Strange message sent by Electron


First of all I want to congratulate Particle as I have been deploying for several years unsurveilled systems using the Electron (2G version) and I am more than satisfied with its reliability. Thank you for such a good device!

This very morning I have deployed a system that reads environmental data -temperature, humidity, ambient light…- and sends them to a server using a proprietary UDP based protocol. Everything works fine, the Electron is accurate as a clock, but sometimes the server receives strange messages not related to the protocol. Astonishingly the 4 bytes of the message are, translated to text, AT+U. The program sends 4 byte ACK messages but not with this content. I have detected that these strange messages are more frequent when the cellular network quality is worse. In addition, when testing the protocol with a photon using wifi, these kind of messages never appear.

The protocol is robust and the system is not affected by these spurious messages, but I am intrigued and I would like to know where they come from. I supose they are related with the communication between the UDP firmware and the UBLOX modem, but any additional information will be welcome.

Regards and thank you for your help.

That is pretty interesting…

You are correct that AT+U is related to the cellular modem. The modem is controlled with an AT command set which are all prefixed by AT+. There isn’t an AT+U command but there is an AT+USOST command which is the UDP transmit command used on the Electron. Likely the modem waiting for the 4-bytes data portion but getting de-synced in some fashion so that a following retry supplies AT+USOST with 4-bytes snipped off and used as data.

Can you confirm what version of Device-OS you are running? How often does this happen? Is there any chance you would be willing to setup some low-level tracing to reproduce the issue and pass that trace along?

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The device is running OS 1.4.2

The strange message does not appear often. With the device placed at is definitive location it has only happened once -it is there less than a day!- and curiously after the first communication with the server.

When testing the system in a different location, with more problems connecting to the cellular network, the strange messages appeared more often, lets say 10 - 20% of the interactions with the server.

No problem in performing low level tracing. I am using the electron in several projects so it will be useful for all of us.


Low-level logging is pretty easy on an Electron.

Go to and flash the three +debug versions of system part 1/2/3 for your electron. If possible, also consider upgrading to 1.4.3 which fixes a low-level reentrancy issue in newlib which can cause rare firmware panics (but wouldn’t be the issue here).

Then make sure your application firmware has a line somewhat like the following to enable logging out the main serial port.

SerialLogHandler *logHandler = new SerialLogHandler(115200, LOG_LEVEL_ALL);

Then just let it run and use particle serial monitor --follow or another serial terminal to log all output to a file. It will have a lot of very verbose logging around the Cell interface and other Device-OS internals which may help shed some light on sequencing around the issue. If you can note what time the AT+U showed up on your server that would also be very helpful as otherwise it might not be immediately apparent from the log.

Thank you, Joel.

The electron in which we detected the problem is installed at its definitive location -in the middle of the mountain- so I will unpack a fresh one this weekend and perform the tests you suggest. I will use firmware 1.4.3. Relating the log to the problem we detected should not be difficult as our server logs and timestamps every transaction that it receives.



First of all, I wish a happy 2020 to the Particle community!

I am having problems trying to debug the system and relate the logs to the strange AT+U messages I get on my server (I still receive unexpected messages, although not very often). I am using Windows 10.

First of all, not all serial tools seem to work. The Serial Monitor from Arduino Ide or a C Serial Port library I use for my developments recognize and open the port, but they do not receive and show data.

The particle tool you suggest resets my computer sometimes when using --follow.

But the main problem is that the log stops while the electron continues working and sending UDP messages. I have used particle serial monitor and Mobaterm application, and in both cases the log stopped after “CIEV matched: 9,1”. It has happened twice, the first time I thought it was due to Mobaterm, but the second one has shown when using the particle CLI, so I think it is a problem related with the electron. I copy below the full, but short, debug session.


Opening serial monitor for com port: "COM46"
Serial monitor opened successfully:
[ ElectronSerialPipe::begin ] pipeTx=0 pipeRx=0

[ Modem::powerOn ] = = = = = = = = = = = = = =
    30.403 AT send       4 "AT\r\n"
    30.543 AT read UNK   3 "AT\r"
    30.544 AT read OK    6 "\r\nOK\r\n"
    30.544 AT send       9 "AT+CGMM\r\n"
    30.577 AT read UNK   8 "AV+CGMM\r"
    30.578 AT read UNK  13 "\r\nSARA-G350\r\n"
    30.579 AT read OK    6 "\r\nOK\r\n"
    30.780 AT send       6 "ATE0\r\n"
    30.812 AT read UNK   5 "A\xd4E0\r"
    30.813 AT read OK    6 "\r\nOK\r\n"
    30.813 AT send      11 "AT+CMEE=2\r\n"
    30.845 AT read OK    6 "\r\nOK\r\n"
    30.845 AT send      19 "AT+CMER=1,0,0,2,1\r\n"
    30.879 AT read OK    6 "\r\nOK\r\n"
    30.879 AT send      15 "AT+IPR=115200\r\n"
    30.910 AT read OK    6 "\r\nOK\r\n"
    31.010 AT send      10 "AT+CPIN?\r\n"
    31.044 AT read ERR  37 "\r\n+CME ERROR: operation not allowed\r\n"
    31.724 AT read  +   14 "\r\n+CIEV: 9,0\r\n"
CIEV matched: 9,0
    32.046 AT send      10 "AT+CPIN?\r\n"
    32.078 AT read  +   16 "\r\n+CPIN: READY\r\n"
    32.079 AT read OK    6 "\r\nOK\r\n"

[ Modem::init ] = = = = = = = = = = = = = = =
    32.079 AT send       9 "AT+CGSN\r\n"
    32.115 AT read UNK  19 "\r\n353161070767705\r\n"
    32.123 AT read OK    6 "\r\nOK\r\n"
    32.123 AT send       9 "AT+CGMI\r\n"
    32.155 AT read UNK  10 "\r\nu-blox\r\n"
    32.157 AT read OK    6 "\r\nOK\r\n"
    32.157 AT send       9 "AT+CGMR\r\n"
    32.189 AT read UNK   9 "\r\n08.70\r\n"
    32.191 AT read OK    6 "\r\nOK\r\n"
    32.191 AT send       6 "ATI9\r\n"
    32.225 AT read UNK  16 "\r\n08.70,A00.02\r\n"
    32.227 AT read OK    6 "\r\nOK\r\n"
    32.227 AT send       9 "AT+CCID\r\n"
    32.261 AT read  +   30 "\r\n+CCID: 8934076500002697332\r\n"
    32.263 AT read OK    6 "\r\nOK\r\n"
    32.263 AT send      11 "AT+CMGF=1\r\n"
    32.296 AT read OK    6 "\r\nOK\r\n"
    32.296 AT send      13 "AT+CNMI=2,1\r\n"
    32.330 AT read OK    6 "\r\nOK\r\n"
    32.330 AT send       9 "AT+CIMI\r\n"
    32.362 AT read UNK  19 "\r\n214074300560129\r\n"
    32.364 AT read OK    6 "\r\nOK\r\n"
    32.364 AT send      13 "AT+COPS=3,2\r\n"
    32.399 AT read OK    6 "\r\nOK\r\n"
    32.399 AT send      11 "AT+UPSV=1\r\n"
    32.432 AT read OK    6 "\r\nOK\r\n"
0000032433 [system] INFO: Sim Ready
0000032433 [system] INFO: ARM_WLAN_WD 1

[ Modem::register ] = = = = = = = = = = = = = =
    32.433 AT send      12 "AT+CGREG=2\r\n"
    32.466 AT read OK    6 "\r\nOK\r\n"
    32.466 AT send      11 "AT+CREG=2\r\n"
    32.498 AT read OK    6 "\r\nOK\r\n"
    32.498 AT send      10 "AT+CREG?\r\n"
    32.532 AT read  +   14 "\r\n+CREG: 2,0\r\n"
    32.534 AT read OK    6 "\r\nOK\r\n"
    32.534 AT send      11 "AT+CGREG?\r\n"
    32.568 AT read  +   15 "\r\n+CGREG: 2,2\r\n"
    32.569 AT read OK    6 "\r\nOK\r\n"
    32.569 AT send      10 "AT+URAT?\r\n"
    32.603 AT read ERR  23 "\r\n+CME ERROR: unknown\r\n"
    32.603 AT send      10 "AT+CREG?\r\n"
    32.637 AT read  +   14 "\r\n+CREG: 2,0\r\n"
    32.639 AT read OK    6 "\r\nOK\r\n"
    32.639 AT send      11 "AT+CGREG?\r\n"
    32.671 AT read  +   15 "\r\n+CGREG: 2,2\r\n"
    32.673 AT read OK    6 "\r\nOK\r\n"
    45.333 AT read  +   14 "\r\n+CIEV: 2,3\r\n"
    45.335 AT read  +   14 "\r\n+CIEV: 9,1\r\n"
CIEV matched: 9,1

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