[SOLVED] Connection to instrument via COM fails
lazarus / 34-Windows

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Eclipticon · 2014-08-22 08:02

Good morning,

in a Lazarus project, I am using a COM interface to connect to an
external device that is connected to the computer running the software
via TCP/IP. I am posting this, because on one system this connection
fails, mysteriously.

From the manufacturer, I have received an instrument.dll and an
instrument.tlb. Unfortunately, details and code are subject to a
confidentiality agreement, so I can only provide pseudocode.

I have two minimal examples, one on Free Pascal:

Code: [Select]uses
   Instrument_TLB; // Imported via the Lazarus "Import Type Library"
function from the .tlb or the .dll

[...]

procedure TForm1.FormCreate(Sender: TObject);
begin
  AInstrument := CoInstrument.Create;
  if AInstrument.Connected then ...
end;
and one on Visual Basic, provided by the manufacturer:

Code: [Select]Private Sub Form_Load()
   Set theInstrument = New Instrument
   If theInstrument.Connected Then ...
End Sub
This VB6 project has the instrument.dll as a reference.

Both the executables as well als the instrument.dll are 32bit. The
behaviour on different computers is as follows (supplemented with
information from Sysinternals Process Explorer):

System A (Windows XP, 32bit, used for compilation): Both the FP and
the VB executable work as expected, a connection can be established.
In Process Explorer, both executables have one thread with
instrument.dll and the TCP/IP connection can be seen to be up.System B
(Windows 7, 64bit): Both the FP and the VB executable work as
expected, a connection can be established. Process Explorer was not
used.System C (Windows 7, 64bit): The VB executable works as expected,
a connection can be established. In Process Explorer the VB executable
has one thread with instrument.dll and the TCP/IP connection can be
seen to be up. The FP executable can NOT connect, there are two
threads with instrument.dll and no TCP/IP connection seen in Process
Explorer.
What I just do not get is why the minimal example with VB6 works fine
while the (essentially identical) example on FP does not work on this
one system. I know that based on the little information I am able to
give, no one can come up with a "solution" - however, advice on how to
investigate this problem further, what tools to use for debugging
would be highly appreciated!

Thanks for your time.

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Laksen · 2014-08-22 08:11

Do you know what the difference between system b and c is?

Did you compile for i386 or x86_64?

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Eclipticon · 2014-08-22 08:16

Quote from: Laksen on August 22, 2014, 10:11:23 amDo you know what the
difference between system b and c is?

There are countless differences in hardware and software on systems B
and C - which could explain if both the VB6 Test and the FP Test fail,
but as the VB6 test works, the interface itself seems to be ok ...

Quote from: Laksen on August 22, 2014, 10:11:23 amDid you compile for
i386 or x86_64?

It was compiled on a i386 system, so i386.

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Laksen · 2014-08-22 14:39

One of the most obvious would be to know if the regional settings of
system b and c are different? Comma seperator, etc.

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Eclipticon · 2014-08-22 15:43

Quote from: Laksen on August 22, 2014, 04:39:35 pmOne of the most
obvious would be to know if the regional settings of system b and c
are different? Comma seperator, etc.

I had not checked this before, but they are identical - both systems B
and C are set to "German (Germany)".

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Never · 2014-08-22 15:49

maybe firewall / antivirus settings also compare the hosts files on
both systems

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Eclipticon · 2014-08-22 16:37

Hi,

it was not the firewall, but your advice checking the firewall made me
have a look at the IP addresses again - it turns out there was 3 times
the correct one in the registry and one time a wrong one (in
HKLM\SOFTWARE\WOW6432Node\...).

Correcting the wrong one AND starting the program in Windows 7
compatibility mode (on windows 7?) fixed the error. I just need to
understand now, why ... especially why the VB test program runs
without problems.

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Never · 2014-08-22 17:14

i'm glad i was helpfull.
just a possibility .................
your server costandly brodcasting  a message on a specific port
(usualy udp port) then the vb app just need to listen to the correct
port to start the communication but......... this is just a quess