National Instruments 320685D-01 Using a Loadable Compiled Module as an External Module , Notification of Changes in Run State

Chapter 2 Using Loadable Compiled Modules

LabWindows/CVI Programmer Reference Manual 2-4

National Instruments Corporation

Compiled modules must adhere to the requirements outlined for the target operating

system. Chapter 3, Windows95/NT Compiler/Linker Issues, Chapter 4, Windows 3.1

Compiler/Linker Issues, and Chapter 5, UNIX Compiler/Linker Issues, of this manual, discuss

operating system requirements.

Using a Loadable Compiled Module as an External Module

You can load a compiled module dynamically from your program. A module you load

dynamically is called an external module. You can load, execute, and unload this external

module programmatically using LoadExternalModule, GetExternalModuleAddr, and

UnloadExternalModule. Refer to Chapter8, Utility Library, of the LabWindows/CVI

Standard Libraries Reference Manual for more information on using these functions.

While you develop and debug the external module, you can list it in the project as a source

file. After you finish debugging the module, you can compile it into an object file or a

Windows 95/NT DLL. External modules must adhere to the requirements outlined for the

target operating system. Chapter3, Windows 95/NT Compiler/Linker Issues, Chapter 4,

Windows3.1 Compiler/Linker Issues, and Chapter 5, UNIX Compiler/Linker Issues, of this

manual, discuss operating system requirements.

Notification of Changes in Run State

You might have to notify certain com piled module s whene ver yo ur program st arts, susp ends,

continues, or stops. For example, if a compiled module has asynchronous callbacks, you must

prevent the callbacks from executing when program execution suspends at a breakpoint.

LabWindows/CVI has a callback mechanism you can use to inform a compiled module of

changes in the program status.

To notify a compiled module of changes in the run state, add a function with the name

__RunStateChangeCallback to the compiled module. LabWindows/CVI automatically

installs the callback for you.

The run state change callback must be in a compiled file, not in a source file. More than one

compiled module can contain functions with this name, because LabWindows/CVI never

enters it into the global name space. The prototype for the callback is as follows:

void CVICALLBACK __RunStateChangeCallback(int action)

libsupp.h defines the actions in the following enumerated type:

enum {

kRunState_Start,

kRunState_Suspend,

kRunState_Resume,

kRunState_AbortingExecution,

kRunState_Stop,