3.4.2 How Do I Link Bootloaders and Downloadable Applications?

Exactly how this is done depends on the device you are using and your project requirements, but the general approach when compiling applications that use a bootloader is to allocate discrete program memory space to the bootloader and application so they have their own dedicated memory. In this way the operation of one cannot affect the other. This will require that either the bootloader or the application is offset in memory. That is, the Reset and interrupt location are offset from address 0 and all program code is offset by the same amount.

Typically the application code is offset, and the bootloader is linked with no offset so that it populates the Reset and interrupt code locations. The bootloader Reset and interrupt code merely contains code which redirects control to the real Reset and interrupt code defined by the application and which is offset.

The contents of the Hex file for the bootloader can be merged with the code of the application by using loadable projects in MPLAB X IDE. (See MPLAB X IDE documentation for details.) This results in a single Hex file that contains the bootloader and application code in the one image. Check for warnings from this application about overlap, which may indicate that memory is in use by both bootloader and the downloadable application.

See the PIC32 Bootloader Application Note (DS01388) on the Microchip website.