The document discusses creating and using dynamic link libraries (DLLs) across different platforms. It provides instructions on how to call functions in a DLL, create a DLL, export functions from a DLL, and handle callbacks between a client and DLL. It also discusses how to recompile a DLL for Android using the Native Development Kit (NDK) since the ARM architecture is different from x86 architectures. Links are provided for additional resources on DLL design patterns, the maXbox toolkit, Android NDK documentation, and Max Kleiner's website for more information.

1. DLL Building Blocks
Yes, we scan…
http://en.wikipedia.org/wiki/Web_of_Things
Max Kleiner
Script: 362_maxon3D_EKON18.TXT

2. Agenda and Tutorial
(DLL 32/64 bit)
2
http://www.softwareschule.ch/download/maxbox_starter28.pdf
• Call a DLL
• Call a DLL+ (Interface, Callback, Events)
• Build a DLL
• Recompile a DLL
• Android NDK and Lazarus
http://scholz2000.com/
136_sysinformation_dll_EKON1.txt
A Short History of Time
1991 Application Program
1995 Application
1998 Applet
2010 App
2015 A (Scholz2000, Android, Arduino, ARM)

3. DLL Primer ••
Call: If you want your library to be called from programs compiled with
other compilers, it is important to specify the correct calling convention.
••
Create: A library can be created just as a program, only it uses the
library keyword, and it has an exports section.
••
Let's get back to the topic and create a DLL callback function:
••
1. declare a function type
• 2. the function itself
• 3. define the DLL reference
• 4. then implement the function in the client
• 5. and call the DLL:
3
136_sysinformation_dll_EKON1.txt 039_pas_dllcall_EKON2.txt
070_pas_functionplotter_digital2.txt

4. CCaallllbbaacckk hhaacckk ssttaacckk
•
4
Callback example in client unit 136_Callback_dll_EKON6.txt
-----------------------------------------------
interface...
1. TCallBackFunction = function(sig: integer):boolean;
2. function callME(sig: integer):boolean;
implement...
3. procedure TestCallBack(myCBFunction: TCallBackFunction); register;
external('watchcom.dll');
4. function callMe(sig: integer): boolean;
begin
{whatever you need to do, case of...}
showmessage('I was called with'+ inttostr(sig));
end;
5. procedure TForm1.Button1Click(sender: TObject);
begin
testCallBack(callMe); //subscribe function in DLL
end;

5. Create a DLL
5
Callback in the DLL
In the DLL you would also declare a function type and a
procedure (or function) itself, so use it like this:
type
TCallBackFunction = function(sig: integer):boolean;
procedure TestCallBack(clientFunc: TCallBackFunction); stdcall;
var sigAlive: boolean;
begin
{timer stuff...
set the signal...}
if(clientFunc(55)) then sigalive := true;
end;
exports TestCallBack;

6. http://max.kleiner.com/dllplus.htm
6
Export an object-reference from a DLL is one approach to get real OO-access
to a DLL. The DLL must create and return the object, so the client
gets the methods without encapsulating.
unit income1;
interface
type
IIncome = class
public
function GetIncome(const aNetto: Currency): Currency;
virtual; abstract;
procedure SetRate(const aPercent, aYear: integer);
virtual; abstract;
function queryDLLInterface(var queryList: TStringList):
TStringList; virtual; abstract;
end;
036_pas_includetest_EKON3.txt
036_pas_dynlib_EKON4.txt
036_pas_DLLTesting_EKON5.tx

7. Solution FPC ELF32
shared object
7
32-bit EXE loads 32-bit DLL, 64-bit EXE loads 64-bit DLL.
************* Simple Sequence Diagram**************
Client DLL
¦ TestCallBack(clientFunc) ¦
¦---------------------------------------------->¦
¦ clientFunc.callMe(sig ) ¦
¦<----------------------------------------------¦
¦ ¦
¦ true (or something to return) ¦
¦---------------------------------------------->¦
¦ ¦
http://wiki.freepascal.org/Android_Programming
http://www.softwareschule.ch/examples/440_DLL_Tutor2.txt
Tutor: http://www.softwareschule.ch/download/maxbox_starter18_3.pdf

8. Solution NDK
The NDK is a toolset that allows you to implement parts of your app using
native-code languages such as C, Pascal, Object Pascal and C++. For certain
types of apps, this can be helpful so you can reuse existing code libraries
written in these languages, but most apps do not need the Android NDK.
Typical good candidates for the NDK are CPU-intensive workloads such as
game engines, signal processing, physics simulation, and so on. When
examining whether or not you should develop in native code, think about your
requirements and see if the Android framework APIs provide the functionality
that you need.
You have to use the Android NDK to recompile the library. The ARM
architecture is completely different from the x86 architecture. The system calls
are different on Linux and Windows.
8
http://www.ntu.edu.sg/home/ehchua/programming/android/android_ndk.html

9. NDK Need Things
If you have the src files for the DLL, try recompiling as an ELF32 shared object, then link
that instead into your Android code (-
below is a Windows solution):
set NDK_HOME=C:Androidandroid-ndk-r9c // customize this var for your own location
set LD_LIBRARY_PATH=%NDK_HOME%platformsandroid-18arch-armusrlib cd
REM -- TEMPORARILY COPY SOME LIBS COMPILER MAY NEED
copy %NDK_HOME%platformsandroid-18arch-armusrlibcrtbegin*.o .
copy %NDK_HOME%platformsandroid-18arch-armusrlibcrtend*.o .
REM -- GENERATE YOUR OBJ FILE
%NDK_HOME%toolchainsarm-linux-androideabi-4.8prebuiltwindows-x86_64binarm-linux-androideabi-
gcc.exe -g -I%NDK_HOME%platforms
android-18arch-armusrinclude -c -fPIC YourLib.c -o YourLib.o
REM -- GENERATE SHARED OBJ FROM OBJ FILE
%NDK_HOME%toolchainsarm-linux-androideabi-4.8prebuiltwindows-x86_64binarm-linux-androideabi-
gcc.exe -g -L%NDK_HOME%platforms
android-18arch-armusrlib -shared -o YourLib_so.so YourLib_so.o
REM -- finally, remove the libraries previously copied to src directory
del .crtbegin*.o
del .crtend*.o
9

10. Optional: Create <project>/jni/Application.mk.
Build your native code by running the 'ndk-build' script from your project's directory.
It is located in the top-level NDK directory:
cd <project>
<ndk>/ndk-build
I discovered that to use the build-ndk script, I don't need a real project.
I created a folder project, with nothing in it except another folder jni, and put all
my sources in that folder.
I then created the Android.mk file and ran the script as described in the ndk docs.
10
Here's the general outline of how you work with the NDK tools:
Place your native sources under <project>/jni/...
Create <project>/jni/Android.mk to describe your native sources to the NDK
build system
http://developer.android.com/sdk/ndk/index.html

11. Thanks! Links to Blocks
the source is the code
http://www.softwareschule.ch/maxbox.htm
http://sourceforge.net/projects/maxbox
http://en.wikipedia.org/wiki/Arduino
http://www.softwareschule.ch/download/webofthings2013.pdf
Book Patterns konkret
http://www.amazon.de/Patterns-konkret-Max-Kleiner/dp/3935042469
maXbox
https://github.com/maxkleiner/maXbox3/releases
11
http://max.kleiner.com/dllplus.htm
http://www.softwareschule.ch/download/dlldesign_ekon9.pdf
http://developer.android.com/sdk/ndk/index.html
http://www.ntu.edu.sg/home/ehchua/programming/android/android_ndk.html

12. Questions? Code a World
hack the earth
12
Yes, we hack…
https://github.com/maxkleiner/maXbox3/releases