USB Communication, Endpoints in Monodroid/Android

1
votes

I have a USB device that I'm attempting to communicate to with my Android 4.1 device using the MonoDroid API, and I've run into some issues setting up a proper connection. First, the steps taken to arrive at what I "think" may be an issue:

  1. Filter my device by vendor and product ID with an intent filter in my AndroidManifest file. This works well, as when I plug in my device my app requests to launch by default, so permissions should correct.
  2. Grab my USB device from an Activity that my intent filter sends the program after discovering said device: UsbDevice device = (UsbDevice)this.Intent.GetParcelableExtra(UsbManager.ExtraDevice);
  3. After checking that there is only one interface present, I grab the associated interface by issuing: UsbInterface intf = device.GetInterface(0);
  4. Check the number of endpoints and grab them. There's 2, as this is an input and output device: UsbEndpoint endpoint_IN = intf.GetEndpoint(0); UsbEndpoint endpoint_OUT = intf.GetEndpoint(1);
  5. Grab a connection to the device using the UsbManager: UsbDeviceConnection connection = device_manager.OpenDevice(device);

However, and I noticed that the endpoint at index 0 of the interface (endpoint_IN above) has UsbAddressing enumeration type "DirMask", where endpoint_OUT has type "Out"; I'd expect endpoint_IN to be "In", which is not the case. What is "DirMask?" The inline documentation states "Documentation for this section has not yet been entered", and the online docs reflect the same: http://api.xamarin.com/?link=T%3aAndroid.Hardware.Usb.UsbAddressing

Could this be my issue? I'm just not really sure. I tried to implement the rest of the communication procedure, but haven't been able to yield any results. For example, the following code should input a command to receive one reading:

Byte[] sys_command = Encoding.ASCII.GetBytes("!001:SYS?\r");
Java.Nio.ByteBuffer sys_command_buffer = Java.Nio.ByteBuffer.Wrap(sys_command);

Java.Nio.ByteBuffer output_buffer = Java.Nio.ByteBuffer.Allocate(4);

UsbRequest request_out = new UsbRequest();
request_out.Initialize(connection, endpoint_OUT);

connection.ClaimInterface(intf, forceClaim);

request_out.Queue(output_buffer, 4);
connection.BulkTransfer(endpoint_IN, sys_command, sys_command.Length, TIMEOUT);

if (connection.RequestWait() == request_out)
    readings.Text = output_buffer.GetFloat(0).ToString();

Any insight?

2
javaandroidusbxamarin.android

2 Answers

0
votes

I had the interface endpoints backwards, all things considered. That is, I was attempting to read/write to the wrong interface.

0
votes

In case anyone else stumbles on this, the DirMask type means look at the Direction attribute of the endpoint instead of the Type attribute. If the Type is DirMask, the Direction could be UsbAddressing.In or Out.

And the Direction of In is the out endpoint, and vice versa (which I'm guessing is why you had them backwards).