User`s guide

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PCIS-DASK Application Hints

5.5 Interrupt Event Message Programming Hints

PCIS-DASK provides two methods to perform interrupt occurrence notification

for NuDAQ DIO cards that have dual interrupt system.

The Event Message method handles event notification through user-defined

callbacks and/or the Windows Message queue (for VB5, through user-defined

callbacks only). When a user-specified interrupt event occurs, PCIS-DASK

calls the user-defined callback (if defined) and/or puts a message into the

Windows Message queue, if you specified a window handle. After receiving the

message, the user’s application can carry out the appropriate task.

The event message mechanism is easy and safe in Windows 98 and NT

systems; however, the time delay between the event and notification is highly

variable and depends largely on how loaded your system is. In addition, if a

callback function is called, succeeding events will not be handled until your

callback has returned. If the time interval between interrupt events is smaller

than the time taken for callback function processing, the succeeding interrupt

events will not be handled. Therefore this mechanism is not suitable for the

frequent interrupt occurrence condition.

The Event Status checking and waiting method handles interrupt event

status checking through Win32 wait functions, such as WaitForSingleObject or

WaitForMultipleObjects. This method is useful for the situation that the

interrupt event occurs very often, and the applications written in the language

that doesn’t support function pointers (e.g. VB4).

1. Through user-defined callbacks and the Windows Message queue

[Example Code Fragment]

card = Register_Card(PCI_7230, card_number);

//INT1 event notification is through window message

DIO_INT1_EventMessage (card, INT1_EXT_SIGNAL, hWnd,

WM_INT, NULL);

//INT2 event notification is through a callback function

DIO_INT2_EventMessage (card, INT2_EXT_SIGNAL, hWnd, NULL,

(void *) cbfn);

… .

//window message handling function

long PASCAL MainWndProc(hWnd, message, wParam,

lParam)

{

switch(message) {

… .