MSC8144E Reference Manual, Rev. 3
1-14
Freescale
Semiconductor
Overview
1.4.4 Memory Management Unit (MMU)
The memory management unit (MMU) controls external memory accesses and translates virtual
addresses to physical addresses.
The MMU is responsible for three main functions:
Supplying program and data access hardware protection for two privilege levels (user and
supervisor) to enable system reliability and easier code development up to an open system
approach.
Implementing a high-speed address translation mechanism that translates from virtual to
physical addresses to support memory relocation and a modular system-independent
software development flow.
Providing cache (L1 and L2) and bus controls for advanced memory management.
Following are some examples of common problems that are solved by simple block translation:
Typically, a non-relocatable code is preferred. Simple address translation between the
virtual and the physical address can assure that it executes without change after it is
swapped from the DDR memory to an arbitrary location in internal MSC8144E memory.
Code does not depend on physical memory allocation and can be written modularly.
Relocatable code is not immune to addressing problems. Global variables can be
addressed relative to the code. However, in a multi-core device such as MSC8144E in
which all the cores may share the same code, these global variables should be addressed
differently depending on the core.
The MMU enables the system designer to integrate system resources better and to define a
cleaner software model. For example, the registers defining protection regions, address
translation regions, cacheable regions, and so on can be combined. In addition, cache usage can
be optimized, based on the specific attributes controlled by the MMU programming.
MMU protection enables implementation of a protected software architecture in which system
code and task code is protected from corruption by an errant task. This increases the mean time
between failures (MTBF) and accelerates the system debugging.
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