ldaexb

Load Acquire Exclusive Byte (A32)

LDAEXB<c> <Rt>, [<Rn>]

Loads a byte, acquires semantics, marks exclusive.

Details

Loads a byte from memory at the address in Rn with Acquire semantics and marks the location as exclusive. The loaded byte is zero-extended and placed in Rt. Acquire semantics ensure that subsequent memory operations are not reordered before this load. No condition flags are affected.

Pseudocode Operation

Rt ← ZeroExtend([Rn], 8); ExclusiveLocal ← TRUE; Acquire()

Example

LDAEXB r3, [r1]

Encoding

Binary Layout
cond
00011
10
1
Rn
Rt
1
1
1
0
1001
1111
 
Format Load Excl
Opcode 0x01D00E9F
Extension A32 (Atomic)

Operands

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

Reference (Arm AArch32 ISA)

Instruction Forms

Encoding Instruction ISA Bit pattern
0x01D00E9F LDAEXB{<c>}{<q>} <Rt>, [<Rn>] A32 cond | 00011 | 10 | 1 | Rn | Rt | 1 | 1 | 1 | 0 | 1001 | 1111
0xE8D00FCF LDAEXB{<c>}{<q>} <Rt>, [<Rn>] T32 11101000110 | 1 | Rn | Rt | 1111 | 1 | 1 | 00 | 1111

Description

Load-Acquire Exclusive Byte loads a byte from memory, zero-extends it to form a 32-bit word, writes it to a register and: The instruction also has memory ordering semantics as described in Load-Acquire, Store-Release. 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];
    AArch32.SetExclusiveMonitors(address, 1);
    R[t] = ZeroExtend(MemO[address, 1], 32);