diff --git a/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/CrossoverTest.java b/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/CrossoverTest.java
index 89e2018..07b2f9c 100644
--- a/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/CrossoverTest.java
+++ b/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/CrossoverTest.java
@@ -14,6 +14,7 @@ import android.util.Log;
 import com.hoho.android.usbserial.driver.UsbSerialDriver;
 import com.hoho.android.usbserial.driver.UsbSerialPort;
 import com.hoho.android.usbserial.driver.UsbSerialProber;
+import com.hoho.android.usbserial.util.TestBuffer;
 import com.hoho.android.usbserial.util.UsbWrapper;
 
 import org.junit.Before;
@@ -24,12 +25,14 @@ import org.junit.rules.TestWatcher;
 import org.junit.runner.Description;
 import org.junit.runner.RunWith;
 
+import java.io.IOException;
 import java.util.EnumSet;
 import java.util.List;
 
 import static org.hamcrest.CoreMatchers.equalTo;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertThat;
 import static org.junit.Assert.fail;
 import static org.junit.Assume.assumeTrue;
@@ -160,4 +163,53 @@ public class CrossoverTest {
         usb2.close();
     }
 
+    @Test
+    public void concurrent() throws Exception {
+        // 115200 baud ~= 11kB/sec => ~1.5 second test duration with 16kB tbuf
+        // concurrent (+ blocking) write calls as tbuf larger than any buffer size returned by UsbWrapper.getWriteSizes()
+        // concurrent read calls in IoManager threads
+        TestBuffer tbuf1 = new TestBuffer(16*1024);
+        TestBuffer tbuf2 = new TestBuffer(16*1024);
+
+        class WriteRunnable implements Runnable {
+            public WriteRunnable(int port) { this.port = port; }
+            private final int port;
+            Exception exc;
+            @Override
+            public void run() {
+                byte[] buf = new byte[1024];
+                try {
+                    for(int i=0; i<tbuf1.buf.length / 1024; i++) {
+                        System.arraycopy(tbuf1.buf, i*1024, buf, 0, 1024);
+                        if (port == 1)
+                            usb1.write(buf);
+                        else
+                            usb2.write(buf);
+                    }
+                } catch (IOException exc) {
+                    this.exc = exc;
+                }
+            }
+        }
+
+        usb1.open();
+        usb2.open();
+        usb1.setParameters(115200, 8, 1, UsbSerialPort.PARITY_NONE);
+        usb2.setParameters(115200, 8, 1, UsbSerialPort.PARITY_NONE);
+        WriteRunnable wr1 = new WriteRunnable(1), wr2 = new WriteRunnable(2);
+        Thread wt1 = new Thread(wr1), wt2 = new Thread(wr2);
+        boolean done1 = false, done2 = false;
+        wt1.start();
+        Thread.sleep(50);
+        wt2.start();
+        while(!done1 && !done2) {
+            if(!done1)
+                done1 = tbuf1.testRead(usb1.read(-1));
+            if(!done2)
+                done2 = tbuf2.testRead(usb2.read(-1));
+        }
+        wt1.join(); wt2.join();
+        assertNull(wr1.exc);
+        assertNull(wr2.exc);
+    }
 }
diff --git a/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/DeviceTest.java b/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/DeviceTest.java
index e55584e..19db649 100644
--- a/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/DeviceTest.java
+++ b/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/DeviceTest.java
@@ -34,6 +34,7 @@ import com.hoho.android.usbserial.driver.UsbSerialPort;
 import com.hoho.android.usbserial.driver.UsbSerialProber;
 import com.hoho.android.usbserial.util.SerialInputOutputManager;
 import com.hoho.android.usbserial.util.TelnetWrapper;
+import com.hoho.android.usbserial.util.TestBuffer;
 import com.hoho.android.usbserial.util.UsbWrapper;
 
 import org.junit.After;
@@ -145,34 +146,6 @@ public class DeviceTest {
         telnet.tearDownFixture();
     }
 
-    private static class TestBuffer {
-        private final byte[] buf;
-        private int len;
-
-        private TestBuffer(int length) {
-            len = 0;
-            buf = new byte[length];
-            int i=0;
-            int j=0;
-            for(j=0; j<length/16; j++)
-                for(int k=0; k<16; k++)
-                    buf[i++]=(byte)j;
-            while(i<length)
-                buf[i++]=(byte)j;
-        }
-
-        private boolean testRead(byte[] data) {
-            assertNotEquals(0, data.length);
-            assertTrue("got " + (len+data.length) +" bytes", (len+data.length) <= buf.length);
-            for(int j=0; j<data.length; j++)
-                assertEquals("at pos "+(len+j), (byte)((len+j)/16), data[j]);
-            len += data.length;
-            //Log.d(TAG, "read " + len);
-            return len == buf.length;
-        }
-    }
-
-
     // clone of org.apache.commons.lang3.StringUtils.indexOfDifference + optional startpos
     private static int indexOfDifference(final CharSequence cs1, final CharSequence cs2) {
         return indexOfDifference(cs1, cs2, 0, 0);
@@ -816,30 +789,6 @@ public class DeviceTest {
         assertEquals(availableDrivers.get(0).getClass(), usb.serialDriver.getClass());
     }
 
-    // return [write packet size, write buffer size(s)]
-    private int[] getWriteSizes() {
-        if (usb.serialDriver instanceof Cp21xxSerialDriver) {
-            if (usb.serialDriver.getPorts().size() == 1) return new int[]{64, 576};
-            else if (usb.serialPort.getPortNumber() == 0) return new int[]{64, 320};
-            else return new int[]{32, 128, 160}; // write buffer size detection is unreliable
-        } else if (usb.serialDriver instanceof Ch34xSerialDriver) {
-            return new int[]{32, 64};
-        } else if (usb.serialDriver instanceof ProlificSerialDriver) {
-            return new int[]{64, 256};
-        } else if (usb.serialDriver instanceof FtdiSerialDriver) {
-            switch (usb.serialDriver.getPorts().size()) {
-                case 1: return new int[]{64, 128};
-                case 2: return new int[]{512, 4096};
-                case 4: return new int[]{512, 2048};
-                default: return null;
-            }
-        } else if (usb.serialDriver instanceof CdcAcmSerialDriver) {
-            return new int[]{64, 128};
-        } else {
-            return null;
-        }
-    }
-
     @Test
     public void writeTimeout() throws Exception {
         usb.open();
@@ -866,7 +815,7 @@ public class DeviceTest {
 
         int writeBufferSize = writePacketSize * writePackets;
         Log.d(TAG, "write packet size = " + writePacketSize + ", write buffer size = " + writeBufferSize);
-        int[] writeSizes = getWriteSizes();
+        int[] writeSizes = usb.getWriteSizes();
         assertNotNull(writeSizes);
         assertEquals("write packet size", writeSizes[0], writePacketSize);
         assertTrue("write buffer size", Arrays.binarySearch(writeSizes, writeBufferSize) > 0);
@@ -967,7 +916,7 @@ public class DeviceTest {
         if(usb.serialDriver instanceof Cp21xxSerialDriver && usb.serialDriver.getPorts().size() == 1)
             purge = false; // purge is blocking
 
-        int[] writeSizes = getWriteSizes();
+        int[] writeSizes = usb.getWriteSizes();
         int writePacketSize = writeSizes[0];
         int writeBufferSize = writeSizes[1];
         int purgeTimeout = 250;
diff --git a/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/util/TestBuffer.java b/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/util/TestBuffer.java
new file mode 100644
index 0000000..95bca8b
--- /dev/null
+++ b/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/util/TestBuffer.java
@@ -0,0 +1,32 @@
+package com.hoho.android.usbserial.util;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertTrue;
+
+public class TestBuffer {
+    public final byte[] buf;
+    public int len;
+
+    public TestBuffer(int length) {
+        len = 0;
+        buf = new byte[length];
+        int i = 0;
+        int j = 0;
+        for (j = 0; j < length / 16; j++)
+            for (int k = 0; k < 16; k++)
+                buf[i++] = (byte) j;
+        while (i < length)
+            buf[i++] = (byte) j;
+    }
+
+    public boolean testRead(byte[] data) {
+        assertNotEquals(0, data.length);
+        assertTrue("got " + (len + data.length) + " bytes", (len + data.length) <= buf.length);
+        for (int j = 0; j < data.length; j++)
+            assertEquals("at pos " + (len + j), (byte) ((len + j) / 16), data[j]);
+        len += data.length;
+        //Log.d(TAG, "read " + len);
+        return len == buf.length;
+    }
+}
diff --git a/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/util/UsbWrapper.java b/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/util/UsbWrapper.java
index 5bf114d..3eab1ec 100644
--- a/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/util/UsbWrapper.java
+++ b/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/util/UsbWrapper.java
@@ -12,7 +12,11 @@ import android.net.Uri;
 import android.util.Log;
 
 import com.hoho.android.usbserial.driver.CdcAcmSerialDriver;
+import com.hoho.android.usbserial.driver.Ch34xSerialDriver;
 import com.hoho.android.usbserial.driver.CommonUsbSerialPort;
+import com.hoho.android.usbserial.driver.Cp21xxSerialDriver;
+import com.hoho.android.usbserial.driver.FtdiSerialDriver;
+import com.hoho.android.usbserial.driver.ProlificSerialDriver;
 import com.hoho.android.usbserial.driver.UsbSerialDriver;
 import com.hoho.android.usbserial.driver.UsbSerialPort;
 
@@ -246,15 +250,40 @@ public class UsbWrapper implements SerialInputOutputManager.Listener {
         }
     }
 
+    // return [write packet size, write buffer size(s)]
+    public int[] getWriteSizes() {
+        if (serialDriver instanceof Cp21xxSerialDriver) {
+            if (serialDriver.getPorts().size() == 1) return new int[]{64, 576};
+            else if (serialPort.getPortNumber() == 0) return new int[]{64, 320};
+            else return new int[]{32, 128, 160}; // write buffer size detection is unreliable
+        } else if (serialDriver instanceof Ch34xSerialDriver) {
+            return new int[]{32, 64};
+        } else if (serialDriver instanceof ProlificSerialDriver) {
+            return new int[]{64, 256};
+        } else if (serialDriver instanceof FtdiSerialDriver) {
+            switch (serialDriver.getPorts().size()) {
+                case 1: return new int[]{64, 128};
+                case 2: return new int[]{512, 4096};
+                case 4: return new int[]{512, 2048};
+                default: return null;
+            }
+        } else if (serialDriver instanceof CdcAcmSerialDriver) {
+            return new int[]{64, 128};
+        } else {
+            return null;
+        }
+    }
+
+
     @Override
     public void onNewData(byte[] data) {
         long now = System.currentTimeMillis();
         if(readTime == 0)
             readTime = now;
         if(data.length > 64) {
-            Log.d(TAG, "usb read: time+=" + String.format("%-3d",now- readTime) + " len=" + String.format("%-4d",data.length) + " data=" + new String(data, 0, 32) + "..." + new String(data, data.length-32, 32));
+            Log.d(TAG, "usb " + devicePort + " read: time+=" + String.format("%-3d",now- readTime) + " len=" + String.format("%-4d",data.length) + " data=" + new String(data, 0, 32) + "..." + new String(data, data.length-32, 32));
         } else {
-            Log.d(TAG, "usb read: time+=" + String.format("%-3d",now- readTime) + " len=" + String.format("%-4d",data.length) + " data=" + new String(data));
+            Log.d(TAG, "usb " + devicePort + " read: time+=" + String.format("%-3d",now- readTime) + " len=" + String.format("%-4d",data.length) + " data=" + new String(data));
         }
         readTime = now;