The KMU FSM is designed to process only one key slot at a time, effectively operating as a memory protection unit for the key storage region. Whenever a key slot is selected, the KMU will allow access to writing, reading, and/or pushing the associated key value according to the selected slot configuration.
A key slot must be selected prior to use, by writing the key slot ID into the KMU SELECTKEYSLOT register. Because the reset value of this register is 0x00000000, there is no key slot associated with ID=0 and no slot is selected by default. All key slots are addressed using IDs from 1 to 128.
SELECTED status is set when a key slot is selected, and a read or write acccess to that keyslot occurs.
BLOCKED status is set when any illegal access to key slot registers is detected.
When the use of the particular key slot is stopped, the key slot selection in SELECTKEYSLOT must be set back to 0.
By default, all KMU key slots will consist of a 128-bit key value of '1's, where the key headers have no secure destination address, or any usage and read restrictions.