[Visual-devel] Re: building visual

[Thomas H. <Tho...@we...>]

On Monday 31 March 2003 16:14, you wrote:
Hi Matej,

> Thank you very much for your effort. Your update fixed the gcc3.2 problem!
Thank you for your reply. I allways like to hear when something works :-)
> I still have some problems with depcomp file, but I'll try to find out
I ralso read your other mail about having solved it. I'm not too good (means 
really bad) in using autoconf. So I', glad to read it was not my fault.
> what's wrong by myself and I'll let you know about it.
> I'm planning to use Visual in combination with MatPLC in a real world
> application - hobby only, so slow progress is to be expected
> . ;-)
I've tried out little of matPLC. I'm sceptical about two aspecte of it's 
behaviour in comparision with real PLCs. This reflects my current knowledge 
and humble opinion. I told the matPLC developers about it, but they to seem 
to be too concerned about it.

1. When I start the GTK hmi demo, the main program is slowed down very much 
during loading.
This is, IMHO, inacceptable for a PLC replacement. Consider the example of an 
elevator (lift) that shall stop in the fifth floor. When passing fifth 
floor's positional contact and  the computer is busy with some other task and 
when matPLC regains conscience, we may be in the seventh floor already. ;-)
A solution to this would require hard realtime capabilities.

2. When the program restarts, it does not preserve any information about the 
process state.
In real PLCs, you have the possibility to store information in battery 
buffered RAM. So, in the elevator example, you may store information about 
having pressed fifth floor command button. You know stop the PLC. The 
elevator also stops, because outputs go to safe state 0. Know you do some 
modifications/maitenance to the PLC program. Set the PLC to "run" state again 
and the elevator will continue it's way to 5th floor.
This is not too important in the elevator example, but in industrial 
machinery, there may be lots of settings which should be preserved over 
restarts.

3. Most PLCs offer the possibility to modify a runnig program.
On some models this can be dangerous also, but it's common practice.

I thought about how to implement these features in a LINUX based soft PLC, 
but it's very low priority to me. I fear it would mean a complete redesign of 
matPLC.


> Let me know if there is anything I could contribute to your project. I have
> some experience in this field (unfortunately only on Windows) - I wrote few
> OPC drivers 
For Windows, I suppose...
I will need OPC communication to VISUAL until june or july. The important 
thing for me is to use VISUAL as a client to an existing OPC server.
I searched for freely available examples. My plan was:
1. get an example to run under wine
2. compile it with wine's libraries and get it to run again
3. extract a minimum of necessary funtions from wine code
Until know, I did not yet succed with point 1 )-:

>...and did some SCADA design with Intellution iFix dynamics in the
> past.
Any suggestions about what is better in intellutions are highly welcome.

Thomas