CSRRW

Control Status Register Read/Write

CSRRW rd, csr, rs1

Atomically swaps values in the CSRs. Reads the old value of the CSR into rd, then writes rs1 to the CSR.

Encoding

Binary Layout

csr

31:20

rs1

19:15

001

14:12

rd

11:7

1110011

6:0

 

Format I-Type

Opcode 0x00001073

Extension Zicsr

Operands

• rd
  Dest (Old Value)
• csr
  CSR Address
• rs1
  Src (New Value)

Example

CSRRW x10, scause, x11

// Writes x11 to 'scause' CSR and reads old 'scause' into x10.

Related

More in Zicsr

Reference

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

Description

CSRRW atomically reads the value of CSR csr into rd, then writes the value from rs1 into the CSR. If rd is x0, the read is skipped and no side-effects from reading occur.

Operation

t = CSRs[csr]; CSRs[csr] = R[rs1]; R[rd] = t;