Thanks, that was very helpful! As a further test I switched Minicom to 'ANSI' 
terminal emulation instead of 'VT102', but there was no improvement. 
Interestingly, U-boot's own menu displays highlighting as it should, but the 
sd-boot menu does not. I'll try to follow up with the U-boot project to see 
what might be going on with their UEFI implementation.

On Sat, Dec 28, 2024, at 19:24, Mantas Mikulėnas wrote:
> On Sat, Dec 28, 2024, 20:38 Kevin P. Fleming 
> <lists.systemd-de...@kevin.km6g.us> wrote:
>> __
>> I've got three machines which have serial (only) consoles, all of which are 
>> using sd-boot from systemd 257. I use Minicom, in VT102 mode, to connect to 
>> these machines, and while the console generally works, there is no 
>> 'highlighting' in the sd-boot menu. As a result it's rather difficult to 
>> choose a non-default entry to boot.
>> 
>> What terminal type is sd-boot expecting?
> 
> None. It outputs text using the EFI ConOut interface, which is not a 
> terminal-style interface at all – it's more like the DOS or Windows console, 
> with discrete APIs for cursor positioning and text formatting [1].
> 
> It's your system firmware which decides how to translate those API calls to 
> VT220 sequences or something similar.
> 
> [1]: 
> https://uefi.org/specs/UEFI/2.9_A/12_Protocols_Console_Support.html#efi-simple-text-output-protocol
>> 

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