.idea/AndroidProjectSystem.xml

@@ -1,6 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="AndroidProjectSystem">
-    <option name="providerId" value="com.android.tools.idea.GradleProjectSystem" />
-  </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:3.9.0'
+    implementation 'com.github.mik3y:usb-serial-for-android:3.8.1'
 }
 ```
 
@@ -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/ACM devices by USB interface types instead of fixed VID+PID,
+*Note*: as of v3.5.0 this library detects CDC devices by USB interface types instead of fixed VID+PID,
-so custom probers are typically not required any more for CDC/ACM devices.
+so custom probers are typically not required any more for CDC 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
@@ -154,23 +154,22 @@ a compatible UsbDevice.
 
 ## Compatible Devices
 
-This library supports USB to serial converter chips with specific drivers
+This library supports USB to serial converter chips:
 * FTDI FT232R, FT232H, FT2232H, FT4232H, FT230X, FT231X, FT234XD
 * Prolific PL2303
 * Silabs CP2102, CP210*
-* Qinheng CH340, CH341A
+* Qinheng CH340, CH341A, CH9102
 
-some other device specific drivers
+devices implementing the CDC/ACM protocol like
-* 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
+* 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)
+
 ## 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:8.9.1'
+        classpath 'com.android.tools.build:gradle:8.8.2'
     }
 }
 

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-8.11.1-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.10.2-all.zip

usbSerialExamples/build.gradle

@@ -3,7 +3,7 @@ plugins {
 }
 
 android {
-    compileSdkVersion 35
+    compileSdkVersion 34
 
     compileOptions {
         sourceCompatibility JavaVersion.VERSION_1_8
@@ -12,7 +12,7 @@ android {
 
     defaultConfig {
         minSdkVersion 17
-        targetSdkVersion 35
+        targetSdkVersion 34
         vectorDrawables.useSupportLibrary = true
 
         missingDimensionStrategy 'device', 'anyDevice'

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(portNum >= driver.getPorts().size()) {
+        if(driver.getPorts().size() < portNum) {
             status("connection failed: not enough ports at device");
             return;
         }

usbSerialForAndroid/build.gradle

@@ -4,11 +4,11 @@ plugins {
 }
 
 android {
-    compileSdkVersion 35
+    compileSdkVersion 34
 
     defaultConfig {
         minSdkVersion 17
-        targetSdkVersion 35
+        targetSdkVersion 34
         consumerProguardFiles 'proguard-rules.pro'
         
         testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"

usbSerialForAndroid/coverage.gradle

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

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

@@ -645,13 +645,7 @@ public class DeviceTest {
             Thread.sleep(10);
             usb.write(new byte[]{(byte) 0xff});
             data = telnet.read(2);
-            if(usb.serialDriver instanceof CdcAcmSerialDriver) {
+            assertThat("19000/7N1", data, equalTo(new byte[]{(byte) 0x80, (byte) 0xff}));
-                // 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;
@@ -724,17 +718,18 @@ 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 MCP2221, other CDC devices might support it
+            // not supported by arduino_leonardo_bridge.ino, other devices might support it
-            assertThat("19200/8N1", data, equalTo(_8n1));
+            usb.setParameters(19200, 7, 1, UsbSerialPort.PARITY_MARK);
+            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);
@@ -763,19 +758,19 @@ 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 MCP2221, other CDC devices might support it
+            // not supported by arduino_leonardo_bridge.ino, other 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);
@@ -797,44 +792,45 @@ public class DeviceTest {
             }
         }
 
-        // shift stopbits into next byte, by using different databits
-        // a - start bit (0)
-        // o - stop bit  (1)
-        // d - data bit
-
-        // out 8N2:   addddddd doaddddddddo
-        //             1000001 0  10001111
-        // in 6N1:    addddddo addddddo
-        //             100000   101000
-        usb.setParameters(19200, 8, UsbSerialPort.STOPBITS_1, UsbSerialPort.PARITY_NONE);
-        telnet.setParameters(19200, 6, 1, UsbSerialPort.PARITY_NONE);
-        usb.write(new byte[]{(byte)0x41, (byte)0xf1});
-        data = telnet.read(2);
         if (usb.serialDriver instanceof CdcAcmSerialDriver) {
-            // MCP2221 slightly slower, looks like 2 stop bits. could be different for other CDC devices
+            usb.setParameters(19200, 8, UsbSerialPort.STOPBITS_1_5, UsbSerialPort.PARITY_NONE);
-            assertThat("19200/8N1", data, equalTo(new byte[]{1, 11}));
+            // software based bridge in arduino_leonardo_bridge.ino is to slow for real test, other devices might support it
-        } else
+        } else {
+            // shift stopbits into next byte, by using different databits
+            // a - start bit (0)
+            // o - stop bit  (1)
+            // d - data bit
+
+            // out 8N2:   addddddd doaddddddddo
+            //             1000001 0  10001111
+            // in 6N1:    addddddo addddddo
+            //             100000   101000
+            usb.setParameters(19200, 8, UsbSerialPort.STOPBITS_1, UsbSerialPort.PARITY_NONE);
+            telnet.setParameters(19200, 6, 1, UsbSerialPort.PARITY_NONE);
+            usb.write(new byte[]{(byte)0x41, (byte)0xf1});
+            data = telnet.read(2);
             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) {
+            }
         }
     }
 
@@ -887,6 +883,8 @@ 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
@@ -1057,17 +1055,18 @@ public class DeviceTest {
 
     @Test
     public void readBufferSize() throws Exception {
-        // looks like devices perform USB read with full mReadEndpoint.getMaxPacketSize() size (16, 32, 64, 512)
+        // looks like devices perform USB read with full mReadEndpoint.getMaxPacketSize() size (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));
-        int len = Math.min(16, usb.serialPort.getReadEndpoint().getMaxPacketSize()/2); // 8 for MCP2221, else 16
+        usb.ioManager.setReadBufferSize(8);
-        usb.ioManager.setReadBufferSize(len/2);
         usb.ioManager.start();
         usb.setParameters(115200, 8, 1, UsbSerialPort.PARITY_NONE);
         telnet.setParameters(115200, 8, 1, UsbSerialPort.PARITY_NONE);
@@ -1076,15 +1075,13 @@ 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(len);
+            data = usb.read(16);
             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 CdcAcmSerialDriver ||
+            else if (usb.serialDriver instanceof ProlificSerialDriver)
-                     usb.serialDriver instanceof ProlificSerialDriver)
+                assertTrue("expected > 0 and < 16 byte, got " + data.length, data.length > 0 && data.length < 16);
-                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) {
@@ -1124,13 +1121,12 @@ public class DeviceTest {
         telnet.write("2aaa".getBytes());
         data = usb.read(4, 8);
         assertThat(data, equalTo("2aaa".getBytes()));
-        telnet.write(new byte[len]);
+        telnet.write(new byte[16]);
-        data = usb.read(len, len/2);
+        data = usb.read(16, 8);
         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 CdcAcmSerialDriver ||
+        else if (usb.serialDriver instanceof ProlificSerialDriver)
-                 usb.serialDriver instanceof ProlificSerialDriver)
+            assertTrue("sporadic issue! expected > 0 and < 16 byte, got " + data.length, data.length > 0 && data.length < 16);
-            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());
@@ -1150,6 +1146,8 @@ 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);
@@ -1222,6 +1220,8 @@ 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);
@@ -1270,10 +1270,16 @@ public class DeviceTest {
 
     @Test
     public void writeSpeed() throws Exception {
-        // see logcat for performance results, speed is near physical limit at 11.5k
+        // see logcat for performance results
+        //
+        // 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="";
@@ -1286,7 +1292,10 @@ public class DeviceTest {
         for(int seconds=1; seconds<=5; seconds++) {
             next += 1000;
             while (System.currentTimeMillis() < next) {
-                line = String.format("%060d,", linenr++);
+                if(longlines)
+                    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)));
@@ -1567,32 +1576,34 @@ public class DeviceTest {
         }
         Log.i(TAG, "average time per read " + (System.currentTimeMillis()-time)/i + " msec");
 
-        int diffLen;
+        if(!(usb.serialDriver instanceof CdcAcmSerialDriver)) {
-        usb.close();
+            int diffLen;
-        // no issue with high transfer rate and long read timeout
+            usb.close();
-        diffLen = readSpeedInt(5, -1, longTimeout);
+            // no issue with high transfer rate and long read timeout
-        if(usb.serialDriver instanceof Ch34xSerialDriver && diffLen == -1)
+            diffLen = readSpeedInt(5, -1, longTimeout);
-            diffLen = 0; // todo: investigate last packet loss
+            if(usb.serialDriver instanceof Ch34xSerialDriver && diffLen == -1)
-        assertEquals(0, diffLen);
+                diffLen = 0; // todo: investigate last packet loss
-        usb.close();
+            assertEquals(0, diffLen);
-        // date loss with high transfer rate and short read timeout !!!
+            usb.close();
-        diffLen = readSpeedInt(5, -1, shortTimeout);
+            // date loss with high transfer rate and short read timeout !!!
+            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
@@ -1797,7 +1808,12 @@ 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);
-        assertThat(Arrays.toString(data), usb.read(4), equalTo(data));
+        if(usb.serialDriver instanceof CdcAcmSerialDriver)
+            // 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));
 
@@ -2296,25 +2312,20 @@ 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.isCp21xxRestrictedPort) {
+        if (usb.serialDriver instanceof CdcAcmSerialDriver) {
+            // 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}));

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

@@ -152,7 +152,7 @@ public class UsbWrapper implements SerialInputOutputManager.Listener {
             if(serialDriver.getDevice().getProductId() == UsbId.FTDI_FT231X)
                 writeBufferSize = 512;
         } else if (serialDriver instanceof CdcAcmSerialDriver) {
-            writePacketSize = 16; writeBufferSize = 32; // MCP2221 values, other devices might be different
+            writePacketSize = 64; writeBufferSize = 128;
         }
 
         readBufferSize = writeBufferSize;