From b9046bceba51bbdc054bf4ee7fe44fb6d8fc5de7 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Tue, 17 Aug 2021 20:42:41 -0500
Subject: [PATCH] fix(apu): disable channel if DAC is disabled

---
 src/apu.rs | 30 +++++++++++++++++++++++++++---
 1 file changed, 27 insertions(+), 3 deletions(-)

diff --git a/src/apu.rs b/src/apu.rs
index 60f98f2..b78fd29 100644
--- a/src/apu.rs
+++ b/src/apu.rs
@@ -456,7 +456,11 @@ impl Channel1 {
 
     /// 0xFF12 | NR12 - Channel 1 Volume Envelope
     pub(crate) fn set_envelope(&mut self, byte: u8) {
-        self.envelope = byte.into()
+        self.envelope = byte.into();
+
+        if !self.is_dac_enabled() {
+            self.enabled = false;
+        }
     }
 
     /// 0xFF13 | NR13 - Channel 1 Frequency low (lower 8 bits only)
@@ -529,6 +533,10 @@ impl Channel1 {
     fn frequency(&self) -> u16 {
         (self.freq_hi.freq_bits() as u16) << 8 | self.freq_lo as u16
     }
+
+    fn is_dac_enabled(&self) -> bool {
+        self.envelope.0 & 0xF8 != 0x00
+    }
 }
 
 #[derive(Debug, Default)]
@@ -591,7 +599,11 @@ impl Channel2 {
 
     /// 0xFF17 | NR22 - Channel 2 Volume ENvelope
     pub(crate) fn set_envelope(&mut self, byte: u8) {
-        self.envelope = byte.into()
+        self.envelope = byte.into();
+
+        if !self.is_dac_enabled() {
+            self.enabled = false;
+        }
     }
 
     /// 0xFF18 | NR23 - Channel 2 Frequency low (lower 8 bits only)
@@ -625,6 +637,10 @@ impl Channel2 {
     fn frequency(&self) -> u16 {
         (self.freq_hi.freq_bits() as u16) << 8 | self.freq_lo as u16
     }
+
+    fn is_dac_enabled(&self) -> bool {
+        self.envelope.0 & 0xF8 != 0x00
+    }
 }
 
 #[derive(Debug, Default)]
@@ -803,7 +819,11 @@ impl Channel4 {
 
     /// 0xFF21 | NR42 - Channel 4 Volume Envelope
     pub(crate) fn set_envelope(&mut self, byte: u8) {
-        self.envelope = byte.into()
+        self.envelope = byte.into();
+
+        if !self.is_dac_enabled() {
+            self.enabled = false;
+        }
     }
 
     /// 0xFF22 | NR43 - Chanel 4 Polynomial Counter
@@ -866,6 +886,10 @@ impl Channel4 {
         }
     }
 
+    fn is_dac_enabled(&self) -> bool {
+        self.envelope.0 & 0xF8 != 0x00
+    }
+
     fn divisor(code: u8) -> u8 {
         if code == 0 {
             return 8;