Quote:
Discussion on ExFAT as it relates to data exchange (SDXC) and booting (EFI/UEFI and ARM standardized boot).
1) exFAT isn't mandated by the UEFI specification to be supported by a compliant implementation. Only FAT12/16/32 are.
2) exFAT is required by SDA to be used as the only FS for SDXC cards.
3) as result of the 2 above, on machines, where an SD card is the only secondary storage to install your OS onto (which is rare even in a low budget ARM SBC space, with the prominent exception of RPi... and definitely is
not what SD cards and exFAT were intended for), you
cannot you cannot use an SDXC card as your OS's installation target on such machines. formatting the card into something else is against 2), trying to use it with exFAT won't work, unless:
1) you provide a UEFI driver, that will materialize SFSP (Simple File System Protocol) for the exFAT volume of the card, which is possible or
2) implement RO exFAT functionality in your loader that will use the UEFI's underlying Block/Disk IO protocols for accessing the medium. this, it seems, is the best (easiest) option for those, willing to use these huge cards and stay compliant. besides, you probably would need to implement similar RO functionality for your fancy FS, which you would want to use on a Boot Volume (where OS lives) and which, of course also wouldn't be supported by UEFI. for example on eMMC modules, HDDs, or even NVMe SSDs, that aren't impossible to be connected to these tiny boards. so, exFAT in this case isn't any different from all those. UEFI unconditionally supports only classical FAT. And ESP is only FAT32. Personally, since I do my lame osdev attempts on the very same cheap ARM SBC landscape, I use cards <32 GB.
This is my comment, related to the last link, because what was there, is anything, but discussion, let alone "useful". I cannot get this bold to ask to remove it from the post, but I can warn, that if someone would want to listen to any line in the 1st post on that link, he/she instantly would get themselves far away from the truth. it's hard to make so many false statements on a squared centimeter as bzt did there.