I am making a CAN simulator for GPS trackers, they only record CAN data and doesn't send ACK. Is it possible to send CAN data with raspberry, using mcp2515/tja1050, without any device on bus that would trigger ACK?
This will usually generate a continuous retransmit.
Some devices have a "one-shot" transmit mode when just sends the CAN frame and does not attempt a retransmission. If you transmitter has this mode you can do what you describe, otherwise you will get a lot of retransmissions.
No it isn't possible, you need at least 2 nodes that are actively participating in the communication. This can however be fixed by just providing another CAN controller on the bus, which doesn't have to do anything intelligent except the ACK part.
For development/debug/test purposes you can however put your own node in "loopback mode", meaning it will speak to itself. Can be handy if you have to proper hardware available yet.
You can try to set the controlmode presume-ack to on.
Assuming you are using the ip command for creating your can sockets that would be something like
ip link set <DEVICE> type can presume-ack on
This will ignore missing ACKs. However I am not sure whether this works with all controllers.
Related
What I mean is that, when I code a project, I need to communicate with the serial port like COM1, COM2... but sometimes there is no device connected and I also can use the function CreateFile to get the COM port handle.
When I use the WriteFile function to send a string to the COM port the software blocks.
After I dig into the problem I find another function GetCommModemStatus which can get status of the COM port but when I use the usb-rs232 transition line, the second parameter always returns 0.
How can I get the COM port status so that I can check if is there some devices connected to the computer?
If I understand correctly, you want to detect if a device is connected to your COM port and ready to accept packets. If that's the case, you need to check control signals (DTR/DSR and CTS/RTS) before sending data, assuming your device is aware of them and sets the appropriate PIN on your DB-9 or DB-25 connector. Some devices rely on software handshaking instead (XON/XOFF) and do not set control signals. Your best bet would be to consult documentation of your device.
I have been using ComPort Library version 4.10 by Dejan Crnila. It does support both hardware and software handshakings, so you can focus on your own code instead of reinventing the wheel.
As several people have already pointed out, it is not a good idea to try to "re-invent the wheel." Except for "quick and dirty" testing, your code will have to handle the com port in a separate thread and the available solutions all make this much easier.
BUT, if you Really want to do it, I'll give you some pointers.
If you are using "WriteFile" then you have probably already figured out the "CreateFile" part of the procedure and how complicated things can get depends upon what kind of IO you specified in that procedure, Overlapped or not. Overlapped IO is more complicated but does let the OS handle some of the burden.
You mentioned that your call to "WriteFile" hangs. You should look up the "SetCommTimeOuts" function. Setting both the WriteTotalTimeoutMultiplier and WriteTotalTimeoutConstant members of TCommTimeouts to zero will tell the OS to return immediately. You may also need to "SetCommMask" if your target uses handshaking.
What happens next really depends on what your target is supposed to do. The GetCommMask function can be used to check the status of the handshake lines.
I'm planing to start some sms based application and currently in feasibility study part. In my application client have to sms their problem to the server and we have to analyse the problem and take reasonable action. Also We have to find the tentative location through which tower they have been connected. I have seen about silent sms feature but not understand. Is any body have experience on how to detect location of sms creator (not in android or iphone). Please help me on determining whether it is possible or not to find the location. If possible then how?
In short this is not possible.
an SMS message weather in PDU mode or text mode does not carry the information to match the source location to the message in any way shape or form.
With reference to the article you linked to in your opening post, I'm sorry to say that there's so much B$$l S$$t in that post that I can smell it from here.
In all the years Iv'e worked with GSM systems, both as a network maintenance engineer and later as a developer writing software to use these systems, not once have I heard of anything such as an 'LMU' or an 'E-OTD' in fact the only acronym that article really got correct was 'BTS' oh and the bit on passing the data over the signalling channel.
As for the silent SMS, well that part actually is true. The special type of SMS they refer to is actually called a Ping-SMS and it exists for exactly the same reason that a regular PING on a TCP/IP network exists, and that's to see if the remote system is alive and responding.
What it's NOT used for is the purpose outlined in the article, and that's for criminal gangs to send it to your phone and find out where you are.
For one, the ONLY people that can correctly send these messages are the telephone operator themselves. That's not to say that it's impossible to send one from a consumer device by directly programming a PDU if you have the necessary equipment and know how. You could for instance pull this stunt off using a normal GSM modem, a batch of AT commands and some serious bit twiddling.
However, since this message would by it's very nature have to go through your operators SMSC and most operators filter out anything from a subscriber connection that's not deemed regular consumer traffic, then there's a high chance this would fail.
You could if you had an account, also send this message using a web sms provider that allowed you to directly construct binary messages, but again they are likely to filter out anything not deemed consumer grade messages.
Finally, if you where to manage to send an SMS to a target device, the target device would not reply with anything anywhere near a chunk of location based info, cell tower, GPS or otherwise. The reason the SMS operators (and ultimately the law enforcement agencies know this info) is because EVERY handset that's attached to the GSM network MUST register itself in the operators MSC (Mobile switching centre), this registration (Known as ratching up) is required by the network so it can track what channels are in use by which device on which towers so that it knows where to send paging and signalling info.
Because of the way the PING SMS works it causes the destination device to re-register itself, usually forcing the MSC to do a location update on the handset which causes a re-registration.
Even then, all you get in the MSC is an identifier of the cell site the device is attached too, so unless you have a database in the organisation of all cell sites along with their exact lat/long co-ordinates, it's really not going to help you all that much.
As for the triangulation aspect, well for that to work you'd need to know at least 2 other transmitters that the device in question can see, and what's more you'd need that device to report that info back to someone inside the network.
Since typically it's only the Ril (Radio interface layer) on the device that actually keeps track of which transmitters it can see, and since the AT commands for many consumer grade GSM modems have the ability to query this information disabled, then it's often not easy to get that info without actually hacking the firmware in the device in question.
How does Google do it? well quite easy, they actually have commercial agreements with network providers that pass the details of registered towers to their back-end infrastructure, in the apps themselves, they have ways of getting the 'BSS List' and sending that list back to Google HQ, where it's cross referenced with the data from the network operator, and the info they have in their own very large transmitter database and finally all this is mashed together with some insane maths to get an approximate location.
Some GSM Modems and some Mobile phone handsets do have the required AT commands enabled to allow you to get this information easy, and if you can then match that information to your own database you can locate the handset your running from, but being able to send a special SMS to another device and get location info back is just a pipe dream nothing more, something like this is only going to work if your target device is already running some custom software that you can control, and if your device is running software that someone else is controlling, then you have bigger problems to worry about.
I need to dump some incoming packets and then prevent them from going up the stack, so that applications won't process them.
Now, tcpdump works at layer 2, right? So ideally I should find some tool that I'd use right after tcpdump that drops selected packets. The filter I apply in tcpdump and when I drop packets is going to be the same.
Anything that already does this?
Now, tcpdump works at layer 2, right? So ideally I should find some tool that I'd use right after tcpdump that drops selected packets.
Tcpdump captures from a network at the link layer, yes. However, "captures", in this case, means "passively taps into the network, getting copies of all packets received and sent". It does not tap into the network in a fashion that allows it to prevent those packets from being processed by the network stack. Think of it as being similar to tapping a phone line - whoever's tapping the line can listen to the conversation, but they can't prevent somebody on one side of the conversation from hearing what the person on the other side says.
Anything that already does this?
There might be, but the mechanism that it would use to do so is probably going to be very dependent on the operating system it's running on. What operating system is the machine on which you need to trap the packets running.
I am trying to find a solution to monitor the traffic (in and out) through a specific port. It is not required to capture the packets, or do anyting else. What it does is to be a traffic listener to make sure there are messages sent to or received from this port every 10 minutes. It has to be running at the background all the time (like a daemon), and without significant performance impact. Based on my research, one choice is to use an existing tool to do that. There are a bunch of tools out there to monitor or sniff the traffic, such as wireshark. Well, seems most of them monitor the traffic passing through a interface, instead of a port, or they can't run as a daemon. Another choice to write a program to do this. SharpPcap seems to be a good choice, but I still need to capture and analyze the packets to know whether such traffic exist. Could somebody suggest what I should do?
SharpPcap handles packet capturing in the same manner as Wireshark, so you can set filters to limit the packet being captured to a specific port the same way in SharpPcap as you can in wireshark. Except, SharpPcap will be a much lighter weight option vs wireshark.
Download the SharpPcap source tree and look at the Example05.SetFilter.
To narrow down the results so you capture only the packets you want to see you'll need to employ a few filters.
Pcap uses a common language across all applications that use it do specify the filters to set. Capture programs that use winpcap (windows) or libpcap (*nix) include, sharppcap, wireshark, pcap.net, winpcap, libpcap, tcpdump, etc... For a great resource on how to use pcap filters see this link.
Here are the filters you need:
ether host ehost
port port
Where the ehost is the MAC address of the computer sending/receiving the packets and the port is the port you want to monitor. So the full filter string would be.
SetFilter("ether host ff:ff:ff:ff:ff:ff and port 60");
The MAC and port here are for illustration purposes only, you'd obviously change them with the values that pertain to your specific setup.
This, used in the SetFilter example will simply print out a line of info with the time of when the packet was captured to the command line every time a packet is captured and meets the criteria if your filter.
If you want more detailed info about the packet, such as info from the headers or the packet's payload, you'll need to parse the incoming raw packet. Be sure to ask for help on the sourceforge project's forum if you need some tips on how to do this. The project developers are very active and always willing to help.
The best way that will limit the impact your tool will have on performance is via an ETW (Event Tracing for Windows) Real-time Consumer (i.e. a tool that activates an ETW trace and reads it immediately instead of saving it to a file). This MSDN sample is a great way to see how to do this via C# and it gives you some code to get started.
My son has a MacOS 9 box to which he is sending remote AppleEvents from his Leopard-based MacBook. Is there any way, programmatically, that I can send remote AppleEvents via TCP/IP from my Windows 7 Toshiba?
If it helps, apple events are sent on port 3031 via TCP/UDP.
From the high level, there are four pieces to apple events:
The data aggregation API (data requests are put into an opaque in memory structure). This API as it stands was wordy and painful to use. Thank goodness you have access to languages that have better data aggregation tools
Conversion/serialization - the opaque data structure is turned into something that can be serialized and transported to another process and for same machine events, this may be a null serialization
Transport the data is transported from one process to another. Single machine is probably just enqueuing a copy of the data. Remote machine is transport over a network protocol, which could be TCP/IP (but it works with AppleTalk as well) and may require authentication.
Deserialization/Conversion
You will most likely need to do steps 2, 3, and 4. If you don't care about getting any information back, you can skip 4, since one of the flags in a sent event is "no reply".
There are a relatively small number of types in the AE data model. I would write code on your OS X machine to send each and every type and reverse engineer the packets when they're sent. To speed up the process you might want to use appscript, on the OS X machine which will let you send events from Ruby, Objective C, or Python.
Sniff the packets between the MacBook and the MacOS 9 box using something like tcpdump or Wireshark. This will tell you what an AppleEvent looks like on the wire.
Then replicate those packets using your programming environment of choice on Windows.
I suggest wrapping up the code that you write into a library that you can reuse in other applications.
Good luck - this might be quite tricky!!
if you're talking about growl notification, there are libraries to use that. for example, here is the growl library for ruby