If the device is in debug interface mode, System OFF will be emulated to ensure that all resources required for debugging are available during System OFF.
See Debug and trace chapter for more information. Resources required for debugging include the following key components: Debug and trace, CLOCK — Clock control, POWER — Power control, NVMC — Non-volatile memory controller, CPU, flash, and RAM. To prevent the CPU from executing unwanted code, an infinite loop must be added directly after entering System OFF mode.