EM20-G Downgrading the firmware

How to tutorials for modems, hotspots, dongles
Forum rules
This forum is for tutorials only--NOT for help or assistance.
Post Reply
User avatar
JimHelms
Site Admin
Posts: 1361
Joined: Tue Dec 19, 2017 8:59 pm
Location: DFW Texas
Has thanked: 79 times
Been thanked: 192 times
Contact:

EM20-G Downgrading the firmware

Post by JimHelms »

OpenWRT based firmware does not support the EM20-G other than MBIM with no AT COM port. Therefore, a patch must be used to communicate with the modem.

The drivers for the modems like Option, QMI, MBIM, etc are "kmod" packages which means they are included in the compiled kernel of OpenWrt. They are programs written in C that get compiled at build time.

Linux has a method that allows changes to be made to the C program when the firmware is being compiled, referred to as "patching". This means extra lines of codes may be added or deleted from the C file before it is compiled.

In Option and QMI drivers there is a list of the supported modem IDs and how to handle that modem. If it isn't on that list it doesn't supported.

Dairyman (who compiles the WiFiX/GoldenOrb/ROOTer images) makes the patch and adds numerous modems so the that their drivers are compiled in an image modified from stock.

With the newest modem firmware on the EM20-G, the router firmware patch looks for the COM Port on ttyUSB2 as opposed to ttyUSB1 where it now located. This results in ttyUSB2 accessing the modem in MBIM without having access to the AT Com port.

We have downgraded several EM20-G's to the EM20GRAR01A06M4G firmware which then allows WiFiX/GoldenOrb/Rooter (with the EM20-G patch) to again access the AT Command port at ttyUSB2.

We are expecting our new WiFiX versions of GoldenOrb (due out soon) to be compatible with the newest EM20-G firmware. Until then, or if using a different version of GoldenOrb with the EM20-G patch, one may consider downgrading the firmware on the EM20-G to the earlier version.

Downgrading the Firmware on the Quectel EM20-G.pdf
You do not have the required permissions to view the files attached to this post.
tambutso
Posts: 35
Joined: Wed Dec 25, 2019 4:37 pm
Has thanked: 17 times
Been thanked: 4 times

Re: EM20-G Downgrading the firmware

Post by tambutso »

Hey Jim, would this be like a generic guide to a Qualcomm based LTE module like the EM20-G? I have a SIM8200 that's based on the SD x55, I'm guessing the general procedure is the same?
User avatar
Didneywhorl
Posts: 3609
Joined: Fri Mar 23, 2018 5:37 pm
Location: USA
Has thanked: 1359 times
Been thanked: 754 times
Contact:

Re: EM20-G Downgrading the firmware

Post by Didneywhorl »

Post Reply

Return to “Tutorials”