Arduino <-> Android, USB Serial, Extrem langsam!

package de.shavenne.android.youcanlisten;

import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.hardware.usb.UsbDevice;
import android.hardware.usb.UsbDeviceConnection;
import android.hardware.usb.UsbManager;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.ImageButton;
import android.widget.TextView;

import com.hoho.android.usbserial.driver.UsbSerialDriver;
import com.hoho.android.usbserial.driver.UsbSerialPort;
import com.hoho.android.usbserial.driver.UsbSerialProber;

import java.io.IOException;
import java.util.List;


public class MainActivity extends ActionBarActivity {
    private PendingIntent PendingIntent_UsbPermission;
    private static int RQS_USB_PERMISSION = 0;
    private final String ACTION_USB_PERMISSION = "de.shavenne.android.youcanlisten";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        final UsbManager manager = (UsbManager) getSystemService(Context.USB_SERVICE);



        List<UsbSerialDriver> availableDrivers = UsbSerialProber.getDefaultProber().findAllDrivers(manager);

        ImageButton buttonUp = (ImageButton) findViewById(R.id.upButton);
        ImageButton buttonDown = (ImageButton) findViewById(R.id.downButton);

        if (!availableDrivers.isEmpty()) {
            UsbSerialDriver driver = availableDrivers.get(0);
            Intent intent_UsbPermission = new Intent(ACTION_USB_PERMISSION);
            PendingIntent_UsbPermission = PendingIntent.getBroadcast(
                    this,      //context
                    RQS_USB_PERMISSION,  //request code
                    intent_UsbPermission, //intent
                    0);      //flags
            IntentFilter intentFilter_UsbPermission = new IntentFilter(ACTION_USB_PERMISSION);

            UsbDevice device = driver.getDevice();
            TextView textView = (TextView) findViewById(R.id.textView);

            String text = device.getDeviceName();
            manager.requestPermission(device, PendingIntent_UsbPermission);

            if(manager.hasPermission(device)) {
                text += " has permission";
            }
            textView.setText(text);


            final UsbDeviceConnection connection = manager.openDevice(device);
            final List<UsbSerialPort> mEntries = driver.getPorts();
            final UsbSerialPort port = mEntries.get(0);
            try {
                port.open(connection);
                port.setParameters(9600, 8, 1, 0);
                buttonUp.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        try {
                            port.write("ToCAN_UP\n".getBytes(), 500);
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                });

                buttonDown.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        try {
                            port.write("ToCAN_DOWN\n".getBytes(), 500);
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                });
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

deineFunktion(){
long start = System.currentTimeMillis();

// ...

Log.d("KlasseXY", "Funktion ausgeführt nach " + (System.currentTimeMillis() - start) + "ms");

}

KlasseXY implements View.OnClickListener