From 73b0a280347520e443229bb37ce1ea3cfd140f02 Mon Sep 17 00:00:00 2001
From: Theron Spiegl <tspiegl@gmail.com>
Date: Wed, 1 Jan 2020 15:28:28 -0600
Subject: [PATCH] fixed DK walking sound though not sure why exactly.

---
 src/apu/mod.rs    | 14 +++++++-------
 src/apu/square.rs | 22 +++++++++++++---------
 src/main.rs       |  2 +-
 3 files changed, 21 insertions(+), 17 deletions(-)

diff --git a/src/apu/mod.rs b/src/apu/mod.rs
index c5725ea..40d1f44 100644
--- a/src/apu/mod.rs
+++ b/src/apu/mod.rs
@@ -97,6 +97,12 @@ impl Apu {
         sample
     }
 
+    fn mix(&self) -> f32 {
+        let square_out = self.square_table[(self.square1.sample + self.square2.sample) as usize];
+        let tnd_out = self.tnd_table[((3*self.triangle.sample)+(2*self.noise.sample) + self.dmc.sample) as usize];
+        square_out + tnd_out
+    }
+
     pub fn write_reg(&mut self, address: usize, value: u8) {
         // println!("writing 0b{:08b} to 0x{:X}", value, address);
         match address {
@@ -128,13 +134,7 @@ impl Apu {
         }
     }
 
-    fn mix(&self) -> f32 {
-        let square_out = self.square_table[(self.square1.sample + self.square2.sample) as usize];
-        let tnd_out = self.tnd_table[((3*self.triangle.sample)+(2*self.noise.sample) + self.dmc.sample) as usize];
-        square_out + tnd_out
-    }
-
-    //     mode 0:    mode 1:       function
+    //   mode 0:    mode 1:       function
     // ---------  -----------  -----------------------------
     // - - - f    - - - - -    IRQ (if bit 6 is clear)
     // - l - l    - l - - l    Length counter and sweep
diff --git a/src/apu/square.rs b/src/apu/square.rs
index 56f1234..4ab3e78 100644
--- a/src/apu/square.rs
+++ b/src/apu/square.rs
@@ -107,17 +107,18 @@ impl Square {
         // When the divider is clocked while at 0, it is loaded with V and clocks the decay level counter.
         if self.envelope_divider == 0 {
             self.envelope_divider = self.envelope;
+            // Then one of two actions occurs: If the counter is non-zero, it is decremented,
+            if self.decay_counter != 0 {
+                self.decay_counter -= 1;
+                // println!("decaying to {}", self.decay_counter);
+            } else if self.length_counter_halt {
+                // otherwise if the loop flag is set, the decay level counter is loaded with 15. 
+                println!("looping decay counter");
+                self.decay_counter = 15;
+            }
         } else {
             self.envelope_divider -= 1;
         }
-        // Then one of two actions occurs: If the counter is non-zero, it is decremented,
-        if self.decay_counter != 0 {
-            self.decay_counter -= 1;
-            // println!("decaying to {}", self.decay_counter);
-        } else if self.length_counter_halt {
-            // otherwise if the loop flag is set, the decay level counter is loaded with 15. 
-            self.decay_counter = 15;
-        }
     }
 
     pub fn clock_length_counter(&mut self) {
@@ -130,7 +131,7 @@ impl Square {
         self.calculate_target_period();
         // When the frame counter sends a half-frame clock (at 120 or 96 Hz), two things happen.
         // 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_period < 8 || self.timer_period > 0x7FF) {
+        if self.sweep_counter == 0 && self.sweep_enabled && !(self.timer_period < 8 || self.target_period > 0x7FF) {
             self.timer_period = self.target_period;
             println!("timer period adjusted to {}", self.timer_period);
         }
@@ -138,6 +139,7 @@ impl Square {
         if self.sweep_counter == 0 || self.sweep_reload {
             self.sweep_counter = self.sweep_divider;
             self.sweep_reload = false;
+            if self.sweep_enabled { self.timer_period = self.target_period; } // This fixes the DK walking sound. Why? Not reflected in documentation.
         } else {
             self.sweep_counter -= 1;
         }
@@ -170,6 +172,7 @@ impl Square {
         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;
+        // println!("using envelope volume: {}", !self.constant_volume_flag);
         self.envelope = value as u16 & 0b1111;
         // if self.constant_volume_flag {
         //     value as u16 & 0b1111
@@ -180,6 +183,7 @@ impl Square {
 
     // $4001/$4005
     pub fn write_sweep(&mut self, value: u8) {
+        // println!("writing sweep 0b{:08b}", value);
         self.sweep_enabled = value >> 7 == 1;
         self.sweep_divider = ((value as u16 >> 4) & 0b111) + 1;
         self.sweep_negate = value & 0b1000 != 0;
diff --git a/src/main.rs b/src/main.rs
index fcaa57d..504cc79 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -69,7 +69,7 @@ fn main() -> Result<(), String> {
             match cpu.apu.clock() {
                 Some(sample) => {
                     sps += 1;
-                    if sps < 44100 {audio_device.queue(&vec![sample]);}
+                    if sps < 44_100 {audio_device.queue(&vec![sample]);}
                 },
                 None => (),
             };