csrrw
Atomic Read/Write CSR
This instruction is defined by:
-
Zicsr, version >= 0
This instruction is included in the following profiles:
Synopsis
Atomically swap values in the CSRs and integer registers.
Read the old value of the CSR, zero-extends the value to XLEN
bits,
and then write it to integer register rd.
The initial value in rs1 is written to the CSR.
If rd=x0
, then the instruction shall not read the CSR and shall not
cause any of the side effects that might occur on a CSR read.
Decode Variables
Bits<12> csr = $encoding[31:20];
Bits<5> rs1 = $encoding[19:15];
Bits<5> rd = $encoding[11:7];
Execution
-
IDL
-
Sail
if (rd != 0) {
X[rd] = CSR[csr].sw_read();
}
CSR[csr].sw_write(X[rs1]);
{
let rs1_val : xlenbits = if is_imm then zero_extend(rs1) else X(rs1);
let isWrite : bool = match op {
CSRRW => true,
_ => if is_imm then unsigned(rs1_val) != 0 else unsigned(rs1) != 0
};
if not(check_CSR(csr, cur_privilege, isWrite))
then { handle_illegal(); RETIRE_FAIL }
else if not(ext_check_CSR(csr, cur_privilege, isWrite))
then { ext_check_CSR_fail(); RETIRE_FAIL }
else {
let csr_val = readCSR(csr); /* could have side-effects, so technically shouldn't perform for CSRW[I] with rd == 0 */
if isWrite then {
let new_val : xlenbits = match op {
CSRRW => rs1_val,
CSRRS => csr_val | rs1_val,
CSRRC => csr_val & ~(rs1_val)
};
writeCSR(csr, new_val)
};
X(rd) = csr_val;
RETIRE_SUCCESS
}
}