytesRead > 0) 
                {
                    (this.m_Activity as MainActivity).PopulateListView (buff, 2);
                    ReceiveFlag = false;
                }
            }
            if (this.m_InterruptIN != null) 
            {
                UsbRequest req = new UsbRequest ();
                if (req.Initialize (this.m_USBConnection, this.m_InterruptIN)) 
                {

                    int maxsize = this.m_InterruptIN.MaxPacketSize;
                    Java.Nio.ByteBuffer buff = Java.Nio.ByteBuffer.Allocate (maxsize);
                    if (req.Queue (buff, maxsize)) 
                    {
                        if (this.m_USBConnection.RequestWait () == req)
                        {
                            byte[] bb = new byte[maxsize];
                            buff.Get (bb, 0, buff.Remaining ());
                            if (bb.Length > 0) 
                            {
                                (this.m_Activity as MainActivity).PopulateListView (bb, 3);
                            }
                        }
                    }
                }
            }
        }
    }
}
}

当我将GPS连接到平板电脑并运行应用程序时，我会收到一些带有00内容的数据包，然后我点击命令按钮，应用程序发送启动会话数据包，BulkTransfer函数返回12表示它成功发送12个字节 but after that no any received byte in broad cast class . 收到的零字节在应用程序开始时显示广播calss以一种方式工作，但我可以接收命令字节，甚至函数返回一个大于零的数字 . 我应该通过控制 endpoints 向GPS发送任何命令吗？没有任何文档来自Garmin关于这个 . 你能告诉我这个代码或程序有什么问题吗？任何帮助或指南都非常感谢

这是Android应用程序的快照，正如我在2016/9/4

的评论中描述的那样

这是我实现此步骤的代码：

private void ButtonClicked(object sender, EventArgs e)
    {
        if (this.m_BulkOut == null || (this.m_BulkIn == null && this.m_InterruptIn == null)) 
        {
            Toast.MakeText (this, "Could not find right endpoints", ToastLength.Long).Show ();
            return;
        }

        if (this.m_USBConnection == null) {
            try {
                this.m_USBConnection = this.m_USBManager.OpenDevice (this.m_GPS);
            } catch {
            }
        }

        if (this.m_USBConnection == null) 
        {
            Toast.MakeText (this, "Can not open USB device", ToastLength.Long).Show ();
            return;
        }

        if (!this.m_USBConnection.ClaimInterface (this.m_USBInterface, true)) 
        {
            Toast.MakeText (this, "Can not claim interface", ToastLength.Long).Show ();
            return;
        } 
        else
            this.PopulateListView (null, (byte)USBOpCode.ClaimInterface);

        int sentBytesCount = 0;

        #region Send Start_Session Packet
        byte[] obuffer = new byte[12];
        byte[] ibuffer = new byte[12];
        for(int i = 0; i < 12; i++)
        {
            obuffer[i] = 0;
            ibuffer[i] = 0;
        }
        obuffer[4]=5;

        UsbRequest req=new UsbRequest();
        if(req.Initialize(this.m_USBConnection,this.m_InterruptIn))
        {
            this.PopulateListView(null,(byte)USBOpCode.InitializeRequest);
            ByteBuffer buff=ByteBuffer.Wrap(ibuffer,0,12);
                //.Allocate(12);
            if(req.Queue(buff, 12))
            {
                this.PopulateListView(null,(byte)USBOpCode.QueueRequest);

                sentBytesCount += this.m_USBConnection.BulkTransfer (this.m_BulkOut, obuffer, obuffer.Length, 100);
                if(sentBytesCount>0)
                    this.PopulateListView(obuffer,(byte)USBOpCode.BultTransferOut);
                sentBytesCount=0;
                sentBytesCount += this.m_USBConnection.BulkTransfer (this.m_BulkOut, obuffer, obuffer.Length, 100);
                if(sentBytesCount>0)
                    this.PopulateListView(obuffer,(byte)USBOpCode.BultTransferOut);
                sentBytesCount=0;
                sentBytesCount += this.m_USBConnection.BulkTransfer (this.m_BulkOut, obuffer, obuffer.Length, 100);
                if(sentBytesCount>0)
                    this.PopulateListView(obuffer,(byte)USBOpCode.BultTransferOut);

                if(this.m_USBConnection.RequestWait() == req)
                    this.PopulateListView(null,(byte)USBOpCode.RequestWait);
                if(true)//buff.Position() > 0)
                {

                    //buff.Get(ibuffer,0,12);
                    this.PopulateListView(ibuffer,(byte)USBOpCode.InterruptIn_Received);
                }
            }
            req.Close();
        }
        this.m_USBConnection.ReleaseInterface(this.m_USBInterface);
        this.PopulateListView(null,(byte)USBOpCode.ReleaseInterface);
        return;

}