On my STM32F7 I have to connect a 3G modem using serial port.
I can communicate with the modem using AT commands.
I would like to use PPPos (PPP over serial) library from LWIP to enter in PPP mode. So I take a long look at the official documentation
http://lwip.wikia.com/wiki/PPP
and
https://github.com/tabascoeye/lwip/blob/master/doc/ppp.txt
I understand the guideline but I'm really surprise there is no implementation example with serial port. Indeed, I think there is a lot of modems that have a serial interface, so I thought i can easily find an example of use.
Anyone have already done that or has an example ?
While I cannot publish my example, the general idea when it comes to integrating TCP/IP stack of your choice with its PPP driver is the same among all serial modems and all TCP/IP stacks that I've worked with.
Generally as you've mentioned, you start with configuring the modem using AT commands - things like checking whether SIM card is present, whether it requires PIN, specifying PIN if needed, checking if it has successfully registered in the network. Possibly reading additional information data such as IMEI, IMSI as well as diagnostic data: signal quality, BER etc. Once you're done, you switch the modem to "data" mode (see ATD*99), wait for the modem to respond to that command and pass the responsibility to the TCP/IP stack, as at this point the modem starts talking PPP.
When it comes to integrating your modem with the stack so it can communicate with it, the implementations I've encountered all require implementing some form of low-level API functions for the stack. For LwIP, the wiki page you've linked in the "PPP over serial" section, it is described quite well how those functions should behave. Because TCP/IP stacks are just a software library not tied to specific hardware and they can be run on almost anything (assuming sufficient resources), specific API implementations such as the one discussed are not always provided - there would have to be a ton of examples for it to provide any value. Although if you google around for it, you might find someone having done it for the MCU that you use personally. Assuming you've already done the part where you successfully comminicate with your modem using AT commands, it shouldn't be much more other than using the send/receive functions you already have. Some slight changes may be required, such as adjusting their behavior (synchronous->asynchronous or vice versa) or redirecting received data to the TCP/IP API receive function instead of your AT command parser. Nonetheless, most of the necessary hard work should be done already.
Once the TCP/IP stack takes over, you continue with the modem using provided stack PPP API. For LwIP see functions such as: pppSetAuth, pppOverSerialOpen. Those will cause the stack to internally handle the necessary communication with the modem over PPP: LCP, PAP/CHAP, IPCP. Once that part is done (you retrieve IP configuration data from the network) it becomes transparent how this operates - it becomes one (of possibly multiple) network interfaces and you use it just as any other one, for example using socket API.
Related
I am currently working on the design of a measurement system. It has a three instruments mounted on a pan/tilt head, but only one serial line from the instruments to the Beaglebone Black (BBB) that controls everything. Instrument A and B are similar (use the same commands and module). I'm using Python to control everything. During testing, I had additional cables so that I could wire each instrument to a separate port on the BBB, but that is not possible in the final setup.
Since I needed some processing capabilities on top of the pan/tilt head anyway, I'm using a PIC24 device to connect all instrument serial connections to.
My idea is to multiplex the 3 serial connections, for instance by adding a prefix A_/B_/C_ to the commands/replies.
This I can do.
Communications and processing for instrument A and B is done by the same Python module, which has a function measure() that takes the serial port (ie. /dev/ttyO4) as one of the parameters. I'll obviously need to adapt this.
I need to find a way to allow different modules to access three "virtual" ports, with the choice of either stream A/B/C.
So in short: I (think I) need some kind of class/... that opens the serial port and multiplexes/demultiplexes three streams. Instrument A and B are not to be used simultaneously, but A/C and B/C can be used at the same time. Timing is not critical, a couple of hundreds of milliseconds delay is not an issue.
One option would be to use a second PIC to do the reverse of the microcontroller near the instruments, but I suppose this should be possible in Python as well...
I think the elegant solution is to add some code for your PIC to work as a Modbus slave.
There seem to be good efforts already done, so maybe you can use something like this as a starting point.
You can have the three UARTs connected to the sensors continuously writing to several Modbus registers and query those from your BBB with something like pymodbus or pylibmodbus.
It will also be possible to use other buses/protocols like CAN, but if you run Modbus directly on the TTL UART (instead of over RS485, which you won't need unless you have long distance or a noisy environment) you don't need any additional hardware. You will have to modify the firmware on your PIC and write some more lines of Python on your BBB.
But if you want to learn something new (assuming you don't know already), Modbus is quite an easy and useful protocol to add to your toolbox. It's still very popular and open (the spec is publicly available and you have tons of info and code).
EDIT: I'm keeping my first answer as a reference for others, but the question did not refer to sharing the same physical cable for multiple ports so what I wrote here is not really useful somebody misunderstands it the same way I did.
This question has come up a number of times, see for instance Receiving data from multiple devices using parallel wired RS232
Serial lines are not intended to be multiplexed, if you decide to follow this route I think you'll get many headaches.
Is there a reason not to use a multipoint protocol like RS485, SPI...? I'm sure you'll be able to find one that works for your needs. For RS485, for instance, the
investment in new hardware would be minimal and the software side would be a piece of cake.
So I am in a bit of a dilemma, I want to create a LED dashboard using my Raspberry Pi, the only problem is how am I going to read the data to the Raspberry Pi using C++? I am thinking about buying an OBD to USB connector and reading the data from there, but it still doesn't change the fact that I would need parse the data, but the only library I found for OBD on C++ is https://github.com/lkrasner/obd-cxx but it does not look promising.
So this is where I turn to the Stack Overflow community to help me out because I have run out of options.
Can the OBD data be read as serial? If it was serial, wouldn't that be too slow for a real-time speedometer? Should I use another port instead of OBD?
I have quickly searched and found this topic: http://blog.lemberg.co.uk/how-guide-obdii-reader-app-development
It is not usb, but it tels about AT commands to communicate with the adaptor. Thus, I would assume the USB one will be visible as a serial interface with the same communication principle. Then you might not need a library, as you can directly read-write your serial device.
Make sure only, that the adaptor you're gonna buy supports the communication protocol of your car (CAN or another). Perhaps also one option to think about is whether the adaptor provides high-level commands for you (then you need to check that the required diagnostics services are supported by the adaptor), or you need to build/parse the raw diagnostic messages yourself (I think this would be more flexible solution).
I am posting here concerning the emulation of computers on the local network, without destroying the local network.
When a computer connects to wifi on your local network, the computer can be seen in the "Network" section of Explorer(on Windows) and can be addressed via internet protocol.
My Goal: I would like to create a program such that I could receive streams of data from a remote computer via radio waves. The communication would be full duplex, there would be a transmitter and a receiver on both ends.
My Idea: I would like to utilize Qt to create an application which would receive and demodulate the radio waves like sound (through OpenAL buffers) which would act similarly to a driver program for the emulated computer connection, without destroying my connection to the local network. In this way, I believe that some truly novel things could be done, as I could for instance, use PuTTY one the emulated connected computer remotely while browsing my local network and the internet from my "base" computer.
Extended explanation: I want to perform a weather balloon project, sending a small computer (likely Raspberry Pi3) via a weather balloon to the far reaches of our atmosphere. One of my worries is being able to communicate with the device, such as receiving locational (telemetry) data in real time and being able to (potentially) retrieve arbitrary data in real time.
I understand that I may very well be approaching this question in the wrong way. There are probably existing systems out there that grant telemetry data and some arbitrary means to transfer file data, of which I am unaware. But from what I have seen, I also cannot find a device that utilizes this approach (packet radio emulation of a computer on the network). I have a personal curiosity towards this approach, and thusly will accept the answer which follows most in line with this approach.
P.S: Video which inspired this idea:
https://www.youtube.com/watch?v=Ueb5JG0dCL8
What you're trying to do is called software-defined radio, and is rather popular. Modern computers, even little ones, are more than powerful enough to do the modulation/demodulation entirely in software.
There's very little left for you to do other than designing the RF channel, purchasing often open-source hardware, and using existing open-source SDR implementations out there. The input/output to your Qt program would be either a QIODevice-like data stream that you'd couple to the SDR library's data scrambler/descrambler, or a packetized data stream that you could run some higher-level protocol on.
Do note that unless you limit yourself to an industrial license-free band, you are likely to need an FCC license to operate the transmitter, and an FAA license to launch the balloon.
Your question is essentially off-topic here. It probably belongs on amateur radio stack exchange under the [sdr] tag.
If you're thinking of implementing a complete WiFi stack using SDR, I'd like to discourage you: it's patent-encumbered up the wazoo, so no open-source implementations exist, and the sheer amount of standardese you'd have to wade through to do a compliant implementation is staggering. We're talking on the order of 5,000 pages of standardese, where almost every other sentence is important so if you ignore it, you're not compliant.
I read some questions here but couldn't really find the specific problem I'am faced with here...
I need to implement a "DeviceCache" in a particular project which caches all device-names found in /proc/net/dev .
The Language is C/++
So I thought about a seperate thread looking every X seconds in the directory mentioned above but was encouraged to find a more direct way.
How can I register a method of my process to the device manager of linux?
Is there a similar way like events/signals?
I looked in other sites but couldn't find any helpful code... Im relatively new to Linux-programming but willing to learn new things :)
Based on your comments, what you really want is to track which network interfaces are operational at any given time.
The only true way to determine if a network interface is up is to test it - after all, the router on the other end may be down. You could send pings out periodically, for example.
However, if you just want to know if the media goes down (ie, the network cable is unplugged), take a look at these SO questions:
Linux carrier detection notification
Get notified about network interface change on Linux
If you just want to be notified of the actual hardware-level registration of interfaces (eg, when a USB NIC is plugged in), you can use udev events if your platform has udev; otherwise, I believe there's another netlink category for hardware addition/removal events.
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I have one computer that is running a c++ program to control a robot and another computer that is running a computer vision system (also written in c++). I would like for these two programs to be able to talk to one another. The communication would not have to be complex, I would just need the robot computer to be able to tell the vision computer when a trial begins and ends (when to start and stop a data collection sequence). Do any of you have advice on how to approach this problem? Rs232 communication between the computers? Some kind of networking solution? smoke signals? Any suggestions would be welcome.
thank you in advance
(edit) In case you think the statement above is vague:
I need to pass a binary (go/don't go) signal from one computer to another. Unfortunately I can't be more specific about what this will look like because (obviously) I don't know what is available. Both computers are on a network, and both computers are running windows. The goal is to syncronize data collected by the computer vision system with actions performed by the robot. The communication does need to be fast enough that it will not slow down either the robot or the computer-vision program. a "good" solution would be 1) easy to implement 2) fast. I do not know much about networking and I am looking for a place to start looking.
thank you again for your assistance
You might use a simple UDP protocol - the advantage being that if you understand the concepts of simple packet protocols on RS232 you'll find it easy to transfer that knowledge to sending the packets via UDP.
If you want a reliable (as in, other parts of the system will worry about errors and retries) stream of bytes between the two PCs, then TCP/IP is not much more complicated to use than UDP.
Both UDP and TCP are accessed through 'sockets'. I'm afraid you'll find that from C++ there is rather a lot of tedious boilerplate to getting that working, but there are lots and lots of examples around.
If they are network-connected you could just use sockets.
The best option will be to use network communication. The easiest way to approach this should be to look at the networking examples in Qt.
You basically will create a client and a server application. You decide what the client does when it sees a certain message from the server. That's all. Qt should take care of the rest of the stuff.
Other answers suggests TCP/IP, UDP, RS232, ... All those things are just options when you use QtNetwork module. I assume that since you ask your question, you don't know about the difference between those. So the safest bet will be to use the highest level (free) library, hence the suggestion to look into Qt.
Another option is to use Boost.Asio. I tend to prefer Qt solution since their API is nicer.
That sounds like a fairly good use for the network socket. If both your machines are on Windows you can even use named pipes.
For Windows, you will need to open the COM n port as a file to communicate over a serial port[1]. I don't have access to my code now, I can look it up when I get home.
RS232 is easy and I like it. However, it it is slow. You need to consider that in your design.
[1] For C++.
Most modern computers have Ethernet capability, so get yourself a cheap hub or switch and look at networking APIs. There's usually some fairly easy socket stuff. One advantage of this is that, if you want to increase communication ability later, such as having your vision software provide instructions and guidance to your robot, you've got the basics set up.
Alternately, set up your vision program so you can start and stop it by hitting random keys. When you're going to use it, put the keyboard in front of the robot computer's CD drive, and eject at the start and end of the robot run.
This may be overkill in your situation, but if I were in your shoes I would probably implement it using the HTTP protocol. The vision computer would run a HTTP server and the robot computer would communicate the state changes using POST requests. The Poco C++ Net library provides you with the facilities required to do this.
I would use a TCP/IP socket for communications. TCP guarantees that the data will make it. So, all you need to do is parse the data.
RS232 is an easy option to program for, however modern PCs don't tend to have RS232 ports. You may need to get USB-RS232 adapters or install a PCI card.
The other problem with RS232 is that you have an additional wire to worry about which can be a nusiance. Also RS232 cables can be limited in length (5-15m) unless you invest in some clunky RS232 repeaters or bluetooth connectors, etc.
On top of all that you're also adding one more item to your project that can go wrong and cost you time in deploying and debugging.
IMO, an elegant engineering solution would be to utilise the hardware that you have and use TCP/IP sockets to communicate.
The web is awash with examples on passing messages between servers and clients:
If you're using Linux:
http://www.linuxhowtos.org/C_C++/socket.htm
Using Windows:
http://www.adp-gmbh.ch/win/misc/sockets.html
I also might look at something like 0MQ to make the connection more robust. It will transmit and reassemble messages regardless of the transport, and handle buffering in the case of temporary loss of connectivity.
But the bottom line is that I would use TCP/IP, but depending on the nature of the robot you may want a slightly more robust connection system than TCP sockets. UDP is nice because it's connectionless-- if the robot temporarily travels out of range/sight/etc you wont have to rebuild the socket and context.