1. Create a native Ada program for the ARM processor.
2. Create an Android app in Eclipse or Android Studio.
3. Deploy the app on your device.

• (If you already have a FreeBSD or PC-BSD system, you can skip this step)
  To generate the native ARM code, I created a PC-BSD 10.1 VirtualBox virtual machine. The reason I picked PC-BSD was because it is based on FreeBSD and comes with a pre-installed GUI. This also allows you to use the GNAT-AUX version of GPS to maintain your Ada code.
  
  The virtual machine for PC-BSD was easily created using a generic Open Virtualization install file (OVA), which can be found here PCBSD 10.1. You can use either VMWare or VirtualBox and import this virtual machine.
  Make sure your virtual machine has access to the internet.
  To make installation of this virtual machine a little easier, I have added a few instructions (also includes manual installation of GNATDroid).
  

• Install the GNATDroid cross compiler on your FreeBSD (or PC-BSD) system.
  GNATDroid is ready to be installed on FreeBSD using ports. For other BSD systems, you need to build these packages from the sources provided on the dragonlace.net pages.
  See http://www.dragonlace.net/posts/GNATDroid_cross-compiler_ports_created_for_FreeBSD for more information.

with Ada.Text_IO; use Ada.Text_IO;

procedure hello_ada is
begin
   loop
      declare
         Line : String := Get_Line;
      begin
         Put_Line ("Hello from Ada!, You entered: " & Line);
         exit when Line'Length = 4 -- ' 
                   and then Line = "exit";
      end;
   end loop;
end hello_ada;

arm-android-eabi-gnatmake hello_ada.adb -largs -fPIC -pie

• Install the latest version of Android Studio for your platform, and download the appropriate SDK's and the NDK plug-in using the SDK Manager. The NDK can be found under SDK tools.
  
  
• Create a new blank (no activity) Android application project in Java called 'hello_ada' and choose your target device. Also pick a package name: 'com.hello_ada' (remove the term 'example'), select the required SDK level and you may also need to check 'use legacy android.support libraries' for this example.
  Note: I used API 30 (Android 11.0) for this example, but other targets are also possible, and you can later change the minSdk value in build.gradle for compatibility with older devices..
  
  
• Complete the dialog by clicking 'Finish''. (You now should have created a project without Java sources)
  Android Studio will now prepare the project. Grab some coffee, this may take a while.
  
  
• Add an Empty Activity named MainActivity and check 'Launcher Activity' (language is Java).
  
  
• Modify the AndroidManifest.xml file and add 'android:extractNativeLibs="true" ' to the Application.
  
  
• By now you should have a project and a file called MainActivity.java. What needs to be done (so we can get some output too) is create a 'Multiline Text' editText control (under 'Text') called editTextTextMultiLine. This can be done by editing res/layout/activity_main.xml using the graphical editor. Set the number of lines to say 30 (lines=30, width=800px) and perhaps add scrollbars too.
  
  
• What still needs to be done is adding the native Ada executable (from PC-BSD) to this project. In Android Studio perform a right-click on 'app' (project view) and select 'new', 'directory'. Type the name: src/main/jniLibs/armeabi-v7a and/or src/main/jniLibs/arm64-v8a depending on your target platform (or create both for compatibility). Use a file explorer to copy the 'hello_ada' executable to this directory and rename it to 'libhello_ada.so'.
  (On your filesystem this should be <project directory>/hello_ada/app/src/main/jniLibs/arm...).
  Important: The executable name must begin with 'lib' and end with '.so' or else the package manager/installer will not copy the file on your Android device into the lib/arm or lib/arm64 directory!
  

package com.hello_ada;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;

import android.content.Context;
import android.content.pm.ApplicationInfo;
import android.content.pm.PackageManager;
import androidx.appcompat.app.AppCompatActivity;
// import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;
import android.widget.EditText;

public class MainActivity extends AppCompatActivity {
    /* Called when the activity is first created. */

    private void logProcess (Process pr, EditText t) throws IOException
    {
        /* This routine reads the output and error streams from a process */
        /* and logs it to an EditText object.                             */

        int read;
        char[] buffer1 = new char[4096];
        StringBuffer output = new StringBuffer();

        try
        {
            BufferedReader reader = new BufferedReader(new InputStreamReader(pr.getInputStream()));
            while ((read = reader.read(buffer1)) > 0) {
                output.append(buffer1, 0, read);
                t.append(output.toString() + "\n");
            }
            reader.close();

            BufferedReader errReader = new BufferedReader(new InputStreamReader(pr.getErrorStream()));
            while ((read = errReader.read(buffer1)) > 0) {
                output.append(buffer1, 0, read);
                t.append(output.toString() + "\n");
            }
            errReader.close();
        }
        catch (Exception e) {
            t.append("Exception " + e.getMessage());
            e.printStackTrace();
        }
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        EditText log_text = (EditText) findViewById (R.id.editTextTextMultiLine);

        log_text.setText("Test native app\n\n");

        Process process = null;

        Context context = getApplicationContext();
        PackageManager pm = context.getPackageManager();

        try
        {
            ApplicationInfo appInfo = pm.getApplicationInfo("com.hello_ada", PackageManager.GET_SHARED_LIBRARY_FILES);
            // log_text.append("native lib dir: " + appInfo.nativeLibraryDir + "\n\n");

            String data_dir = appInfo.nativeLibraryDir;

            String filename = "/libhello_ada.so";
            File hello_ada_file = new File (data_dir + filename);

            /* Check if the executable exists */
            process = Runtime.getRuntime().exec("ls -l " + data_dir + filename);
            process.waitFor();
            logProcess (process, log_text);

            /* Start the Ada process */
            // You can use the ProcessBuilder or just call 'exec'.
            //ProcessBuilder prb = new ProcessBuilder ("." + data_dir + filename);
            //process = prb.start();
            process = Runtime.getRuntime().exec("." + data_dir + filename);

            log_text.append("process started\n\n");

            /* Open streams to this process. It should be running now */
            /* and waiting for input.                                 */
            BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(process.getOutputStream()));
            BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));

            /* Now you can send text (or commands!) to the Ada program */
            writer.write("Hello from Java!\n");
            writer.flush();

            /* Read the result */
            log_text.append("Received: " + reader.readLine() + "\n\n");

            /* Make sure the Ada process terminates: */
            writer.write("exit" + '\n');
            writer.flush();

            log_text.append("Received: " + reader.readLine() + "\n\n");

        } catch (IOException e) {
            /* TODO Auto-generated catch block */
            log_text.append("io exception: " + e.getMessage());
            e.printStackTrace();
        } catch (InterruptedException e) {
            /* TODO Auto-generated catch block */
            log_text.append("interrupted exception: " + e.getMessage());
            e.printStackTrace();
        } catch (Exception e) {
            log_text.append("exception: " + e.getMessage());
            e.printStackTrace();
        }
    }
}