Does LV8.2 support this kind of parameter passing between LV and DLL.

[huangjack]

I am trying to use "Call Library Function Node" to call a DLL to control a device.
The prototype of one function in the DLL is:  function putcommand(prec: pointer):longint;
The mannual describes the function as following:
 
"Together with the Putcommand function ,a 32 bit pointer, which points to command
message structur (see below) is to be transferred to the DLL."
 
TCommandMsg = packed record
                     ApId : longint;
                     commandnr : word;
                     command : tcommand;
              end;
where the  "tcommand" structure is shown below:
tcommand = packed record
                  commandID : word;
                  param : tparam;
           end;
 
Both the type and size of the fields within the two structures are given.
 
How can I pass the parameter from LV to the DLL?
 
Thanks

[tbd]

To answer the question in this message's Subject:

Yes! - assuming the "tcommand" and "tparam" parameters are not pointers.

One builds an array of bytes representing the "flattened" (AKA "serialized") TCommandMsg structure and configures the CLF to pass an array-pointer.  The DLL receives the pointer and assumes it points to a struct - which it will IF the array has been packed correctly.  To pack the array correctly means knowing exactly how many bytes each parameter requires, and, if passing a numeric, whether the DLL expects the least-significant byte first (Little-Endian) or the MSB first - Big Endian.  When LabVIEW flattens numerics, it arranges the bytes in Big Endian order.

here's a list of the data-types shown below, in order

"C" type      LV type  Identifier

longint (I32) ("Apld")

word    (U16) ("commandnr")

word    (U16) ("commanIDr")

?(tparam) (?)   ("param")

of what "C" datatype(s) is tparam composed?

Cheers.

---

huangjack wrote:

I am trying to use "Call Library Function Node" to call a DLL to control a device.
The prototype of one function in the DLL is:  function putcommand(prec: pointer):longint;
The mannual describes the function as following:
 
"Together with the Putcommand function ,a 32 bit pointer, which points to command
message structur (see below) is to be transferred to the DLL."
 
TCommandMsg = packed record
                     ApId : longint;
                     commandnr : word;
                     command : tcommand;
              end;
where the  "tcommand" structure is shown below:
tcommand = packed record
                  commandID : word;
                  param : tparam;
           end;
 
Both the type and size of the fields within the two structures are given.
 
How can I pass the parameter from LV to the DLL?
 
Thanks

---

Message Edited by tbd on 02-17-2008 01:57 PM

[huangjack]

Hi,

Thank you for the explaination.

The tparam is a case structure.

tparam = packed record
                   case byte of
                         1 : (B1,B2,B3,B4 : byte);
                         2 : (w1,w2 : word);
                         3 : (i1,i2 : smallint);
                         4 : (r1 : single);
                         5 : (l1 : longint);
end;

So there is a structure in structure in structure. How can I pack such data into array?

Can I list all the parameters with corrsponding types , then pack them into a cluster.

After that, I flatten the cluster and wire to the CLF which has been configured to pass an array-pointer.

Do you think it's gonna work or I have not got what you said?

Thanks

tbd wrote:

To answer the question in this message's Subject:

Yes! - assuming the "tcommand" and "tparam" parameters are not pointers.

One builds an array of bytes representing the "flattened" (AKA "serialized") TCommandMsg structure and configures the CLF to pass an array-pointer.  The DLL receives the pointer and assumes it points to a struct - which it will IF the array has been packed correctly.  To pack the array correctly means knowing exactly how many bytes each parameter requires, and, if passing a numeric, whether the DLL expects the least-significant byte first (Little-Endian) or the MSB first - Big Endian.  When LabVIEW flattens numerics, it arranges the bytes in Big Endian order.

here's a list of the data-types shown below, in order

"C" type      LV type  Identifier

longint (I32) ("Apld")

word    (U16) ("commandnr")

word    (U16) ("commanIDr")

?(tparam) (?)   ("param")

of what "C" datatype(s) is tparam composed?

Cheers.

---

huangjack wrote:

I am trying to use "Call Library Function Node" to call a DLL to control a device.
The prototype of one function in the DLL is:  function putcommand(prec: pointer):longint;
The mannual describes the function as following:
 
"Together with the Putcommand function ,a 32 bit pointer, which points to command
message structur (see below) is to be transferred to the DLL."
 
TCommandMsg = packed record
                     ApId : longint;
                     commandnr : word;
                     command : tcommand;
              end;
where the  "tcommand" structure is shown below:
tcommand = packed record
                  commandID : word;
                  param : tparam;
           end;
 
Both the type and size of the fields within the two structures are given.
 
How can I pass the parameter from LV to the DLL?
 
Thanks

---

Message Edited by tbd on 02-17-2008 01:57 PM
 

I think it woud be a good idea.   (Mahatma Gandhi when asked what he thought of Western civilization)

[tbd]

---

The tparam is a case structure.

tparam = packed record
                   case byte of
                         1 : (B1,B2,B3,B4 : byte);
                         2 : (w1,w2 : word);
                         3 : (i1,i2 : smallint);
                         4 : (r1 : single);
                         5 : (l1 : longint);
end;

Great - in that case we just keep appending data-bytes.  There's actually a clean shortcut that can work here.  Instead of explicitly building an array from individual numerics, we can just "serialize" a LabVIEW nested-cluster control.  There's a "hidden" requirement though, the cluster elements must be ordered precisely.  If you right-click on the cluster-border and choose "Reorder Cluster Control" you'll see that each element of a cluster is indexed - and this order must match the order in your "C" type-defs.

Warning: I wasn't sure if small int was 1 byte or 2 - I made it one byte.  Note there's also a case to allow big-endian/little-endian byte-swapping.

I wouldn't expect all this to work the first-time - there are many details and CLF/DLL calls tend to be very "sensitive" - but. it can work!

Cheers!