mnret

Machine mode resume from the RNMI or Double Trap handler

This instruction is defined by:

Encoding

Synopsis

MNRET is an M-mode-only instruction that uses the values in mnepc and mnstatus to return to the program counter, privilege mode, and virtualization mode of the interrupted context. This instruction also sets mnstatus.NMIE. If MNRET changes the privilege mode to a mode less privileged than M, it also sets mstatus.MPRV to 0. If the Zicfilp extension is implemented, then if the new privileged mode is y, MNRET sets ELP to the logical AND of yLPE (see Section 22.1.1) and mnstatus.MNPELP.

Access

M	HS	U	VS	VU
Always	Always	Always	Always	Always

Always

Decode Variables

Execution

Pruned, XLEN == 64
Original

CSR[mstatus].MPRV = 0;

CSR[mnstatus].NMIE = 1'b1;
set_mode(PrivilegeMode::U);
CSR[mnstatus].MNPP = 2'd0;
$pc = $bits(CSR[CSR[mnepc]]);

if (CSR[mnstatus].MNPP != 2'b11) {
  if (implemented?(ExtensionName::U)) {
    CSR[mstatus].MPRV = 0;
  }
  if (implemented?(ExtensionName::Smdbltrp)) {
    if (xlen() == 64) {
      CSR[mstatus].MDT = 1'b0;
    } else {
      CSR[mstatush].MDT = 1'b0;
    }
  }
}
CSR[mnstatus].NMIE = 1'b1;
if (CSR[mnstatus].MNPP == 2'b00) {
  set_mode(PrivilegeMode::U);
} else if (CSR[mnstatus].MNPP == 2'b01) {
  set_mode(PrivilegeMode::S);
} else if (CSR[mnstatus].MNPP == 2'b11) {
  set_mode(PrivilegeMode::M);
}
CSR[mnstatus].MNPP = implemented?(ExtensionName::U) ? 2'b00 : 2'b11;
$pc = $bits(CSR[CSR[mnepc]]);