From 17024c439aff1171959f4e8df795a14267ada07b Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Wed, 9 Jun 2021 22:02:39 -0500
Subject: [PATCH] chore(ppu): emu now properly handles VRAM and OAM write
 guards

---
 src/bus.rs | 17 ++++++-----------
 src/ppu.rs | 33 ++++++++++++++++-----------------
 2 files changed, 22 insertions(+), 28 deletions(-)

diff --git a/src/bus.rs b/src/bus.rs
index bd8180c..ca1bcf4 100644
--- a/src/bus.rs
+++ b/src/bus.rs
@@ -1,6 +1,5 @@
 use crate::cartridge::Cartridge;
 use crate::high_ram::HighRam;
-use crate::instruction::Cycle;
 use crate::interrupt::{Interrupt, InterruptFlag};
 use crate::joypad::Joypad;
 use crate::ppu::{Ppu, PpuMode};
@@ -159,7 +158,7 @@ impl BusIo for Bus {
             0x8000..=0x9FFF => {
                 // 8KB Video RAM
                 match self.ppu.stat.mode() {
-                    PpuMode::VBlank => 0xFF,
+                    PpuMode::Drawing => 0xFF,
                     _ => self.ppu.read_byte(addr),
                 }
             }
@@ -266,14 +265,10 @@ impl BusIo for Bus {
             }
             0x8000..=0x9FFF => {
                 // 8KB Video RAM
-
-                // TODO: Fix timing issues in the PPU
-                // match self.ppu.stat.mode() {
-                //     PpuMode::VBlank => {}
-                //     _ => self.ppu.write_byte(addr, byte),
-                // }
-
-                self.ppu.write_byte(addr, byte)
+                match self.ppu.stat.mode() {
+                    PpuMode::Drawing => {}
+                    _ => self.ppu.write_byte(addr, byte),
+                }
             }
             0xA000..=0xBFFF => {
                 // 8KB External RAM
@@ -365,7 +360,7 @@ impl BusIo for Bus {
                             self.boot = None;
                         }
                     }
-                    _ => {} // unimplemented!("Unable to write to {:#06X} in I/O Registers", addr),
+                    _ => unimplemented!("Unable to write to {:#06X} in I/O Registers", addr),
                 };
             }
             0xFF80..=0xFFFE => {
diff --git a/src/ppu.rs b/src/ppu.rs
index cc66c71..55d9378 100644
--- a/src/ppu.rs
+++ b/src/ppu.rs
@@ -67,6 +67,10 @@ impl BusIo for Ppu {
 
 impl Ppu {
     pub(crate) fn clock(&mut self) {
+        if !self.ctrl.lcd_enabled() {
+            return;
+        }
+
         self.cycle += 1;
 
         match self.stat.mode() {
@@ -78,7 +82,14 @@ impl Ppu {
                 self.scan_oam();
             }
             PpuMode::Drawing => {
-                if self.x_pos >= 160 {
+                if self.ctrl.lcd_enabled() {
+                    // Only Draw when the LCD Is Enabled
+                    self.draw(self.cycle.into());
+                } else {
+                    self.reset();
+                }
+
+                if self.x_pos == 160 {
                     if self.stat.hblank_int() {
                         // Enable HBlank LCDStat Interrupt
                         self.int.set_lcd_stat(true);
@@ -103,11 +114,6 @@ impl Ppu {
                     self.fifo.obj.clear();
 
                     self.stat.set_mode(PpuMode::HBlank);
-                } else if self.ctrl.lcd_enabled() {
-                    // Only Draw when the LCD Is Enabled
-                    self.draw(self.cycle.into());
-                } else {
-                    self.reset();
                 }
             }
             PpuMode::HBlank => {
@@ -413,19 +419,12 @@ impl Ppu {
     }
 
     fn reset(&mut self) {
-        // FIXME: Discover what actually is supposed to be reset here
-
-        self.scan_state = Default::default();
-        self.cycle = Cycle::new(0);
-
-        self.x_pos = 0;
-        self.window_stat = Default::default();
-        self.stat.set_mode(PpuMode::OamScan);
         self.pos.line_y = 0;
+        self.stat.set_mode(PpuMode::HBlank);
 
-        self.fetch.back.reset();
-        self.fetch.obj.reset();
-        self.obj_buffer.clear();
+        // TODO: Is this an unnecessary performance hit?
+        let mut blank = WHITE.repeat(self.frame_buf.len() / 4);
+        self.frame_buf.swap_with_slice(&mut blank);
     }
 
     pub fn copy_to_gui(&self, frame: &mut [u8]) {