apu
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@ -63,8 +63,8 @@ impl Apu {
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let square_table = (0..31).map(|x| 95.52/(8128.0 / x as f32) + 100.0).collect();
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let tnd_table = (0..203).map(|x| 163.67/(24329.0 / x as f32) + 100.0).collect();
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Apu {
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square1: Square::new(),
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square2: Square::new(),
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square1: Square::new(false),
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square2: Square::new(true),
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triangle: Triangle::new(),
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noise: Noise::new(),
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dmc: DMC::new(),
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@ -175,6 +175,8 @@ impl Apu {
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|| (self.frame_counter == 4 && self.current_frame == 3)
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|| (self.frame_counter == 5 && self.current_frame == 4) {
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// step length counters and sweep units
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self.square1.clock_sweep();
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self.square2.clock_sweep();
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self.square1.clock_length_counter();
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self.square2.clock_length_counter();
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self.triangle.clock_length_counter();
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@ -7,58 +7,61 @@ const DUTY_CYCLE_SEQUENCES: [[u8; 8]; 4] = [
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pub struct Square {
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pub sample: u16,
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divider: u16,
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pub enabled: bool,
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duty_cycle: [u8; 8],
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duty_counter: usize,
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envelope: u16,
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start: bool,
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divider: u16,
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decay_counter: u16,
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constant_volume_flag: bool, // (0: use volume from envelope; 1: use constant volume)
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start: bool,
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length_counter_halt: bool, // (this bit is also the envelope's loop flag)
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pub length_counter: u8,
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timer: u16,
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timer_period: u16,
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sweep: u8,
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sweep_divider: u8,
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sweep_divider: u8, // Period, P
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shift_count: u8,
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sweep_adder_overflow: bool,
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sweep_counter: u8,
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sweep_enabled: bool,
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sweep_negate: bool,
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sweep_reload: bool,
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second_channel: bool, // hack to detect timing difference in clock_sweep()
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}
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impl Square {
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pub fn new() -> Self {
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pub fn new(second_channel: bool) -> Self {
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Square {
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sample: 0,
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divider: 0,
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enabled: false,
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duty_cycle: DUTY_CYCLE_SEQUENCES[0],
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duty_counter: 0,
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envelope: 0,
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start: false,
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divider: 0,
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decay_counter: 0,
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constant_volume_flag: false,
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start: false,
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timer: 0,
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timer_period: 0,
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sweep: 0,
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sweep_divider: 0,
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shift_count: 0,
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sweep_adder_overflow: false,
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sweep_period: 0,
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sweep_counter: 0,
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sweep_enabled: false,
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sweep_negate: false,
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sweep_reload: false,
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length_counter: 0,
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length_counter_halt: false,
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second_channel: second_channel,
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}
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}
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@ -74,7 +77,7 @@ impl Square {
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// Update volume for this channel
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// The mixer receives the current envelope volume except when
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self.sample = if self.duty_cycle[self.duty_counter] == 0 // The sequencer output is zero, or
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|| self.sweep_adder_overflow // overflow from the sweep unit's adder is silencing the channel,
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|| self.sweep_period > 0x7FF // overflow from the sweep unit's adder is silencing the channel,
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|| self.length_counter == 0 // the length counter is zero, or
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|| self.timer < 8 { // the timer has a value less than eight.
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0
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@ -116,7 +119,25 @@ impl Square {
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}
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pub fn clock_sweep(&mut self) {
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// If the divider's counter is zero, the sweep is enabled, and the sweep unit is not muting the channel: The pulse's period is adjusted.
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if self.sweep_counter == 0 {
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self.sweep_enabled == true;
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}
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}
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fn adjust_sweep(&mut self) {
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let change = self.timer_period >> self.shift_count;
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if self.sweep_negate {
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self.timer_period -= change;
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if self.second_channel {
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self.timer_period -= 1;
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}
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} else {
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self.timer_period += change;
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}
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if self.sweep_counter == 0 {
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self.sweep_enabled = true;
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}
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}
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// $4000/$4004
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@ -125,24 +146,25 @@ impl Square {
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self.duty_cycle = DUTY_CYCLE_SEQUENCES[(value >> 6) as usize];
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self.length_counter_halt = value & (1<<5) != 0;
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self.constant_volume_flag = value & (1<<4) != 0;
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if self.constant_volume_flag {
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self.envelope = value as u16 & 0b1111;
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self.envelope = if self.constant_volume_flag {
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value as u16 & 0b1111
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} else {
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self.envelope = self.decay_counter;
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}
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self.decay_counter
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};
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}
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// $4001/$4005
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pub fn write_sweep(&mut self, value: u8) {
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self.sweep_enabled = value >> 7 == 1;
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self.sweep_divider = value >> 4 & 0b111;
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self.sweep_divider = ((value >> 4) & 0b111) + 1;
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self.sweep_negate = value & 0b1000 != 0;
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self.shift_count = value & 0b111;
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self.sweep_reload = true;
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}
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// $4002/$4006
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pub fn write_timer_low(&mut self, value: u8) {
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self.timer &= 0b11111111_00000000;
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self.timer &= 0b00000111_00000000;
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self.timer |= value as u16;
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}
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