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# 1.8.3 USB Host MSD Bootloader Configurations

Bootloader Specific User Configurations

- Bootloader Media Type:

  - Change the Media Type to USB Mass Storage Device

- Bootloader NVM Memory Used:

  - Specifies the memory peripheral used by bootloader to perform Flash operations
  - The name of the peripheral will vary from device to device

- Bootloader Size (Bytes):

  - Specifies the maximum size of Flash required by the bootloader
  - This size is calculated based on Bootloader type and Memory used
  - This size will vary from device to device and should always be aligned to device erase unit size

- Enable Bootloader Trigger From Firmware:

  - This Option can be used to Force Trigger bootloader from application firmware after a soft reset. It does so by reserving the specified number of bytes in SRAM from the start of the RAM. The reserved memory is updated by the application with a pre-defined pattern. The bootloader firmware in the bootloader_Trigger() routine, can check the reserved memory for the pre-defined pattern and enter Bootloader mode if the pattern matches.

  - Number Of Bytes To Reserve From Start Of RAM:

    - This option adds the provided offset to RAM Start address in bootloader linker script
    - Application firmware can store some pattern in the reserved bytes region from RAM start for bootloader to check at reset in bootloader_Trigger() function

- Application Binary Image Path:

  - Application binary image file name with path. If only file name is mentioned bootloader will try to open the file from the root directory

  - Default: image.bin

  - Can be used to specify custom paths based on requirement

    - Example: dir1/dir2/app.bin

File System Configurations

- Use File System Auto Mount Feature:

  - Enabled by default when File System Bootloader is added

- Media Type:

  - Change the Media Type to SYS_FS_MEDIA_TYPE_MSD

- Make FAT File System Read-only:

  - Enabled by default when File System Bootloader is added as there are no write operations to be done

  - Enabling this option also saves significant amount of Flash memory

Bootloader System Configurations

- Application Start Address (Hex):
  - Start address of the application which will programmed by bootloader
  - This value is filled by bootloader when its loaded which is equal to the bootloader size. It can be modified as per user need.
  - This value will be used by bootloader to jump to application at device reset

Bootloader Linker Pre Processor Macros for Cortex-M Based MCUs

- Based on the configurations the above linker pre processor macros will be generated in MPLAB X xc32-ld settings
  - ROM_LENGTH specifies the size of the bootloader

Rev: G