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

Application Level Programmers’ Model
ThumbEE Handler Base Register. This contains the base address for ThumbEE handlers.
A handler is a short, commonly executed, sequence of instructions. It is typically, but not always,
associated directly with one or more bytecodes or other intermediate language elements.
Changes to these CP14 registers have the same synchronization requirements as changes to the CP15
registers. These are described in:
Changes to CP15 registers and the memory order model on page B3-77 for a VMSA implementation
Changes to CP15 registers and the memory order model on page B4-28 for a PMSA implementation.
ThumbEE is an unprivileged, user-level facility, and there are no special provisions for using it securely. For
more information, see ThumbEE and the Security Extensions on page B1-73.
ThumbEE Configuration Register (TEECR)
The ThumbEE Configuration Register (TEECR) controls unprivileged access to the ThumbEE Handler
Base Register.
The TEECR is:
a CP14 register
a 32-bit register, with access rights that depend on the current privilege:
— the result of an unprivileged write to the register is UNDEFINED
— unprivileged reads, and privileged reads and writes, are permitted.
when the Security Extensions are implemented, a Common register.
The format of the TEECR is:
31 1 0
UNK/SBZP XED
Bits [31:1] UNK/SBZP.
XED, bit [0] Execution Environment Disable bit. Controls unprivileged access to the ThumbEE Handler
Base Register:
0 Unprivileged access permitted.
1 Unprivileged access disabled.
The reset value of this bit is 0.
The effects of a write to this register on ThumbEE configuration are only guaranteed to be visible to
subsequent instructions after the execution of an ISB instruction, an exception entry or an exception return.
However, a read of this register always returns the value most recently written to the register.
To access the TEECR, read or write the CP14 registers with an MRC or MCR instruction with set to 6,
set to c0, set to c0, and set to 0. For example:
MRC p14, 6, , c0, c0, 0 ; Read ThumbEE Configuration Register
MCR p14, 6, , c0, c0, 0 ; Write ThumbEE Configuration Register
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