BM818 data connections work through an M.2->USB adapter but not in a phone
I currently only have a US modem at hand for testing (had to give my EU modem to Bushan). But I can see:
data is unsusable, only a few bytes/kbytes go through, then it dies
calls, neither incoming nor outgoing, work, Calls gives reason "Call disconnect (unknown reason)". When I try to call the phone I get "user can not be reached", like hte phone would not be registered to the network at all anymore
OK, so, I just tested data again - but not in the phone. I used the external enclusure and hung the modem off my laptop, using Debian bullseye.
The modem works prettty much out of the box with onboard ModemManager etc. After setting APN, username, password etc. corectly I can setup a connection via teh GNOME NetworkManager frontend, initiate and - bam! Connected.
The connections is stable, it holds up, does not die (so far).
It also has acceptable throughput, noot fast but OK. I guess this also has to do with O2 in my town here and that I may not be eligible for LTE speed with the pre paid SIM I am using. I get between 30kbytes/s and 40kbytes/s download. But sustained, i.e. no drop outs, no hangs.
I also used ssh to login to a server of mine and was amazed about the low latency! I could uuse the shell almost like normal!
This tells me that the BM818 modem is not the problem with the non working or super slow data thoughput we see on the phone.
Now we have to hunt for the bottleneck, I see several possible problems:
- the USB data path in the phone is broken - but then we should also see general USB errors?
- the antennas in the phone are so bad that they prevent proper operation beyond just connecting
- some part of our software stack has an issue - kernel, kernel driver, libqmi, ModemManager
That's what I have installed on the laptop:
ii modemmanager 1.10.4-0.1 amd64 D-Bus service for managing modems ii libqmi-glib5:amd64 1.22.4-0.1 amd64 Support library to use the Qualcomm MSM Interface (QMI) protocol ii libqmi-proxy 1.22.4-0.1 amd64 Proxy to communicate with QMI ports ii libqmi-utils 1.22.4-0.1 amd64 Utilities to use the QMI protocol from the command line