mret

Machine Exception Return

This instruction is defined by:

Sm, version >= 0

This instruction is included in the following profiles:

Encoding

Assembly format

`mret `

Synopsis

Returns from an exception in M-mode.

Access

M	HS	U	VS	VU
Always	Never	Never	Never	Never

Always

Never

Decode Variables

Execution

IDL
Sail

if (implemented?(ExtensionName::S) && CSR[mstatus].MPP != 2'b11) {
  CSR[mstatus].MPRV = 0;
}
CSR[mstatus].MIE = CSR[mstatus].MPIE;
CSR[mstatus].MPIE = 1;
if (CSR[mstatus].MPP == 2'b00) {
  set_mode(PrivilegeMode::U);
} else if (CSR[mstatus].MPP == 2'b01) {
  set_mode(PrivilegeMode::S);
} else if (CSR[mstatus].MPP == 2'b11) {
  set_mode(PrivilegeMode::M);
}
CSR[mstatus].MPP = implemented?(ExtensionName::U) ? 2'b00 : 2'b11;
$pc = $bits(CSR[mepc]);

{
  if   cur_privilege != Machine
  then { handle_illegal(); RETIRE_FAIL }
  else if not(ext_check_xret_priv (Machine))
  then { ext_fail_xret_priv(); RETIRE_FAIL }
  else {
    set_next_pc(exception_handler(cur_privilege, CTL_MRET(), PC));
    RETIRE_SUCCESS
  }
}