ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition

A9.3 Additional instructions in Thumb and ThumbEE instruction sets
ThumbEE
On a processor with the ThumbEE extension, there are two additional 32-bit instructions, ENTERX and LEAVEX.
These are available in both Thumb state and ThumbEE state.
A9.3.1 ENTERX, LEAVEX
ENTERX causes a change from Thumb state to ThumbEE state, or has no effect in ThumbEE state.
LEAVEX causes a change from ThumbEE state to Thumb state, or has no effect in Thumb state.
Encoding T1 ThumbEE
ENTERX Not permitted in IT block.
LEAVEX Not permitted in IT block.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
1 1 1 1 0 0 1 1 1 0 1 1 (1)(1)(1) (1) 1 0 (0) 0 (1)(1)(1)(1) 0 0 0 J (1)(1)(1)(1)
is_enterx = (J == ‘1’);
Assembler syntax
ENTERX Encoded as J = 1
LEAVEX Encoded as J = 0
where:
See Standard assembler syntax fields on page A8-7. An ENTERX or LEAVEX instruction must
be unconditional.
Operation
if is_enterx then
SelectInstrSet(InstrSet_ThumbEE);
else
SelectInstrSet(InstrSet_Thumb);
Exceptions
None.
ARM DDI 0406B Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. A9-7