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Programmer’s Model
ARM DDI 0363E Copyright © 2009 ARM Limited. All rights reserved. 2-3
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2.2 Instruction set states
The processor has two instruction set states:
ARM state The processor executes 32-bit, word-aligned ARM instructions in this
state.
Thumb state The processor executes 32-bit and 16-bit halfword-aligned Thumb
instructions in this state.
Note
Transition between ARM state and Thumb state does not affect the processor mode or the
register contents.
2.2.1 Switching state
The instruction set state of the processor can be switched between ARM state and Thumb state:
• Using the
BX
and
BLX
instructions, by a load to the PC, or with a data-processing instruction
that does not set flags, with the PC as the destination register. Switching state is described
in the ARM Architecture Reference Manual.
Note
When the
BXJ
instruction is used the processor invokes the
BX
instruction.
• Automatically on an exception. You can write an exception handler routine in ARM or
Thumb code. For more information, see Exceptions on page 2-16.
2.2.2 Interworking ARM and Thumb state
The processor enables you to mix ARM and Thumb code. For more information about
interworking ARM and Thumb, see the RealView Compilation Tools Developer Guide.