Call 3rd party DLL from ATL COM

(1) use tool to generate def and .lib from DLL ( assuming no header file)
    http://purefractalsolutions.com/show.php?a=utils/expdef

(2) VC++ project linker-->input additional dependency

(3) declare and use in CPP

extern "C"   unsigned char Open_USB();
extern "C"   unsigned char Accept_LED(int value);
extern "C"  void Set_Callback(void* pAny);

void(__stdcall*p)(int);  // calling convention matching far pascal, for most c function

//void __cdecl* p;  // ptrAny


static void __stdcall CB1(int value)  {..} instance function would hast this->* so callback must use static to remove this.

 p = &CB1;
 ::Open_USB();
 ::Accept_LED(0);
 ::Set_Callback(p);

again cannot use __cdecl must use __stdcall. It turns out Calling Conversion even affect [DllImport] when re-target .net 4.0 from .net 4.0, must specify CDecl in DllImports