reznez 0.0.0

The high accuracy NES Emulator
Documentation 
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use crate::apu::length_counter::LengthCounter;
use crate::apu::timer::Timer;
use crate::util::integer::U4;
use crate::util::bit_util;

#[derive(Default)]
pub struct PulseChannel {
    enabled: bool,

    duty: Duty,
    constant_volume: bool,
    volume_or_envelope: U4,

    //sweep: Sweep,
    timer: Timer,
    pub(super) length_counter: LengthCounter,

    sequence_index: usize,
}

impl PulseChannel {
    pub fn write_control_byte(&mut self, value: u8) {
        self.duty =                 ((value & 0b1100_0000) >> 6).into();
        self.length_counter.set_halt((value & 0b0010_0000) != 0);
        self.constant_volume =       (value & 0b0001_0000) != 0;
        self.volume_or_envelope =    (value & 0b0000_1111).into();
    }

    #[allow(clippy::unused_self)]
    pub fn write_sweep_byte(&mut self, _value: u8) {
        //self.sweep = Sweep::from_u8(value);
    }

    pub fn write_timer_low_byte(&mut self, value: u8) {
        self.timer.set_period_low(value);
    }

    pub fn write_length_and_timer_high_byte(&mut self, value: u8) {
        if self.enabled {
            self.length_counter.set_count_from_lookup((value & 0b1111_1000) >> 3);
        }

        self.sequence_index = 0;
        self.timer.set_period_high_and_reset_index(value & 0b0000_0111);
    }

    pub(super) fn set_enabled(&mut self, enabled: bool) {
        self.enabled = enabled;
        if !self.enabled {
            self.length_counter.set_to_zero();
        }
    }

    pub(super) fn active(&self) -> bool {
        !self.length_counter.is_zero()
    }

    pub(super) fn on_cycle_step(&mut self) {
        let wrapped_around = self.timer.tick();
        if wrapped_around {
            self.sequence_index += 1;
            self.sequence_index %= 8;
        }
    }

    pub(super) fn sample_volume(&self) -> f32 {
        let on_duty = self.duty.is_on_at(self.sequence_index);
        let non_short_period = self.timer.period() >= 8;
        let non_zero_length = !self.length_counter.is_zero();

        let enabled = self.enabled && on_duty && non_short_period && non_zero_length;
        if enabled {
            f32::from(self.volume_or_envelope.to_u8())
        } else {
            0.0
        }
    }
}

#[derive(Clone, Copy, Default)]
pub enum Duty {
    #[default]
    Low     = 0b0100_0000,
    Medium  = 0b0110_0000,
    High    = 0b0111_1000,
    Negated = 0b1001_1111,
}

impl Duty {
    fn is_on_at(self, sequence_index: usize) -> bool {
        bit_util::get_bit(self as u8, sequence_index)
    }
}

impl From<u8> for Duty {
    fn from(value: u8) -> Self {
        match value {
            0 => Duty::Low,
            1 => Duty::Medium,
            2 => Duty::High,
            3 => Duty::Negated,
            _ => unreachable!(),
        }
    }
}

/*
#[derive(Default)]
pub struct Sweep {
    enabled: bool,
    period: U3,
    period_change: PeriodChange,
    shift_count: U3,
}

impl Sweep {
    fn from_u8(value: u8) -> Sweep {
        Sweep {
            enabled:        (value & 0b1000_0000) != 0,
            period:        ((value & 0b0111_0000) >> 4).into(),
            period_change: ((value & 0b0000_1000) >> 3).into(),
            shift_count:    (value & 0b0000_0111).into(),
        }
    }
}

#[derive(Default)]
pub enum PeriodChange {
    #[default]
    Increase,
    Decrease,
}

impl From<u8> for PeriodChange {
    fn from(item: u8) -> Self {
        match item {
            0 => PeriodChange::Increase,
            1 => PeriodChange::Decrease,
            _ => unreachable!(),
        }
    }
}
*/