6.4.3 Operating Modes

The Boot ROM operation is logically divided into the following four modes, each serving a distinct purpose during the device startup and debug process:
  1. Boot Mode

    This mode is entered immediately after any type of Reset when no debugger probe is present. In this mode, the Boot ROM performs system initialization, fuse integrity checks, and attempts to boot the device using the user-configured settings.

    Under normal operation, the device will then transition to Mission mode.

    When a boot error occurs, a boot failure signal can be transmitted (see the Boot Failure Signal section), and the device resets.

    When a boot error occurs and a debugger is connected, Interactive mode is invoked.

  2. Interactive Mode (IMODE)

    The Boot ROM enters IMODE under either of the following conditions:

    • A boot failure occurs and a debugger is connected
    • A debugger explicitly requests entry into IMODE to perform advanced operations
    The IMODE allows to perform tasks such as:
    • Full chip erase
    • Device locking (setting DAL = 0)
    • Configuration Flash Memory (CFM) integrity checks
    Some tasks may be prohibited due to deliberate locking or protection measures.

    IMODE is always exited by a Reset. The cause of the Reset can be an IMODE command, a hard fault, the absence of a connected debugger, or any regular Reset source. The device will then enter Boot mode.

  3. Mission Mode

    This mode allows the device to begin execution from the first mutable application executable location in Flash.

    The device remains in Mission mode until it is reset for any reason. After a Reset, the device will enter Boot mode.

  4. Park Mode

    This mode is invoked under certain conditions after a cold-plugging sequence. Park mode is specifically designed to enable the debugger to offer additional debug features. Refer to the Programming Specifications section for information on invoking and exiting this mode.