target sdk 35

Used separate threads for reading and writing, enhancing concurrency and performance.

Note: before was possible to start `SerialInputOutputManager` with `Executors.newSingleThreadExecutor().submit(ioManager)`. Now you have to use `ioManager.start()`

.idea/AndroidProjectSystem.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="AndroidProjectSystem">
+    <option name="providerId" value="com.android.tools.idea.GradleProjectSystem" />
+  </component>
+</project>

.idea/compiler.xml

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
   <component name="CompilerConfiguration">
-    <bytecodeTargetLevel target="17" />
+    <bytecodeTargetLevel target="21" />
   </component>
 </project>

.idea/misc.xml

@@ -1,3 +1,4 @@
+<?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
   <component name="ExternalStorageConfigurationManager" enabled="true" />
   <component name="NullableNotNullManager">
@@ -5,7 +6,7 @@
     <option name="myDefaultNotNull" value="androidx.annotation.NonNull" />
     <option name="myNullables">
       <value>
-        <list size="17">
+        <list size="18">
           <item index="0" class="java.lang.String" itemvalue="org.jetbrains.annotations.Nullable" />
           <item index="1" class="java.lang.String" itemvalue="javax.annotation.Nullable" />
           <item index="2" class="java.lang.String" itemvalue="javax.annotation.CheckForNull" />
@@ -23,12 +24,13 @@
           <item index="14" class="java.lang.String" itemvalue="io.reactivex.rxjava3.annotations.Nullable" />
           <item index="15" class="java.lang.String" itemvalue="org.jspecify.nullness.Nullable" />
           <item index="16" class="java.lang.String" itemvalue="jakarta.annotation.Nullable" />
+          <item index="17" class="java.lang.String" itemvalue="org.jspecify.annotations.Nullable" />
         </list>
       </value>
     </option>
     <option name="myNotNulls">
       <value>
-        <list size="16">
+        <list size="17">
           <item index="0" class="java.lang.String" itemvalue="org.jetbrains.annotations.NotNull" />
           <item index="1" class="java.lang.String" itemvalue="javax.annotation.Nonnull" />
           <item index="2" class="java.lang.String" itemvalue="edu.umd.cs.findbugs.annotations.NonNull" />
@@ -45,11 +47,12 @@
           <item index="13" class="java.lang.String" itemvalue="io.reactivex.rxjava3.annotations.NonNull" />
           <item index="14" class="java.lang.String" itemvalue="jakarta.annotation.Nonnull" />
           <item index="15" class="java.lang.String" itemvalue="org.jspecify.nullness.NonNull" />
+          <item index="16" class="java.lang.String" itemvalue="org.jspecify.annotations.NonNull" />
         </list>
       </value>
     </option>
   </component>
-  <component name="ProjectRootManager" version="2" languageLevel="JDK_17" default="true" project-jdk-name="jbr-17" project-jdk-type="JavaSDK">
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_21" default="true" project-jdk-name="jbr-21" project-jdk-type="JavaSDK">
     <output url="file://$PROJECT_DIR$/build/classes" />
   </component>
   <component name="ProjectType">

.idea/runConfigurations.xml

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="RunConfigurationProducerService">
+    <option name="ignoredProducers">
+      <set>
+        <option value="com.intellij.execution.junit.AbstractAllInDirectoryConfigurationProducer" />
+        <option value="com.intellij.execution.junit.AllInPackageConfigurationProducer" />
+        <option value="com.intellij.execution.junit.PatternConfigurationProducer" />
+        <option value="com.intellij.execution.junit.TestInClassConfigurationProducer" />
+        <option value="com.intellij.execution.junit.UniqueIdConfigurationProducer" />
+        <option value="com.intellij.execution.junit.testDiscovery.JUnitTestDiscoveryConfigurationProducer" />
+        <option value="org.jetbrains.kotlin.idea.junit.KotlinJUnitRunConfigurationProducer" />
+        <option value="org.jetbrains.kotlin.idea.junit.KotlinPatternConfigurationProducer" />
+      </set>
+    </option>
+  </component>
+</project>

README.md

@@ -45,7 +45,7 @@ If using gradle kotlin  use line
 Add library to dependencies
 ```gradle
 dependencies {
-    implementation 'com.github.mik3y:usb-serial-for-android:3.8.0'
+    implementation 'com.github.mik3y:usb-serial-for-android:3.9.0'
 }
 ```
 
@@ -145,8 +145,8 @@ UsbSerialProber prober = new UsbSerialProber(customTable);
 List<UsbSerialDriver> drivers = prober.findAllDrivers(usbManager);
 // ...
 ```
-*Note*: as of v3.5.0 this library detects CDC devices by USB interface types instead of fixed VID+PID,
+*Note*: as of v3.5.0 this library detects CDC/ACM devices by USB interface types instead of fixed VID+PID,
-so custom probers are typically not required any more for CDC devices.
+so custom probers are typically not required any more for CDC/ACM devices.
 
 Of course, nothing requires you to use UsbSerialProber at all: you can
 instantiate driver classes directly if you know what you're doing; just supply
@@ -154,22 +154,23 @@ a compatible UsbDevice.
 
 ## Compatible Devices
 
-This library supports USB to serial converter chips:
+This library supports USB to serial converter chips with specific drivers
 * FTDI FT232R, FT232H, FT2232H, FT4232H, FT230X, FT231X, FT234XD
 * Prolific PL2303
 * Silabs CP2102, CP210*
-* Qinheng CH340, CH341A, CH9102
+* Qinheng CH340, CH341A
 
-devices implementing the CDC/ACM protocol like
+some other device specific drivers
-* Arduino using ATmega32U4
-* Digispark using V-USB software USB
-* BBC micro:bit using ARM mbed DAPLink firmware
-* ...
-
-and some device specific drivers:
 * GsmModem devices, e.g. for Unisoc based Fibocom GSM modems
 * Chrome OS CCD (Closed Case Debugging)
 
+and devices implementing the generic CDC/ACM protocol like
+* Qinheng CH9102
+* Microchip MCP2221
+* Arduino using ATmega32U4
+* Digispark using V-USB software USB
+* ...
+
 ## Help & Discussion
 
 For common problems, see the [FAQ](https://github.com/mik3y/usb-serial-for-android/wiki/FAQ) wiki page.

build.gradle

@@ -6,7 +6,7 @@ buildscript {
         google()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:8.4.0'
+        classpath 'com.android.tools.build:gradle:8.9.1'
     }
 }
 

gradle/wrapper/gradle-wrapper.properties

@@ -3,4 +3,4 @@ distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-8.6-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.11.1-all.zip

usbSerialExamples/build.gradle

@@ -3,7 +3,7 @@ plugins {
 }
 
 android {
-    compileSdkVersion 34
+    compileSdkVersion 35
 
     compileOptions {
         sourceCompatibility JavaVersion.VERSION_1_8
@@ -12,7 +12,7 @@ android {
 
     defaultConfig {
         minSdkVersion 17
-        targetSdkVersion 34
+        targetSdkVersion 35
         vectorDrawables.useSupportLibrary = true
 
         missingDimensionStrategy 'device', 'anyDevice'
@@ -28,6 +28,6 @@ android {
 
 dependencies {
     implementation project(':usbSerialForAndroid')
-    implementation 'androidx.appcompat:appcompat:1.6.1'
+    implementation 'androidx.appcompat:appcompat:1.6.1' // later versions have minsdk 21
-    implementation 'com.google.android.material:material:1.11.0'
+    implementation 'com.google.android.material:material:1.11.0' // later versions have minsdk 19
 }

usbSerialExamples/src/main/java/com/hoho/android/usbserial/examples/TerminalFragment.java

@@ -214,7 +214,7 @@ public class TerminalFragment extends Fragment implements SerialInputOutputManag
             status("connection failed: no driver for device");
             return;
         }
-        if(driver.getPorts().size() < portNum) {
+        if(portNum >= driver.getPorts().size()) {
             status("connection failed: not enough ports at device");
             return;
         }

usbSerialForAndroid/build.gradle

@@ -4,11 +4,11 @@ plugins {
 }
 
 android {
-    compileSdkVersion 34
+    compileSdkVersion 35
 
     defaultConfig {
         minSdkVersion 17
-        targetSdkVersion 34
+        targetSdkVersion 35
         consumerProguardFiles 'proguard-rules.pro'
         
         testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
@@ -31,12 +31,13 @@ android {
 }
 
 dependencies {
-    implementation "androidx.annotation:annotation:1.8.0"
+    implementation "androidx.annotation:annotation:1.9.1"
     testImplementation 'junit:junit:4.13.2'
-    testImplementation 'org.mockito:mockito-core:5.12.0'
+    testImplementation 'org.mockito:mockito-core:5.15.2'
-    androidTestImplementation 'androidx.test:core:1.5.0'
+    androidTestImplementation 'androidx.appcompat:appcompat:1.6.1' // later versions have minsdk 21
-    androidTestImplementation 'androidx.test:runner:1.5.2'
+    androidTestImplementation 'androidx.test:core:1.5.0' // later versions have minsdk 19
-    androidTestImplementation 'commons-net:commons-net:3.10.0'
+    androidTestImplementation 'androidx.test:runner:1.5.2' // later versions have minsdk 19
+    androidTestImplementation 'commons-net:commons-net:3.9.0' // later versions fail on old Android devices with missing java.time.Duration class
     androidTestImplementation 'org.apache.commons:commons-lang3:3.14.0'
 }
 

usbSerialForAndroid/coverage.gradle

@@ -8,7 +8,7 @@ android {
             // Used as fallback in usbSerialExample/build.gradle -> missingDimensionStrategy, but not for coverage report
             dimension 'device'
         }
-        arduino {
+        mcp2221 {
             dimension 'device'
             testInstrumentationRunnerArguments = ['test_device_driver': 'CdcAcm']
         }

usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/DeviceTest.java

@@ -645,7 +645,13 @@ public class DeviceTest {
             Thread.sleep(10);
             usb.write(new byte[]{(byte) 0xff});
             data = telnet.read(2);
-            assertThat("19000/7N1", data, equalTo(new byte[]{(byte) 0x80, (byte) 0xff}));
+            if(usb.serialDriver instanceof CdcAcmSerialDriver) {
+                // not supported by MCP2221, other CDC devices might support it
+                assertThat("19000/7N1", data, equalTo(new byte[]{(byte) 0x00, (byte) 0xff}));
+                return;
+            } else {
+                assertThat("19000/7N1", data, equalTo(new byte[]{(byte) 0x80, (byte) 0xff}));
+            }
         } catch (UnsupportedOperationException e) {
                 if(!usb.isCp21xxRestrictedPort)
                     throw e;
@@ -718,18 +724,17 @@ public class DeviceTest {
         usb.setParameters(19200, 7, 1, UsbSerialPort.PARITY_ODD);
         usb.write(_8n1);
         data = telnet.read(4);
-        assertThat("19200/7O1", data, equalTo(_7o1));
-
-        usb.setParameters(19200, 7, 1, UsbSerialPort.PARITY_EVEN);
-        usb.write(_8n1);
-        data = telnet.read(4);
-        assertThat("19200/7E1", data, equalTo(_7e1));
-
         if (usb.serialDriver instanceof CdcAcmSerialDriver) {
-            // not supported by arduino_leonardo_bridge.ino, other devices might support it
+            // not supported by MCP2221, other CDC devices might support it
-            usb.setParameters(19200, 7, 1, UsbSerialPort.PARITY_MARK);
+            assertThat("19200/8N1", data, equalTo(_8n1));
-            usb.setParameters(19200, 7, 1, UsbSerialPort.PARITY_SPACE);
         } else {
+            assertThat("19200/7O1", data, equalTo(_7o1));
+
+            usb.setParameters(19200, 7, 1, UsbSerialPort.PARITY_EVEN);
+            usb.write(_8n1);
+            data = telnet.read(4);
+            assertThat("19200/7E1", data, equalTo(_7e1));
+
             usb.setParameters(19200, 7, 1, UsbSerialPort.PARITY_MARK);
             usb.write(_8n1);
             data = telnet.read(4);
@@ -758,19 +763,19 @@ public class DeviceTest {
         data = usb.read(4);
         assertThat("19200/7E1", data, equalTo(_7e1));
 
+        telnet.setParameters(19200, 7, 1, UsbSerialPort.PARITY_MARK);
+        telnet.write(_8n1);
+        data = usb.read(4);
+        assertThat("19200/7M1", data, equalTo(_7m1));
+
+        telnet.setParameters(19200, 7, 1, UsbSerialPort.PARITY_SPACE);
+        telnet.write(_8n1);
+        data = usb.read(4);
+        assertThat("19200/7S1", data, equalTo(_7s1));
+
         if (usb.serialDriver instanceof CdcAcmSerialDriver) {
-            // not supported by arduino_leonardo_bridge.ino, other devices might support it
+            ; // not supported by MCP2221, other CDC devices might support it
         } else {
-            telnet.setParameters(19200, 7, 1, UsbSerialPort.PARITY_MARK);
-            telnet.write(_8n1);
-            data = usb.read(4);
-            assertThat("19200/7M1", data, equalTo(_7m1));
-
-            telnet.setParameters(19200, 7, 1, UsbSerialPort.PARITY_SPACE);
-            telnet.write(_8n1);
-            data = usb.read(4);
-            assertThat("19200/7S1", data, equalTo(_7s1));
-
             usb.setParameters(19200, 7, 1, UsbSerialPort.PARITY_ODD);
             telnet.setParameters(19200, 8, 1, UsbSerialPort.PARITY_NONE);
             telnet.write(_8n1);
@@ -792,45 +797,44 @@ public class DeviceTest {
             }
         }
 
-        if (usb.serialDriver instanceof CdcAcmSerialDriver) {
+        // shift stopbits into next byte, by using different databits
-            usb.setParameters(19200, 8, UsbSerialPort.STOPBITS_1_5, UsbSerialPort.PARITY_NONE);
+        // a - start bit (0)
-            // software based bridge in arduino_leonardo_bridge.ino is to slow for real test, other devices might support it
+        // o - stop bit  (1)
-        } else {
+        // d - data bit
-            // shift stopbits into next byte, by using different databits
-            // a - start bit (0)
-            // o - stop bit  (1)
-            // d - data bit
 
-            // out 8N2:   addddddd doaddddddddo
+        // out 8N2:   addddddd doaddddddddo
-            //             1000001 0  10001111
+        //             1000001 0  10001111
-            // in 6N1:    addddddo addddddo
+        // in 6N1:    addddddo addddddo
-            //             100000   101000
+        //             100000   101000
-            usb.setParameters(19200, 8, UsbSerialPort.STOPBITS_1, UsbSerialPort.PARITY_NONE);
+        usb.setParameters(19200, 8, UsbSerialPort.STOPBITS_1, UsbSerialPort.PARITY_NONE);
-            telnet.setParameters(19200, 6, 1, UsbSerialPort.PARITY_NONE);
+        telnet.setParameters(19200, 6, 1, UsbSerialPort.PARITY_NONE);
-            usb.write(new byte[]{(byte)0x41, (byte)0xf1});
+        usb.write(new byte[]{(byte)0x41, (byte)0xf1});
-            data = telnet.read(2);
+        data = telnet.read(2);
+        if (usb.serialDriver instanceof CdcAcmSerialDriver) {
+            // MCP2221 slightly slower, looks like 2 stop bits. could be different for other CDC devices
+            assertThat("19200/8N1", data, equalTo(new byte[]{1, 11}));
+        } else
             assertThat("19200/8N1", data, equalTo(new byte[]{1, 5}));
 
-            // out 8N2:   addddddd dooaddddddddoo
+        // out 8N2:   addddddd dooaddddddddoo
-            //             1000001 0   10011111
+        //             1000001 0   10011111
-            // in 6N1:    addddddo addddddo
+        // in 6N1:    addddddo addddddo
-            //             100000   110100
+        //             100000   110100
-            try {
+        try {
-                usb.setParameters(19200, 8, UsbSerialPort.STOPBITS_2, UsbSerialPort.PARITY_NONE);
+            usb.setParameters(19200, 8, UsbSerialPort.STOPBITS_2, UsbSerialPort.PARITY_NONE);
-                telnet.setParameters(19200, 6, 1, UsbSerialPort.PARITY_NONE);
+            telnet.setParameters(19200, 6, 1, UsbSerialPort.PARITY_NONE);
-                usb.write(new byte[]{(byte) 0x41, (byte) 0xf9});
+            usb.write(new byte[]{(byte) 0x41, (byte) 0xf9});
-                data = telnet.read(2);
+            data = telnet.read(2);
-                assertThat("19200/8N1", data, equalTo(new byte[]{1, 11}));
+            assertThat("19200/8N1", data, equalTo(new byte[]{1, 11}));
-            } catch(UnsupportedOperationException e) {
+        } catch(UnsupportedOperationException e) {
-                if(!usb.isCp21xxRestrictedPort)
+            if(!usb.isCp21xxRestrictedPort)
-                    throw e;
+                throw e;
-            }
+        }
-            try {
+        try {
-                usb.setParameters(19200, 8, UsbSerialPort.STOPBITS_1_5, UsbSerialPort.PARITY_NONE);
+            usb.setParameters(19200, 8, UsbSerialPort.STOPBITS_1_5, UsbSerialPort.PARITY_NONE);
-                // todo: could create similar test for 1.5 stopbits, by reading at double speed
+            // todo: could create similar test for 1.5 stopbits, by reading at double speed
-                //       but only some devices support 1.5 stopbits and it is basically not used any more
+            //       but only some devices support 1.5 stopbits and it is basically not used any more
-            } catch(UnsupportedOperationException ignored) {
+        } catch(UnsupportedOperationException ignored) {
-            }
         }
     }
 
@@ -883,8 +887,6 @@ public class DeviceTest {
         usb.setParameters(baudRate, 8, 1, UsbSerialPort.PARITY_NONE);
         telnet.setParameters(baudRate, 8, 1, UsbSerialPort.PARITY_NONE);
         int purgeTimeout = 250;
-        if(usb.serialDriver instanceof CdcAcmSerialDriver)
-            purgeTimeout = 500;
         purgeWriteBuffer(purgeTimeout);
 
         // determine write buffer size
@@ -1055,18 +1057,17 @@ public class DeviceTest {
 
     @Test
     public void readBufferSize() throws Exception {
-        // looks like devices perform USB read with full mReadEndpoint.getMaxPacketSize() size (32, 64, 512)
+        // looks like devices perform USB read with full mReadEndpoint.getMaxPacketSize() size (16, 32, 64, 512)
         // if the buffer is smaller than the received result, it is silently lost
         //
         // for buffer > packet size, but not multiple of packet size, the same issue happens, but typically
         // only the last (partly filled) packet is lost.
-        if(usb.serialDriver instanceof CdcAcmSerialDriver)
-            return; // arduino sends each byte individually, so not testable here
         byte[] data;
         boolean purge = true;
 
         usb.open(EnumSet.of(UsbWrapper.OpenCloseFlags.NO_IOMANAGER_START));
-        usb.ioManager.setReadBufferSize(8);
+        int len = Math.min(16, usb.serialPort.getReadEndpoint().getMaxPacketSize()/2); // 8 for MCP2221, else 16
+        usb.ioManager.setReadBufferSize(len/2);
         usb.ioManager.start();
         usb.setParameters(115200, 8, 1, UsbSerialPort.PARITY_NONE);
         telnet.setParameters(115200, 8, 1, UsbSerialPort.PARITY_NONE);
@@ -1075,13 +1076,15 @@ public class DeviceTest {
         telnet.write("1aaa".getBytes());
         data = usb.read(4);
         assertThat(data, equalTo("1aaa".getBytes()));
-        telnet.write(new byte[16]);
+
+        telnet.write(new byte[len]);
         try {
-            data = usb.read(16);
+            data = usb.read(len);
             if (usb.serialDriver instanceof Cp21xxSerialDriver && usb.serialDriver.getPorts().size() == 1)
                 assertNotEquals(0, data.length); // can be shorter or full length
-            else if (usb.serialDriver instanceof ProlificSerialDriver)
+            else if (usb.serialDriver instanceof CdcAcmSerialDriver ||
-                assertTrue("expected > 0 and < 16 byte, got " + data.length, data.length > 0 && data.length < 16);
+                     usb.serialDriver instanceof ProlificSerialDriver)
+                assertTrue("expected > 0 and < "+len+" byte, got " + data.length, data.length > 0 && data.length < len);
             else // ftdi, ch340, cp2105
                 assertEquals(0, data.length);
         } catch (IOException ignored) {
@@ -1121,12 +1124,13 @@ public class DeviceTest {
         telnet.write("2aaa".getBytes());
         data = usb.read(4, 8);
         assertThat(data, equalTo("2aaa".getBytes()));
-        telnet.write(new byte[16]);
+        telnet.write(new byte[len]);
-        data = usb.read(16, 8);
+        data = usb.read(len, len/2);
         if (usb.serialDriver instanceof Cp21xxSerialDriver && usb.serialDriver.getPorts().size() == 1)
             assertNotEquals(0, data.length); // can be shorter or full length
-        else if (usb.serialDriver instanceof ProlificSerialDriver)
+        else if (usb.serialDriver instanceof CdcAcmSerialDriver ||
-            assertTrue("sporadic issue! expected > 0 and < 16 byte, got " + data.length, data.length > 0 && data.length < 16);
+                 usb.serialDriver instanceof ProlificSerialDriver)
+            assertTrue("sporadic issue! expected > 0 and < "+len+" byte, got " + data.length, data.length > 0 && data.length < len);
         else // ftdi, ch340, cp2105
             assertEquals(0, data.length);
         telnet.write("2ccc".getBytes());
@@ -1146,8 +1150,6 @@ public class DeviceTest {
     @Test
     // provoke data loss, when data is not read fast enough
     public void readBufferOverflow() throws Exception {
-        if(usb.serialDriver instanceof CdcAcmSerialDriver)
-            telnet.writeDelay = 10; // arduino_leonardo_bridge.ino sends each byte in own USB packet, which is horribly slow
         usb.open();
         usb.setParameters(115200, 8, 1, UsbSerialPort.PARITY_NONE);
         telnet.setParameters(115200, 8, 1, UsbSerialPort.PARITY_NONE);
@@ -1220,8 +1222,6 @@ public class DeviceTest {
         if(usb.serialDriver instanceof Ch34xSerialDriver)
             baudrate = 38400;
         int writeAhead = 5*baudrate/10; // write ahead for another 5 second read
-        if(usb.serialDriver instanceof CdcAcmSerialDriver)
-            writeAhead = 50;
 
         usb.open(EnumSet.of(UsbWrapper.OpenCloseFlags.NO_IOMANAGER_START));
         usb.ioManager.setReadTimeout(readTimeout);
@@ -1270,16 +1270,10 @@ public class DeviceTest {
 
     @Test
     public void writeSpeed() throws Exception {
-        // see logcat for performance results
+        // see logcat for performance results, speed is near physical limit at 11.5k
-        //
-        // CDC arduino_leonardo_bridge.ino has transfer speed ~ 100 byte/sec
-        // all other devices can get near physical limit:
-        // longlines=true:, speed is near physical limit at 11.5k
-        // longlines=false: speed is 3-4k for all devices, as more USB packets are required
         usb.open();
         usb.setParameters(115200, 8, 1, UsbSerialPort.PARITY_NONE);
         telnet.setParameters(115200, 8, 1, UsbSerialPort.PARITY_NONE);
-        boolean longlines = !(usb.serialDriver instanceof CdcAcmSerialDriver);
 
         int linenr = 0;
         String line="";
@@ -1292,10 +1286,7 @@ public class DeviceTest {
         for(int seconds=1; seconds<=5; seconds++) {
             next += 1000;
             while (System.currentTimeMillis() < next) {
-                if(longlines)
+                line = String.format("%060d,", linenr++);
-                    line = String.format("%060d,", linenr++);
-                else
-                    line = String.format("%07d,", linenr++);
                 usb.write(line.getBytes());
                 expected.append(line);
                 data.append(new String(telnet.read(0)));
@@ -1425,19 +1416,16 @@ public class DeviceTest {
         usb.setParameters(19200, 8, 1, UsbSerialPort.PARITY_NONE);
         telnet.setParameters(19200, 8, 1, UsbSerialPort.PARITY_NONE);
         usb.ioManager.setThreadPriority(Process.THREAD_PRIORITY_DEFAULT);
+        assertEquals(SerialInputOutputManager.State.STOPPED, usb.ioManager.getState());
         usb.ioManager.start();
         usb.waitForIoManagerStarted();
-        assertTrue("iomanager thread", usb.hasIoManagerThread());
+        assertEquals(SerialInputOutputManager.State.RUNNING, usb.ioManager.getState());
+        assertTrue("iomanager thread", usb.hasIoManagerThreads());
         try {
             usb.ioManager.start();
             fail("already running error expected");
         } catch (IllegalStateException ignored) {
         }
-        try {
-            usb.ioManager.run();
-            fail("already running error expected");
-        } catch (IllegalStateException ignored) {
-        }
         try {
             usb.ioManager.setThreadPriority(Process.THREAD_PRIORITY_LOWEST);
             fail("setThreadPriority IllegalStateException expected");
@@ -1462,23 +1450,12 @@ public class DeviceTest {
         telnet.write(new byte[1]); // now uses 8 byte buffer
         usb.read(3);
 
-        // writebuffer resize
+        // small writebuffer
         try {
             usb.ioManager.writeAsync(new byte[8192]);
             fail("expected BufferOverflowException");
         } catch (BufferOverflowException ignored) {}
 
-        usb.ioManager.setWriteBufferSize(16);
-        usb.ioManager.writeAsync("1234567890AB".getBytes());
-        try {
-            usb.ioManager.setWriteBufferSize(8);
-            fail("expected BufferOverflowException");
-        } catch (BufferOverflowException ignored) {}
-        usb.ioManager.setWriteBufferSize(24); // pending date copied to new buffer
-        telnet.write("a".getBytes());
-        assertThat(usb.read(1), equalTo("a".getBytes()));
-        assertThat(telnet.read(12), equalTo("1234567890AB".getBytes()));
-
         // small readbuffer
         usb.ioManager.setReadBufferSize(8);
         Log.d(TAG, "setReadBufferSize(8)");
@@ -1490,74 +1467,42 @@ public class DeviceTest {
         telnet.write("d".getBytes());
         assertThat(usb.read(1), equalTo("d".getBytes()));
 
+        SerialInputOutputManager ioManager = usb.ioManager;
+        assertEquals(SerialInputOutputManager.State.RUNNING, usb.ioManager.getState());
         usb.close();
-        for (int i = 0; i < 100 && usb.hasIoManagerThread(); i++) {
+        for (int i = 0; i < 100 && usb.hasIoManagerThreads(); i++) {
             Thread.sleep(1);
         }
-        assertFalse("iomanager thread", usb.hasIoManagerThread());
+        assertFalse("iomanager threads", usb.hasIoManagerThreads());
-        SerialInputOutputManager.DEBUG = false;
+        assertNull(usb.ioManager);
+        assertEquals(SerialInputOutputManager.State.STOPPED, ioManager.getState());
 
-        // legacy start
+        usb.open();
-        usb.open(EnumSet.of(UsbWrapper.OpenCloseFlags.NO_IOMANAGER_START)); // creates new IoManager
+        ioManager = usb.ioManager;
-        usb.setParameters(19200, 8, 1, UsbSerialPort.PARITY_NONE);
+        assertEquals(SerialInputOutputManager.State.RUNNING, usb.ioManager.getState());
-        telnet.setParameters(19200, 8, 1, UsbSerialPort.PARITY_NONE);
+        usb.serialPort.close(); // stop before ioManager
-        usb.ioManager.setThreadPriority(Process.THREAD_PRIORITY_DEFAULT);
+        for (int i = 0; i < 100 && usb.hasIoManagerThreads(); i++) {
-        Executors.newSingleThreadExecutor().submit(usb.ioManager);
+            Thread.sleep(1);
-        usb.waitForIoManagerStarted();
-        try {
-            usb.ioManager.start();
-            fail("already running error expected");
-        } catch (IllegalStateException ignored) {
         }
+        assertFalse("iomanager threads", usb.hasIoManagerThreads());
+        assertEquals(SerialInputOutputManager.State.STOPPED, usb.ioManager.getState());
+
+        SerialInputOutputManager.DEBUG = false;
     }
 
     @Test
     public void writeAsync() throws Exception {
         byte[] data, buf = new byte[]{1};
 
-        // w/o timeout: write delayed until something is read
+        // write immediately, without waiting for read
         usb.open();
         usb.setParameters(19200, 8, 1, UsbSerialPort.PARITY_NONE);
         telnet.setParameters(19200, 8, 1, UsbSerialPort.PARITY_NONE);
         usb.ioManager.writeAsync(buf);
         usb.ioManager.writeAsync(buf);
-        data = telnet.read(1);
-        assertEquals(0, data.length);
-        telnet.write(buf);
-        data = usb.read(1);
-        assertEquals(1, data.length);
         data = telnet.read(2);
         assertEquals(2, data.length);
         usb.close();
-
-        // with timeout: write after timeout
-        usb.open(EnumSet.of(UsbWrapper.OpenCloseFlags.NO_IOMANAGER_START));
-        usb.ioManager.setReadTimeout(100);
-        usb.ioManager.start();
-        usb.setParameters(19200, 8, 1, UsbSerialPort.PARITY_NONE);
-        telnet.setParameters(19200, 8, 1, UsbSerialPort.PARITY_NONE);
-        usb.ioManager.writeAsync(buf);
-        usb.ioManager.writeAsync(buf);
-        data = telnet.read(2);
-        assertEquals(2, data.length);
-        usb.ioManager.setReadTimeout(200);
-
-        // with internal SerialTimeoutException
-        TestBuffer tbuf = new TestBuffer(usb.writeBufferSize + 2*usb.writePacketSize);
-        byte[] pbuf1 = new byte[tbuf.buf.length - 4];
-        byte[] pbuf2 = new byte[1];
-        System.arraycopy(tbuf.buf, 0,pbuf1, 0, pbuf1.length);
-        usb.ioManager.setWriteTimeout(20); // tbuf len >= 128, needs 133msec @ 9600 baud
-        usb.setParameters(9600, 8, 1, UsbSerialPort.PARITY_NONE);
-        telnet.setParameters(9600, 8, 1, UsbSerialPort.PARITY_NONE);
-        usb.ioManager.writeAsync(pbuf1);
-        for(int i = pbuf1.length; i < tbuf.buf.length; i++) {
-            Thread.sleep(20);
-            pbuf2[0] = tbuf.buf[i];
-            usb.ioManager.writeAsync(pbuf2);
-        }
-        while(!tbuf.testRead(telnet.read(-1)))
-            ;
     }
 
     @Test
@@ -1622,34 +1567,32 @@ public class DeviceTest {
         }
         Log.i(TAG, "average time per read " + (System.currentTimeMillis()-time)/i + " msec");
 
-        if(!(usb.serialDriver instanceof CdcAcmSerialDriver)) {
+        int diffLen;
-            int diffLen;
+        usb.close();
-            usb.close();
+        // no issue with high transfer rate and long read timeout
-            // no issue with high transfer rate and long read timeout
+        diffLen = readSpeedInt(5, -1, longTimeout);
-            diffLen = readSpeedInt(5, -1, longTimeout);
+        if(usb.serialDriver instanceof Ch34xSerialDriver && diffLen == -1)
-            if(usb.serialDriver instanceof Ch34xSerialDriver && diffLen == -1)
+            diffLen = 0; // todo: investigate last packet loss
-                diffLen = 0; // todo: investigate last packet loss
+        assertEquals(0, diffLen);
-            assertEquals(0, diffLen);
+        usb.close();
-            usb.close();
+        // date loss with high transfer rate and short read timeout !!!
-            // date loss with high transfer rate and short read timeout !!!
+        diffLen = readSpeedInt(5, -1, shortTimeout);
-            diffLen = readSpeedInt(5, -1, shortTimeout);
 
-            assertNotEquals("sporadic issue!", 0, diffLen);
+        assertNotEquals("sporadic issue!", 0, diffLen);
 
-            // data loss observed with read timeout up to 200 msec, e.g.
+        // data loss observed with read timeout up to 200 msec, e.g.
-            //  difference at 181 len 64
+        //  difference at 181 len 64
-            //        got 000020,0000021,0000030,0000031,0000032,0
+        //        got 000020,0000021,0000030,0000031,0000032,0
-            //   expected 000020,0000021,0000022,0000023,0000024,0
+        //   expected 000020,0000021,0000022,0000023,0000024,0
-            // difference at 341 len 128
+        // difference at 341 len 128
-            //        got 000048,0000049,0000066,0000067,0000068,0
+        //        got 000048,0000049,0000066,0000067,0000068,0
-            //   expected 000048,0000049,0000050,0000051,0000052,0
+        //   expected 000048,0000049,0000050,0000051,0000052,0
-            // difference at 724 len 704
+        // difference at 724 len 704
-            //        got 0000112,0000113,0000202,0000203,0000204,
+        //        got 0000112,0000113,0000202,0000203,0000204,
-            //   expected 0000112,0000113,0000114,0000115,0000116,
+        //   expected 0000112,0000113,0000114,0000115,0000116,
-            // difference at 974 len 8
+        // difference at 974 len 8
-            //        got 00231,0000232,0000234,0000235,0000236,00
+        //        got 00231,0000232,0000234,0000235,0000236,00
-            //   expected 00231,0000232,0000233,0000234,0000235,00
+        //   expected 00231,0000232,0000233,0000234,0000235,00
-        }
     }
 
     @Test
@@ -1854,12 +1797,7 @@ public class DeviceTest {
         assertThat(usb.getControlLine(usb.serialPort::getCD), equalTo(inputLineFalse));
         assertThat(usb.getControlLine(usb.serialPort::getRI), equalTo(usb.inputLinesOnlyRtsCts ? Boolean.FALSE : inputLineTrue));
         telnet.write(data);
-        if(usb.serialDriver instanceof CdcAcmSerialDriver)
+        assertThat(Arrays.toString(data), usb.read(4), equalTo(data));
-            // arduino: control line feedback as serial_state notification is not implemented.
-            // It does not send w/o RTS or DTR, so these control lines can be partly checked here.
-            assertEquals(0, usb.read().length);
-        else
-            assertThat(Arrays.toString(data), usb.read(4), equalTo(data));
         usb.write(data);
         assertThat(Arrays.toString(data), telnet.read(4), equalTo(data));
 
@@ -1997,6 +1935,22 @@ public class DeviceTest {
         }
     }
 
+    @Test
+    public void flowControlBase() throws Exception {
+        usb.open();
+        usb.setParameters(115200, 8, 1, UsbSerialPort.PARITY_NONE);
+        assertEquals(FlowControl.NONE, usb.serialPort.getFlowControl());
+        assertTrue(usb.serialPort.getSupportedFlowControl().contains(FlowControl.NONE));
+        for(FlowControl flowControl : FlowControl.values()) {
+            if(usb.serialPort.getSupportedFlowControl().contains(flowControl)) {
+                usb.serialPort.setFlowControl(flowControl);
+                assertEquals(flowControl, usb.serialPort.getFlowControl());
+            } else {
+                assertThrows(UnsupportedOperationException.class, () -> usb.serialPort.setFlowControl(flowControl));
+            }
+        }
+    }
+
     @Test
     public void flowControlXonXoff() throws Exception {
         final byte[] off_on = new byte[]{'x',CommonUsbSerialPort.CHAR_XOFF,'y',CommonUsbSerialPort.CHAR_XON,'z'};
@@ -2006,12 +1960,11 @@ public class DeviceTest {
         usb.open(EnumSet.of(UsbWrapper.OpenCloseFlags.NO_IOMANAGER_THREAD, UsbWrapper.OpenCloseFlags.NO_CONTROL_LINE_INIT));
         telnet.setParameters(115200, 8, 1, UsbSerialPort.PARITY_NONE);
         usb.setParameters(115200, 8, 1, UsbSerialPort.PARITY_NONE);
-        assertEquals(FlowControl.NONE, usb.serialPort.getFlowControl());
+        if(!usb.serialPort.getSupportedFlowControl().contains(FlowControl.XON_XOFF)) {
-        if (!usb.serialPort.getSupportedFlowControl().contains(FlowControl.XON_XOFF_INLINE) &&
-                !usb.serialPort.getSupportedFlowControl().contains(FlowControl.XON_XOFF)) {
-            assertThrows(UnsupportedOperationException.class, () -> usb.serialPort.setFlowControl(FlowControl.XON_XOFF_INLINE));
-            assertThrows(UnsupportedOperationException.class, () -> usb.serialPort.setFlowControl(FlowControl.XON_XOFF));
             assertThrows(UnsupportedOperationException.class, () -> usb.serialPort.getXON());
+        }
+        if (!usb.serialPort.getSupportedFlowControl().contains(FlowControl.XON_XOFF_INLINE) &&
+            !usb.serialPort.getSupportedFlowControl().contains(FlowControl.XON_XOFF)) {
             Assume.assumeTrue("flow control not supported", false);
         }
         if (usb.serialPort.getSupportedFlowControl().contains(FlowControl.XON_XOFF_INLINE) &&
@@ -2020,11 +1973,8 @@ public class DeviceTest {
         }
         if (usb.serialPort.getSupportedFlowControl().contains(FlowControl.XON_XOFF_INLINE)) {
             filter = new XonXoffFilter();
-            assertThrows(UnsupportedOperationException.class, () -> usb.serialPort.setFlowControl(FlowControl.XON_XOFF));
             usb.serialPort.setFlowControl(FlowControl.XON_XOFF_INLINE);
             assertEquals(FlowControl.XON_XOFF_INLINE, usb.serialPort.getFlowControl());
-            assertThrows(UnsupportedOperationException.class, () -> usb.serialPort.getXON());
-
             assertTrue(filter.getXON());
             assertThat(filter.filter(off_on), equalTo(off_on_filtered));
             assertTrue(filter.getXON());
@@ -2034,7 +1984,6 @@ public class DeviceTest {
             assertTrue(filter.getXON());
         } else {
             filter = null;
-            assertThrows(UnsupportedOperationException.class, () -> usb.serialPort.setFlowControl(FlowControl.XON_XOFF_INLINE));
             usb.serialPort.setFlowControl(FlowControl.XON_XOFF);
             assertEquals(FlowControl.XON_XOFF, usb.serialPort.getFlowControl());
             assertTrue(usb.serialPort.getXON());
@@ -2203,17 +2152,10 @@ public class DeviceTest {
         usb.setParameters(115200, 8, 1, UsbSerialPort.PARITY_NONE);
 
         // early exit, if flow control not supported
+        if (!usb.serialPort.getSupportedFlowControl().contains(flowControl))
+            Assume.assumeTrue("flow control not supported", false);
         assertEquals(usb.inputLinesConnected ? EnumSet.of(ControlLine.RI) : EnumSet.noneOf(ControlLine.class), usb.serialPort.getControlLines()); // [1]
-        assertEquals(FlowControl.NONE, usb.serialPort.getFlowControl());
+        usb.serialPort.setFlowControl(flowControl);
-        try {
-            usb.serialPort.setFlowControl(flowControl);
-        } catch (UnsupportedOperationException ignored) {
-            if (usb.serialPort.getSupportedFlowControl().contains(flowControl)) {
-                assertTrue("flow control support expected", false);
-            } else {
-                Assume.assumeTrue("flow control not supported", false);
-            }
-        }
         assertEquals(flowControl, usb.serialPort.getFlowControl());
         if (!usb.inputLinesConnected)
             Assume.assumeTrue("flow control lines not connected", false);
@@ -2354,20 +2296,25 @@ public class DeviceTest {
     @Test
     public void setBreak() throws Exception {
         usb.open();
+        if (usb.serialDriver instanceof CdcAcmSerialDriver) {
+            // not supported by MCP2221, other CDC devices might support it
+            try {
+                usb.serialPort.setBreak(true);
+                fail("setBreak error expected");
+            } catch (IOException ignored) {
+            }
+            return;
+        }
         telnet.setParameters(19200, 8, 1, UsbSerialPort.PARITY_NONE);
         usb.setParameters(19200, 8, 1, UsbSerialPort.PARITY_NONE);
         doReadWrite("");
-        usb.serialPort.setBreak(true);
         Thread.sleep(100);
         usb.serialPort.setBreak(false);
         // RFC2217 has SET_CONTROL + REQ_BREAK_STATE request, but this is not supported by pyserial
         // as there is no easy notification on <break> condition. By default break is returned as
         // 0 byte on Linux, see https://man7.org/linux/man-pages/man3/termios.3.html -> BRKINT
         byte[] data = telnet.read(1);
-        if (usb.serialDriver instanceof CdcAcmSerialDriver) {
+        if(usb.isCp21xxRestrictedPort) {
-            // BREAK forwarding not implemented by arduino_leonardo_bridge.ino
-            assertThat("<break>", data, equalTo(new byte[]{}));
-        } else if(usb.isCp21xxRestrictedPort) {
             assertThat("<break>", data, equalTo(new byte[]{0x55})); // send the last byte again?
         } else {
             assertThat("<break>", data, equalTo(new byte[]{0}));
@@ -2528,7 +2475,8 @@ public class DeviceTest {
         assertThrows(UnsupportedOperationException.class, wrongSerialPort::getControlLines);
         assertEquals(EnumSet.of(FlowControl.NONE), wrongSerialPort.getSupportedFlowControl());
         assertEquals(FlowControl.NONE, wrongSerialPort.getFlowControl());
-        assertThrows(UnsupportedOperationException.class, () -> wrongSerialPort.setFlowControl(FlowControl.NONE));
+        wrongSerialPort.setFlowControl(FlowControl.NONE);
+        assertThrows(UnsupportedOperationException.class, () -> wrongSerialPort.setFlowControl(FlowControl.RTS_CTS));
         assertThrows(UnsupportedOperationException.class, () -> wrongSerialPort.purgeHwBuffers(true, true));
         assertThrows(UnsupportedOperationException.class, () -> wrongSerialPort.setBreak(true));
     }

usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/util/UsbWrapper.java

@@ -33,6 +33,8 @@ import java.util.concurrent.Callable;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 
+import androidx.core.content.ContextCompat;
+
 public class UsbWrapper implements SerialInputOutputManager.Listener {
 
     public final static int     USB_READ_WAIT = 500;
@@ -92,7 +94,7 @@ public class UsbWrapper implements SerialInputOutputManager.Listener {
             intent.setPackage(context.getPackageName());
             PendingIntent permissionIntent = PendingIntent.getBroadcast(context, 0, intent, flags);
             IntentFilter filter = new IntentFilter("com.android.example.USB_PERMISSION");
-            context.registerReceiver(usbReceiver, filter, Context.RECEIVER_NOT_EXPORTED);
+            ContextCompat.registerReceiver(context, usbReceiver, filter, Context.RECEIVER_NOT_EXPORTED);
             usbManager.requestPermission(serialDriver.getDevice(), permissionIntent);
             for(int i=0; i<5000; i++) {
                 if(granted[0] != null) break;
@@ -150,7 +152,7 @@ public class UsbWrapper implements SerialInputOutputManager.Listener {
             if(serialDriver.getDevice().getProductId() == UsbId.FTDI_FT231X)
                 writeBufferSize = 512;
         } else if (serialDriver instanceof CdcAcmSerialDriver) {
-            writePacketSize = 64; writeBufferSize = 128;
+            writePacketSize = 16; writeBufferSize = 32; // MCP2221 values, other devices might be different
         }
 
         readBufferSize = writeBufferSize;
@@ -256,12 +258,15 @@ public class UsbWrapper implements SerialInputOutputManager.Listener {
         throw new IOException("IoManager not started");
     }
 
-    public boolean hasIoManagerThread() {
+    public boolean hasIoManagerThreads() {
+        int c = 0;
         for (Thread thread : Thread.getAllStackTraces().keySet()) {
-            if (thread.getName().equals(SerialInputOutputManager.class.getSimpleName()))
+            if (thread.getName().equals(SerialInputOutputManager.class.getSimpleName() + "_read"))
-                return true;
+                c += 1;
+            if (thread.getName().equals(SerialInputOutputManager.class.getSimpleName() + "_write"))
+                c += 1;
         }
-        return false;
+        return c == 2;
     }
 
     // wait full time

usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/CommonUsbSerialPort.java

@@ -10,13 +10,13 @@ import android.hardware.usb.UsbDevice;
 import android.hardware.usb.UsbDeviceConnection;
 import android.hardware.usb.UsbEndpoint;
 import android.hardware.usb.UsbRequest;
+import android.os.Build;
 import android.util.Log;
 
 import com.hoho.android.usbserial.util.MonotonicClock;
 
 import java.io.IOException;
 import java.nio.ByteBuffer;
-import java.security.InvalidParameterException;
 import java.util.EnumSet;
 
 /**
@@ -29,7 +29,7 @@ public abstract class CommonUsbSerialPort implements UsbSerialPort {
     public static boolean DEBUG = false;
 
     private static final String TAG = CommonUsbSerialPort.class.getSimpleName();
-    private static final int MAX_READ_SIZE = 16 * 1024; // = old bulkTransfer limit
+    private static final int MAX_READ_SIZE = 16 * 1024; // = old bulkTransfer limit prior to Android 9
 
     protected final UsbDevice mDevice;
     protected final int mPortNumber;
@@ -208,7 +208,7 @@ public abstract class CommonUsbSerialPort implements UsbSerialPort {
             //     /system/lib64/libandroid_runtime.so (android_hardware_UsbDeviceConnection_request_wait(_JNIEnv*, _jobject*, long)+84)
             // data loss / crashes were observed with timeout up to 200 msec
             long endTime = testConnection ? MonotonicClock.millis() + timeout : 0;
-            int readMax = Math.min(length, MAX_READ_SIZE);
+            int readMax = (Build.VERSION.SDK_INT >= Build.VERSION_CODES.P) ? length : Math.min(length, MAX_READ_SIZE);
             nread = mConnection.bulkTransfer(mReadEndpoint, dest, readMax, timeout);
             // Android error propagation is improvable:
             //  nread == -1 can be: timeout, connection lost, buffer to small, ???
@@ -334,7 +334,10 @@ public abstract class CommonUsbSerialPort implements UsbSerialPort {
     public EnumSet<ControlLine> getSupportedControlLines() throws IOException { return EnumSet.noneOf(ControlLine.class); }
 
     @Override
-    public void setFlowControl(FlowControl flowcontrol) throws IOException { throw new UnsupportedOperationException(); }
+    public void setFlowControl(FlowControl flowcontrol) throws IOException {
+        if (flowcontrol != FlowControl.NONE)
+            throw new UnsupportedOperationException();
+    }
 
     @Override
     public FlowControl getFlowControl() { return mFlowControl; }

usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/UsbSerialPort.java

@@ -175,7 +175,7 @@ public interface UsbSerialPort extends Closeable {
      * @param parity one of {@link #PARITY_NONE}, {@link #PARITY_ODD},
      *               {@link #PARITY_EVEN}, {@link #PARITY_MARK}, or {@link #PARITY_SPACE}.
      * @throws IOException on error setting the port parameters
-     * @throws UnsupportedOperationException if values are not supported by a specific device
+     * @throws UnsupportedOperationException if not supported or values are not supported by a specific device
      */
     void setParameters(int baudRate, int dataBits, int stopBits, @Parity int parity) throws IOException;
 
@@ -257,6 +257,7 @@ public interface UsbSerialPort extends Closeable {
      *
      * @return EnumSet.contains(...) is {@code true} if set, else {@code false}
      * @throws IOException if an error occurred during reading
+     * @throws UnsupportedOperationException if not supported
      */
     EnumSet<ControlLine> getControlLines() throws IOException;
 

usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/util/SerialInputOutputManager.java

@@ -9,21 +9,23 @@ package com.hoho.android.usbserial.util;
 import android.os.Process;
 import android.util.Log;
 
-import com.hoho.android.usbserial.driver.SerialTimeoutException;
 import com.hoho.android.usbserial.driver.UsbSerialPort;
 
 import java.io.IOException;
 import java.nio.ByteBuffer;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.atomic.AtomicReference;
 
 /**
- * Utility class which services a {@link UsbSerialPort} in its {@link #run()} method.
+ * Utility class which services a {@link UsbSerialPort} in its {@link #runWrite()} ()} and {@link #runRead()} ()} ()} methods.
  *
  * @author mike wakerly (opensource@hoho.com)
  */
-public class SerialInputOutputManager implements Runnable {
+public class SerialInputOutputManager {
 
     public enum State {
         STOPPED,
+        STARTING,
         RUNNING,
         STOPPING
     }
@@ -33,9 +35,6 @@ public class SerialInputOutputManager implements Runnable {
     private static final String TAG = SerialInputOutputManager.class.getSimpleName();
     private static final int BUFSIZ = 4096;
 
-    /**
-     * default read timeout is infinite, to avoid data loss with bulkTransfer API
-     */
     private int mReadTimeout = 0;
     private int mWriteTimeout = 0;
 
@@ -46,7 +45,8 @@ public class SerialInputOutputManager implements Runnable {
     private ByteBuffer mWriteBuffer = ByteBuffer.allocate(BUFSIZ);
 
     private int mThreadPriority = Process.THREAD_PRIORITY_URGENT_AUDIO;
-    private State mState = State.STOPPED; // Synchronized by 'this'
+    private final AtomicReference<State> mState = new AtomicReference<>(State.STOPPED);
+    private CountDownLatch mStartuplatch = new CountDownLatch(2);
     private Listener mListener; // Synchronized by 'this'
     private final UsbSerialPort mSerialPort;
 
@@ -57,7 +57,7 @@ public class SerialInputOutputManager implements Runnable {
         void onNewData(byte[] data);
 
         /**
-         * Called when {@link SerialInputOutputManager#run()} aborts due to an error.
+         * Called when {@link SerialInputOutputManager#runRead()} ()} or {@link SerialInputOutputManager#runWrite()} ()} ()} aborts due to an error.
          */
         void onRunError(Exception e);
     }
@@ -87,8 +87,9 @@ public class SerialInputOutputManager implements Runnable {
      * @param threadPriority  see {@link Process#setThreadPriority(int)}
      * */
     public void setThreadPriority(int threadPriority) {
-        if (mState != State.STOPPED)
+        if (!mState.compareAndSet(State.STOPPED, State.STOPPED)) {
             throw new IllegalStateException("threadPriority only configurable before SerialInputOutputManager is started");
+        }
         mThreadPriority = threadPriority;
     }
 
@@ -97,7 +98,7 @@ public class SerialInputOutputManager implements Runnable {
      */
     public void setReadTimeout(int timeout) {
         // when set if already running, read already blocks and the new value will not become effective now
-        if(mReadTimeout == 0 && timeout != 0 && mState != State.STOPPED)
+        if(mReadTimeout == 0 && timeout != 0 && mState.get() != State.STOPPED)
             throw new IllegalStateException("readTimeout only configurable before SerialInputOutputManager is started");
         mReadTimeout = timeout;
     }
@@ -145,83 +146,152 @@ public class SerialInputOutputManager implements Runnable {
     }
 
     /**
-     * when using writeAsync, it is recommended to use readTimeout != 0,
+     * write data asynchronously
-     * else the write will be delayed until read data is available
      */
     public void writeAsync(byte[] data) {
         synchronized (mWriteBufferLock) {
             mWriteBuffer.put(data);
+            mWriteBufferLock.notifyAll(); // Notify waiting threads
         }
     }
 
     /**
-     * start SerialInputOutputManager in separate thread
+     * start SerialInputOutputManager in separate threads
      */
     public void start() {
-        if(mState != State.STOPPED)
+        if(mState.compareAndSet(State.STOPPED, State.STARTING)) {
+            mStartuplatch = new CountDownLatch(2);
+            new Thread(this::runRead, this.getClass().getSimpleName() + "_read").start();
+            new Thread(this::runWrite, this.getClass().getSimpleName() + "_write").start();
+            try {
+                mStartuplatch.await();
+                mState.set(State.RUNNING);
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+            }
+        } else {
             throw new IllegalStateException("already started");
-        new Thread(this, this.getClass().getSimpleName()).start();
+        }
     }
 
     /**
-     * stop SerialInputOutputManager thread
+     * stop SerialInputOutputManager threads
      *
      * when using readTimeout == 0 (default), additionally use usbSerialPort.close() to
      * interrupt blocking read
      */
-    public synchronized void stop() {
+    public void stop() {
-        if (getState() == State.RUNNING) {
+        if(mState.compareAndSet(State.RUNNING, State.STOPPING)) {
+            synchronized (mWriteBufferLock) {
+                mWriteBufferLock.notifyAll(); // wake up write thread to check the stop condition
+            }
             Log.i(TAG, "Stop requested");
-            mState = State.STOPPING;
         }
     }
 
-    public synchronized State getState() {
+    public State getState() {
-        return mState;
+        return mState.get();
     }
 
     /**
-     * Continuously services the read and write buffers until {@link #stop()} is
+     * @return true if the thread is still running
-     * called, or until a driver exception is raised.
      */
-    @Override
+    private boolean isStillRunning() {
-    public void run() {
+        State state = mState.get();
-        synchronized (this) {
+        return ((state == State.RUNNING) || (state == State.STARTING))
-            if (getState() != State.STOPPED) {
+            && !Thread.currentThread().isInterrupted();
-                throw new IllegalStateException("Already running");
+    }
-            }
+
-            mState = State.RUNNING;
+    /**
-        }
+     * Notify listener of an error
-        Log.i(TAG, "Running ...");
+     *
-        try {
+     * @param e the exception
-            if(mThreadPriority != Process.THREAD_PRIORITY_DEFAULT)
+     */
-                Process.setThreadPriority(mThreadPriority);
+    private void notifyErrorListener(Throwable e) {
-            while (true) {
+        Listener listener = getListener();
-                if (getState() != State.RUNNING) {
+        if (listener != null) {
-                    Log.i(TAG, "Stopping mState=" + getState());
+            try {
-                    break;
+                listener.onRunError(e instanceof Exception ? (Exception) e : new Exception(e));
-                }
+            } catch (Throwable t) {
-                step();
+                Log.w(TAG, "Exception in onRunError: " + t.getMessage(), t);
-            }
-        } catch (Exception e) {
-            if(mSerialPort.isOpen()) {
-                Log.w(TAG, "Run ending due to exception: " + e.getMessage(), e);
-            } else {
-                Log.i(TAG, "Socket closed");
-            }
-            final Listener listener = getListener();
-            if (listener != null) {
-              listener.onRunError(e);
-            }
-        } finally {
-            synchronized (this) {
-                mState = State.STOPPED;
-                Log.i(TAG, "Stopped");
             }
         }
     }
 
-    private void step() throws IOException {
+    /**
+     * Set the thread priority
+     */
+    private void setThreadPriority() {
+        if (mThreadPriority != Process.THREAD_PRIORITY_DEFAULT) {
+            Process.setThreadPriority(mThreadPriority);
+        }
+    }
+
+    /**
+     * Continuously services the read buffers until {@link #stop()} is called, or until a driver exception is
+     * raised.
+     */
+    void runRead() {
+        Log.i(TAG, "runRead running ...");
+        try {
+            setThreadPriority();
+            mStartuplatch.countDown();
+            do {
+                stepRead();
+            } while (isStillRunning());
+            Log.i(TAG, "runRead: Stopping mState=" + getState());
+        } catch (Throwable e) {
+            if (Thread.currentThread().isInterrupted()) {
+                Log.w(TAG, "runRead: interrupted");
+            } else if(mSerialPort.isOpen()) {
+                Log.w(TAG, "runRead ending due to exception: " + e.getMessage(), e);
+            } else {
+                Log.i(TAG, "runRead: Socket closed");
+            }
+            notifyErrorListener(e);
+        } finally {
+            if (mState.compareAndSet(State.RUNNING, State.STOPPING)) {
+                synchronized (mWriteBufferLock) {
+                    mWriteBufferLock.notifyAll(); // wake up write thread to check the stop condition
+                }
+            } else if (mState.compareAndSet(State.STOPPING, State.STOPPED)) {
+                Log.i(TAG, "runRead: Stopped mState=" + getState());
+            }
+        }
+    }
+
+    /**
+     * Continuously services the write buffers until {@link #stop()} is called, or until a driver exception is
+     * raised.
+     */
+    void runWrite() {
+        Log.i(TAG, "runWrite running ...");
+        try {
+            setThreadPriority();
+            mStartuplatch.countDown();
+            do {
+                stepWrite();
+            } while (isStillRunning());
+            Log.i(TAG, "runWrite: Stopping mState=" + getState());
+        } catch (Throwable e) {
+            if (Thread.currentThread().isInterrupted()) {
+                Log.w(TAG, "runWrite: interrupted");
+            } else if(mSerialPort.isOpen()) {
+                Log.w(TAG, "runWrite ending due to exception: " + e.getMessage(), e);
+            } else {
+                Log.i(TAG, "runWrite: Socket closed");
+            }
+            notifyErrorListener(e);
+        } finally {
+            if (!mState.compareAndSet(State.RUNNING, State.STOPPING)) {
+                if (mState.compareAndSet(State.STOPPING, State.STOPPED)) {
+                    Log.i(TAG, "runWrite: Stopped mState=" + getState());
+                }
+            }
+        }
+    }
+
+    private void stepRead() throws IOException {
         // Handle incoming data.
         byte[] buffer;
         synchronized (mReadBufferLock) {
@@ -239,39 +309,28 @@ public class SerialInputOutputManager implements Runnable {
                 listener.onNewData(data);
             }
         }
+    }
 
+    private void stepWrite() throws IOException, InterruptedException {
         // Handle outgoing data.
-        buffer = null;
+        byte[] buffer = null;
         synchronized (mWriteBufferLock) {
-            len = mWriteBuffer.position();
+            int len = mWriteBuffer.position();
             if (len > 0) {
                 buffer = new byte[len];
                 mWriteBuffer.rewind();
                 mWriteBuffer.get(buffer, 0, len);
                 mWriteBuffer.clear();
+                mWriteBufferLock.notifyAll(); // Notify writeAsync that there is space in the buffer
+            } else {
+                mWriteBufferLock.wait();
             }
         }
         if (buffer != null) {
             if (DEBUG) {
-                Log.d(TAG, "Writing data len=" + len);
+                Log.d(TAG, "Writing data len=" + buffer.length);
-            }
-            try {
-                mSerialPort.write(buffer, mWriteTimeout);
-            } catch (SerialTimeoutException ex) {
-                synchronized (mWriteBufferLock) {
-                    byte[] buffer2 = null;
-                    int len2 = mWriteBuffer.position();
-                    if (len2 > 0) {
-                        buffer2 = new byte[len2];
-                        mWriteBuffer.rewind();
-                        mWriteBuffer.get(buffer2, 0, len2);
-                        mWriteBuffer.clear();
-                    }
-                    mWriteBuffer.put(buffer, ex.bytesTransferred, buffer.length - ex.bytesTransferred);
-                    if (buffer2 != null)
-                        mWriteBuffer.put(buffer2);
-                }
             }
+            mSerialPort.write(buffer, mWriteTimeout);
         }
     }
 

usbSerialForAndroid/src/test/java/android/util/Log.java

@@ -17,6 +17,11 @@ public class Log {
         return 0;
     }
 
+    public static int w(String tag, String msg, Throwable tr) {
+        System.out.println("WARN: " + tag + ": " + msg + " / " + tr.getMessage());
+        return 0;
+    }
+
     public static int e(String tag, String msg) {
         System.out.println("ERROR: " + tag + ": " + msg);
         return 0;

usbSerialForAndroid/src/test/java/com/hoho/android/usbserial/util/SerialInputOutputManagerTest.java

@@ -0,0 +1,55 @@
+package com.hoho.android.usbserial.util;
+
+import static org.junit.Assert.assertEquals;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+import android.hardware.usb.UsbEndpoint;
+import android.os.Process;
+
+import com.hoho.android.usbserial.driver.CommonUsbSerialPort;
+
+import org.junit.Test;
+
+public class SerialInputOutputManagerTest {
+
+
+    // catch all Throwables in onNewData() and onRunError()
+    @Test
+    public void throwable() throws Exception {
+
+        class ExceptionListener implements SerialInputOutputManager.Listener {
+            public Exception e;
+            @Override public void onNewData(byte[] data) { throw new RuntimeException("exception1"); }
+            @Override public void onRunError(Exception e) { this.e = e; throw new RuntimeException("exception2"); }
+        }
+        class ErrorListener implements SerialInputOutputManager.Listener {
+            public Exception e;
+            @Override public void onNewData(byte[] data) { throw new UnknownError("error1"); }
+            @Override public void onRunError(Exception e) { this.e = e; throw new UnknownError("error2");}
+        }
+
+        UsbEndpoint readEndpoint = mock(UsbEndpoint.class);
+        when(readEndpoint.getMaxPacketSize()).thenReturn(16);
+        CommonUsbSerialPort port = mock(CommonUsbSerialPort.class);
+        when(port.getReadEndpoint()).thenReturn(readEndpoint);
+        when(port.read(new byte[16], 0)).thenReturn(1);
+        when(port.isOpen()).thenReturn(true);
+        SerialInputOutputManager manager = new SerialInputOutputManager(port);
+        manager.setThreadPriority(Process.THREAD_PRIORITY_DEFAULT);
+
+        ExceptionListener exceptionListener = new ExceptionListener();
+        manager.setListener(exceptionListener);
+        manager.runRead();
+        assertEquals(RuntimeException.class, exceptionListener.e.getClass());
+        assertEquals("exception1", exceptionListener.e.getMessage());
+
+        ErrorListener errorListener = new ErrorListener();
+        manager.setListener(errorListener);
+        manager.runRead();
+        assertEquals(Exception.class, errorListener.e.getClass());
+        assertEquals("java.lang.UnknownError: error1", errorListener.e.getMessage());
+        assertEquals(UnknownError.class, errorListener.e.getCause().getClass());
+        assertEquals("error1", errorListener.e.getCause().getMessage());
+    }
+}