Programmers Model
ARM DDI 0388I
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3-8
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Non-Confidential
3.7
Modes of operation and execution
This section describes the instruction set states and modes of the Cortex-A9 processor in:
•
3.7.1
Operating states
The processor has the following instruction set states controlled by the T bit and J bit in the
CPSR.
ARM state
The processor executes 32-bit, word-aligned ARM instructions.
Thumb state
The processor executes 16-bit and 32-bit, halfword-aligned Thumb
instructions.
Jazelle state
The processor executes variable length, byte-aligned Jazelle instructions.
ThumbEE state
The processor executes a variant of the Thumb instruction set designed as
a target for dynamically generated code. This is code compiled on the
device either shortly before or during execution from a portable bytecode
or other intermediate or native representation.
The J bit and the T bit determine the instruction set used by the processor.
shows the
encoding of these bits.
Note
Transition between ARM and Thumb states does not affect the processor mode or the register
contents. See the
ARM Architecture Reference Manual
for information on entering and exiting
ThumbEE state.
Table 3-1 CPSR J and T bit encoding
J
T
Instruction set state
0
0
ARM
0
1
Thumb
1
0
Jazelle
1
1
ThumbEE