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My #Librem5 is behind the scenes here - taking this picture. It shows a working connection between the L5 (connected to the other side of the grey usb-c cable) and my Librem14 running minicom.
While #PureOS is running the output of the GPS module is transmitted over serial.
During boot I'll hopefully be able to get the serial console to u-boot soon.
More information can be found here: https://source.puri.sm/Librem5/community-wiki/-/wikis/hardware/Serial-Console#thunderbolt-alt-mode-for-muxing-uart-onto-usb-c-sbu-pins
It's been some way to go, but now I'm in control of my #Librem5: I can access the boot prompt.
I'm used to be able to do so to debug boot problems (in those rare cases) using grub.
Nice side effect: this version of u-boot (build to support uart2 instead of uart1) does support booting from sdcard.
Best part of it: No need to open the L5 at all and thereby low risk of breaking anything.
Would be nice to find a cheaper device than DELL TB16 to trigger thunderbolt alt mode...