Serial Port RS232 and ANDROID

The article below is dedicated to the description of the possibility to use COM port in applications for OS Android. It is needed when your application must receive/send data from the other device having only Serial port RS 232 as means of communication.

What do we need?

First, it is necessary to download Android NDK to work with native code in Java.
 http://developer.android.com/tools/sdk/ndk/index.html
It will be necessary to call code on C to work with the serial port; Second, it is necessary to check-out source code of the project from svn to work with Serial port RS 232.
svn checkout

http://android-serialport-api.googlecode.com/svn/trunk/android-serialport-api

android-serialport-api

Organization of the project

It is necessary for us to create a folder /jni and to copy the contents of a folder /jni of the project, downloaded from svn (or simply to copy all folder /jni), in Android project. After that we need to add the following files from the downloaded project:
  • SerialPort.java
  • Application.java
  • SerialPortActivity.java
  • SerialPortFinder.java
The given files allow us to work with the COM port but you will need to edit them to serve the needs of the project. It is known all devices in the systems similar to a *nix one are on a path /dev. To establish path to the device (COM port) and baud rate it is necessary to set appropriate values of fields in Application.java file:
String path = -path to device-;
int baudrate = -baud rate-;
Class SerialPortActivity.java is an extension of Activity class and contains an abstract method protected abstract void onDataReceived (final byte [] buffer, final int size). You can inherit the Activity from this class where there will be work with Serial Port, and to process data acquisition from the port having redefined the method onDataReceived.
@Override
	protected void onDataReceived(final byte[] buffer, final int size) {
		runOnUiThread(new Runnable() {
			public void run() {
					//TO DO your logic

			}
		});
	}
It is possible to extract logic of information system of port in your own class/classes and not to use the inheritance from SerialPortActivity.java. You can receive the lists of all devices and their paths by means of class SerialPortFinder.java with its methods getAllDevices () and getAllDevicesPath () accordingly. Write-In port is carried out by using a simple record in OutputStream created by means of class SerialPort.java, COM port.
mOutputStream.write(new String(“text”).getBytes());
mOutputStream.write('\n');

JNI & NDK

Native code loading in Android application may be found in class SerialPort.java by calling System.loadLibrary (‘ serial_port ‘):
private native static FileDescriptor open(String path, int baudrate, int flags);
	public native void close();
	static {
		System.loadLibrary("serial_port");
	}
The parameter serial_port is a module that has occurred as a result of code C compilation through/via NDK. It is specified in file make /jni/Android.mk. File SerialPort.c in /jni folder contains native functions of the system calls to work with Serial port. Such parameters for COM port as Data bits, Parity, Stop bits and the others may be changed in this file by means of structure termios, for example:
                cfg.c_cflag |= ~PARENB;
		cfg.c_cflag &= ~CSTOPB;
		cfg.c_cflag &= ~CSIZE;
		cfg.c_cflag |= CS8;
(Data bits=8, Parity=none, Stop bits=1)
This information about termios.h may be found under the following link:  http://pubs.opengroup.org/onlinepubs/007908775/xsh/termios.h.html After changing the file SerialPort.c it is necessary to compile libraries as follows:
  • Open command line
  • Go to the NDK folder
  • Set path to the Android project – set NDK_PROJECT_PATH= -path to your android project-
  • Run – ndk-build
The libraries will be compiled and added in a folder /libs of your project. After that it is possible to perform the following command in order to install Android application in a device:
adb install -path to you .apk file-
Evgeny G.
January 23, 2018
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