I have a simple xbee network operating where there are a bunch of slaves operating remotely and all talking to one master, who is connected to the server computer. That works no problem.
The slaves all send their ID as part of the packet and I'd like to have the master deliberately send an Ack after a delay. I'm trying to figure out how to do this efficiently and it seems that the only plausible way that doesn't involve reprogramming the master before each Ack is to send the Ack to all slaves and have them ignore the packet if it's not meant for them.
That solution is ok - I just can't figure out the command to use to do this. Is there some sort of Serial sendAll command? All of the devices are on the same ATID.
Typically in this situation, you would configure the master in API mode so you would get "Receive Explicit" frames with source addressing information, and could send with the "Transmit Explicit" frame type, and include addressing information in your frames.
If you use AT mode (transparent serial mode), then you're stuck having to change the DH and DL parameters on your coordinator every time you want to change who you send to. You should avoid using broadcast packets, since each one results in lots of network traffic (IIRC, each router will send the broadcast packet three times).
I do not know of a good XBee library on the Arduino, but it might be possible to port Digi's Open Source ANSI C XBee Host Library to that platform.
Related
I want to broadcast a request to all client that are connected to my esp8266 12f access-point
I used this to create a connection per client, means if there're 3 clients it will create 3 connections.
for mac,ip in pairs(wifi.ap.getclient()) do
srv= net.createConnection(net.TCP, 0)
srv:on("receive", function(client, b_response) srv:close() collectgarbage() end)
srv:on("connection", function(client, b_request) client:send(request) end)
srv:connect(80, ip)
end
I tried the broadcast ip srv:connect(80, "255.255.255.255") but nothing was sent
The Problem :-
What I used that every srv will overwrite the previous srv so I can not get a response if it was delayed, even so I can name every srv with a different name like srv_1, srv_2, srv_3 but this take too much memory.
What I want
Create only one connection ?
Your code is using TCP, which is inherently a single connection, point-to-point protocol. There's no such thing as a "broadcast" TCP connection. TCP simply does not work using broadcast. That's like trying to use a car as a boat.
If you're sending a small amount of information, you might try UDP instead. The drawbacks are that UDP is unreliable - you can't be certain your message was received - and you'd need a lot more code to receive a response, if you want one, and you'd need to build a reliability mechanism (retransmit if no answer received, detect retransmissions in case the answer was dropped) if you care about that.
I'd recommend that you check out the MQTT protocol - it's designed to make it easy to communicate with multiple clients. It's lightweight and MQTT clients run well on NodeMCU and Arduino processors. There's an MQTT client built into NodeMCU's LUA implementation.
The downside is you'd need an MQTT broker that all of your NodeMCU's will connect to. The broker is usually run on a more capable processor (a Raspberry Pi is a good choice) or externally on the Internet (Adafruit offers a broker at https://io.adafruit.com/), although there are some implementations that run on an ESP8266.
Is it possible to build a modbus-RTU ethernet gateway using a linux box or arduino?
I have plc slaves linked together using modbus RTU, and I want to connect one of them over TCP with my pc as master.
I wonder if I can use a linux box (rasbery pi/raspbian) connected to a router, as a modbus-to-tcp converter by piping the usb port to my local ip on some port, as one plc will be connected in modbus rtu to the linux box`s usb port.
Piping command will be something Like this:
nc -l 5626 > /dev/ttyUSB0 < /dev/ttyUSB0
My goal is to connect a pc (networked with the linux box) to that plc through the linux box using modbus.
Yes you can use a linux box with ethernet port.
Its not a simple 'nc' is it.
First things first, you need to know, Does your PLC's support Modbus TCP or Modbus RTU over TCP.
bcos both the formats are not the same, they are not interchangeable.
once you ascertain this, you need to write a TCP Client to Connect to the Slaves as they run the Servers.
If they don't support Modbus TCP yet, you need to write a TCP servers as well.
on top of that, you have the handshaking delays and half open connections and what not.
If it is a commercial device, you need to look at the setup it will be running as well.
Hope this helps
I'm not entirely sure as to what your requirements are, but you may want to have a look at the following library. It's a Modbus TCP->RTU library I assume you can use.
https://github.com/3cky/mbusd
Best Regards
While it's certainly possible to build a Modbus TCP/RTU gateway, you won't be able to do it with a simple nc command, for two reasons:
The actual Modbus protocol data unit (PDU), merely containing the Modbus function code and data, is embedded in an application data unit (ADU) so the request reaches the correct device free of communication errors. This ADU is different for RTU and TCP. Generically, the ADU looks like this:
------------------------------------------
| Additional address | PDU | Error check |
------------------------------------------
For RTU, the "Additional address" is a single byte identifying the unit/slave on the serial line, and the "Error check" is a 16-bit CRC.
For TCP, the "Additional address" is the 7-byte Modbus application protocol header (MBAP), consisting of transaction identifier, protocol identifier, and a length field (2 bytes each), plus a single byte identifying the unit/slave (usually 255, though for a gateway, this would be the ID of the RTU slave behind it). The "Error check" is empty (zero bytes) as that is already taken care of by TCP.
The communication semantics are different for RTU and TCP.
For RTU, you write a request to the serial line, wait for the reply, and only then write the next request. There must be 3½ characters of silence between frames.
For TCP, you can in principle have multiple connections being served concurrently. If you tried to forward two TCP requests to the serial line simultaneously, chaos would ensue.
Still, you can build a working gateway with a slightly more complicated program than nc:
Accept connections on TCP port 5626 (note that the actually recommended port number for Modbus TCP is 502), convert the received TCP ADUs to RTU ADUs and put them into a queue together with a back channel.
Another part of your program takes one item at a time from that queue, sends the ADU over the serial line and reports the result back through the back channel. Then it goes on the to the next item, and so on.
The results arriving on the back channels are converted to TCP ADUs and sent back on the respective TCP connection.
This would certainly work on a Raspberry Pi, and possibly also on Arduino, depending on how large you want your queue to be.
Sources:
http://www.modbus.org/docs/Modbus_Application_Protocol_V1_1b.pdf
http://www.modbus.org/docs/Modbus_Messaging_Implementation_Guide_V1_0b.pdf
I'm doing a security analysis project on an IoT device that uses an unencrypted BLE connection (with ATT protocol) and I want to spoof an individual BLE packet with the source address of an already connected device. Is there some tool or API that would allow me to do this easily? I've already tried gatttool and spooftooph but they seem to be connection based and don't allow you to send out single packets with modified fields (as far as I could tell).
You will need some hardware where you can access the radio peripheral directly. What you basically need to do is to find or write a ble sniffer firmware, with the modification that it at a given moment sends a packet on the connection it is currently listening to. But note that the signal strength must be stronger than the original device's signal so it doesn't interfere.
The only open source project I'm aware of is Ubertooth. You will also be able to do this with an nRF52 but then you need to write your own sniffer firmware since Nordic Semiconductor's is closed source.
I can't comment on Emils reply yet, < 50 rep:
Nordic Semis nRF Sniffer v2 needs only the nRF52DK and wireshark to work as a general BLE sniffer. At 40$ it's not that expensive. I know for a fact they will release a new dongle soon that will sell for ~10-15 bucks if you can wait a a month or two.
I am developing a logic core to perform data transfer between a FPGA and a PC over ethernet, using a LAN8710 PHY on my FPGA board.
I've achieved to transfer some UDP data packets from the FPGA to the PC. It's a simple core that complies with the PHY transfer requirements. It builds the UDP package and transfer it to the PC.
To check the reception on the PC, I am using Wireshark and as said above, I receive the packets correctly. I've checked the reception with a simple UDP receiver written by myself.
But, I've noticed that I only receive these packets when Wireshark is running on the PC. I mean, if Wireshark is ON, my application receives the packets too, and the counter of received packets of the following picture increases. (This picture is not mine, just one from the internet)
http://i.stack.imgur.com/wsChT.gif
If I close Wireshark, the PC stops receiving packets and the counter of received packets stops. My application stops receiving too.
Although novice on networking topics, I suspect that this issue is related to PC-side. Seems like Wireshark is "opening/closing" the ethernet communication channel, or something like that. Does anyone knows about this issue?
To build a functional core to transfer data between a PC and the FPGA, I've developed a core to transfer and receive UDP packets. Next step will be ARP implementation (to let the PC identify my FPGA board, as I understand). What protocols are necessary to perform full-duplex data transfer between this 2 devices?
Thank you very much in advance,
migue.
Check whether you are able to get appropriate receive interrupt at ethernet driver level on PC-side for a single transmitted packet by FPGA. If you do not get the receive interrupt, check on the transmit side(FPGA) for appropriate transmit interrupts for packet that is being transmitted. This should mostly help you in cornering the issue.
As far as i know, wireshark is just a packet analyzer/sniffer. However, if wireshark is suspected, one option could be to try with alternate packet sniffer to rule out if any such scenario is happening.
A handy tool for determining problems in network and also for determining the network statistics shall be netstat. netstat -sp udp shall list down the statistics only for UDP. There are many other parameters that can be used with netstat for diagnosis.
After many months I solved it, I post to help someone stucked in the same point.
Finally I figured out that Wireshark uses a tool to access the network link layer of the computer. This tool allows Wireshark to sniff all incoming and outgoing packets at a specified network device. To do this, the first step is to OPEN the network device, and that's why my program only worked if Wireshark was open.
Regards.
So I was curious if this is possible at all. Currently i have a program running in a micro controller (digi rabbit) that reads SPI data from a chip. I also have TCP/IP protocol set in this program so it sends the SPI data to the server. Microcontroller is programmed in C. Server is in java. I convert SPI data into string and send it over, the server reads the raw data.
But i wanted to know if there is a way that I can read the data from Ethernet port. So what i want is one end of cat 5 cable on micro controller and the other on Ethernet port of the computer. Just for testing purposes that micro controller port and everything is installed properly, before i turn on the server. I am not that experienced with networking. So if anyone can point to a blog, or any tips that would be great. My question is how would i go about it?
Thank You
What you want to do is called raw Ethernet. Of course this can be done.
On the microcontroller side you need to follow its Ethernet controller datasheet to send out and receive packets. On the PC side this is a bit more complicated and depends on the OS that is running on the PC. On Windows you can use the WinPcap driver to send and receive raw Ethernet packets.
Be aware, that both Ethernet controllers, the one on the PC and the one on the microcontroller, filter all incoming packets that do not contain the receivers MAC address or any multicast/broadcast address. For a simple check the broadcast address (all address bits are 1) will do.
Also note, that the OS on your PC will transmit all kind of packets as soon as the link is established. So you may use a unique protocol identifier in the type field of your raw Ethernet frame. Check Wikipedia's article about Ethernet frames. Btw. don't get confused. You only need to send MAC-adresses, Ethertype and the payload. Everything else, like the CRC, preamble etc., is added by the Ethernet controller automatically.