14.1 Overview
The ARMv8-M Architecture defines a mechanism whereby an implementation defined mechanism (i.e., a component in the surrounding system) can define whether any particular address is exempt from checking, and is non-secure callable, or Secure. The Implementation Defined Attribution Unit partitions the memory map into IDAU regions which are subdivisions of the System Bus MAIN regions. IDAU region size and decoding granularity are either fixed or configurable from the APB configuration registers. The MAIN region subdivisions are watermark based.