Ublox cellular: broken support for custom board

[pilotak]

Description

PR #10877 really breaks support for custom targets with ublox modem, everything is target specific and not modem specific. I'm using SARA-G350 (part of C027) with STM32F412ZG/STM32F303RE.

Following command is not supported on this modem and fails to connect, it should be moved to a line 62 where this variable is used

https://github.com/ARMmbed/mbed-os/blob/431c4c19ae2056785c85e2a119ed51dd35f79f3c/features/cellular/framework/targets/UBLOX/AT/UBLOX_AT_CellularContext.cpp#L52

Following part is limiting, this is where it should be specified #ifdef TARGET_UBLOX_C027 || TARGET_HAS_G350 or similar.

https://github.com/ARMmbed/mbed-os/blob/431c4c19ae2056785c85e2a119ed51dd35f79f3c/features/cellular/framework/targets/UBLOX/AT/UBLOX_AT.cpp#L98-L110

I know that i can override init() but than there would a problem with config_authentication_parameters() because it's private and of course overriding it takes aditional 192 bytes extra space

Issue request type

[ ] Question
[ ] Enhancement
[x] Bug

[ciarmcom]

Internal Jira reference: https://jira.arm.com/browse/MBOCUSTRIA-1576

[jarvte]

@pilotak First one is an easy fix but the second one is a trickier. We don't have target for SARA-G350 to differentiate variants of C027 like we have for C030 (for example UBLOX_C030_R41XM). Should there be different variants of C027? @mudassar-ublox do you have suggestions how to fix this?

[jarvte]

@pilotak are you using SARA-G350 as a shield? Then you should set "provide-default" to true in /features/cellular/framework/targets/UBLOX/AT/mbed_lib.json

[pilotak]

No i have a custom board (as description says). I thought that it would be nice to have all modems done like components for example storage. You just specify you have a ublox and which type, you override get_target_default_instance with your pins and you done. At the moment it's tied up to a specific board and if you decide to make you own board with different processor you are in trouble.

I noticed that Quectel has modems split into each one and not tied up to MCU which makes a goal for custom targets. I realize that managing one code for all the ublox modems is easier but you need to use same MCU because of library only.

At the moment i have my own init without config_authentication_parameters(); as this is for PDP and therefore not relevant when using AT commands and stack on modem and i don't have to make the function public. Another change a did as it works better/faster is to exclude modem shutdown in init. The reason behind it is that if you call disconnect() it will disconnect you from internet not from a cell. Next call to connect() will shutdown and wake up modem again, do network registration to catch a cell and than connect to internet = a lot of time wasted. If there isn't that command it takes ~2 sec to reconnect internet because it is already attached a cell. Maybe this is a mandatory for R412 i don't know but not for G350 as it works like a charm https://github.com/ARMmbed/mbed-os/blob/431c4c19ae2056785c85e2a119ed51dd35f79f3c/features/cellular/framework/targets/UBLOX/AT/UBLOX_AT.cpp#L99

@jarvte Could i kindly ask you to move the RAT thing where it belongs or do you want me to create a PR?

[jarvte]

Yes, I will do a PR to move the RAT thing.

[pilotak]

@jarvte What are your thoughts on above? (modems as component and init delays)