139 lines
3.5 KiB
Rust
139 lines
3.5 KiB
Rust
// Square wave generator
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use crate::sound::AudioComponent;
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use crate::sound::OUTPUT_SAMPLE_RATE;
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#[derive(Debug)]
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pub enum DutyCycle {
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Duty0, // 12.5%
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Duty1, // 25.0%
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Duty2, // 50.0%
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Duty3, // 75.0%
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}
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impl Default for DutyCycle {
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fn default() -> Self {
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DutyCycle::Duty2
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}
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}
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#[derive(Debug, Default)]
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pub struct SquareWaveGenerator {
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frequency: f32,
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time: f32,
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pub duty_cycle: DutyCycle,
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gb_reg_freq: u16,
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// Sweep settings (if existing)
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sweep_change_period: u8,
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// selects the inc/dec mode of the sweep. Dec if set
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sweep_dec: bool,
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// Sweep speed (n/128th)
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sweep_change: u8,
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// Current sweep clock cycle
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sweep_clock: u8,
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// sweep_freq_shadow: f32,
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}
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impl SquareWaveGenerator {
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fn update_frequency(&mut self) {
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self.frequency = 131072f32 / ((2048 - self.gb_reg_freq) as f32);
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}
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pub fn set_lower_freq(&mut self, freq: u8) {
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self.gb_reg_freq &= 0xFF00;
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self.gb_reg_freq |= freq as u16;
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self.update_frequency();
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}
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pub fn set_higher_freq(&mut self, freq: u8) {
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self.gb_reg_freq &= 0x00FF;
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self.gb_reg_freq |= ((freq & 7) as u16) << 8;
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self.update_frequency();
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}
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pub fn set_sweep_reg(&mut self, reg: u8) {
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//Bit 6-4 - Sweep Time
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//Bit 3 - Sweep Increase/Decrease
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// 0: Addition (frequency increases)
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// 1: Subtraction (frequency decreases)
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//Bit 2-0 - Number of sweep shift (n: 0-7)
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self.sweep_change_period = (reg >> 4) & 0b0111;
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self.sweep_dec = reg & (1 << 3) > 0;
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self.sweep_change = reg & 0b111;
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self.sweep_clock = 0;
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}
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pub fn sweep_clock(&mut self) {
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// This should be sampled at 128Hz
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if self.sweep_change_period > 0 // enabled
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&& self.sweep_clock >= self.sweep_change_period
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// sweep time hit
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{
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self.sweep_clock = 0;
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let change = self.frequency / (2f32.powi(self.sweep_change as _));
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self.frequency += if self.sweep_dec { -change } else { change };
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}
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}
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pub fn reset(&mut self) {
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self.time = 0f32;
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}
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pub fn sample(&self) -> u8 {
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if self.frequency > 0f32 {
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let mut temp = self.time * self.frequency;
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temp -= temp.trunc();
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match self.duty_cycle {
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DutyCycle::Duty0 => {
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if temp < 0.125 {
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255
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} else {
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0
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}
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}
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DutyCycle::Duty1 => {
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if temp < 0.25 {
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255
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} else {
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0
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}
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}
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DutyCycle::Duty2 => {
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if temp < 0.5 {
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255
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} else {
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0
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}
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}
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DutyCycle::Duty3 => {
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if temp < 0.75 {
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255
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} else {
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0
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}
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}
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}
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} else {
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0
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}
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}
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pub fn set_duty_cycle(&mut self, bits: u8) {
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self.duty_cycle = match bits {
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0 => DutyCycle::Duty0,
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1 => DutyCycle::Duty1,
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2 => DutyCycle::Duty2,
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_ => DutyCycle::Duty3,
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};
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}
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}
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impl AudioComponent for SquareWaveGenerator {
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fn clock(&mut self) {
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self.time += 1f32 / (OUTPUT_SAMPLE_RATE as f32);
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}
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}
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