nRF91 SLM + Zephyr Modem Driver Problems

RE: nRF91 SLM + Zephyr Modem Driver Problems

Tomi Fontanilles — Tue, 17 Sep 2024 15:03:41 GMT

Hey, just a quick answer to the point just raised (because I unfortunately currently don't have much time to allocate to this topic).

The CMUX channel switching is not needed per se. It's how Zephyr's cellular modem driver was made, according to my understanding because the author was working with some modem that has this behavior of automatically switching the CMUX channels when deregistration happens.

One potential more robust approach would be to allow disabling this behavior in the driver, or to add an "undial" modem chat script as was discussed recently in order to make sure that the modem end (SLM in this case) is actually ordered to switch AT channels by the driver.

Those modifications shouldn't be too complicated, especially if you are familiar with the driver already. I could likely provide some assistance (both in Zephyr and NCS) if you undertook to do something to improve this.

RE: nRF91 SLM + Zephyr Modem Driver Problems

spurious_emitter — Tue, 17 Sep 2024 14:57:05 GMT

Hello Jonas,

Thanks for taking the time document everything here! As we've discussed on Discord, I also ran into this issue a few months ago. Tomi Font was super helpful and responsive while debugging the issue at the time, but unfortunately I don't think that we were ever able to find a solution that solved the issue reliably. I'd agree that the CMUX channel switching seems to create a lot of unnecessary headaches without any obvious benefit. Could someone address why that's needed?

Thanks,

Ryan

RE: nRF91 SLM + Zephyr Modem Driver Problems

Øyvind — Tue, 17 Sep 2024 13:45:38 GMT

Hello Jonas,

I have been assigned your ticket and will need to discuss these issues with our developers.

Will get back to by end of Thursday.

Kind regards,
Øyvind