From 5d64e539a781574a6028bba5c24ad040066bcd02 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Tue, 17 Aug 2021 23:14:56 -0500
Subject: [PATCH] fix(apu): resolve off-by-one error

---
 src/apu.rs       |  4 ++--
 src/apu/types.rs | 10 +++-------
 2 files changed, 5 insertions(+), 9 deletions(-)

diff --git a/src/apu.rs b/src/apu.rs
index 1b94377..9c76f76 100644
--- a/src/apu.rs
+++ b/src/apu.rs
@@ -101,8 +101,6 @@ impl Apu {
         if self.falling_edge(12, div) {
             use FrameSequencerState::*;
 
-            self.sequencer.next();
-
             match self.sequencer.state() {
                 Length => self.handle_length(),
                 LengthAndSweep => {
@@ -112,6 +110,8 @@ impl Apu {
                 Envelope => self.handle_envelope(),
                 Nothing => {}
             }
+
+            self.sequencer.next();
         }
 
         self.div_prev = Some(div);
diff --git a/src/apu/types.rs b/src/apu/types.rs
index 7a36f3d..01a8016 100644
--- a/src/apu/types.rs
+++ b/src/apu/types.rs
@@ -531,13 +531,9 @@ pub(super) mod fs {
 
             self.step = (self.step + 1) % 8;
             self.state = match self.step {
-                0 => Length,
-                1 => Nothing,
-                2 => LengthAndSweep,
-                3 => Nothing,
-                4 => Length,
-                5 => Nothing,
-                6 => LengthAndSweep,
+                1 | 3 | 5 => Nothing,
+                0 | 4 => Length,
+                2 | 6 => LengthAndSweep,
                 7 => Envelope,
                 _ => unreachable!("Step {} is invalid for the Frame Sequencer", self.step),
             };