1.7.2 Bootloader System Level Execution Flow

Basic Bootloader system level execution flow

  • The Bootloader code starts executing on a device Reset

  • If there are no conditions to enter the Firmware Upgrade mode, the Bootloader starts executing the user application

  • The Bootloader performs Flash erase/program operations while in the Firmware Upgrade mode

Live Update Bootloader system level execution flow

  • Supported for the devices which have a Dual Bank Flash memory

Cortex-M Based MCUs:

  • Special NVM Fuse setting (AFIRST) is used to identify which bank is mapped to NVM main address space after reset

  • The bootloader live update code responsible to program the inactive bank is part of the application it self. Which means the programming operation can happen while the application is running

    • Live Update Application = (Bootloader Code in Live Update mode + Application code)

  • The application code is responsible to send a request to bootloader live update code to perform a bank swap and reset to run the new firmware programmed in Inactive bank

MIPS Based MCUs:

  • Switcher Application in Boot Flash memory is required to select the bank with latest firmware

    • At reset switcher first maps Bank 1 to lower region and reads the serial numbers from both banks

    • If Bank 2 serial number is greater than Bank 1 serial number, it maps Bank 2 to lower region by setting the Swap bit and runs the new firmware from BANK 2 else continues to run firmware from BANK 1

  • The bootloader live update code responsible to program the inactive bank is part of the application it self. Which means the programming operation can happen while the application is running

    • Live Update Application = (Bootloader Code in Live Update mode + Application code)

  • The bootloader live update code will always program the new image in the inactive bank

  • The application code is responsible to send a request to bootloader live update code to perform a bank swap and reset to run the new firmware programmed in Inactive bank

  • Once this request is received the bootloader live update code performs below operation before initiating a reset to run new firmware

    • Inactive Serial number = Active serial number + 1