Why LabVIEW crashes when I'm trying to use "in" and "out" in my DLL?

Question

Calling function from DLL using Call Library Function.
Function source:
extern "C" __declspec(dllexport) long ReadPort(long base, long off)
unsigned char c;
long d;
__asm
push eax
push dx
push ax
mov eax, base
add eax, off
mov dx, ax
in al, dx
mov c, al
pop ax
pop dx
pop eax
d = c;
return d;
Using LabVIEW 5.0 and MSVC 6
OS: Win2k

Answer 1

> I am sure... When I delete "in" command from DLL source, it works...
> but when I use "in" or "out" assembler command, LV crashes (sometimes
> without any error message)...
>
Windowd 2000, and most of the more modern MS OSes do not allow direct
access to HW. That means that applications do not have permission to
call in and out instructions. Those instructions are protected and any
app calling them will be terminated because it did something illegal.
To get direct I/O to work, you should look for the driver on the NI web
site that will redirect it for you.
Greg McKaskle