fixed timer_period bug, cleaned up. square channels kind of working. need to figure out how to sample properly.

src/apu/mod.rs

@@ -30,7 +30,8 @@ use dmc::DMC;
 // TODO: organize APU structs
 
 const FRAME_COUNTER_STEPS: [usize; 5] = [3728, 7456, 11185, 14914, 18640];
-const CYCLES_PER_SAMPLE: f32 = 894_886.5/44_100.0; // APU frequency over sample frequency. May need to turn this down slightly as it's outputting less than 44_100Hz.
+// const CYCLES_PER_SAMPLE: f32 = 894_886.5/44_100.0; // APU frequency over sample frequency. May need to turn this down slightly as it's outputting less than 44_100Hz.
+const CYCLES_PER_SAMPLE: f32 = 19.65;
 const LENGTH_COUNTER_TABLE: [u8; 32] = [
     10, 254, 20,  2, 40,  4, 80,  6, 160,  8, 60, 10, 14, 12, 26, 14,
     12,  16, 24, 18, 48, 20, 96, 22, 192, 24, 72, 26, 16, 28, 32, 30,
@@ -111,6 +112,7 @@ impl Apu {
     }
 
     pub fn write_reg(&mut self, address: usize, value: u8) {
+        // println!("writing 0b{:08b} to 0x{:X}", value, address);
         match address {
             0x4000 => self.square1.write_duty(value),
             0x4001 => self.square1.write_sweep(value),

src/apu/square.rs

@@ -75,7 +75,7 @@ impl Square {
         }
         // Update volume for this channel
         // The mixer receives the current envelope volume except when
-        self.sample = if self.duty_cycle[self.duty_counter] == 0 // The sequencer output is zero, or
+        self.sample = if self.duty_cycle[self.duty_counter] == 0 // the sequencer output is zero, or
             || self.sweep_divider > 0x7FF // overflow from the sweep unit's adder is silencing the channel,
             || self.length_counter == 0 // the length counter is zero, or
             || self.timer < 8 { // the timer has a value less than eight.
@@ -83,7 +83,6 @@ impl Square {
             } else {
                 self.decay_counter
             };
-        println!("{}", self.sample);
     }
 
     pub fn clock_envelope(&mut self) {
@@ -101,7 +100,7 @@ impl Square {
     pub fn clock_length_counter(&mut self) {
         if !(self.length_counter == 0 || self.length_counter_halt) {
             self.length_counter -= 1;
-        }    
+        }
     }
 
     fn clock_envelope_divider(&mut self) {
@@ -136,7 +135,7 @@ impl Square {
         }
         // 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.
         if self.sweep_counter == 0 && self.sweep_enabled && !(self.timer < 8 || self.sweep_divider > 0x7FF) {
-            self.adjust_sweep();
+            self.timer_period = self.sweep_divider;
         }
         // If the divider's counter is zero or the reload flag is true: The counter is set to P and the reload flag is cleared. Otherwise, the counter is decremented.
         if self.sweep_counter == 0 || self.sweep_reload {
@@ -147,13 +146,9 @@ impl Square {
         }
     }
 
-    fn adjust_sweep(&mut self) {
-        self.timer_period = self.sweep_divider;
-    }
-
     // $4000/$4004
     pub fn write_duty(&mut self, value: u8) {
-        // TODO: The duty cycle is changed (see table below), but the sequencer's current position isn't affected. 
+        // The duty cycle is changed (see table below), but the sequencer's current position isn't affected.
         self.duty_cycle = DUTY_CYCLE_SEQUENCES[(value >> 6) as usize];
         self.length_counter_halt = value & (1<<5) != 0;
         self.constant_volume_flag = value & (1<<4) != 0;
@@ -175,8 +170,8 @@ impl Square {
 
     // $4002/$4006
     pub fn write_timer_low(&mut self, value: u8) {
-        self.timer &= 0b00000111_00000000; // mask off everything but high 3 bits of 11-bit timer
-        self.timer |= value as u16; // apply low 8 bits
+        self.timer_period &= 0b00000111_00000000; // mask off everything but high 3 bits of 11-bit timer
+        self.timer_period |= value as u16; // apply low 8 bits
     }
 
     // $4003/$4007
@@ -186,8 +181,8 @@ impl Square {
             self.length_counter = super::LENGTH_COUNTER_TABLE[value as usize >> 3];
         }
         let timer_high = value as u16 & 0b0000_0111;
-        self.timer &= 0b11111000_11111111; // mask off high 3 bits of 11-bit timer
-        self.timer |= timer_high << 8; // apply high timer bits in their place
+        self.timer_period &= 0b11111000_11111111; // mask off high 3 bits of 11-bit timer
+        self.timer_period |= timer_high << 8; // apply high timer bits in their place
         // The sequencer is immediately restarted at the first value of the current sequence. The envelope is also restarted. The period divider is not reset.
         self.duty_counter = 0;
         self.start = true;

src/audio.rs

@@ -2,28 +2,6 @@ extern crate sdl2;
 
 use sdl2::audio::{AudioCallback, AudioSpecDesired};
 
-// pub struct Speaker {
-//     buffer: [f32; 4096*4],
-//     head: usize,
-// }
-
-// impl AudioCallback for Speaker {
-//     type Channel = f32;
-//     fn callback(&mut self, out: &mut [f32]) {
-//         for (i, x) in out.iter_mut().enumerate() {
-//             *x = self.buffer[i+self.head]; // get data from apu
-//         }
-//         self.head = (self.head + 4096) % (4096*4)
-//     }
-// }
-
-// impl Speaker {
-//     pub fn append(&mut self, sample: f32) {
-//         self.buffer[self.head] = sample;
-//         self.head = (self.head + 1) % (4096*4);
-//     }
-// }
-
 pub fn initialize(context: &sdl2::Sdl) -> Result<sdl2::audio::AudioQueue<f32>, String> {
     let audio_subsystem = context.audio()?;
 
@@ -35,5 +13,3 @@ pub fn initialize(context: &sdl2::Sdl) -> Result<sdl2::audio::AudioQueue<f32>, S
 
     audio_subsystem.open_queue(None, &desired_spec)
 }
-
-// problem is: how to get data into callback from outside? can't change its signature. can't sneak it in through struct as struct is consumed by the audio device

src/main.rs

@@ -37,7 +37,6 @@ fn main() -> Result<(), String> {
     // Set up audio
     let mut audio_device = audio::initialize(&sdl_context).expect("Could not create audio device");
     let mut half_cycle = false;
-    let mut audio_buffer = Vec::<f32>::new();
     audio_device.resume();
 
     // Initialize hardware components
@@ -70,19 +69,11 @@ fn main() -> Result<(), String> {
             match cpu.apu.clock() {
                 Some(sample) => {
                     sps += 1;
-                    // if sample != 0.0 {
-                    //     println!("sample {}", sample);
-                    // }
-                    audio_buffer.push(sample)
+                    audio_device.queue(&vec![sample]);
                 },
                 None => (),
             };
         }
-        if audio_buffer.len() == 44_100 {
-            // println!("queueing: {:?}", &audio_buffer[..32]);
-            audio_device.queue(&audio_buffer);
-            audio_buffer = vec![];
-        }
         // clock PPU three times for every CPU cycle
         for _ in 0..cpu_cycles * 3 {
             let (pixel, end_of_frame) = cpu.ppu.clock();
@@ -130,5 +121,13 @@ fn main() -> Result<(), String> {
     Ok(())
 }
 
-// TODO: reset function?
-// TODO: save/load functionality
+/*
+TODO:
+- remaining APU channels
+- common mappers
+- battery-backed RAM solution
+- GUI? drag and drop ROMs?
+- reset function
+- save/load/pause functionality
+
+*/