AMOADD.W

Atomic Add Word

AMOADD.W rd, rs2, (rs1)

Atomically adds a value to a word in memory.

Encoding

Binary Layout

00000

31:27

aq

26

rl

25

rs2

24:20

rs1

19:15

010

14:12

rd

11:7

0101111

6:0

 

Format R-Type (Atomic)

Opcode 0x0000202F

Extension A

Operands

• rd
  Dest (Old Value)
• rs2
  Value to Add
• rs1
  Address

Example

AMOADD.W x10, x11, (x12)

// Atomically adds x11 to memory at x12. Old value stored in x10.

Related

Across architectures

Atomic Fetch and Add : how x86, ARM, RISC-V, and PowerISA each do this.

More in A

Reference

View in RISC-V Unprivileged ISA Specification ↗ RISC-V ISA Manual

Description

AMOADD.W atomically loads a word from the address in rs1 into rd, then adds rs2 to it, and stores the result back to that address.

Operation

temp = M[R[rs1]]; M[R[rs1]] = temp + R[rs2]; R[rd] = temp;