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/* The emulator fetch-execute-interrupt dispatch loop. */
union FetchResult = {
F_Base : word, /* Base ISA */
F_RVC : half, /* Compressed ISA */
F_Error : (ExceptionType, xlenbits) /* exception and PC */
}
function isRVC(h : half) -> bool =
~ (h[1 .. 0] == 0b11)
val fetch : unit -> FetchResult effect {escape, rmem, rreg, wmv, wreg}
function fetch() -> FetchResult =
/* check for legal PC */
if (PC[0] != 0b0 | (PC[1] != 0b0 & (~ (haveRVC()))))
then F_Error(E_Fetch_Addr_Align, PC)
else match translateAddr(PC, Execute, Instruction) {
TR_Failure(e) => F_Error(e, PC),
TR_Address(ppclo) => {
/* split instruction fetch into 16-bit granules to handle RVC, as
* well as to generate precise fault addresses in any fetch
* exceptions.
*/
match checked_mem_read(Instruction, ppclo, 2) {
MemException(e) => F_Error(E_Fetch_Access_Fault, PC),
MemValue(ilo) => {
if isRVC(ilo) then F_RVC(ilo)
else {
PChi : xlenbits = PC + 2;
match translateAddr(PChi, Execute, Instruction) {
TR_Failure(e) => F_Error(e, PChi),
TR_Address(ppchi) => {
match checked_mem_read(Instruction, ppchi, 2) {
MemException(e) => F_Error(E_Fetch_Access_Fault, PChi),
MemValue(ihi) => F_Base(append(ihi, ilo))
}
}
}
}
}
}
}
}
/* returns whether an instruction was retired, and whether to increment the step count in the trace */
val step : int -> (bool, bool) effect {barr, eamem, escape, exmem, rmem, rreg, wmv, wreg}
function step(step_no) =
match curInterrupt(cur_privilege, mip, mie, mideleg) {
Some(intr, priv) => {
print_bits("Handling interrupt: ", intr);
handle_interrupt(intr, priv);
(false, false)
},
None() => {
match fetch() {
F_Error(e, addr) => {
handle_mem_exception(addr, e);
(false, false)
},
F_RVC(h) => {
match decodeCompressed(h) {
None() => {
print("[" ^ string_of_int(step_no) ^ "] [" ^ cur_privilege ^ "]: " ^ BitStr(PC) ^ " (" ^ BitStr(h) ^ ") <no-decode>");
handle_decode_exception(EXTZ(h));
(false, true)
},
Some(ast) => {
print("[" ^ string_of_int(step_no) ^ "] [" ^ cur_privilege ^ "]: " ^ BitStr(PC) ^ " (" ^ BitStr(h) ^ ") " ^ ast);
nextPC = PC + 2;
(execute(ast), true)
}
}
},
F_Base(w) => {
match decode(w) {
None() => {
print("[" ^ string_of_int(step_no) ^ "] [" ^ cur_privilege ^ "]: " ^ BitStr(PC) ^ " (" ^ BitStr(w) ^ ") <no-decode>");
handle_decode_exception(EXTZ(w));
(false, true)
},
Some(ast) => {
print("[" ^ string_of_int(step_no) ^ "] [" ^ cur_privilege ^ "]: " ^ BitStr(PC) ^ " (" ^ BitStr(w) ^ ") " ^ ast);
nextPC = PC + 4;
(execute(ast), true)
}
}
}
}
}
}
val loop : unit -> unit effect {barr, eamem, escape, exmem, rmem, rreg, wmv, wreg}
function loop () = {
let insns_per_tick = plat_insns_per_tick();
i : int = 0;
step_no : int = 0;
while (~ (htif_done)) do {
minstret_written = false; /* see note for minstret */
let (retired, stepped) = step(step_no);
PC = nextPC;
if retired then retire_instruction();
if stepped then step_no = step_no + 1;
/* check htif exit */
if htif_done then {
let exit_val = unsigned(htif_exit_code);
if exit_val == 0 then print("SUCCESS")
else print_int("FAILURE: ", exit_val);
} else {
/* update time */
i = i + 1;
if i == insns_per_tick then {
tick_clock();
/* for now, we drive the platform i/o at every clock tick. */
tick_platform();
i = 0;
}
}
}
}
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