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NUC970 Technical Reference Manual
Publication Release Date: Dec. 15, 2015
- 60 -
Revision V1.30
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ARM9EJ-S Core
I-Cache
16 kB
MMU
D-Cache
16 kB
Bus Interface Unit
ARM926EJ-S Processor
Instruction
AHB Interface
Data
AHB Interface
D-EXT
I-EXT
MUX
MUX
Embedded
ICE-RT Logic
TAP
Controller
JTAG
Interface
Figure 5.1-1 ARM926EJ-S Block Diagram
5.1.2 System Control Coprocessor (CP15)
The system control coprocessor (CP15) is used to configure and control the ARM926EJ-S
processor. The caches, Memory Management Unit (MMU), and most other system options are
controlled using CP15 registers. User can only access CP15 registers with MRC and MCR
instruction in a privileged mode. Access CP15 registers with CDP, LDC, STC, MCRR, and MRRC
instructions and unprivileged MRC or MCR instruction causes the undefined instruction exception
to be taken.
5.1.3 Memory Management Unit (MMU)
The ARM926EJ-S MMU is an ARM architecture v5 MMU. It provides virtual memory features
required by systems operating on platforms such as Symbian OS, WindowsCE, and Linux. A
single set of two-level page tables stored in main memory is used to control the address
translation, permission checks, and memory region attributes for both data and instruction
accesses.
The MMU uses a single unified Translation Lookaside Buffer (TLB) to cache the information held
in the page tables. To support both sections and pages, there are two levels of address