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:
•
•
Cortex-A9 processor power control
•
•
.
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 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
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-
Clocked
Clocked
Run Mode with
MPE disabled
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Coprocessor Access Control Register
for information about disabling the MPE
Clocked
No clock
Run Mode with
MPE powered off
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Powered off
The MPE can be implemented in a separate power
domain and be powered off separately
Clocked