Enum Stepping 

pub enum Stepping {
    Fixed,
    Early,
}

Which VR4300 stepping a console carries.

The only behavior that currently depends on it is the FP multiplication erratum, and that dependency is why this is modeled as console state rather than folded into mul: an unconditional erratum would make every multiply on every console wrong, and most consoles do not have it.

Variants

Fixed

A later stepping, with the multiplication erratum fixed.

The default, because it is the majority of hardware and because the erratum’s output is undocumented — see Stepping::has_mul_erratum.

Early

An early stepping carrying the erratum: NUS-01 and NUS-02 (Japan only) and NUS-03 (the first US revision).

Implementations

impl Stepping

pub const fn has_mul_erratum(self) -> bool

Does this stepping carry the FP multiplication erratum?

Why the erratum is not implemented

The trigger is documented (n64brew_wiki/markdown/VR4300.md): a multiply whose preceding multiply had a NaN, zero or infinity operand “may produce unexpected results”. GCC’s -mfix4300 works around it by inserting two nops after every MUL.S/MUL.D/MULT.

What the corrupted output actually is has never been characterized — our own ref-docs/2026-07-20-vr4300-timing-supplement.md lists it under undocumented constants, with only trigger conditions known. So the erratum can be detected here but not reproduced, and inventing a plausible wrong value would be exactly the fitted-constant failure docs/accuracy-ledger.md forbids: every later result built on it would stop being evidence.

Accuracy-ledger U-7. Selecting Stepping::Early therefore changes nothing yet — it exists so that when the output is characterized, the switch is already in the right place rather than threaded through afterwards.

Trait Implementations

impl Clone for Stepping

fn clone(&self) -> Stepping

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Stepping

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Stepping

fn default() -> Stepping

Returns the “default value” for a type.

impl<'de> Deserialize<'de> for Stepping

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl PartialEq for Stepping

fn eq(&self, other: &Stepping) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Serialize for Stepping

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl Copy for Stepping

impl Eq for Stepping

impl StructuralPartialEq for Stepping