5.2 Check Status Byte

The bootloader and the host application will communicate program status through a Reset Byte value, also known as a State Flag or Status Byte.

Overview

In the Check Reset Byte verification method, also known as a Check State Flag verification method, the bootloader will verify that the application image space was programmed successfully by checking for a pre-configured byte value at a preconfigured memory location that both the host and the bootloader have access to. This does not check the validity of the application image, it only checks to see if the bootloader populated the application image into the program memory and set the State Flag value to the predefined “valid application” byte value.

Verification Flow

The Check Reset Byte verification follows a relatively similar program flow as Check Reset Vector. The main difference is that instead of checking the Reset Vector for “non-blank” data, one specific byte in the Reset Vector will be checked for a value that either indicates “valid application” or “bootloader needed”. These status value are known by both the bootloader and the host application to communicate the end application’s state across the entire ecosystem. This method is unable to perform integrity or authenticity checks and simply checks for a successful programming step.