apu

src/apu/mod.rs

@@ -3,6 +3,10 @@ mod square;
 mod triangle;
 mod dmc;
 
+// APU clock ticks every other CPU cycle.
+// Frame counter only ticks every 3728.5 APU ticks, and in audio frames of 4 or 5.
+// Length counter controls note durations.
+
 pub struct Apu {
     square1:  Square,
     square2:  Square,
@@ -83,6 +87,10 @@ impl Apu {
         }
     }
 
+    pub fn clock(&mut self) {
+
+    }
+
     fn write_reg(&mut self, address: usize, value: u8) {
         match address {
             0x4000 => self.square1.duty(value),
@@ -118,6 +126,11 @@ impl Apu {
         square_out + tnd_out
     }
 
+    //     mode 0:    mode 1:       function
+    // ---------  -----------  -----------------------------
+    // - - - f    - - - - -    IRQ (if bit 6 is clear)
+    // - l - l    - l - - l    Length counter and sweep
+    // e e e e    e e e - e    Envelope and linear counter
     fn step_frame_counter(&mut self, value: u8) {
         // 0 selects 4-step sequence, 1 selects 5-step sequence
         if value & (1<<7) == 0 { 

src/audio.rs

@@ -3,7 +3,7 @@ extern crate sdl2;
 use sdl2::audio::{AudioCallback, AudioSpecDesired};
 
 pub struct Speaker {
-    buffer: [u8; 4096],
+    buffer: [f32; 4096],
 }
 
 impl AudioCallback for Speaker {

src/cpu/mod.rs

@@ -190,7 +190,7 @@ impl Cpu {
         // look up instruction in table and execute
         self.opcode_table[opcode](self, address, mode);
         // maintain 1 apu cycle per 2 cpu cycles
-        if self.
+        self.even = if self.even { self.apu.step(); false } else { true };
         // return how many cycles it took
         self.clock - clock
     }

src/ppu/mod.rs

@@ -64,8 +64,8 @@ pub struct Ppu {
     grayscale:                     bool,
     show_background_left:          bool, // 1: Show background in leftmost 8 pixels of screen, 0: Hide
     show_sprites_left:             bool, // 1: Show sprites in leftmost 8 pixels of screen, 0: Hide
-    show_background:           bool, // 1: Show background
+    show_background:               bool, // 1: Show background
-    show_sprites:              bool, // 1: Show sprites
+    show_sprites:                  bool, // 1: Show sprites
     emphasize_red:                 bool, // Emphasize red
     emphasize_green:               bool, // Emphasize green
     emphasize_blue:                bool, // Emphasize blue