ldrex

Load Register Exclusive (Thumb)

LDREX <Rt>, [<Rn>]

Loads word and sets exclusive monitor (Thumb).

Pseudocode Operation

address ← Rn
Rt ← [address]
SetExclusiveMonitor(address)

Example

LDREX r3, [r1]

Encoding

Binary Layout

11101000010

31:21

1

20

Rn

19:16

Rt

15:12

1111

11:8

imm8

7:0

 

Format Thumb Load Excl

Opcode 0xE8500F00

Extension A32 (Atomic)

Operands

• Rt
  Transfer general-purpose register (load/store)
• Rn
  First source / base general-purpose register

Related

Other forms of ldrex

• ldrex Load Register Exclusive (A32)

More in A32 (Atomic)

Reference

View in Arm A64 ISA Reference ↗ Arm AArch32 ISA

Instruction Forms

Encoding	Instruction		ISA		Bit pattern
0x01900F9F	LDREX{<c>}{<q>} <Rt>, [<Rn> {, {#}<imm>}]		A32		cond | 00011 | 00 | 1 | Rn | Rt | 1 | 1 | 1 | 1 | 1001 | 1111
0xE8500F00	LDREX{<c>}{<q>} <Rt>, [<Rn> {, #<imm>}]		T32		11101000010 | 1 | Rn | Rt | 1111 | imm8

Description

Load Register Exclusive calculates an address from a base register value and an immediate offset, loads a word from memory, writes it to a register and: For more information about support for shared memory see Synchronization and semaphores. For information about memory accesses see Memory accesses.

Operation

if ConditionPassed() then
    EncodingSpecificOperations();
    address = R[n] + imm32;
    AArch32.SetExclusiveMonitors(address,4);
    R[t] = MemA[address,4];