National Instruments PC-OPDIO-16 Manuale Utente

     

Huge Buffer Access   

Unlike C and C++, Turbo Pascal does not support huge pointers.  Consequently, you must
perform your own pointer arithmetic when accessing memory buffers greater than 64 KB in size.
Essentially, whenever you increment a pointer to a buffer of memory, you should check the low
word of the pointer to see if it rolls over from $FFFF back to $0000.  In this case, you need to
increment the high word of the pointer by a value given as 

Ofs(AHIncr)

.  This increments the

Windows selector by the correct amount and references the next 64 KB segment.  By using
record variants like 

PMemory

 used in 

DAQOP_TP.PAS

, you can easily access both the pointer

and the high and low words of the pointer value.  For more details, please see your Turbo Pascal
manuals.

    

String Passing

    

Normally, standard Pascal strings consist of an array of up to 255 characters, with the first byte
reserved for the length of the existing string.  However, Windows and NI-DAQ functions expect
a null-terminated string, such as those used in the C language.  Fortunately, Turbo Pascal for
Windows extends the string syntax to support the null-terminated string.  To use this option,
check to ensure that the extended syntax compiler option 

{$X+}

 is enabled (which is the

default), and then declare the string as an array of characters, as in the following example:

type

Tfilename = array[0..80] of Char;

begin

err := DAQ_to_Disk(.., Tfilename, ...);

In addition, Turbo Pascal has a predefined pointer to a null-terminated string called 

PChar

.  To

pass a null-terminated string to a procedure or function, pass either a 

PChar

 pointer variable to

the string, or pass the name itself without an index.

    

Parameter Passing

    

By default, Pascal passes parameters by value.  Include the 

var

 keyword if you need to pass by

reference.

DAQ_Monitor

Align_DMA_Buffer

newestPtIndex and AlignIndex