SerialInputOutputManager: use optimal read buffer size to reduce latency for FTDI and CH34x

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

@@ -66,16 +66,10 @@ public abstract class CommonUsbSerialPort implements UsbSerialPort {
         return mPortNumber;
     }
 
-    /**
-     * Returns the write endpoint.
-     * @return write endpoint
-     */
+    @Override
     public UsbEndpoint getWriteEndpoint() { return mWriteEndpoint; }
 
-    /**
-     * Returns the read endpoint.
-     * @return read endpoint
-     */
+    @Override
     public UsbEndpoint getReadEndpoint() { return mReadEndpoint; }
 
     /**

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

@@ -8,6 +8,7 @@ package com.hoho.android.usbserial.driver;
 
 import android.hardware.usb.UsbDevice;
 import android.hardware.usb.UsbDeviceConnection;
+import android.hardware.usb.UsbEndpoint;
 import android.hardware.usb.UsbManager;
 
 import androidx.annotation.IntDef;
@@ -74,6 +75,18 @@ public interface UsbSerialPort extends Closeable {
      */
     int getPortNumber();
 
+    /**
+     * Returns the write endpoint.
+     * @return write endpoint
+     */
+    UsbEndpoint getWriteEndpoint();
+
+    /**
+     * Returns the read endpoint.
+     * @return read endpoint
+     */
+    UsbEndpoint getReadEndpoint();
+
     /**
      * The serial number of the underlying UsbDeviceConnection, or {@code null}.
      *

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

@@ -34,7 +34,7 @@ public class SerialInputOutputManager implements Runnable {
     private final Object mReadBufferLock = new Object();
     private final Object mWriteBufferLock = new Object();
 
-    private ByteBuffer mReadBuffer = ByteBuffer.allocate(BUFSIZ);
+    private ByteBuffer mReadBuffer; // default size = getReadEndpoint().getMaxPacketSize()
     private ByteBuffer mWriteBuffer = ByteBuffer.allocate(BUFSIZ);
 
     public enum State {
@@ -62,11 +62,13 @@ public class SerialInputOutputManager implements Runnable {
 
     public SerialInputOutputManager(UsbSerialPort serialPort) {
         mSerialPort = serialPort;
+        mReadBuffer = ByteBuffer.allocate(serialPort.getReadEndpoint().getMaxPacketSize());
     }
 
     public SerialInputOutputManager(UsbSerialPort serialPort, Listener listener) {
         mSerialPort = serialPort;
         mListener = listener;
+        mReadBuffer = ByteBuffer.allocate(serialPort.getReadEndpoint().getMaxPacketSize());
     }
 
     public synchronized void setListener(Listener listener) {