GL-X750 Spitz + EP06-A | Cannot select /dev/ttyUSB2

Technical Support for Routers
1

Hi All,

I have a GL-X750 Spitz where I’m trying to get working with Visible/Verizon. I was initially having issues getting it to connect but finally got it to connect with /dev/ttyUSB2, albeit at low speeds. So I started tinkering around, and now I can no longer go back to /dev/ttyUSB2. I get a “device busy” error when attempting to select it. /dev/ttyUSB3 works, but it’s dreadfully slow. ttyUSB3 is even much slower than ttyUSB2. I searched for answers on how to get back to /dev/ttyUSB2, but came up empty handed.

I can still send AT commands just fine to /dev/ttyUSB2. I just can’t select it. Thanks for any help in advance.

Cheers,
Kermee

2

ttyUSB2 is generally used for AT command and ttyUSB3 is used for data.

It is possible to use ttyUSB2 as data and ttyUSB3 as AT command but I think this is not the default config. Seems some program locked the port.

Maybe just power cycle the device or modem?

3

I have a Spitz running 4.0 release70307, US Verizon LTE, EP06-A, I can usually connect but am frequently disconnected, I suspect Verizon may be causing the disconnects at times, it seems like any sustained download will cause a disconnect. Watching logread -f it seems like the retry might be too aggressive too. Sometimes I also get into a state where /dev/ttyUSB2 disappears:

Sun Feb 18 17:08:45 2024 daemon.err modem_AT: (modem_AT.c:319) The /dev/ttyUSB2 does not open,continue to try.

root@GL-X750:~# ls /dev/ttyU*
/dev/ttyUSB0  /dev/ttyUSB1  /dev/ttyUSB3  /dev/ttyUSB4

Sometimes just waiting or using the modem UI to abort/restart the connection works, rebooting works. Usually can’t reset the modem from the UI since /dev/ttyUSB2 is missing.

4

It seems a software problem. I will ask guys to have a check.

5

Please help check log information:

dmesg | grep ttyUSB

6 
 -----------------------------------------------------
 OpenWrt 22.03.4, r20123-38ccc47687
 -----------------------------------------------------
root@spitz:~# dmesg | grep ttyUSB
[   41.985360] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB0
[   41.999671] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB1
[   42.013903] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB2
[   42.028209] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB3

My loss of ttyUSB2 was sporadic, and I think the cause may have been related to lots of modem up/down events and probably me resetting the modem. I haven’t lost the ttyUSB2 device recently.

7

mwan3 seems to have been a problem for me, connection would complete (Verizon US LTE) then mwan3 pings would failover and drop the connection (with no other WAN connections). Disabling two of the mwan3 interfaces fixed the problem. I might explore adjusting the targets and timeouts but since I only have the one WAN connection, failing over doesn’t really make sense.