I have a composite USB gadget that I want to connect to an Android phone. It contains the following serial, MTP, and mass storage interfaces:
interface :: id : 0, name : CDC Abstract Control Model (ACM), alt 0 [0002h:0002h:0001h] CDC Control
interface :: id : 1, name : CDC ACM Data, alt 0 [000ah:0000h:0000h] CDC Data
interface :: id : 2, name : MTP, alt 0 [00ffh:00ffh:0000h] Vendor Specific
interface :: id : 3, name : Mass Storage, alt 0 [0008h:0006h:0050h] Mass Storage
My problem is in attempting to open both the serial and MTP interfaces. Here is my code:
private class SetupInterfacesRunnable implements Runnable
{
@Override
public void run()
{
synchronized(MyService.this)
{
usbManager = (UsbManager) getSystemService(Context.USB_SERVICE);
usbConnection = usbManager.openDevice(usbDevice);
/*
interface :: id : 0, name : CDC Abstract Control Model (ACM), alt 0 [0002h:0002h:0001h] CDC Control
interface :: id : 1, name : CDC ACM Data, alt 0 [000ah:0000h:0000h] CDC Data
interface :: id : 2, name : MTP, alt 0 [00ffh:00ffh:0000h] Vendor Specific
interface :: id : 3, name : Mass Storage, alt 0 [0008h:0006h:0050h] Mass Storage
*/
// Interface 1 on the composite usb device is cdc acm data.
serialPort = UsbSerialDevice.createUsbSerialDevice(usbDevice, usbConnection, 1);
if(serialPort != null)
{
if(serialPort.open())
{
serialPort.setBaudRate(115200);
serialPort.setDataBits(UsbSerialInterface.DATA_BITS_8);
serialPort.setParity(UsbSerialInterface.PARITY_NONE);
serialPort.setStopBits(UsbSerialInterface.STOP_BITS_1);
serialPort.setFlowControl(UsbSerialInterface.FLOW_CONTROL_OFF);
mUIHandler.post(notifyRadgetConnected);
// set the callback to catch serial data
serialPort.read(mCallback);
mUIHandler.post(handshake);
}else
{
// Serial port could not be opened, maybe an I/O error or it CDC driver was chosen it does not really fit
LoggerV2.e("Failed to open device serial port");
}
}else
{
// No driver for given device, even generic CDC driver could not be loaded
LoggerV2.e("Failed to find driver for the serial device");
}
// Interface 2 on the composite usb device is MTP.
MtpDevice mtpDevice = new MtpDevice(usbDevice);
if (!mtpDevice.open(usbConnection)) {
LoggerV2.e("Failed to obtain device mtp storage");
}
}
}
}
The serial implementation I am using (felHR85/UsbSerial) is able to open a single interface, however, I cannot see an easy way to implement the MTPDevice class in this manner.
It seems that the Android MTP API wants an entire device/connection to open when the open function is called.
native_open(mDevice.getDeviceName(), connection.getFileDescriptor());
API docs: https://developer.android.com/reference/android/mtp/MtpDevice.html
Source Code: https://android.googlesource.com/platform/frameworks/base/+/master/media/java/android/mtp/MtpDevice.java
I cannot see a way to open only a single interface. Am I missing some trivial way of opening multiple interfaces on the same device using connections?
The short answer/workaround is to run the MTP responder on interface 0 and then open up the serial port after the MTP device.
The longer answer is... After digging through the code a bit, I found where the native_open call filters through the follow source files:
MtpDevice.cpp: https://android.googlesource.com/platform/frameworks/av/+/master/media/mtp/MtpDevice.cpp
In MtpDevice.cpp, it seems that I would fail with the "endpoints not found\n" error message printed to the log as though it could not find the correct endpoints.
For now I ended up working around this by reordering the interfaces with MTP first:
interface :: id : 0, name : MTP, alt 0 [00ffh:00ffh:0000h] Vendor Specific
interface :: id : 1, name : CDC Abstract Control Model (ACM), alt 0 [0002h:0002h:0001h] CDC Control
interface :: id : 2, name : CDC ACM Data, alt 0 [000ah:0000h:0000h] CDC Data
interface :: id : 3, name : Mass Storage, alt 0 [0008h:0006h:0050h] Mass Storage
This allows me to first open the MTP device, then open the serial by interface:
private class SetupInterfacesRunnable implements Runnable
{
@Override
public void run()
{
synchronized(RadgetService.this)
{
usbManager = (UsbManager) getSystemService(Context.USB_SERVICE);
usbConnection = usbManager.openDevice(usbDevice);
/*
interface :: id : 0, name : MTP, alt 0 [00ffh:00ffh:0000h] Vendor Specific
interface :: id : 1, name : CDC Abstract Control Model (ACM), alt 0 [0002h:0002h:0001h] CDC Control
interface :: id : 2, name : CDC ACM Data, alt 0 [000ah:0000h:0000h] CDC Data
interface :: id : 3, name : Mass Storage, alt 0 [0008h:0006h:0050h] Mass Storage
*/
// Interface 0 on the composite device is MTP
MtpDevice mtpDevice = new MtpDevice(usbDevice);
if (!mtpDevice.open(usbConnection)) {
LoggerV2.e("Failed to obtain radget mtp storage");
}
else
{
LoggerV2.i("Opened MTP storage: %s", mtpDevice.getDeviceName());
int[] storageIds = mtpDevice.getStorageIds();
if (storageIds == null) {
LoggerV2.i("No mtp storage id's found");
return;
}
/*
* scan each storage
*/
for (int storageId : storageIds) {
LoggerV2.i("~~~~Storage id: %d~~~~", storageId);
scanObjectsInStorage(mtpDevice, storageId, 0, 0);
}
}
// Interface 2 on the composite usb device is cdc acm data.
serialPort = UsbSerialDevice.createUsbSerialDevice(usbDevice, usbConnection, 2);
if(serialPort != null)
{
if(serialPort.open())
{
serialPort.setBaudRate(115200);
serialPort.setDataBits(UsbSerialInterface.DATA_BITS_8);
serialPort.setParity(UsbSerialInterface.PARITY_NONE);
serialPort.setStopBits(UsbSerialInterface.STOP_BITS_1);
serialPort.setFlowControl(UsbSerialInterface.FLOW_CONTROL_OFF);
mUIHandler.post(notifyRadgetConnected);
// set the callback to catch serial data
serialPort.read(mCallback);
mUIHandler.post(handshake);
}else
{
// Serial port could not be opened, maybe an I/O error or it CDC driver was chosen it does not really fit
LoggerV2.e("Failed to open device serial port");
}
}else
{
// No driver for given device, even generic CDC driver could not be loaded
LoggerV2.e("Failed to find driver for serial device");
}
}
}
}