I am designing scalable PPP [mean it can be extended to over Ethernet, over HDLC, over ATM etc.]. I was stuck in determining whether State Machine is hadle by PPP stack [means i have design Base class for PPPStack in which FSM, encode, decode etc is there] or PPPoE [which is derived from my PPP Base Class PPPStack].
I am designing PPP using C++, so that it can be extended to oE, oATM etc.
PPP frame encoding in done in PPP itself and PPPoE [of which PPP frame is add after discovery and start of session].
This is first time i am writing Scalable, If anybody involved in Scalable Architecture would love hear points from them too:)
Thank you so much in advance
PPP does have a state machine, several in fact. The link is started, authorized, and kept up by a state machine.
The LCP, link control protocol, however, is a much more complex state machine you'll need to deal with.
There are a lot of resources about PPP, and I'm afraid the only question I saw in your post was
"I was stuck in determing wheter State Machine is hadle by PPP stack or PPPoE."
The answer is PPP does have several state machines.
PPPoE might also have another state machine or two, but I haven't checked into that.
Here are a few resources that might help you:
Very nice document with a good LCP state transition table:
http://scholar.lib.vt.edu/theses/available/etd-04252000-20310024/unrestricted/chapter4.pdf
Excellent powerpoint overview talking about many aspects of PPP:
http://www.cs.huji.ac.il/~sans/students_lectures/PPP-Intro.ppt
Also, a google search is likely to be useful:
http://www.google.com/search?q=ppp%20state%20machine
Good luck, and feel free to revise your question if I didn't understand it.
-Adam
Related
I did my best to search all topics regarding to SCADA and developing your own C++ desktop application to communicate with PLCs, but could not find any recent, or in my opinion, relevant topics that fit what I needed. If I missed them, a link to them would be very much appreciated. If I also happened to post this in the wrong section, or you can think of a better section for me to post this in, I will take it there.
With that said, I thank you in advance for taking the time to read my questions, and appreciate any input you have to offer.
A little bit about what I'm doing
I'm currently in school for electromechanical engineering, and for my final year project I am developing a desktop application in C++ to monitor PLCs we have located within one of our labs.
Within this lab, I have a pre-existing ethernet network connecting all PLCs to single point, which I am tying into with a PC, and will be doing all my work from there.
I will be developing the application in Qt for an easy way to design the GUI, and giving me access to the QNetworkInterface as well as QTcpSocket.
With that said, I wouldn't go as far as saying I'm an experienced programmer, but I have been fooling around with a few languages (i.e.: python, c++, c, php) for quite a few years, and am still learning, considering the learning NEVER stops.
My questions
Is there any reference material I can read, that you can suggest, on the subject to more easily understand what sort of process I need to go through to receive information (i.e.: individual I/Os, status bits, tags, logs, etc...) from the PLCs directly, and not through an OPC server?
If an OPC server is required, I've never dealt with OPC links other than using Rockwell Automations RSLinx to grab tags and display their values within excel (I had created a prototype using that exact method to start, but would like to move away from excel, and if possible, the OPC server (RSLinx) as well). What would you suggest to someone who knows nothing about the subject of OPC servers, or to my knowledge, OPC in general?
Have any of you previously written your own application to do something similar, if not of the same nature to what I'm trying to accomplish?
What advice or suggestions would you give for someone who is attempting this type of project?
PS: As a start for this project, I would initially just want to get the reading of the I/Os (tags or addresses) to view what their current values are (closed or open for inputs, energized or not for outputs). But eventually I would also like to be able to write values to tags on the PLCs I'm monitoring based on the values I've received from them.
PSS: I would like to note again, that I am still a student, and am still learning about this subject in it's entirety. I would just like to ask for your patience, as I may not grasp things completely the first time!
If I've missed any information you feel is pertinent to be able to provide an answer, please let me know! I will do my best to come up with said information in a timely manner!
Thank you!
EDIT #1: Added in another question, and altered my first question slightly
EDIT #2: Fixed up question 2
IMHO a SCADA program should have as a minimum requirement to be able to connect to an OPC server. OPC is used for most commercial PLCs.
Strictly speaking there is no need to have an OPC server/client approach but it gives you flexibility and gives you an abstraction model. If you want to directly connect to PLCs using a protocol then that is of course possible as well. You then need to know more details about the protocols and their various versions.
Yes I worked for a few years in a team that developed a commercial SCADA application.
It is very easy to get lost in details in such a project so try to keep things as simple as possible. By using OPC you will save time instead of fiddling directly with the protocols. You could add the ability to add custom-drivers for other protocols - depending on your timeframe. Try to model up your project before you start coding to a birdsview of the model and avoid getting lost in the details.
I would stay well away from looking to write your own code to connect directly
to an AB PLC - there are products out there that you can use in your application:
http://www.rtaautomation.com/software/ethernetip/client/tagc/ControlWin.html
http://www.automatedsolutions.com/products/dotnet/ascomm/
You would be better to use OPC - you can write you own OPC client if you want and follow examples you find here:
http://www.opcconnect.com/source.php#freesource
According to this http://www.control.com/thread/1026173407 you should be able to get source code of Kepwares OPC Quick Client.
It would probably be easier to just use a library as in this example (RSLogix,C#):
http://www.mesta-automation.com/opc-client-with-c-an-how-to-video/
You might find this of use:
http://www.rockwellautomation.co.kr/applications/gs/ap/GSKR.nsf/files/rslinxsdk_ma_eng.pdf/$file/rslinxsdk_ma_eng.pdf
Some resources:
http://www.opcconnect.com/ ,
http://www.mesta-automation.com/
Answer to question #4 - realize that your lab technically could contain ANY manufacturer's PLCs in the future. If you ever took a Data Communications class, you realize that for N different PLC types, you would have to write N different communication drivers for your PLC client.
This is where standards are helpful. Without the use of a standard protocol, scaling your lab could become more time consuming and less manageable. This is why communications standards exist.
HOWEVER, not all PLCs necessarily support the standard(s) you may decide upon.
The best choice is OPC/UA. Many PLCs have server drivers readily available. That means that your client just needs to understand 1 protocol (OPC/UA), and then it can "easily" be connected to any PLC that has a driver for that standard.
After that, there is OPC. After that, Modbus (TCP and RTU flavors), a relatively simple industry standard that is supported by most PLCs. EtherNet/IP is also a possible choice, although not all PLCs support it in a "server" role (many do support it as a client, but that is not what you need).
have a look at pycomm in github or pylogix at github which are Python written drivers to link to clx plc.
I am completely new for EtherCAT. And I am looking for a good starting point to study EtherCAT master.
I found that there is a great open source implementation called SOEM.
But without any background of EtherCAT, it is really hard to understand the code.
Could anybody help me to find the way studying EtherCAT master?
To start you need to understand the technology before you can dive into the master. I'd recommend the following three resources.
EtherCAT Technology (Section I)
This is an overview of the technology and definitely where you want to start.
EtherCAT Registers (Section II)
This is a dry read, but a good reference to understand the different registers that are used to communicate between an EtherCAT master and slave.
ET1100 Hardware Data Sheet
Even drier, but this is a datasheet for a common ASIC for building an EtherCAT slave. It can help you understand even more detail about the communication between an EtherCAT master and slave.
To properly implement an EtherCAT master is no easy task and requires a lot of reading. There is more documentation available but it requires a membership to the EtherCAT Technology Group. That's where you can get access to more technical information.
Another EtherCAT master open source project, that I'm familiar with, is IgH
The best way to go through EtherCAT master is IgH website
http://etherlab.org/en/ethercat/index.php
They also have the source code for the etherCAT master and other software components. download the zip in linux and enjoy EtherCAT
I am really passionate about the machine learning,data mining and computer vision fields and I was thinking at taking things a little bit further.
I was thinking at buying a LEGO Mindstorms NXT 2.0 robot for trying to experiment machine learning/computer vision and robotics algorithms in order to try to understand better several existing concepts.
Would you encourage me into doing so? Do you recommend any other alternative for a practical approach in understanding these fields which is acceptably expensive like(nearly 200 - 250 pounds) ? Are there any mini robots which I can buy and experiment stuff with?
If your interests are machine learning, data mining and computer vision then I'd say a Lego mindstorms is not the best option for you. Not unless you are also interested in robotics/electronics.
Do do interesting machine learning you only need a computer and a problem to solve. Think ai-contest or mlcomp or similar.
Do do interesting data mining you need a computer, a lot of data and a question to answer. If you have an internet connection the amount of data you can get at is only limited by your bandwidth. Think netflix prize, try your hand at collecting and interpreting data from wherever. If you are learning, this is a nice place to start.
As for computer vision: All you need is a computer and images. Depending on the type of problem you find interesting you could do some processing of random webcam images, take all you holiday photo's and try to detect where all your travel companions are in them. If you have a webcam your options are endless.
Lego mindstorms allows you to combine machine learning and computer vision. I'm not sure where the datamining would come in, and you will spend (waste?) time on the robotics/electronics side of things, which you don't list as one of your passions.
Well, I would take a look at the irobot create... well within your budget, and very robust.
Depending on your age, you may not want to be seen with a "lego robot" if you are out of college :-)
Anyway, I buy the creates in batches for my lab. You can link to them with a hard cable(cheap) or put a blue tooth interface on it.
But a webcam on that puppy, hook it up to a multicore machine and you have an awesome working robot for the things you want to explore.
Also, the old roombas had a ttl level serial port (if that did not make sense to you , then skip it). I don't know about the new ones. So, it was possible to control any roomba vacuum from a laptop.
The Number One rule, and I cannot emphasize this enough: Have a reliable platform for experimentation. If you hand build something, just for basic functionality, you will spend all your time on minor issues and not get to the fun stuff.
Anyway. best of luck.
I've been trying to wrap my head around embedded. Since I will be self-taught in this specific niche, I realize it will be harder to get a job in the field, so I'm hoping to add a completed project to my resume to prove to potential employers that I've done it and can do it again for them.
Can someone suggest a project that I can undertake as a single person and actually be able to finish, but at the same time not too simple that it doesn't prove anything? Something reasonable that I can aim for.
If you can substantiate your example with a project you worked on yourself, and mention how many people were involved, and how long it took to finish it, that would also help me gauge the difficulty of projects I see in general and rule out the ones that are probably too big for my capacity. It's very difficult to gauge the amount of work a project needs from my position.
You should take a look at the arduino. To quote their site:
Arduino is an open-source electronics prototyping platform based on flexible, easy-to-use hardware and software. It's intended for artists, designers, hobbyists, and anyone interested in creating interactive objects or environments.
There is a really handy playground listing a bunch of personal projects on the arduino, any one of which might fulfil your need to do some embedded development. You can also trawl around the internet (e.g. instructables) to find many other interesting arduino applications -- I particularly like the one building a fancy control system for an espresso machine, and, of course, there is the mandatory fart detecting chair that tweets its findings.
Being an arduino experimenter myself, I can attest to the simplicity and power of this device -- and the great fun you will have playing with it. If you want to get started quickly, I can recommend buying the starter kit from the very helpful people at oomlout.
Are you looking specifically at embedded software development, or are you interested in circuit board design as well?
If it's just software, then I would suggest getting hold of an ARM development board (Possibly the Philips LPC range - sparkfun have some nice ones) that you can program via a bootloader over usb and start hacking. Get one with a display and an ethernet port and you can build up to making some sort of network attached sensor (temperature, water level, object counter, etc). Start out little (turn on a LED from a button) and work your way up.
If you're also into the electronics side of things, I'd suggest something like an MP3 (or WAV) player and maybe stick to the AVR or PIC 8bit microcontrollers (AVR is used on the Arduino) as these are a little easier to deal with than ARM. Here you could start with a usb powered device that streams wav files from a PC serial port out to a pair of headphones, and build up to a battery powered board, feeding data to an MP3 decoder IC from an SD card.
Some things you may want to learn & demonstrate:
Understands the bounds of working with limited resources, including memory management (dynamic and/or static); resource management (locks, semaphores, mutex); multiple tasks (interrupts); and appropriate data structures
Ability to interface with other devices/ICs over various interconnects (analog & digital IO, serial bus (RS232, I2C, SPI))
Ability to sanely structure a program and segment the various modules without producing 'spaghetti' code
Ability to use source and integrate 3rd party libraries where appropriate (think FAT filesystem, or TCP/IP stack)
Misc Tips:
read and understand the datasheets (yes all of them)
code and test on the desktop where possible, but understand that there are differences and bugs will still creep through (this is where it helps to be using a tool-chain that is common with the desktop - GCC is good, but the tools are generally CLI)
use assert a lot - you can flash the line number of a failed assert using a single LED - this is invaluable
Most of all have fun - it still makes me smile when you first get a new component working (display, motor, sensor). Embedded makes the world go round :)
Is there a good tool out there that can model an application concurrency/locking scheme in a graphical way and that can simulate some of the aspects?
I know that Petri nets can be used for that more or less, but I don't know a good GUI tool that can design and simulate.
Is UML in any way usable for such purposes?
Any good links are very appreciated.
UML Activity Diagrams can be expressed as Petri nets (e.g. see this paper). Unfortunately I don't know any good industrial oriented tools for simulation of Petri Nets or Activity Diagram (but there are many academic projects which you can easily find).
Are you sure that you want to simulate your model (by simulation I mean that you actually want to sit and look how your Perti net is being executed)? Usually this type of analysis is applicable for small and simple algorithms. In real world situation you probably would like to do model checking of your algorithm rather than simulation. I would recommend you to check SPIN (used by many companies, e.g. Siemens). Also I have a positive experience with Alloy and Prism. But if your focus is on verifying parallel algorithms I would suggest you to consider SPIN first.
Edit: I checked some tools for simulation and I can advise looking at
1) http://sourceforge.net/projects/visual-petri/
2) http://www.renew.de/
3) http://www.winpesim.de/index.html
SPIN is a popular tool for verification of distributed systems but is command line only I think. But on the Spin webpage there is a link to a closely related GUI tool called GOAL
I'm doubt this is what you are looking for, but I'll throw in my two cents:
At my university, in our class on concurrent software systems, we use a tool called Labelled Transition System Analyser (LTSA). It's actually a language that you can use to model the behavior of a system.
The "code" is turned into a state diagram and a transition table.
Here is an interactive Java applet which can design and run a Petri net.
It's been a long time since I've looked at it, but it sounds like Ptolemy would be a good fit.
You can check Petri Net Sim, to simulate common/timed/colored Petrinets, it comes with a nice GUI that displays Petri Net execution in real time.
Try using the concurrency tool, LTSA. Java program. (Labelled Transition System Analyser), to simulate programs. You can download it from:
http://www.doc.ic.ac.uk/ltsa/
But you have to be patient while using it, it can take a couple of hours to learn how to use it. Probably works best while modeling Java programs.
And it's always good to use UML models of course :)