Trying to read answer from CdcAcmSerialDriver on a slow command returns 0

[StanislavStamatov]

I am sending a command that typically returns answer slower than other commands. Interesting thing is that if i am in debug and i stop for 5 minutes before trying to read and then i read, the answer is returned as expected, but if i start reading in a loop immediately the answer never comes even if i wait for 10 or 15 minutes. If i put tread.sleep for 5 minutes before the read() again answer never comes. If i use SerialInputOutputManager for event-driven read again the answer never comes. I tried different baudrates but the result is the same. I downloaded the UsbSerialExample project and there the command takes some time and then return answer as expected. The expected answer is 908 bytes.

Here is the code i am using. If i send a command that returns answer faster there is no problem.
Code example.txt

` public byte[] SeekUSBDeviceAndSendCommand(boolean fiscal)
{
UsbManager manager = (UsbManager) App.currentActivity.getSystemService(Context.USB_SERVICE);

    if (manager != null) {
        HashMap<String, UsbDevice> deviceList = manager.getDeviceList();
        Iterator<UsbDevice> deviceIterator = deviceList.values().iterator();
        while (deviceIterator.hasNext()) {
            UsbDevice device = deviceIterator.next();
            if (DaisyCommunicationUSB.checkUSBDeviceVID_PID(device, fiscal))
            {
                HashMap<String, Object> params = new HashMap<String, Object>();

                params.put("id", 2);
                params.put("jsonrpc", "2.0");
                params.put("method", "ReadDayInfo");
                params.put("params", 245);

                String jsonCommand = new Gson().toJson(params);
                
                UsbSerialDriver driver = UsbSerialProber.getDefaultProber().probeDevice(device);
                UsbSerialPort port = driver.getPorts().get(0); // Most devices have just one port (port 0)
                UsbDeviceConnection connection = manager.openDevice(driver.getDevice());

                if (connection == null && !manager.hasPermission(device)) {
                    int flags = Build.VERSION.SDK_INT >= Build.VERSION_CODES.M ? PendingIntent.FLAG_MUTABLE : 0;
                    Intent intent = new Intent(BuildConfig.APPLICATION_ID + ".GRANT_USB");
                    intent.setPackage(App.currentActivity.getPackageName());
                    PendingIntent usbPermissionIntent = PendingIntent.getBroadcast(App.currentActivity, 0, intent, flags);
                    manager.requestPermission(driver.getDevice(), usbPermissionIntent);
                }

	    byte[] readBuffer = new byte[8192];

                try {
                    port.open(connection);
                    port.setParameters(19200, UsbSerialPort.DATABITS_8, UsbSerialPort.STOPBITS_1, UsbSerialPort.PARITY_NONE);

                    //SerialInputOutputManager usbIoManager = new SerialInputOutputManager(port, this);
                    //usbIoManager.start(); // todo with ioManager with event driven read

                    port.write(jsonCommand.getBytes(), 2000);

                    int len = -1;

                    while (len <= 0) {
                        len = port.read(readBuffer, 2000);

                        if (len <= 0) {
                            try {
                                Thread.sleep(500);
                            } catch (InterruptedException e) {
                                throw new RuntimeException(e);
                            }
                        }
                    }

                    } catch (IOException e) {
                          throw new RuntimeException(e);
                    }

                return readBuffer;
            }
        }
    }

return null;
} `