2026-05-15 15:30:54

Author: mohanson

src/apu.rs

@@ -305,38 +305,34 @@ impl Swp {
     }
 }
 
-/// 15-bit LFSR with optional 7-bit feedback path for CH4.
+// 15-bit LFSR with optional 7-bit feedback path for CH4.
 struct Lfsr {
     n: u16,
 }
 
 impl Lfsr {
-    fn new() -> Self {
+    fn power_up() -> Self {
         Self { n: 0x7fff }
     }
 
     fn reload(&mut self) {
         self.n = 0x7fff;
     }
 
-    /// Returns true iff the new low bit is 1 (the channel outputs `~bit0`).
-    fn step(&mut self, w7: bool) -> bool {
+    // Returns true if the new low bit is 1 (the channel outputs ~bit0).
+    fn step(&mut self, reg: &Reg) -> bool {
         let b = ((self.n ^ (self.n >> 1)) & 1) as u16;
         self.n = (self.n >> 1) | (b << 14);
-        if w7 {
+        if reg.width7() {
             self.n = (self.n & !(1 << 6)) | (b << 6);
         }
         self.n & 1 == 0
     }
 }
 
-// ────────────────────────────────────────────────────────────────────────────
-// Square channels.
-// ────────────────────────────────────────────────────────────────────────────
-
 const DUTY: [u8; 4] = [0b0000_0001, 0b1000_0001, 0b1000_0111, 0b0111_1110];
 
-/// CH1: square wave with sweep.
+// CH1: square wave with sweep.
 struct Sq1 {
     r: Reg,
     on: bool,
@@ -690,15 +686,15 @@ impl Ns {
             tmr: Tmr::power_up(8),
             lc: Lc::power_up(),
             env: Env::power_up(),
-            lfsr: Lfsr::new(),
+            lfsr: Lfsr::power_up(),
             blip: Blip::power_up(sr),
         }
     }
 
     fn tick(&mut self, c: u32) {
         let v = i32::from(self.env.v);
         for _ in 0..self.tmr.step(c) {
-            let hi = self.lfsr.step(self.r.width7());
+            let hi = self.lfsr.step(&self.r);
             let a = if !self.on || self.env.v == 0 {
                 0
             } else if hi {