amocas.b.aq

Atomic compare-and-swap byte (acquire)

This instruction is defined by:

Encoding

Synopsis

Atomically with acquire ordering:

Load the byte at address xs1
Write the sign-extended value into xd
Compare the loaded value with the least-significant byte of register xs2
If equal, write the least-significant byte of register xs2+1 to the address in xs1

Access

M	HS	U	VS	VU
Always	Always	Always	Always	Always

Always

Decode Variables

Bits<5> xs2 = $encoding[24:20];
Bits<5> xs1 = $encoding[19:15];
Bits<5> xd = $encoding[11:7];

Execution

Pruned, XLEN == 64
Original

raise(ExceptionCode::IllegalInstruction, mode(), $encoding);

if (!implemented?(ExtensionName::Zabha)) {
  raise(ExceptionCode::IllegalInstruction, mode(), $encoding);
}
memory_model_acquire();
XReg virtual_address = X[xs1];

Exceptions

This instruction may result in the following synchronous exceptions:

IllegalInstruction