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Angel

DllCall problem with visa32.dll

2 posts in this topic

Hi,

I am trying to create some functions that will people control intruments (osciloscopes, signal generators, spectrum analyzers, etc) through VISA and GPIB. To do so I am trying to call the visa32.dll from AutoIt by means of DllCall.

However I am having trouble with this as I don't seem to be calling the functions properly as I do not get the proper responses from the DLL.

I've reviewed my code several times but I can't see what I am doing wrong, other than the fact that some of the paremeters are supposed to be unsigned integers but I am telling DllCall that they are integers.

So I will post here the original C calls to the functions (which I've used and work in C) and my "AutoIt equivalents". I hope that someone can spot my mistake and help me finish this which I think would be of great use for the "lab rats" like me which are using AutoIt :-). The code is a bit long but I've tried to comment a lot. I've put the functions that I want to call followed by the "translation" using C types (like int, char, etc). Then I put an example that works in C.

Here I go:

The C- code:

#cs
 ; The C code from wich this was copied:
  // First some typedefs and #defines required to understand the function prototypes
  typedef unsigned long    ViUInt32;
  typedef ViUInt32          ViObject;
  typedef ViObject          ViSession;
  typedef ViUInt32          ViAccessMode;
  typedef signed long        ViInt32;
  typedef ViInt32            ViStatus;
  
  #define VI_NULL            (0)
  
  // Then the function prototypes themselves
  
  // viStatus viOpenDefaultRM (*viSession) => signed int viOpenDefaultRM(*unsigned long)
  // viStatus viOpen (viSession, char*, viAccessMode, ViUInt32, *viSession); => signed int viOpen(unsigned long, char*, unsigned long, unsigned long, *unsigned long)
  // viStatus viQueryf (viSession, char*, char*, ...); => like fprintf(fid, command, format_string, params...)
  // viStatus viClose(viSession)
  
  // And the example code
  int int_instr;
  char s_out[255];
  errStatus = viOpenDefaultRM (&DEFAULT_RM);
  errStatus = viOpen (DEFAULT_RM, "GPIB0::20::0", VI_NULL, VI_NULL, &int_instr);
  errStatus = viQueryf (int_ret, "*IDN?\n", "%s", s_out);
  viClose(int_ret);
#ce

This small example gets the "GPIB ID" of the instrument in address 1.

Here is the same code in AutoIt:

Global Const $VI_NULL = 0

; VISA variables
Dim $DEFAULT_RM = 0
Dim $int_instr = 0
Dim $s_out = ""
Dim $v_results

;- Open VISA RESOURCE MANAGER
; errStatus = viOpenDefaultRM (&DEFAULT_RM);
; signed int viOpenDefaultRM(*unsigned long)
$v_results = DllCall("visa32.dll", "int","viOpenDefaultRM", "int_ptr",$DEFAULT_RM)
DebugMsg("@error = " & @error)
DebugMsg("errStatus = " & $v_results[0])
$DEFAULT_RM = $v_results[1]
DebugMsg("$DEFAULT_RM = " & $DEFAULT_RM)

;- Open the INSTRUMENT CONNECTION
; errStatus = viOpen (DEFAULT_RM, "GPIB0::20::0", VI_NULL, VI_NULL, &int_instr);
; signed int viOpen(unsigned long, char*, unsigned long, unsigned long, *unsigned long)
$v_results = DllCall("visa32.dll", "long","viOpen", "long", $DEFAULT_RM, "str","GPIB::1::0", "long",$VI_NULL, "long",$VI_NULL,"long_ptr",$int_instr)
DebugMsg("@error = " & @error)
DebugMsg("errStatus = " & $v_results[0])
$int_instr = $v_results[1]
DebugMsg("$int_instr = " & $int_instr)

;- Send QUERY to instrument and get ANSWER
; errStatus = viQueryf (int_instr, "*IDN?\n", "%s", s_out);
; signed int viQueryf (unsigned long, char*, char*, char*);
;errStatus = viQueryf (h_instr, s_command, "%s", string);
$v_results = DllCall("visa32.dll", "int","viQueryf", "int",$int_instr, "str","*IDN?", "str","%s", "str", $s_out)
DebugMsg("@error = " & @error)
DebugMsg("errStatus = " & $v_results[0])
$s_out = $v_results[1]
DebugMsg("$s_out = " & $s_out)

;- Close INSTRUMENT Connection
; viClose(int_instr);
$v_results = DllCall("visa32.dll", "int","viClose", "int",$int_instr)
DebugMsg($v_results)
$errStatus = $v_results[0]


Func DebugMsg($s_msg)
  MsgBox(0,"Debug",$s_msg)
EndFunc

When I run it I do not see any @error problems but when I get to the query I get an error. Even before that I see that the call to viOpen sets $int_instr to the same value as the call to viOpenDefaultRM sets $DEFAULT_RM, which cannot be, as they are suposed to be handles to different things.

So does someone see what I am doing wrong. I really think that having VISA and GPIB control in AutoIT would be great!

Thanks in advance,

Angel

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I've found the source of the problem. As usual I had not properly read the documentation. I really should listen to Valik when he gives me some advice!

The problem was that DllCall returns a copy of ALL the parameters of the function! I thought that it only returned a copy of the modified parameters!

I think that this should be put in bold in the documentation :-)

Cheers,

Angel

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