From 5a42d76f1ea57ccb993b8c7d5ce617947d19bf3e Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Sun, 21 Mar 2021 00:01:21 -0500
Subject: [PATCH] feat: implement LCDSTAT interrupt

---
 src/bus.rs | 11 ++++++++++-
 src/cpu.rs | 16 ----------------
 src/ppu.rs | 34 +++++++++++++++++++++++++++-------
 3 files changed, 37 insertions(+), 24 deletions(-)

diff --git a/src/bus.rs b/src/bus.rs
index 4e692fe..74ab198 100644
--- a/src/bus.rs
+++ b/src/bus.rs
@@ -223,7 +223,16 @@ impl Bus {
                     0xFF42 => self.ppu.pos.scroll_y = byte,
                     0xFF43 => self.ppu.pos.scroll_x = byte,
                     0xFF44 => self.ppu.pos.line_y = byte,
-                    0xFF45 => self.ppu.pos.ly_compare = byte == 0x01, // FIXME: We don't consider the possibility of a byte being different form 0x00 or 0x01
+                    0xFF45 => {
+                        // Update LYC
+                        self.ppu.pos.ly_compare = byte;
+
+                        // Update Coincidence Flag
+                        if self.ppu.stat.coincidence_intr() {
+                            let are_equal = self.ppu.pos.line_y == byte;
+                            self.ppu.stat.set_coincidence(are_equal);
+                        }
+                    }
                     0xFF47 => self.ppu.monochrome.bg_palette = byte.into(),
                     0xFF48 => self.ppu.monochrome.obj_palette_0 = byte.into(),
                     0xFF49 => self.ppu.monochrome.obj_palette_1 = byte.into(),
diff --git a/src/cpu.rs b/src/cpu.rs
index 738bb48..ac20718 100644
--- a/src/cpu.rs
+++ b/src/cpu.rs
@@ -76,24 +76,9 @@ impl Cpu {
     pub fn step(&mut self) -> Cycles {
         let opcode = self.fetch();
         let instr = self.decode(opcode);
-
-        // println!(
-        //     "Addr: {:#06X} | Opcode: {:#04X} | Instr: {:X?}",
-        //     self.reg.pc, opcode, instr
-        // );
-
         let cycles = self.execute(instr);
 
-        // if self.bus.read_byte(0xFF02) == 0x81 {
-        //     let c = self.bus.read_byte(0xFF01) as char;
-        //     self.bus.write_byte(0xFF02, 0x00);
-
-        //     print!("{}", c);
-        //     std::io::stdout().flush().unwrap();
-        // }
-
         self.bus.step(cycles);
-
         self.handle_interrupts();
 
         cycles
@@ -188,7 +173,6 @@ impl Cpu {
 
                     // Disable all future interrupts
                     self.set_ime(false);
-
                     self.execute(Instruction::CALL(Always, register))
                 }
                 None => Cycles::new(0), // NO Interrupts were enabled and / or requested
diff --git a/src/ppu.rs b/src/ppu.rs
index 1b2260c..73e78bd 100644
--- a/src/ppu.rs
+++ b/src/ppu.rs
@@ -39,9 +39,6 @@ impl Ppu {
     pub fn step(&mut self, cycles: Cycles) {
         self.cycles += cycles;
 
-        // let tmp: u32 = self.cycles.into();
-        // println!("Mode: {:?} | Cycles: {}", self.mode, tmp);
-
         match self.stat.mode() {
             Mode::OamScan => {
                 if self.cycles >= 80.into() {
@@ -59,6 +56,10 @@ impl Ppu {
                 if self.cycles >= 172.into() {
                     self.cycles %= 172;
 
+                    if self.stat.hblank_intr() {
+                        self.interrupt.set_lcd_stat(true);
+                    }
+
                     self.stat.set_mode(Mode::HBlank);
                     self.draw_scanline();
                 }
@@ -71,12 +72,26 @@ impl Ppu {
 
                     let next_mode = if self.pos.line_y >= 144 {
                         self.interrupt.set_vblank(true);
+
+                        if self.stat.vblank_intr() {
+                            self.interrupt.set_lcd_stat(true);
+                        }
+
                         Mode::VBlank
                     } else {
+                        if self.stat.oam_intr() {
+                            self.interrupt.set_lcd_stat(true);
+                        }
+
                         Mode::OamScan
                     };
 
                     self.stat.set_mode(next_mode);
+
+                    if self.stat.coincidence_intr() {
+                        let are_equal = self.pos.line_y == self.pos.ly_compare;
+                        self.stat.set_coincidence(are_equal);
+                    }
                 }
             }
             Mode::VBlank => {
@@ -90,6 +105,11 @@ impl Ppu {
                         self.stat.set_mode(Mode::OamScan);
                         self.pos.line_y = 0;
                     }
+
+                    if self.stat.coincidence_intr() {
+                        let are_equal = self.pos.line_y == self.pos.ly_compare;
+                        self.stat.set_coincidence(are_equal);
+                    }
                 }
             }
         }
@@ -192,11 +212,11 @@ impl Interrupt {
 bitfield! {
     pub struct LCDStatus(u8);
     impl Debug;
-    pub lyc_ly_intr, set_lyc_ly_intr: 6;
+    pub coincidence_intr, set_coincidence_intr: 6;
     pub oam_intr, set_oam_intr: 5;
     pub vblank_intr, set_vblank_intr: 4;
     pub hblank_intr, set_hblank_intr: 3;
-    pub coincidence, _: 2; // LYC == LY Flag
+    pub coincidence, set_coincidence: 2; // LYC == LY Flag
     from into Mode, _mode, set_mode: 1, 0;
 }
 
@@ -215,7 +235,7 @@ impl Clone for LCDStatus {
 
 impl Default for LCDStatus {
     fn default() -> Self {
-        Self(0)
+        Self(0x80) // bit 7 is always 1
     }
 }
 
@@ -268,7 +288,7 @@ pub struct ScreenPosition {
     pub scroll_y: u8,
     pub scroll_x: u8,
     pub line_y: u8,
-    pub ly_compare: bool,
+    pub ly_compare: u8,
     pub window_y: u8,
     pub window_x: u8,
 }