Unrecognized option ttyUSB3

Followed Setting up the PPP connection on a brand-new install on a Pi3 with latest (as of 2020-06-15) Raspberry OS Lite - however i am running into issues

unrecognized option ‘/dev/ttyUSB3’

have read Raspberry Pi + LTE Base HAT : ttyUSB3 not found -however I will say that this shield has worked on this pi previously - only diference

  1. Previously Full Raspbian install
  2. I have added a SixFab Power Shield in

cant imagine there are any incompatibility there - might need to test a new USB cable, but this has worked previously

have removed the Power Shield, and still the same issue… so as suspected i’ve done something stupid! (missed to install something due to using Raspbian Lite?)

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another difference i had overlooked is that I was running with a EC25 previously, i have swapped that back in and it works perfectly. so i wonder if the new modem i am using has an issue.

– update on my debugging efforts –

Ok, so i made a really basic assumption that turned out, it seems, to be false - as all other modems I had used worked out the box I assumed this one would to. But checking into the kernel source, it would appear support is not in there yet.

I have modified the appropriate sources according to the datasheet - rebuilt the kernel and its booting and running fine, but the modem is still not showing up or creating the appropriate dev/ttyUSB* devices. Not sure why yet

[  210.917320] usb 1-1.4: new high-speed USB device number 16 using dwc_otg
[  211.017325] usb 1-1.4: device descriptor read/64, error -71
[  211.237317] usb 1-1.4: device descriptor read/64, error -71
[  211.457324] usb 1-1.4: new high-speed USB device number 17 using dwc_otg
[  211.557329] usb 1-1.4: device descriptor read/64, error -71
[  211.777326] usb 1-1.4: device descriptor read/64, error -71
[  211.897445] usb 1-1-port4: attempt power cycle
[  212.557335] usb 1-1.4: new high-speed USB device number 18 using dwc_otg
[  212.997344] usb 1-1.4: device not accepting address 18, error -71
[  213.097327] usb 1-1.4: new high-speed USB device number 19 using dwc_otg
[  213.537334] usb 1-1.4: device not accepting address 19, error -71
[  213.537467] usb 1-1-port4: unable to enumerate USB device

I seem to recall seeing similar issues when hitting power limits - i will dig around for a better power supply and see if might help.

For anyone in the future who discovers this, undervoltage was the issue! didn’t expect this modem to have that issue when the EC25 was ok, but there you go!