|
Hi all,
I am developing a driver for communication with some PLC's. First, I thought to create a win32 dll, but because I need to be able to send and receive messages, I start using MFC.
One of the requirements of the driver was that it could be used in VC++, Visual Basic, VB.NET, C# (so a lot of different languages).
Well, because I have developed a class that needs to be called in the dll (so you can use driver->Connect() and so on), I needed to export a class. But, in this case, other languages such as visual basic wouldn't understand the dll.
Then, someone gave me the advice to use COM objects. Well, it seems very hard to learn using COM, and some people say it will not be used anymore soon.
Now is my question, what is the best way to develop this driver???
Thanks!
Geert
[url]http://geert.yoki.org[/url]
|
|
|
|
|
Hi !
I'm somewhat unsure what you're trying to do. I take it that PLC stands for Programmable Logic Controller, yes ? In this case, how do these controllers connect to your PC ? Do you have any hardware-level drivers which allow sending and receiving data from the controller ? Or is it your task to develop a Windows hardware driver to communicate with the controllers ?
If you're developing a hardware driver, DO NOT USE MFC. That's something you just DO NOT do. Drivers are written mainly in C, and do not use MFC. If you've never written a hardware driver, then you're in for a mess. First write the driver itself, then consider options on how to allow client access to the driver. Do not incorporate direct client access to the driver itself (that means, use a DLL to interface a client application to the driver), because this hampers the reliability of the driver. Unreliable drivers will crash the OS.
If you already have a device driver provided by the PLC manufacturer, that allows you to send and receive data from the controller, and you're building the DLL that allows flexible access to the driver, then you can use MFC if you need to, but it's again not recommended. MFC is mainly for user interface applications, or solid Windows applications.
In this case, the best option is to create a COM component which, when opened up, opens a handle to the device driver, and then offers an interface through which data can be written and read. Writing a COM component is quite easy when you use the wizards. They generate most of the background code and your job is to implement the actual business logic.
To get you started on COM development, consult your local library for possible books. Rest assured, COM will not go anywhere, it will remain around for a long time still. Learning it is useful, because a lot of Windows subsystems, such as WMI or DirectX, are implemented as COM objects.
If you need more information, post more details on the project, such as what the PLC actually is, if you have a hardware driver from the manufacturer and what the precise task you're trying to accomplish is.
-Antti Keskinen
----------------------------------------------
"If we wrote a report stating we saw a jet fighter with a howitzer, who's going to believe us ?"
-- R.A.F. pilot quote on seeing a Me 262 armed with a 50mm Mauser cannon.
|
|
|
|
|
Thanks a lot for your answer!
Well, you are right, PLC stands for Programmable Logic Controller. The communication is done via TCP/IP, so I can use winsock for communication.
In my driver I have developed several classes. One to communicate with the PLC using winsock, one to communicate with the user, and a few extra classes.
I don't think (at least I hope) that I don't have to write real hardware drivers, because that wouldn't be nice...
You say I shouldn't use MFC. Well, I didn't plan to use it, but I needed a window handle to communicate with winsock (to receive messages). To do this, I needed the class CWnd, which belongs to MFC. Are there other possibilities to be able to receive messages???
Geert
[url]http://geert.yoki.org[/]
|
|
|
|
|
Hello !
Ah, this explains a lot. You're writing the user-mode component that allows communication with the device. The hardware drivers are already there, so you don't need to write them.
To help you get started, decide how the user should be able to use the PLCs. What services do they require ? Must they be able to write a program for the PLC and upload it ? Should they be able to read the program from the device and need a way of illustrating (such as a schematic) which shows what the device is currently programmed to accomplish ? Drawing a diagram (UML or otherwise) helps you design a solid structure on which to build.
After these decisions, the rest is quite trivial. You should follow standard COM strategy, in which you do not provide a direct access (a handle) to the device, but an interface, through which interaction is done. This will limit the user's possibilities to those which you have previously outlined, thus eliminating the user from accidentally or purposefully misusing your device. Writing an interface is as simple as writing a pure virtual base class, deriving from this class, and implementing the methods in the derived class. Then, you create a DLL which generates the class objects for each PLC device connected, and offers a routine through which a pointer to the interface class is returned to the caller.
Using interface classes is very useful. You only need to provide the base class header file for the user, alongside with the exported DLL routines, a possible .lib file, and the actual DLL. No source code is required, because the runtime will worry about redirecting the virtual function calls to the object in which these functions are implemented. Namely, the one which the DLL creates and upkeeps.
The internal implementation of the DLL depends on how you wish to present it. Winsock makes use of window objects to handle messaging (a Windows Message is sent whenever data is sent/received or the device is connected). You don't need MFC to create window objects. Just register a WNDCLASS structure and call CreateWindow, like in a normal Win32 program.
Unless you already knew, MFC is a collection of classes which wrap standard Windows routines. For example, CWnd is class which encapsulates the creation and displaying of a Windows window object. But you don't have to rely on MFC to create the window objects. You can create them manually as well.
There are many, many websites which show you how to create Win32 window objects. MSDN is full of examples: just whip out any Hello World -example for Windows, and you'll see how it's done. The key strategy is that although your DLL creates a window object, the object itself is made to be 0 pixels in heigth and width. Thus, it is invisible to the end user, although it is still there. This is a common strategy, and it's called 'hidden message windows'.
If you feel you're in a loss with standard Windows programming, I heartly recommend investing on the Charles Peltzoid's book 'Programming Windows'. It is The Bible of every Windows programmer and a must have if you intend to write Windows programs without MFC, or wish to learn more on how Windows OS works.
-Antti Keskinen
----------------------------------------------
"If we wrote a report stating we saw a jet fighter with a howitzer, who's going to believe us ?"
-- R.A.F. pilot quote on seeing a Me 262 armed with a 50mm Mauser cannon.
|
|
|
|
|
Thanks a lot for your answer!
There are some other things I need with this "driver". Users should be able to call the dll from visual basic, visual basic.net, c# and c++. That is the reason why some people said I have to use COM.
The first thing I did was develop a usefull architecture for the driver. This is done in UML. But because I normally develop applications using OO, I also designed the driver that way. I wanted the user to be able to call a connection like this:
MyObject->GetPLCConnection(index)->Connect();
But visual basic is not made for OO 
Now, I am thinking of this:
1 COM object to communication with the PLC (for single connection). 1 COM object to hold all the connections the user wants.
But then there is one problem left. How do I call functions from the collection COM to the connection COM.
I hope it's clear what I mean...
Thanks a lot so far for your time!
Geert
[url]http://geert.yoki.org[/]
|
|
|
|
|
Hi !
COM offers language indepence, thus it is the most reasonable choice if you want your object to be usable from all languages which support COM. These include, but are not limited to, Visual C++/Basic/C#/.NET. Even PHP supports COM these days...
However, back into the issue. The object-oriented approach is correct on this problem, but it seems you've started with wrong presumptions. First of, you don't need multiple COM objects. A single COM object which has multiple interfaces is enough. One interface for enumerating the available PLC devices and offering an index of the device, a second interface for connecting and disconnecting from the PLC and possibly a third interface which allows reading/writing from the device. And 1...n classes which implement these interfaces. 3 in the biggest case, 1 in the simplest case.
The keyword here is multiple inheritance. Consider this example:
class IEnumPLCDevices
{
public:
virtual DWORD GetPLCList(int* nArray, int& nAmountOfDevices) = 0;
};<DIV>
class IConnectPLCDevice
{
public:
virtual DWORD ConnectToDevice(int nIndex, IPLCDevice** plcDeviceInterface) = 0;
};<DIV>
class IPLCDevice
{
public:
virtual DWORD Read(int nByteCount, void** pDestination) = 0;
virtual DWORD Write(int nByteCount, void* pSource) = 0;
};<DIV>
class PrivatePLCCollection : public IEnumPLCDevices, public IConnectPLCDevice, public IPLCDevice
{
public:
.
.
};Here is the simplest model I can use to fathom an object-oriented DLL. It is not a COM example, but it follows the 'interface' idealism I showed earlier.
You don't need to seperate the communication and connections to different COM objects. They can co-exist peacefully inside a single object. You must remember here that a COM object is not the same thing as a C++ class. A COM object can have multiple C++ classes inside it. For an example, consider DirectX. It has multiple interfaces, and even more classes. Some classes implement more than one interface. However, each DirectX component is a single, independent COM object, such as Direct3D. You don't need the DirectSound object to use the Direct3D object's services, but the Direct3D object offers all the services to create, populate and manipulate 3D scenes. Lots of services (classes/interfaces), but a single COM object.
I believe there are some examples in CodeProject on writing COM objects. See under General -> COM/DCOM/COM+. You should read the articles marked with 'beginner' through to gain understanding on how COM works. Then you can start implementing your own object, either by following the examples, or simply by exploring.
-Antti Keskinen
----------------------------------------------
"If we wrote a report stating we saw a jet fighter with a howitzer, who's going to believe us ?"
-- R.A.F. pilot quote on seeing a Me 262 armed with a 50mm Mauser cannon.
|
|
|
|
|
Thanks a lot!
Thank god I can still use COM 
I have read some tutorials and can get a dll server and client communicate. One question left, and you are the best
I tried to set return values of COM interface methods to BOOL or double. But, it says I MUST use HRESULT. Then why can I choose for the other ones??? And with your example, is it possible to call a plc connect function like this:
MyObject->GetPLCConnection(index)->Connect(). In other words, can I return a pointer to another interface class with a function in a COM object??
Geert
http://geert.yoki.org
|
|
|
|
|
Hi
Tischnoetentoet wrote:
One question left, and you are the best
I'm far from the best, but I know my stuff. Guess that's one of the hazards of being a professional  Thanks anyway
All COM methods must return a HRESULT to the client. This is by design, because the clients use SUCCEEDED and FAILED macros to determine if they should continue with or retry the process, and the HRESULT values are designed to support these macros. This way, the client does not need to know what return values the server gives, other than the knowledge that SUCCEEDED and FAILED macros determine if it can continue using the object.
If you must return a value to indicate the amount of PLC objects, you can use a reference variable or a pointer. Just create a function that takes an int& as variable, fill in the number of devices, and return a HRESULT that the enumeration was succesfull. The client can then check the integer to know how many devices there are.
If you follow the standard, like you should, then a call chain like the one you describe is not possible, because each function must return a HRESULT. If you break the standard, you can do whatever you please, but your component is no longer COM compliant, and it might fail to work on a different language. Generally, you shouldn't require the client to build large call chains, instead, implement the HRESULT GetPLCConnection(int nIndex, IPLCDevice** pDeviceInterface). For this function, you pass the index value of the desired device and the interface pointer's address, and it returns you with a success code and a working pointer to the correct interface. IF the device doesn't exist, it NULLs the pointer and returns a failure code.
Another reason for avoiding call chains is the reference counting. Whenever a COM object refers an interface, it increments the counter. When all interfaces are released, the counter goes zero, and the object can free the class responsible for serving this interface. If you build long call chains, the reference counting will not work, and your COM object does not act like a COM object should. Again, because different languages offer different levels of access to COM, your object might work on C++ (which has pointers) but fail on Visual Basic (which doesn't have them). In general, avoid call chains when dealing with COM. It makes your code and documentation much easier to follow for those people who have used COM earlier and know the way it should function. Breaking the standard will cause professionals to life an eyebrow towards your code, even if it would still work.
Hope this helps
-Antti Keskinen
----------------------------------------------
"If we wrote a report stating we saw a jet fighter with a howitzer, who's going to believe us ?"
-- R.A.F. pilot quote on seeing a Me 262 armed with a 50mm Mauser cannon.
|
|
|
|
|
Antti Keskinen wrote:
Hope this helps
And IF it is helpful!
Thanks for all your time and effort! It really helped me a lot! I think I know the basics so I can start trying to develop my own object.
Thanks!
Geert
http://geert.yoki.org
|
|
|
|
|
Hi all,
I am currently trying to find a charting package for our VC++ application. We have a requirement to display data in line, area, scatter, and possibly 2d contour maps. We are displaying large amounts of data which means refreshing quarter of million points in a scatter plot becomes very time consuming.
I would be grateful if anyone could recommend any charting packages which may help.
Many thanks in advance...
|
|
|
|
|
Would an embedded Excel chart suffice?
"Opinions are neither right nor wrong. I cannot change your opinion. I can, however, change what influences your opinion." - David Crow
|
|
|
|
|
You might want to look at GigaSoft.
It's reasonably expensive, but I've used it a lot and seems to work well.
Karl - WK5M
PP-ASEL-IA (N43CS)
<kmedcalf@ev1.net>
PGP Key: 0xDB02E193
PGP Key Fingerprint: 8F06 5A2E 2735 892B 821C 871A 0411 94EA DB02 E193
|
|
|
|
|
How to get information about other applications running with our application?
like, Which applications are running currently?
|
|
|
|
|
Are you talking about EnumProcesses()?
"Opinions are neither right nor wrong. I cannot change your opinion. I can, however, change what influences your opinion." - David Crow
|
|
|
|
|
How can i make a customized keyboard
any idea and suggestions please
|
|
|
|
|
|
If I am wrong what I am asking Plz do correct me
1. How can I change The Source IP in the IP Header
2. How can I change The Source IP in the HTTP Header
Actually I want to sumit some data from my VC App on a form in a web site which does not allow submission more than once from a single IP address
Thnx in Advance
AD
|
|
|
|
|
The following RFCs will help
Internet Protocol[^]
Transmission Control Protocol (TCP)[^]
NOTE: Normally HTTP uses TCP port 80.
Ant.
I'm hard, yet soft.
I'm coloured, yet clear.
I'm fruity and sweet.
I'm jelly, what am I? Muse on it further, I shall return! - David Walliams (Little Britain)
|
|
|
|
|
Hi,
I have to work on Windows Themes. I should be able to apply different themes to my application. These new themes must be applicaple only to my application and not to the entire Windows. On browsing the Google and other websites I learnt that UXTHEME.DLL has to be used to change the windows themes.
But I have no idea as to how to use this Dll to change the theme of only my application. I need to give an option in my application, say in the form of menu option showing the available themes, and allow the user to select one among them and then apply the theme to my application. My application should work similar to YahooMessager where we can select available skins/themes and it gets applied only to that messenger application.
I have never worked in this area. It would be of great help to me if any one can give me some inputs in this area.
Thanks
Madhavi.
|
|
|
|
|
Hi !
You should consider keeping a data value in registry that tells which 'theme' the user has selected. Then in the application, load this value and paint your windows and controls accordingly. It's called 'skinning an application' and is a very popular theme around the Net.
The UXTHEME.DLL is a library related to Windows Themes (how Windows windows, buttons etc look like). You should never change this DLL, although you can load it to make your application have the 'Windows XP' look and feel.
An alternative is to look for fore-skinned control packages, such as Dundas Ultimate Toolbox or Codejock's Xtreme Toolkit. These both contain hundreds of components in building custom-looking UIs. Both of these toolkits currently focus on providing Office 2003 look and feel.
One option is to just use Paint and draw your UI. Then use window region clipping and painting to push this 'drawing' as your main window. This is how the popular media player Winamp is constructed, for example. All the sections of the window are loaded from a bitmap or graphics file that can be custom generated. Creating a new UI is as easy as drawing a new graphic and making it follow an already working graphic file's layout.
-Antti Keskinen
----------------------------------------------
"If we wrote a report stating we saw a jet fighter with a howitzer, who's going to believe us ?"
-- R.A.F. pilot quote on seeing a Me 262 armed with a 50mm Mauser cannon.
|
|
|
|
|
Hello:
I have developed an MFC exe using a library that uses MFC objects. It pretends to be a driver for Bluetooth. This application uses a modal CDialog as main object. I am trying to convert this app to dll, in order to let the applications accesss bluetooth. I have designed an interface with two exported functions, Read and Write. I have done the dll but when it is initiated by the client it gets blocked as it uses a modal CDialog. I have tried to convert it to modeless but I don´t see the way as it has no parent window. Any idea of how can I solve the problem?
Thanks in advance,
Mikel Fernandez
|
|
|
|
|
lmfernandez wrote:
I have tried to convert it to modeless but I don´t see the way as it has no parent window.
Pass the desktop window as the parent. GetDesktopWindow() should help.
Ant.
I'm hard, yet soft.
I'm coloured, yet clear.
I'm fruity and sweet.
I'm jelly, what am I? Muse on it further, I shall return! - David Walliams (Little Britain)
|
|
|
|
|
GetDesktopWindow() returns NULL. Do you know any reason?
|
|
|
|
|
Are you trying to use the DLL before there is a desktop. From a driver or a service for instance!?
Ant.
I'm hard, yet soft.
I'm coloured, yet clear.
I'm fruity and sweet.
I'm jelly, what am I? Muse on it further, I shall return! - David Walliams (Little Britain)
|
|
|
|
|
Hi
I made an application that operates on the serialport. Using "CreateFile" I must include windows.h
Now I have re-written my app and wanted to include an image in the GUI, so I used "Picturebox".
However, with the picturebox and the picture, it looks like I cannot include the headerfile windows.h.
When I include it , I get the message:
error C2039: "GetObjectA" is not a member of "System::Resources::ResourceManager"
This errormessage is pointing to the line in my code dealing with the image.
Does anybody know what I have done wrong?
regards
donE
|
|
|
|
|
General 
News 
Suggestion 
Question 
Bug 
Answer 
Joke 
Praise 
Rant 
Admin 
Submit an article or tip
