Changing between A32 and T32 instruction set states
A processor that is executing A32 instructions is operating in A32 instruction set state. A processor that is executing T32 instructions is operating in T32 instruction set state. For brevity, this document refers to them as the A32 state and T32 state respectively.
A processor in A32 state cannot execute T32 instructions, and a processor in T32 state cannot execute A32 instructions. You must ensure that the processor never receives instructions of the wrong instruction set for the current state.
The initial state after reset depends on the processor being used and its configuration.
To direct armasm to generate A32 or T32
instruction encodings, you must set the assembler mode using an
THUMB directive. Assembly code using
directives can still be assembled, but Arm® recommends you use the
for new code.
These directives do not change the instruction set state of
the processor. To do this, you must use an appropriate instruction,
change between A32 and T32 states when performing a branch.