SARA R410 instability when connected with weak signal to AT&T

Has anyone else experienced the SARA R410 locking up under low signal conditions when connected to AT&T? Usually when I see it happen, it goes like this:

  1. Open a TCP socket and send some data
  2. Close the socket, modem replies “OK”
  3. The next time I am ready to send some data, the modem is totally unresponsive to the AT terminal.

I am using all of the recommended response timeouts listed in the AT Manual and all PSM (power save mode) is disabled.

The only way to recover is a hard reset using the reset pin on the modem.

I have been battling this for a while. Using a higher gain antenna seemed to help, but I am still dealing with this. Resetting the modem within the program is no problem, I am just worried about long term damage to the modem. Sometimes 10+ resets are required per day.

Sounds similar to:

Yes, very similar. I don’t see that any solution was found…

The only way I have found to keep the modem from locking up is this:

  1. Open socket, send data
  2. Close socket
  3. Put the modem into AT+CFUN=0 mode
  4. Before sending more data, put modem back to AT+CFUN=1 mode and re-attach.

I just had a QUECTEL LTE BG96 based modem:
fail in the same way as the SARA-R4 modems have been failing on AT&T.
(e.g. firmware lockup with modem reenumerating on the USB bus as
I suspect the root of the problem is with Qualcomm, which would explain why we’re not seeing a solution from uBlox and Hologram.
Seems like AT&T might be interested in getting this fixed, as it seems to impact only their towers.

Interesting… Have you seen this behavior on any other network? AT&T cat m1 is the only network available to me.

I can confirm the issue is present with a cat m1 sim directly from AT&T marketplace as well as the hologram sim.

As a work-around, I have been using the strategy I described in post #3. It seems like the less time the modem is attached to the network, the less chance there is of this problem.

genosensor, zbelding, I too am having the Nova fail on ATT after an indeterminate amount of time. I have a Raspberry Pi 3+ that will work great for anywhere from 3 hours to more than 3 days but the error is always the same, the system seems to lose communications with the modem (lock up?) and the solution that I have found is either a graceful power down of the Pi including pulling the power supply or physically pulling the Nova from the USB port (very hard power down!) and re-inserting it. I have not seen any of the Hologram support people answering any of the forums for the last month so we might be on our own.

Looks like Ublox just released a firmware update addressing this!:

L0. A.02.16

Found this in release notes:

[u-blox ID 5226]: Device crashing on live AT&T network in idle mode when SIB decode is triggered by ML1 before finishing the Page decodes

That is a great find.

Just emailed ublox and ask for the update files.

Will update, test as soon as I get them and report back.

I have been running the new firmware for 5 days now. No modem lockups!

I updated two modems as well with no issue.

I too had the ATT lockup problem back in March and just gave up. Any chance you could put the firmware and update tool on Dropbox or google drive and share a link?

Just get in touch with ublox, they will give you what you need. My device does not have the Modem USB available, so I updated via AT terminal and x-modem.

I’ve emailed them. It seems like they make this hard. Why not just post the updates?

No modem lockups for almost two weeks. I would say this has cured the AT&T issues I have been dealing with.

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