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# 1.6.1 How the USB Device HID Bootloader Library Works

The USB Device HID Bootloader firmware communicates with the Unified Host application running on Host PC by using a predefined communication protocol.

The USB Device HID Bootloader works in two different modes:

Basic Mode

- This mode is supported for all the devices

- Resides from:

  - The starting location of the Flash memory region for Cortex-M based MCUs

  - The starting location of the Boot Flash memory region or Program Flash memory region for MIPS based MCUs devices

- The Bootloader performs Flash erase/program/verify operations with the application hex sent from host PC using the Unified Bootloader Host Application while in the Firmware Upgrade mode

  - Bootloader always performs Flash operation from the address received via hex record

  - The application can use the entire Flash memory region starting from the end of bootloader space

- Jumps to the application once programming is completed

Live Update Mode

- This mode is supported for the devices which have a Dual Bank Flash memory

- Resides from:

  - The starting location of the Flash memory region of both the banks on Cortex-M based MCUs along with application code

  - The starting location of the Program Flash memory region of both the banks for MIPS based MCUs devices along with application code

- The Bootloader task performs Flash erase/program/verify operations with the application hex sent from host PC using the Unified Bootloader Host Application in the Inactive bank

- Performs a bank swap and reset to run the application programmed in inactive bank on application task request

Rev: G