Bme Decorated Stores - NXP Semiconductors MKL27Z128VFM4 Reference Manual

Functional description
Recall the combination of the basic load and store instructions of the Cortex-M
instruction set architecture (v6M, v7M) plus the concept of decorated storage provided by
the BME, the resulting implementation provides a robust and efficient read-modify-write
capability to this class of ultra low-end microcontrollers. The resulting architectural
capability defined by this core platform function is targeted at the manipulation of n-bit
fields in peripheral registers and is consistent with I/O hardware addressing in the
Embedded C standard. For most BME commands, a single core read or write bus cycle is
converted into an atomic read-modify-write, that is, an indivisible "read followed by a
write" bus sequence.
Consider decorated store operations first, then decorated loads.

42.3.1 BME decorated stores

The functions supported by the BME's decorated stores include three logical operators
(AND, OR, XOR) plus a bit field insert.
For all these operations, BME converts a single decorated AHB store transaction into a 2-
cycle atomic read-modify-write sequence, where the combined read-modify operation is
performed in the first AHB data phase, and then the write is performed in the second
AHB data phase.
A generic timing diagram of a decorated store showing a peripheral bit field insert
operation is shown as follows:
KL27 Sub-Family Reference Manual , Rev. 5, 01/2016
834 Freescale Semiconductor, Inc.