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5 Verification Schemes
This section discusses the various methods of application verification provided to the users by the bootloader module.
5.1 Check Reset Vector

In this method the bootloader will check for a non-void value at a predefined location within the end application’s reset vector.

1 MCC Melody Bootloader: 8-bit
2 User Interface
3 Unified Bootloader Host Application (UBHA)
4 Use Case Examples

This section explains how to configure various bootloaders using MPLAB® X IDE and MCC Melody.
5 Verification Schemes
This section discusses the various methods of application verification provided to the users by the bootloader module.
- 5.1 Check Reset Vector
  
  In this method the bootloader will check for a non-void value at a predefined location within the end application’s reset vector.
- 5.2 Check Status Byte
  
  In this method the bootloader and the host application will communicate program status through a reset byte value, also known as a State Flag or Status Byte.
- 5.3 Checksum
  
  In this method the application image will be verified by calculating a checksum on the application space and comparing the result to a pre-calculated checksum in the bootloader. To learn more about checksum, read this reference.
- 5.4 Cyclic Redundancy Check
  
  In these methods the bootloader uses a CRC signature for application validation. To learn more about the steps for the CRC verification of memory, refer to this reference.
6 Bootload Communication Protocol: 8-bit
7 References
Microchip Information

5.1 Check Reset Vector

In this method the bootloader will check for a non-void value at a predefined location within the end application’s reset vector.

Overview

In the Check Reset Vector verification method, the bootloader will verify that the application image space has some form of data present that is not null. This does not check the validity or authenticity of the application image, it only verifies that something has been programmed into the application space. It also does not check for any memory errors in FLASH. This form of verification is very quick and results in very fast entry to the application from the bootloader. It does not provide any integrity checks and it cannot detect if the memory has been corrupted during transfer.

Verification Flow

In Check Reset Vector verification the program flow checks the end application’s reset vector address. This verification method relies on the assumption that if there is a 0xFF value at the start of that reset vector address then that the device has been erased and the bootloader needs to start loading a new application image. In the event of a device reset or a normal start up, this verification method will check for a 0xFF in the application reset vector space and if needed will start running the bootloader, otherwise the bootloader will just start running the end application that is present at that address.

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