In AM62AX devices the MCU domain can be reset isolated from the MAIN domain in cases where the MCU domain R5 core runs a safety application. The MCU domain can run a safety application when reset isolated to:
When enabling reset isolation MCU domain can also be debug isolated, restricting JTAG access to MCU domain.
If MCU domain is isolated from accessing MAIN domain when enabling reset isolation (MCU domain running a safety critical firmware accessing only MCU domain peripherals), the MCU firmware should not access any MAIN domain peripherals.
When the MCU domain is monitoring the MAIN domain the MCU domain is not isolated from accessing MAIN domain peripherals and registers. In such a use case the MCU domain can access MAIN domain.
After reset isolation, the MAIN domain firmware should not access any MCU domain peripherals or registers. Before accessing the MCU domain registers the MAIN domain firmware should check the for the MCU MAGIC WORD in the mirrored MAIN domain register.
SBL running in MAIN domain also checks for the MAGIC WORD and only conditionally loads and runs MCU application.
SBL also checks if reset isolation is not enabled and sends a TISCI message to change dev group to ALL so that MCU domain is also initialized by system firmware. SBL also turns on the MCU PLL if reset isolation is not enabled.
The board config dev group is changed to MAIN Domain only so that System Firmware does not access the MCU domain registers on bootup. The dev group is incremented to dev group ALL by SBL on sending a TISCI message, so that the system firmware initializes the MCU domain