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Chapter 42
Bit Manipulation Engine (BME)
42.1 Introduction
The Bit Manipulation Engine (BME) provides hardware support for atomic read-modify-
write memory operations to the peripheral address space in Cortex-M0+ based
microcontrollers.
This architectural capability is also known as "decorated storage" as it defines a
mechanism for providing additional semantics for load and store operations to memory-
mapped peripherals beyond just the reading and writing of data values to the addressed
memory locations. In the BME definition, the "decoration", that is, the additional
semantic information, is encoded into the peripheral address used to reference the
memory.
By combining the basic load and store instructions of the ARM Cortex-M instruction set
architecture (v6M, v7M) with 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.
BME decorated references are only available on system bus transactions generated by the
processor core and targeted at the standard 512 KB peripheral address space based at
1
0x4000_0000
. The decoration semantic is embedded into address bits[28:19], creating a
448 MB space at addresses 0x4400_0000–0x5FFF_FFFF for AIPS; these bits are
stripped out of the actual address sent to the peripheral bus controller and used by the
BME to define and control its operation.
1. To be perfectly accurate, the peripheral address space occupies a 516 KB region: 512 KB based at 0x4000_0000 plus a 4
KB space based at 0x400F_F000 for GPIO accesses. This organization provides compatibility with the Kinetis K Family.
Attempted accesses to the memory space located between 0x4008_0000 - 0x400F_EFFF are error terminated due to an
illegal address.
Freescale Semiconductor, Inc.
KL27 Sub-Family Reference Manual , Rev. 5, 01/2016
831
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