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Wouldn't a regular filesystem format of the card have the same effect - wipe the file? Wouldn't such SD cards be fatally flawed for most applications? My camera, drone, etc. all format the cards.

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I vaguely recall thinking the file was just some sort of serial number or stock tracking metadata when I deleted it. It might have instead failed for quite mundane reasons such as low quality manufacture. I don't know.

Exposing the firmware in this fashion would be a bad idea for all of these reasons. It is a good thing that SD card manufacturers don't do this any more, if they ever did.

Firmware definitely would not be on the filesystem layer or even accessible on the block device.

You'd think yeah

It isn't. Before a chip has firmware loaded, it can't decode filesystems.

That doesn't at all mean that the firmware can't be exposed through the filesystem. Is that a bad idea? Almost certainly. Is it possible? Absolutely yes.

Even after a chip has firmware loaded, which controller can make logical sense of a filesystem?

According to SDXC specs, the controller looks for exFAT markers to relocate the table and bitmap to smaller AU units.

exfatprogs can pack bitmap with table for SDHC and lower: https://manpages.debian.org/experimental/exfatprogs/mkfs.exf...

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