otadata

The small record that tells the bootloader which slot to start and what state it is in.

The otadata partition holds two copies of the boot-selection record, each with a sequence number, a state and a CRC, so a power cut while updating it leaves one valid copy.

Examples

After a cable upload, otadata's record has ota_seq 1, so the bootloader starts ota_0; sequence number 2 would select ota_1.
A power cut while writing the new otadata record leaves a copy whose CRC fails, so the bootloader falls back to the other copy and the old slot.