64.5.6.1 Protection Unit

The Protection Unit is used to centralize all alarms coming from the different monitors. When an alarm is detected, the Protection Unit sends a Clear signal to the logic, which starts the secure memories Erase sequence if the memory is not empty.

The Protection Unit can also send:

  • an IRQ interrupt signal (only in Normal mode)
  • an SWKUP wake-up signal (only in Backup mode).

When an interrupt or a wake-up signal is generated, it is up to the user to detect the source of the alarm and to act accordingly, for example, to clear the secure memories content or not.

As soon as an alarm is detected, the corresponding bit is set in the Status register (SECUMOD_SR). The only way to clear this bit is to set it in the Status Clear register (SECUMOD_SCR).

Note: Once a status bit is raised, it should not be cleared before the next slow clock period. If a clear does occur, the status bit rises again and the same alarm will be seen twice. To prevent this, it is recommended to wait at least one slow clock period after reading the Status register before clearing the status bits.

If a Clear of the secure memories content has been performed by logic, an ERASE_DONE flag is set to indicate that the secure memories content is not valid anymore. While the secure memories are erased, write accesses have no effect and read accesses return a static and invalid value (except for BUSRAM1KB).