The MCU is kept in sleep mode after applying the reset until the firmware boot code is downloaded by the kernel device driver into the internal memory of the MCU. After downloading the boot code and completing the MCU initialization sequence, the control software communicates with the MCU using a mailbox mechanism implemented in the internal SRAM of the MCU. The MCU sends an acknowledgment to the control software and performs the encoding/decoding operation. When the requested operation is complete, the MCU communicates the status to the control software.
For more details about control software and MCU firmware, refer to Application Software Development.