Functional Description
ARM DDI 0388I Copyright © 2008-2012 ARM. All rights reserved. 2-10
ID073015 Non-Confidential
2.4 Power management
The processor provides mechanisms to control both dynamic and static power dissipation. Static
power control is implementation-specific. This section describes:
• Energy efficiency features
• Cortex-A9 processor power control.
• Power domains on page 2-13.
• Cortex-A9 voltage domains on page 2-13.
2.4.1 Energy efficiency features
The features of the Cortex-A9 processor that improve energy efficiency include:
• accurate branch and return prediction, reducing the number of incorrect instruction fetch
and decode operations
• the use of physically addressed caches, reducing the number of cache flushes and refills,
saving energy in the system
• the use of micro TLBs reduces the power consumed in translation and protection lookups
for each cycle
• caches that use sequential access information to reduce the number of accesses to the tag
RAMs and to unnecessary accesses to data RAMs
• instruction loops that are smaller than 64 bytes often complete without additional
instruction cache accesses, so lowering power consumption.
2.4.2 Cortex-A9 processor power control
Place holders for level-shifters and clamps are inserted around the Cortex-A9 processor to ease
the implementation of different power domains.
The Cortex-A9 processor can have the following power domains:
• a power domain for Cortex-A9 processor logic
• a power domain for Cortex-A9 processor MPE
• a power domain for Cortex-A9 processor RAMs.
Table 2-2 shows the power modes.
Table 2-2 Cortex-A9 processor power modes
Mode
Cortex-A9
processor
RAM arrays
Cortex-A9
processor
logic
Cortex-A9
data engine
Description
Full Run Mode Powered-up Powered-up Powered-up -
Clocked Clocked
Run Mode with
MPE disabled
Powered-up Powered-up Powered-up See Coprocessor Access Control Register on
page 4-29 for information about disabling the MPE
Clocked No clock
Run Mode with
MPE powered off
Powered-up Powered-up Powered off The MPE can be implemented in a separate power
domain and be powered off separately
Clocked
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