The minidriver program in this example is a simple implementation that you can use for debugging purposes. It counts the number of times it's called for each phase of the boot process and stores that information in its data area. Once the system is booted, a program can read the data area and retrieve this information. No hardware access is required for this minidriver.
In this example, the size of the data area is 64 KB. If you decrease the value of mdriver_max (the amount of data that's copied from flash to RAM between calls of your minidriver) from its default 16 KB, then you may need to increase the size of the data area because the handler function will be called more times.