---------English----------
I was wondering how navigation in the librem 5 BIOS will work? Will it be necessary to connect a USB keyboard or will navigation be done with the volume keys? And how acess it?
Also, will it be possible to boot from a USB key and a micro-SD card? My intention is to install Kde Plasma Mobile on the SD card and keep PureOS on the EMMC
If you were thinking about anything like a traditional BIOS as it can be seen in most x86 hardware - no, ARM boards usually don’t have that. Instead, they are initialized using a small bootloader named uboot that only outputs a few text messages and has a very basic shell. Don’t expect a “fancy” text-ui like on an x86 machine here.
I even assume you won’t see any output as end-user on the screen of the device (before the kernel boots) unless you attach a serial console to the device.
U-boot is the equivalent of the BIOS, but accessing it might be a little complicated, because it needs a serial connection. This may require a special cable to connect it to a computer. It’s no fancy text UI, but rather u-boot shell.
The image we’ll ship on the phones won’t boot from USB or SD, because this could be a security issue for a device people carry everywhere. Nevertheless, so many people want that functionality that I’m sure it won’t be long before unofficial u-boot with that function appears somewhere.