Update readme

README.md

@@ -7,8 +7,9 @@ Any help or suggestion is welcome!
 
 ## TODO
 - [x] CPU implementation
-- [ ] Interrupts
-- [ ] Timing
+- [x] Interrupts (interrupts test not passing yet)
+- [x] Timer
+- [x] Joypad (not configurable yet)
 - [ ] PPU implementations
 - [ ] Gameboy boot ROM
 - [x] Render the pixels

src/bus.rs

@@ -5,8 +5,10 @@ use crate::utils::{
     join_bytes
 };
 use crate::rom::ROM;
-use crate::ppu::{PPU, LCDStatus, LCDStatusModeFlag};
-use crate::cpu::{InterruptFlag};
+use crate::ppu::{PPU, LCDStatus, LCDStatusModeFlag, LCD_STATUS_ADDRESS, LCD_CONTROL_ADDRESS, LCD_Y_ADDRESS};
+use crate::cpu::{Interrupt};
+use crate::timer::{TIMER_DIVIDER_REGISTER_ADDRESS};
+use crate::joypad::{Joypad, JOYPAD_ADDRESS};
 
 pub struct AddressRange {
     begin: u16,
@@ -39,6 +41,7 @@ pub const NOT_USABLE: AddressRange                = AddressRange{begin: 0xFEA0,
 pub const IO_REGISTERS: AddressRange              = AddressRange{begin: 0xFF00, end: 0xFF7F};
 pub const HIGH_RAM: AddressRange                  = AddressRange{begin: 0xFF80, end: 0xFFFE};
 pub const INTERRUPT_ENABLE_REGISTER: AddressRange = AddressRange{begin: 0xFFFF, end: 0xFFFF};
+pub const INTERRUPT_ENABLE_ADDRESS: u16 = 0xFFFF;
 pub const INTERRUPT_FLAG_ADDRESS: u16 = 0xFF0F;
 
 pub struct Bus {
@@ -51,6 +54,7 @@ impl Bus {
         let game_rom = match ROM::load_file("ignore/tetris.gb".to_string()) {
         // let game_rom = match ROM::load_file("roms/cpu_instrs.gb".to_string()) {
         // let game_rom = match ROM::load_file("roms/cpu_instrs_individual/01-special.gb".to_string()) {
+        // let game_rom = match ROM::load_file("roms/cpu_instrs_individual/02-interrupts.gb".to_string()) {
         // let game_rom = match ROM::load_file("roms/cpu_instrs_individual/03-op sp,hl.gb".to_string()) {
         // let game_rom = match ROM::load_file("roms/cpu_instrs_individual/04-op r,imm.gb".to_string()) {
         // let game_rom = match ROM::load_file("roms/cpu_instrs_individual/05-op rp.gb".to_string()) {
@@ -64,8 +68,10 @@ impl Bus {
             // _ => ROM::from_bytes(&[0; 0xFFFF])
             _ => panic!("Could not read ROM"),
         };
+        let mut data = [0x00; 0x10000];
+        data[JOYPAD_ADDRESS as usize] = 0b11001111;
         Self {
-            data: [0x00; 0x10000],
+            data,
             game_rom,
         }
     }
@@ -73,12 +79,9 @@ impl Bus {
     pub fn read(&self, address: u16) -> u8 {
         if BANK_ZERO.in_range(address) || BANK_SWITCHABLE.in_range(address) {
             return self.game_rom.read(address);
-        } else if VIDEO_RAM.in_range(address) {
-            if PPU::get_lcd_status(self, LCDStatus::ModeFlag(LCDStatusModeFlag::TransferringToLCD)) {
-                return 0xFF
-            }
-        } else if IO_REGISTERS.in_range(address) {
-            return self.data[address as usize];
+        }
+        if address == JOYPAD_ADDRESS {
+            println!("Joypad read {:08b}", self.data[address as usize]);
         }
         self.data[address as usize]
     }
@@ -89,11 +92,11 @@ impl Bus {
 
     pub fn write(&mut self, address: u16, data: u8) {
         if address == 0xFF01 {
-            print!("{}", data as char); 
+            // print!("{}", data as char); 
         }
 
         if BANK_ZERO.in_range(address) || BANK_SWITCHABLE.in_range(address) {
-            println!("WRITING TO ROM");
+            // println!("WRITING TO ROM");
         } else if WORK_RAM_1.in_range(address) || WORK_RAM_2.in_range(address) {
             self.data[address as usize] = data;
             // Copy to the ECHO RAM
@@ -103,29 +106,46 @@ impl Bus {
         } else if ECHO_RAM.in_range(address) {
             self.data[address as usize] = data;
             self.data[(WORK_RAM_1.begin() + (address - ECHO_RAM.begin())) as usize] = data; // Copy to the working RAM
-        } else if VIDEO_RAM.in_range(address) {
-            //if !PPU::get_lcd_status(self, LCDStatus::ModeFlag(LCDStatusModeFlag::TransferringToLCD)) {
-                self.data[address as usize] = data;
-            // }
+        } else if address == TIMER_DIVIDER_REGISTER_ADDRESS {
+            self.data[address as usize] = 0x00;
+        } else if address == LCD_STATUS_ADDRESS {
+            // Prevent user from modifying LCD Status mode
+            let byte = self.data[address as usize];
+            self.data[address as usize] = (data & 0b1111_1100) | (byte & 0b0000_0011);
+        } else if address == LCD_CONTROL_ADDRESS && get_bit(data, BitIndex::I7) {
+            self.data[address as usize] = data;
+            self.data[LCD_Y_ADDRESS as usize] = 0x00;
+        } else if address == JOYPAD_ADDRESS {
+            println!("Joypad write: {:08b}", data);
+            let byte = self.data[JOYPAD_ADDRESS as usize];
+            self.data[JOYPAD_ADDRESS as usize] = (data & 0b00110000) | 0b11000000 | (byte & 0b00001111);
         } else {
             self.data[address as usize] = data;
         }
     }
 
+    pub fn force_write(&mut self, address: u16, data: u8) {
+        self.data[address as usize] = data;
+    }
+
     pub fn write_16bit(&mut self, address: u16, data: u16) {
         let bytes = data.to_le_bytes();
         self.write(address, bytes[0]);
         self.write(address.wrapping_add(1), bytes[1]);
     }
 
-    pub fn set_flag(&mut self, flag: InterruptFlag, val: bool) {
+    pub fn set_interrupt_enable(&mut self, interrupt: Interrupt, val: bool) {
+        let byte = self.read(INTERRUPT_ENABLE_ADDRESS);
+        self.write(INTERRUPT_ENABLE_ADDRESS, interrupt.set(byte, val));
+    }
+
+    pub fn set_interrupt_flag(&mut self, interrupt: Interrupt, val: bool) {
         let byte = self.read(INTERRUPT_FLAG_ADDRESS);
-        self.write(INTERRUPT_FLAG_ADDRESS, match flag {
-           InterruptFlag::VBlank => set_bit(byte, val, BitIndex::I0),
-           InterruptFlag::LCDSTAT => set_bit(byte, val, BitIndex::I1),
-           InterruptFlag::Timer => set_bit(byte, val, BitIndex::I2),
-           InterruptFlag::Serial => set_bit(byte, val, BitIndex::I3),
-           InterruptFlag::Joypad => set_bit(byte, val, BitIndex::I4),
-        });
+        self.write(INTERRUPT_FLAG_ADDRESS, interrupt.set(byte, val));
+    }
+
+    pub fn get_interrupt(&mut self, interrupt: Interrupt) -> bool {
+        let byte = self.read(INTERRUPT_ENABLE_ADDRESS) & self.read(INTERRUPT_FLAG_ADDRESS);
+        interrupt.get(byte)
     }
 }

src/cpu.rs

@@ -8,7 +8,7 @@ use crate::utils::{
     sub_half_carry,
     add_half_carry_16bit,
 };
-use crate::bus::Bus;
+use crate::bus::{Bus, INTERRUPT_ENABLE_ADDRESS, INTERRUPT_FLAG_ADDRESS};
 
 #[derive(Debug, Copy, Clone)]
 pub enum Register {
@@ -53,7 +53,8 @@ pub enum FlagRegister {
     Carry, // Set if a carry was ocurrend from the last math operation or if register A is the smaller value when executing the CP instruction
 }
 
-pub enum InterruptFlag {
+#[derive(Debug, Copy, Clone)]
+pub enum Interrupt {
     VBlank,
     LCDSTAT,
     Timer,
@@ -61,14 +62,32 @@ pub enum InterruptFlag {
     Joypad,
 }
 
-impl InterruptFlag {
-    pub fn get_bit_index(interrupt: InterruptFlag) -> BitIndex {
-        match interrupt {
-            InterruptFlag::VBlank  => BitIndex::I0,
-            InterruptFlag::LCDSTAT => BitIndex::I1,
-            InterruptFlag::Timer   => BitIndex::I2,
-            InterruptFlag::Serial  => BitIndex::I3,
-            InterruptFlag::Joypad  => BitIndex::I4,
+impl Interrupt {
+    fn get_bit_index(&self) -> BitIndex {
+        match self {
+           Interrupt::VBlank  => BitIndex::I0,
+           Interrupt::LCDSTAT => BitIndex::I1,
+           Interrupt::Timer   => BitIndex::I2,
+           Interrupt::Serial  => BitIndex::I3,
+           Interrupt::Joypad  => BitIndex::I4,
+        }
+    }
+
+    pub fn get(&self, byte: u8) -> bool {
+        get_bit(byte, self.get_bit_index())
+    }
+
+    pub fn set(&self, byte: u8, val: bool) -> u8 {
+        set_bit(byte, val, self.get_bit_index())
+    }
+    
+    pub fn get_vector(&self) -> u16 {
+        match self {
+           Interrupt::VBlank  => 0x40,
+           Interrupt::LCDSTAT => 0x48,
+           Interrupt::Timer   => 0x50,
+           Interrupt::Serial  => 0x58,
+           Interrupt::Joypad  => 0x60,
         }
     }
 }
@@ -811,11 +830,19 @@ pub enum Opcode {
 #[derive(Debug, Copy, Clone)]
 pub struct Cycles(pub usize); 
 
+impl Cycles {
+    pub fn to_t(&self) -> usize {
+        self.0 * 4
+    }
+}
+
 pub struct CPU {
     registers: Registers,
     cycles: Cycles,
     last_op_cycles: Cycles,
     exec_calls_count: usize,
+    is_halted: bool,
+    ime: bool, // Interrupt Master Enable
 }
 
 impl CPU {
@@ -825,6 +852,8 @@ impl CPU {
             cycles: Cycles(0),
             last_op_cycles: Cycles(0),
             exec_calls_count: 0,
+            is_halted: false,
+            ime: true,
         }
     }
 
@@ -837,8 +866,11 @@ impl CPU {
     }
 
     fn increment_cycles(&mut self, cycles: Cycles) {
-        let Cycles(c) = cycles;
-        self.cycles.0 += c;
+        self.cycles.0 += cycles.0;
+    }
+
+    fn decrement_cycles(&mut self, cycles: Cycles) {
+        self.cycles.0 -= cycles.0;
     }
 
     pub fn reset_cycles(&mut self) {
@@ -876,20 +908,54 @@ impl CPU {
         );
     }
 
+    pub fn handle_interrupt(&mut self, bus: &mut Bus, interrupt: Interrupt) {
+        bus.set_interrupt_enable(interrupt, false);
+        bus.set_interrupt_flag(interrupt, false);
+        let vector = interrupt.get_vector();
+        self.exec(Opcode::CALL(OpcodeParameter::U16(vector)), bus);
+        println!("Interrupt: {:?}", interrupt);
+    }
+
+    pub fn check_interrupts(&mut self, bus: &mut Bus) -> Option<Interrupt> {
+        if !self.ime && !self.is_halted {
+            return None;
+        }
+        if bus.read(INTERRUPT_ENABLE_ADDRESS) & bus.read(INTERRUPT_FLAG_ADDRESS) != 0 {
+            self.is_halted = false;
+        }
+        if bus.get_interrupt(Interrupt::VBlank) {
+            return Some(Interrupt::VBlank);
+        } else if bus.get_interrupt(Interrupt::LCDSTAT) {
+            return Some(Interrupt::LCDSTAT);
+        } else if bus.get_interrupt(Interrupt::Timer) {
+            return Some(Interrupt::Timer);
+        } else if bus.get_interrupt(Interrupt::Serial) {
+            return Some(Interrupt::Serial);
+        } else if bus.get_interrupt(Interrupt::Joypad) {
+            return Some(Interrupt::Joypad);
+        }
+        None
+    }
+
     pub fn run(&mut self, bus: &mut Bus) {
         let cycles_start = self.get_cycles();
-        let program_counter = self.registers.get(Register::PC);
-        let parameter_bytes = OpcodeParameterBytes::from_address(program_counter, bus);
-        let (opcode, cycles) = parameter_bytes.parse_opcode();
-        if !env::var("CPU_LOG").is_err() {
-            self.log(parameter_bytes);
+        if let Some(interrupt) = self.check_interrupts(bus) {
+            self.handle_interrupt(bus, interrupt);
+            self.increment_cycles(Cycles(5));
+        } else if !self.is_halted {
+            let program_counter = self.registers.get(Register::PC);
+            let parameter_bytes = OpcodeParameterBytes::from_address(program_counter, bus);
+            let (opcode, cycles) = parameter_bytes.parse_opcode();
+            if !env::var("CPU_LOG").is_err() {
+                self.log(parameter_bytes);
+            }
+            self.increment_cycles(cycles);
+            self.exec(opcode, bus);
+        } else if self.is_halted {
+            self.increment_cycles(Cycles(1));
         }
-        self.increment_cycles(cycles);
-        self.exec(opcode, bus);
         let cycles_end = self.get_cycles();
-
         self.set_last_op_cycles(cycles_start, cycles_end);
-        // self.increment_exec_calls_count();
     }
 
     pub fn exec(&mut self, opcode: Opcode, bus: &mut Bus) {
@@ -1713,21 +1779,22 @@ impl CPU {
             // Enable interrupts
             Opcode::EI => {
                 self.registers.increment(Register::PC, 1);
-                bus.write(0xFFFF, 0xFF); // Disable all interrupts
+                self.ime = true;
             },
             // Disable interrupts
             Opcode::DI => {
                 self.registers.increment(Register::PC, 1);
-                bus.write(0xFFFF, 0x00); // Disable all interrupts
+                self.ime = false;
             },
             // Same as enabling interrupts and then executing RET
             Opcode::RETI => {
                 self.exec(Opcode::EI, bus);
                 self.exec(Opcode::RET(OpcodeParameter::NoParam), bus);
             },
-            // WIP
+            // Don't execute instructions until an interrupt is requested
             Opcode::HALT => {
                 self.registers.increment(Register::PC, 1);
+                self.is_halted = true;
             },
             Opcode::STOP => {
                 self.registers.increment(Register::PC, 2);
@@ -1865,16 +1932,16 @@ mod tests {
         let mut bus = Bus::new();
         let addr = 0xFF00;
         cpu.registers.set(Register::A, 0xF1);
-        cpu.exec(Opcode::LD(OpcodeParameter::FF00plusU8_Register(4, Register::A)), &mut bus);
-        assert_eq!(bus.read(addr + 4), 0xF1);
+        cpu.exec(Opcode::LD(OpcodeParameter::FF00plusU8_Register(0x42, Register::A)), &mut bus);
+        assert_eq!(bus.read(addr + 0x42), 0xF1);
         assert_eq!(cpu.registers.get(Register::PC), 0x102);
 
         let mut cpu = CPU::new();
         let mut bus = Bus::new();
         let addr = 0xFF00;
         cpu.registers.set(Register::A, 0x00);
-        bus.write(addr + 4, 0xF1);
-        cpu.exec(Opcode::LD(OpcodeParameter::Register_FF00plusU8(Register::A, 4)), &mut bus);
+        bus.write(addr + 0x42, 0xF1);
+        cpu.exec(Opcode::LD(OpcodeParameter::Register_FF00plusU8(Register::A, 0x42)), &mut bus);
         assert_eq!(cpu.registers.get(Register::A), 0xF1);
         assert_eq!(cpu.registers.get(Register::PC), 0x102);
 

src/emulator.rs

@@ -1,26 +1,107 @@
 use std::{thread, time};
+use winit_input_helper::WinitInputHelper;
+use winit::event::{VirtualKeyCode};
 
-use crate::cpu::{CPU, Cycles};
+use crate::cpu::{CPU, Cycles, Interrupt};
 use crate::ppu::PPU;
 use crate::bus::Bus;
+use crate::timer::Timer;
+use crate::joypad::{Joypad, Button, JOYPAD_ADDRESS};
 
 pub struct Emulator {
     cpu: CPU,
     ppu: PPU,
     bus: Bus,
+    timer: Timer,
+    joypad: Joypad,
 }
 
 impl Emulator {
     pub fn new() -> Self {
+        let mut joypad: Joypad = Joypad::new();
         Self {
             cpu: CPU::new(),
             ppu: PPU::new(),
             bus: Bus::new(),
+            timer: Timer::new(),
+            joypad: Joypad::new(),
+        }
+    }
+
+    pub fn handle_input(&mut self, input: &WinitInputHelper) {
+        let mut change = false;
+        if input.key_pressed(VirtualKeyCode::K) {
+            change = true;
+            self.joypad.press(Button::A);
+        }
+        if input.key_pressed(VirtualKeyCode::J) {
+            change = true;
+            self.joypad.press(Button::B);
+        }
+        if input.key_pressed(VirtualKeyCode::W) {
+            change = true;
+            self.joypad.press(Button::Up);
+        }
+        if input.key_pressed(VirtualKeyCode::S) {
+            change = true;
+            self.joypad.press(Button::Down);
+        }
+        if input.key_pressed(VirtualKeyCode::A) {
+            change = true;
+            self.joypad.press(Button::Left);
+        }
+        if input.key_pressed(VirtualKeyCode::D) {
+            change = true;
+            self.joypad.press(Button::Right);
+        }
+        if input.key_pressed(VirtualKeyCode::N) {
+            change = true;
+            self.joypad.press(Button::Start);
+        }
+        if input.key_pressed(VirtualKeyCode::B) {
+            change = true;
+            self.joypad.press(Button::Select);
+        }
+
+        if input.key_released(VirtualKeyCode::K) {
+            change = true;
+            self.joypad.release(Button::A);
+        }
+        if input.key_released(VirtualKeyCode::J) {
+            change = true;
+            self.joypad.release(Button::B);
+        }
+        if input.key_released(VirtualKeyCode::W) {
+            change = true;
+            self.joypad.release(Button::Up);
+        }
+        if input.key_released(VirtualKeyCode::S) {
+            change = true;
+            self.joypad.release(Button::Down);
+        }
+        if input.key_released(VirtualKeyCode::A) {
+            change = true;
+            self.joypad.release(Button::Left);
+        }
+        if input.key_released(VirtualKeyCode::D) {
+            change = true;
+            self.joypad.release(Button::Right);
+        }
+        if input.key_released(VirtualKeyCode::N) {
+            change = true;
+            self.joypad.release(Button::Start);
+        }
+        if input.key_released(VirtualKeyCode::B) {
+            change = true;
+            self.joypad.release(Button::Select);
+        }
+        if change {
+            self.bus.force_write(JOYPAD_ADDRESS, self.joypad.get(&self.bus));
+            self.bus.set_interrupt_flag(Interrupt::Joypad, true);
         }
     }
 
     pub fn draw(&mut self, frame: &mut [u8]) {
-        // self.ppu.draw_background(&mut self.bus);
         let ppu_frame = self.ppu.get_rgba_frame();
         for (i, pixel) in frame.chunks_exact_mut(4).enumerate() {
             pixel.copy_from_slice(&ppu_frame[i]);
@@ -30,8 +111,9 @@ impl Emulator {
     pub fn run(&mut self, cpu_cycles: Cycles) {
         self.cpu.reset_cycles();
         while self.cpu.get_cycles().0 <= cpu_cycles.0 {
-            self.ppu.do_cycle(&mut self.bus);
             self.cpu.run(&mut self.bus);
+            self.ppu.do_cycles(&mut self.bus, self.cpu.get_last_op_cycles());
+            self.timer.do_cycles(&mut self.bus, self.cpu.get_last_op_cycles());
         }
     }
 
@@ -40,7 +122,6 @@ impl Emulator {
         while !exit {
             self.cpu.run(&mut self.bus);
 
-            // thread::sleep(time::Duration::from_millis(100));
             // exit = self.cpu.get_exec_calls_count() >= 1258895; // log 1
             // exit = self.cpu.get_exec_calls_count() >= 1068422; // log 3
             // exit = self.cpu.get_exec_calls_count() >= 1262766; // log 4

src/joypad.rs

@@ -0,0 +1,91 @@
+use crate::bus::{Bus};
+use crate::utils::{BitIndex, get_bit};
+
+pub const JOYPAD_ADDRESS: u16 = 0xFF00;
+
+#[derive(Debug, Copy, Clone)]
+pub enum Button {
+    A,
+    B,
+    Up,
+    Down,
+    Left,
+    Right,
+    Start,
+    Select
+}
+
+pub struct Joypad {
+    a: bool,
+    b: bool,
+    up: bool,
+    down: bool,
+    left: bool,
+    right: bool,
+    start: bool,
+    select: bool,
+}
+
+impl Joypad {
+    pub fn new() -> Self {
+        Self {
+            a: false,
+            b: false,
+            up: false,
+            down: false,
+            left: false,
+            right: false,
+            start: false,
+            select: false,
+        }
+    }
+
+    pub fn press(&mut self, button: Button) {
+        println!("{:?} pressed", button);
+        match button {
+            Button::A      => self.a = true,
+            Button::B      => self.b = true,
+            Button::Up     => self.up = true,
+            Button::Down   => self.down = true,
+            Button::Left   => self.left = true,
+            Button::Right  => self.right = true,
+            Button::Start  => self.start = true,
+            Button::Select => self.select = true,
+        };
+    }
+
+    pub fn release(&mut self, button: Button) {
+        println!("{:?} released", button);
+        match button {
+            Button::A      => self.a = false,
+            Button::B      => self.b = false,
+            Button::Up     => self.up = false,
+            Button::Down   => self.down = false,
+            Button::Left   => self.left = false,
+            Button::Right  => self.right = false,
+            Button::Start  => self.start = false,
+            Button::Select => self.select = false,
+        };
+    }
+
+    pub fn get(&self, bus: &Bus) -> u8 {
+        let byte = bus.read(JOYPAD_ADDRESS);
+        let direction = !get_bit(byte, BitIndex::I4);
+        let action = !get_bit(byte, BitIndex::I5);
+
+        let action = true;
+        let direction = true;
+
+        0b11000000 |
+        (byte & 0b00110000) |
+        (
+            (!((direction && self.down) || (action && self.start)) as u8) << 3
+        ) | (
+            (!((direction && self.up) || (action && self.select)) as u8) << 2
+        ) | (
+            (!((direction && self.left) || (action && self.b)) as u8) << 1
+        ) | (
+            (!((direction && self.right) || (action && self.a)) as u8)
+        )
+    }
+}

src/lib.rs

@@ -1,7 +1,9 @@
 pub mod utils;
 pub mod cpu;
 pub mod ppu;
+pub mod timer;
 pub mod rom;
 pub mod bus;
+pub mod joypad;
 pub mod emulator;
 pub mod render;

src/ppu.rs

@@ -5,7 +5,7 @@ use crate::utils::{
     to_bit_index,
 };
 use crate::bus::{Bus, AddressRange, BANK_ZERO, VIDEO_RAM};
-use crate::cpu::{Cycles, InterruptFlag};
+use crate::cpu::{Cycles, Interrupt};
 
 #[derive(Debug, Copy, Clone)]
 enum Pixel {
@@ -18,17 +18,41 @@ enum Pixel {
 #[derive(Debug, Copy, Clone)]
 struct ColorPalette(u8, u8, u8, u8);
 
+#[derive(Debug, Copy, Clone)]
 pub enum LCDControl {
-    DisplayEnable,
+    LCDEnable,
     WindowTileMapAddress,
     WindowEnable,
-    BackgroundWindowTileAddress,
+    TileAddressMode,
     BackgroundTileMapAddress,
     ObjectSize,
     ObjectEnable,
     BackgroundPriority,
 }
 
+impl LCDControl {
+    fn get_bit_index(&self) -> BitIndex {
+        match self {
+            LCDControl::LCDEnable                   => BitIndex::I7,
+            LCDControl::WindowTileMapAddress        => BitIndex::I6,
+            LCDControl::WindowEnable                => BitIndex::I5,
+            LCDControl::TileAddressMode             => BitIndex::I4,
+            LCDControl::BackgroundTileMapAddress    => BitIndex::I3,
+            LCDControl::ObjectSize                  => BitIndex::I2,
+            LCDControl::ObjectEnable                => BitIndex::I1,
+            LCDControl::BackgroundPriority          => BitIndex::I0,
+        }
+    }
+
+    pub fn get(&self, byte: u8) -> bool {
+        get_bit(byte, self.get_bit_index())
+    }
+
+    pub fn set(&self, byte: u8, val: bool) -> u8 {
+        set_bit(byte, val, self.get_bit_index())
+    }
+}
+
 pub enum LCDStatusModeFlag {
     HBlank,
     VBlank,
@@ -51,26 +75,31 @@ pub const WIDTH: u32 = LCD_WIDTH;
 pub const HEIGHT: u32 = LCD_HEIGHT;
 pub const FRAME_BUFFER_LENGTH: u32 = WIDTH * HEIGHT;
 
-const LCD_CONTROL_ADDRESS: u16 = 0xFF40;
-const LCD_STATUS_ADDRESS: u16 = 0xFF41;
+pub const LCD_CONTROL_ADDRESS: u16 = 0xFF40;
+pub const LCD_STATUS_ADDRESS: u16 = 0xFF41;
 
-const SCROLL_Y_ADDRESS: u16 = 0xFF42;
-const SCROLL_X_ADDRESS: u16 = 0xFF43;
-const LCD_Y_ADDRESS: u16 = 0xFF44;
-const LCD_Y_COMPARE_ADDRESS: u16 = 0xFF45;
-const DMA_ADDRESS: u16 = 0xFF46;
-const BACKGROUND_PALETTE_ADDRESS: u16 = 0xFF47;
-const OBJECT_PALETTE_0_ADDRESS: u16 = 0xFF48;
-const OBJECT_PALETTE_1_ADDRESS: u16 = 0xFF49;
-const WINDOW_X_ADDRESS: u16 = 0xFF4A;
-const WINDOW_Y_ADDRESS: u16 = 0xFF4B;
-const TILE_MAP_ADDRESS: u16 = 0x9800;
+pub const SCROLL_Y_ADDRESS: u16 = 0xFF42;
+pub const SCROLL_X_ADDRESS: u16 = 0xFF43;
+pub const LCD_Y_ADDRESS: u16 = 0xFF44;
+pub const LCD_Y_COMPARE_ADDRESS: u16 = 0xFF45;
+pub const DMA_ADDRESS: u16 = 0xFF46;
+pub const BACKGROUND_PALETTE_ADDRESS: u16 = 0xFF47;
+pub const OBJECT_PALETTE_0_ADDRESS: u16 = 0xFF48;
+pub const OBJECT_PALETTE_1_ADDRESS: u16 = 0xFF49;
+pub const WINDOW_X_ADDRESS: u16 = 0xFF4A;
+pub const WINDOW_Y_ADDRESS: u16 = 0xFF4B;
+pub const TILE_MAP_ADDRESS: u16 = 0x9800;
 
 pub struct PPU {
     cycles: Cycles,
     rgba_frame: [[u8; 4]; FRAME_BUFFER_LENGTH as usize],
 }
 
+enum TileNumber {
+    Base(u16),
+    Absolute(u8),
+}
+
 impl PPU {
     pub fn new() -> Self {
         Self {
@@ -87,42 +116,57 @@ impl PPU {
         self.cycles.0 += cycles.0;
     }
 
-    pub fn do_cycle(&mut self, bus: &mut Bus) {
-        // Mode 1 Vertical blank
-        if PPU::get_lcd_y(bus) >= 144 {
-            if PPU::get_lcd_y(bus) == 144 {
-                bus.set_flag(InterruptFlag::VBlank, true);
-                PPU::set_lcd_status(bus, LCDStatus::ModeFlag(LCDStatusModeFlag::VBlank), true);
-            }
-        } else {
+    pub fn do_cycles(&mut self, bus: &mut Bus, cycles: Cycles) {
+        let mut count = 0;
+        while count < cycles.0 {
+            self.cycle(bus);
+            count += 1;
+        }
+    }
+
+    pub fn cycle(&mut self, bus: &mut Bus) {
+        self.increment_cycles(Cycles(1));
+        if !PPU::get_lcd_control(bus, LCDControl::LCDEnable) {
+            return;
+        }
+
+        if PPU::get_lcd_y(bus) < 144 {
             if self.cycles.0 == 0 {
                 // Mode 2 OAM scan
                 PPU::set_lcd_status(bus, LCDStatus::ModeFlag(LCDStatusModeFlag::SearchingOAM), true);
+                if PPU::get_lcd_status(bus, LCDStatus::Mode2OAMInterrupt) {
+                    PPU::request_interrupt(bus, Interrupt::LCDSTAT);
+                }
             } else if self.cycles.0 == 80 + 1 {
                 // Mode 3 drawing pixel line. This could also last 289 cycles
-                bus.set_flag(InterruptFlag::LCDSTAT, true);
                 self.draw_line(bus);
                 PPU::set_lcd_status(bus, LCDStatus::ModeFlag(LCDStatusModeFlag::TransferringToLCD), true);
             } else if self.cycles.0 == 80 + 172 + 1 {
                 // Mode 0 Horizontal blank. This could last 87 or 204 cycles depending on the mode 3
-                bus.set_flag(InterruptFlag::LCDSTAT, true);
                 PPU::set_lcd_status(bus, LCDStatus::ModeFlag(LCDStatusModeFlag::HBlank), true);
+                if PPU::get_lcd_status(bus, LCDStatus::Mode0HBlankInterrupt) {
+                    PPU::request_interrupt(bus, Interrupt::LCDSTAT);
+                }
+            }
+        } else if PPU::get_lcd_y(bus) == 144 && self.cycles.0 == 0 {
+            // Mode 1 Vertical blank
+            PPU::set_lcd_status(bus, LCDStatus::ModeFlag(LCDStatusModeFlag::VBlank), true);
+            if PPU::get_lcd_status(bus, LCDStatus::Mode1VBlankInterrupt) {
+                PPU::request_interrupt(bus, Interrupt::VBlank);
             }
         }
 
-        let lyc_compare = PPU::get_lcd_y(bus) == bus.read(LCD_Y_COMPARE_ADDRESS);
-        PPU::set_lcd_status(bus, LCDStatus::LYCInterrupt, lyc_compare);
-        if lyc_compare {
-            bus.set_flag(InterruptFlag::LCDSTAT, true);
-        }
-        self.increment_cycles(Cycles(1));
-
         // Horizontal scan completed
         if self.cycles.0 > 456 {
             self.reset_cycles();
 
             PPU::set_lcd_y(bus, PPU::get_lcd_y(bus) + 1);
 
+            let lyc_compare = PPU::get_lcd_y(bus) == bus.read(LCD_Y_COMPARE_ADDRESS);
+            PPU::set_lcd_status(bus, LCDStatus::LYCFlag, lyc_compare);
+            if PPU::get_lcd_status(bus, LCDStatus::LYCInterrupt) && lyc_compare {
+                PPU::request_interrupt(bus, Interrupt::LCDSTAT);
+            }
             // Frame completed
             if PPU::get_lcd_y(bus) > 153 {
                 PPU::set_lcd_y(bus, 0);
@@ -130,6 +174,12 @@ impl PPU {
         }
     }
 
+    fn request_interrupt(bus: &mut Bus, interrupt: Interrupt) {
+        if PPU::get_lcd_control(bus, LCDControl::LCDEnable) {
+            bus.set_interrupt_flag(interrupt, true);
+        }
+    }
+
     fn get_lcd_y(bus: &Bus) -> u8 {
         bus.read(LCD_Y_ADDRESS)
     }
@@ -142,59 +192,40 @@ impl PPU {
         bus.read(SCROLL_X_ADDRESS)
     }
 
-    fn set_scroll_x(bus: &mut Bus, val: u8) {
-        bus.write(SCROLL_X_ADDRESS, val);
-    }
-
     fn get_scroll_y(bus: &Bus) -> u8 {
         bus.read(SCROLL_Y_ADDRESS)
     }
 
-    fn set_scroll_y(bus: &mut Bus, val: u8) {
-        bus.write(SCROLL_Y_ADDRESS, val);
+    fn get_window_x(bus: &Bus) -> u8 {
+        bus.read(WINDOW_X_ADDRESS)
+    }
+
+    fn get_window_y(bus: &Bus) -> u8 {
+        bus.read(WINDOW_Y_ADDRESS)
     }
 
     pub fn get_lcd_control(bus: &Bus, control: LCDControl) -> bool {
         let byte = bus.read(LCD_CONTROL_ADDRESS);
-        match control {
-            LCDControl::DisplayEnable               => get_bit(byte, BitIndex::I7),
-            LCDControl::WindowTileMapAddress        => get_bit(byte, BitIndex::I6),
-            LCDControl::WindowEnable                => get_bit(byte, BitIndex::I5),
-            LCDControl::BackgroundWindowTileAddress => get_bit(byte, BitIndex::I4),
-            LCDControl::BackgroundTileMapAddress    => get_bit(byte, BitIndex::I3),
-            LCDControl::ObjectSize                  => get_bit(byte, BitIndex::I2),
-            LCDControl::ObjectEnable                => get_bit(byte, BitIndex::I1),
-            LCDControl::BackgroundPriority          => get_bit(byte, BitIndex::I0),
-        }
+        control.get(byte)
     }
 
     fn set_lcd_control(bus: &mut Bus, control: LCDControl, val: bool) {
         let mut byte = bus.read(LCD_CONTROL_ADDRESS);
-        byte = match control {
-            LCDControl::DisplayEnable               => set_bit(byte, val, BitIndex::I7),
-            LCDControl::WindowTileMapAddress        => set_bit(byte, val, BitIndex::I6),
-            LCDControl::WindowEnable                => set_bit(byte, val, BitIndex::I5),
-            LCDControl::BackgroundWindowTileAddress => set_bit(byte, val, BitIndex::I4),
-            LCDControl::BackgroundTileMapAddress    => set_bit(byte, val, BitIndex::I3),
-            LCDControl::ObjectSize                  => set_bit(byte, val, BitIndex::I2),
-            LCDControl::ObjectEnable                => set_bit(byte, val, BitIndex::I1),
-            LCDControl::BackgroundPriority          => set_bit(byte, val, BitIndex::I0),
-        };
-        bus.write(LCD_CONTROL_ADDRESS, byte);
+        bus.write(LCD_CONTROL_ADDRESS, control.set(byte, val));
     }
 
     pub fn get_lcd_status(bus: &Bus, status: LCDStatus) -> bool {
         let byte = bus.read(LCD_STATUS_ADDRESS);
         match status {
-            LCDStatus::LYCInterrupt => get_bit(byte, BitIndex::I6),
-            LCDStatus::Mode2OAMInterrupt => get_bit(byte, BitIndex::I5),
+            LCDStatus::LYCInterrupt         => get_bit(byte, BitIndex::I6),
+            LCDStatus::Mode2OAMInterrupt    => get_bit(byte, BitIndex::I5),
             LCDStatus::Mode1VBlankInterrupt => get_bit(byte, BitIndex::I4),
             LCDStatus::Mode0HBlankInterrupt => get_bit(byte, BitIndex::I3),
-            LCDStatus::LYCFlag => get_bit(byte, BitIndex::I2),
+            LCDStatus::LYCFlag              => get_bit(byte, BitIndex::I2),
             LCDStatus::ModeFlag(mode) => match mode {
-                LCDStatusModeFlag::HBlank => (byte & 0b00000011) == 0,
-                LCDStatusModeFlag::VBlank => (byte & 0b00000011) == 1,
-                LCDStatusModeFlag::SearchingOAM => (byte & 0b00000011) == 2,
+                LCDStatusModeFlag::HBlank            => (byte & 0b00000011) == 0,
+                LCDStatusModeFlag::VBlank            => (byte & 0b00000011) == 1,
+                LCDStatusModeFlag::SearchingOAM      => (byte & 0b00000011) == 2,
                 LCDStatusModeFlag::TransferringToLCD => (byte & 0b00000011) == 3,
             },
         }
@@ -203,22 +234,70 @@ impl PPU {
     fn set_lcd_status(bus: &mut Bus, status: LCDStatus, val: bool) {
         let mut byte = bus.read(LCD_STATUS_ADDRESS);
         byte = match status {
-            LCDStatus::LYCInterrupt => set_bit(byte, val, BitIndex::I6),
-            LCDStatus::Mode2OAMInterrupt => set_bit(byte, val, BitIndex::I5),
+            LCDStatus::LYCInterrupt         => set_bit(byte, val, BitIndex::I6),
+            LCDStatus::Mode2OAMInterrupt    => set_bit(byte, val, BitIndex::I5),
             LCDStatus::Mode1VBlankInterrupt => set_bit(byte, val, BitIndex::I4),
             LCDStatus::Mode0HBlankInterrupt => set_bit(byte, val, BitIndex::I3),
-            LCDStatus::LYCFlag => set_bit(byte, val, BitIndex::I2),
+            LCDStatus::LYCFlag              => set_bit(byte, val, BitIndex::I2),
             LCDStatus::ModeFlag(mode) => match mode {
-                LCDStatusModeFlag::HBlank => (byte & 0b11111100) | 0,
-                LCDStatusModeFlag::VBlank => (byte & 0b11111100) | 1,
-                LCDStatusModeFlag::SearchingOAM => (byte & 0b11111100) | 2,
+                LCDStatusModeFlag::HBlank            => (byte & 0b11111100) | 0,
+                LCDStatusModeFlag::VBlank            => (byte & 0b11111100) | 1,
+                LCDStatusModeFlag::SearchingOAM      => (byte & 0b11111100) | 2,
                 LCDStatusModeFlag::TransferringToLCD => (byte & 0b11111100) | 3,
             },
         };
         bus.write(LCD_STATUS_ADDRESS, byte);
     }
 
-    pub fn draw_line(&mut self, bus: &Bus) {
+    fn get_tile_bytes(x: u8, y: u8, tile_number: TileNumber, default_method: bool, bus: &Bus) -> (u8, u8) {
+        let index_x = x as u16 / 8;
+        let index_y = (y as u16 / 8) * 32;
+        let index = index_x + index_y;
+        let tile_line = (y).rem_euclid(8) * 2;
+        let tile_number =  match tile_number {
+            TileNumber::Base(base) => bus.read(base + index as u16),
+            TileNumber::Absolute(num) => bus.read(0x8000 + num as u16),
+
+        } as u16;
+        let addr = if default_method {
+            0x8000 + tile_line as u16 + (tile_number * 16)
+        } else {
+            let tile_number = (tile_number as i8) as i16;
+            let tile_line = tile_line as i16;
+            let base = (0x9000 as u16) as i16;
+            (base + tile_line + (tile_number * 16)) as u16
+        };
+
+        (bus.read(addr), bus.read(addr + 1))
+    }
+
+    fn get_window_pixel(lcd_x: u8, bus: &Bus) -> Option<Pixel> {
+        let lcd_y = PPU::get_lcd_y(bus);
+        let window_x = (PPU::get_window_x(bus) as i8 - 7) as u8;
+        let window_y = PPU::get_window_y(bus);
+
+        if window_x != lcd_x || window_y != lcd_y {
+            return None;
+        }
+
+        let x = lcd_x - window_x;
+        let y = lcd_y - window_x;
+
+        let default_mode = PPU::get_lcd_control(bus, LCDControl::TileAddressMode);
+        let tilemap_area = match PPU::get_lcd_control(bus, LCDControl::WindowTileMapAddress) {
+            true  => 0x9C00,
+            false => 0x9800,
+        };
+        let (tile_byte_1, tile_byte_2) = PPU::get_tile_bytes(x, y, TileNumber::Base(tilemap_area), default_mode, bus);
+
+        let palette = bus.read(BACKGROUND_PALETTE_ADDRESS);
+        let pixels = PPU::get_byte_pixels(tile_byte_1, tile_byte_2, palette);
+
+        Some(pixels[(x as usize).rem_euclid(8)])
+    }
+
+    fn draw_line(&mut self, bus: &Bus) {
+        let palette = bus.read(BACKGROUND_PALETTE_ADDRESS);
         let lcd_y = PPU::get_lcd_y(bus);
         if lcd_y as u32 >= LCD_HEIGHT {
             return;
@@ -227,26 +306,40 @@ impl PPU {
         while (lcd_x as u32) < LCD_WIDTH {
             let y = lcd_y.wrapping_add(PPU::get_scroll_y(bus));
             let x = lcd_x.wrapping_add(PPU::get_scroll_x(bus));
-            let index_x = x as u16 / 8;
-            let index_y = (y as u16 / 8) * 32;
-            let index = index_x + index_y;
-            let tile_line = (y).rem_euclid(8) * 2;
-            let tile_number = bus.read(0x9800 + index as u16) as u16;
-            let addr = 0x8000 + tile_line as u16 + (tile_number * 16);
 
-            let tile_byte_1 = bus.read(addr);
-            let tile_byte_2 = bus.read(addr + 1);
+            let default_mode = PPU::get_lcd_control(bus, LCDControl::TileAddressMode);
+            let tilemap_area = match PPU::get_lcd_control(bus, LCDControl::BackgroundTileMapAddress) {
+                true  => 0x9C00,
+                false => 0x9800,
+            };
+            let (tile_byte_1, tile_byte_2) = PPU::get_tile_bytes(x, y, TileNumber::Base(tilemap_area), default_mode, bus);
 
-            let pixels = PPU::get_byte_pixels(tile_byte_1, tile_byte_2);
+            let bg_pixels = PPU::get_byte_pixels(tile_byte_1, tile_byte_2, palette);
 
-            for pixel in pixels {
+            for pixel in bg_pixels {
                 let idx = lcd_x as usize + (lcd_y as usize * LCD_WIDTH as usize);
                 self.rgba_frame[idx] = PPU::get_rgba(pixel);
+                if PPU::get_lcd_control(bus, LCDControl::WindowEnable) {
+                    if let Some(window_pixel) = PPU::get_window_pixel(lcd_x, bus) {
+                        self.rgba_frame[idx] = PPU::get_rgba(window_pixel);
+                    }
+                }
+
                 lcd_x += 1;
             }
         }
     }
 
+    fn get_palette(index: u8, palette_byte: u8) -> u8 {
+        match index {
+            0b00 => palette_byte & 0b11,
+            0b01 => (palette_byte >> 2) & 0b11,
+            0b10 => (palette_byte >> 4) & 0b11,
+            0b11 => (palette_byte >> 6) & 0b11,
+            _ => 0b00,
+        }
+    }
+
     fn get_pixel(two_bit_pixel: u8) -> Pixel {
         match two_bit_pixel {
             0x00 => Pixel::White,
@@ -266,17 +359,17 @@ impl PPU {
         }
     }
 
-    fn get_byte_pixels(byte1: u8, byte2: u8) -> [Pixel; 8] {
-        let mut pixels: [Pixel; 8] = [Pixel::White; 8];
-        pixels[0] = PPU::get_pixel(((get_bit(byte1, BitIndex::I7) as u8) << 1) | (get_bit(byte2, BitIndex::I7) as u8));
-        pixels[1] = PPU::get_pixel(((get_bit(byte1, BitIndex::I6) as u8) << 1) | (get_bit(byte2, BitIndex::I6) as u8));
-        pixels[2] = PPU::get_pixel(((get_bit(byte1, BitIndex::I5) as u8) << 1) | (get_bit(byte2, BitIndex::I5) as u8));
-        pixels[3] = PPU::get_pixel(((get_bit(byte1, BitIndex::I4) as u8) << 1) | (get_bit(byte2, BitIndex::I4) as u8));
-        pixels[4] = PPU::get_pixel(((get_bit(byte1, BitIndex::I3) as u8) << 1) | (get_bit(byte2, BitIndex::I3) as u8));
-        pixels[5] = PPU::get_pixel(((get_bit(byte1, BitIndex::I2) as u8) << 1) | (get_bit(byte2, BitIndex::I2) as u8));
-        pixels[6] = PPU::get_pixel(((get_bit(byte1, BitIndex::I1) as u8) << 1) | (get_bit(byte2, BitIndex::I1) as u8));
-        pixels[7] = PPU::get_pixel(((get_bit(byte1, BitIndex::I0) as u8) << 1) | (get_bit(byte2, BitIndex::I0) as u8));
-        pixels
+    fn get_byte_pixels(byte1: u8, byte2: u8, palette: u8) -> [Pixel; 8] {
+        [
+            PPU::get_pixel(PPU::get_palette(((byte1 >> 7) & 0b01) | ((byte2 >> 6) & 0b10), palette)),
+            PPU::get_pixel(PPU::get_palette(((byte1 >> 6) & 0b01) | ((byte2 >> 5) & 0b10), palette)),
+            PPU::get_pixel(PPU::get_palette(((byte1 >> 5) & 0b01) | ((byte2 >> 4) & 0b10), palette)),
+            PPU::get_pixel(PPU::get_palette(((byte1 >> 4) & 0b01) | ((byte2 >> 3) & 0b10), palette)),
+            PPU::get_pixel(PPU::get_palette(((byte1 >> 3) & 0b01) | ((byte2 >> 2) & 0b10), palette)),
+            PPU::get_pixel(PPU::get_palette(((byte1 >> 2) & 0b01) | ((byte2 >> 1) & 0b10), palette)),
+            PPU::get_pixel(PPU::get_palette(((byte1 >> 1) & 0b01) | (byte2        & 0b10), palette)),
+            PPU::get_pixel(PPU::get_palette((byte1        & 0b01) | ((byte2 << 1) & 0b10), palette)),
+        ]
     }
 
     pub fn get_rgba_frame(&self) -> &[[u8; 4]; FRAME_BUFFER_LENGTH as usize] {

src/render.rs

@@ -47,6 +47,8 @@ pub fn start_eventloop() {
                 return;
             }
 
+            emulator.handle_input(&input);
+
             // Resize the window
             if let Some(size) = input.window_resized() {
                 pixels.resize_surface(size.width, size.height);

src/timer.rs

@@ -0,0 +1,76 @@
+use crate::cpu::{Interrupt, Cycles};
+use crate::bus::Bus;
+use crate::utils::{
+    BitIndex,
+    get_bit,
+};
+
+pub const TIMER_DIVIDER_REGISTER_ADDRESS: u16 = 0xFF04;
+pub const TIMER_COUNTER_ADDRESS: u16          = 0xFF05;
+pub const TIMER_MODULO_ADDRESS: u16           = 0xFF06;
+pub const TIMER_CONTROL_ADDRESS: u16          = 0xFF07;
+
+pub struct Timer {
+    cycles: Cycles,
+}
+
+impl Timer {
+
+    pub fn new() -> Self {
+        Self {
+            cycles: Cycles(0),
+        }
+    }
+
+    fn increment_cycles(&mut self, cycles: Cycles) {
+        self.cycles.0 += cycles.0;
+    }
+
+    fn reset_cycles(&mut self) {
+        self.cycles.0 = 0;
+    }
+    
+    pub fn do_cycles(&mut self, bus: &mut Bus, cycles: Cycles) {
+        let mut count = 0;
+        while count < cycles.to_t() {
+            self.cycle(bus);
+            count += 1;
+        }
+    }
+
+    fn cycle(&mut self, bus: &mut Bus) {
+        let div = bus.read(TIMER_DIVIDER_REGISTER_ADDRESS);
+        bus.write(TIMER_DIVIDER_REGISTER_ADDRESS, div.wrapping_add(1));
+
+        if Timer::is_timer_enabled(bus) {
+            let tima = bus.read(TIMER_COUNTER_ADDRESS);
+            let tima_rate = Timer::get_tima_rate(bus);
+            if self.cycles.0 >= tima_rate {
+                if tima.checked_add(1) == None {
+                    bus.write(TIMER_COUNTER_ADDRESS, bus.read(TIMER_MODULO_ADDRESS));
+                    bus.set_interrupt_flag(Interrupt::Timer, false);
+                } else {
+                    bus.write(TIMER_COUNTER_ADDRESS, tima.wrapping_add(1));
+                }
+                self.reset_cycles();
+            }
+        }
+
+        self.increment_cycles(Cycles(1));
+    }
+
+    fn is_timer_enabled(bus: &Bus) -> bool {
+        get_bit(bus.read(TIMER_CONTROL_ADDRESS), BitIndex::I2)
+    }
+
+    fn get_tima_rate(bus: &Bus) -> usize {
+        let clock_select = bus.read(TIMER_CONTROL_ADDRESS) & 0b0000_0011;
+        match clock_select {
+            0b00 => 16,
+            0b01 => 64,
+            0b10 => 256,
+            0b11 => 1024,
+            _ => 1,
+        }
+    }
+}