OEM Firmware Ratchet Level

Only MB1-BCT is ratchet protected using hardware fuses.
Fuses are field programmable and can be updated when the device is in the field.
The ratchet value is thermometer encoded (a numerical value between 0 to N). For example, the number of bits set from LSB denotes the ratchet value.
Besides MB1-BCT, all OEM owned firmware loaded during boot are ratcheted using their absolute ratchet value in MB1-BCT.
OEM owned firmware ratchet versions are set in MB1-BCT and their corresponding BCH during flashing or offline image creation. For more information, see Bootburn.