src/bus.rs

@@ -54,15 +54,14 @@ pub const INTERRUPT_FLAG_ADDRESS: u16 = 0xFF0F;
 pub struct Bus {
     game_rom: ROM,
     data: [u8; 0x10000],
-    pub reset_timer: bool,
 }
 
 impl Bus {
     pub fn new() -> Self {
-        // let game_rom = match ROM::load_file("ignore/dr-mario.gb".to_string()) {
+        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/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()) {
@@ -77,7 +76,6 @@ impl Bus {
             _ => panic!("Could not read ROM"),
         };
         let mut data = [0x00; 0x10000];
-        data[0xFF00] = 0b11001111;
         data[0xFF01] = 0x00;
         data[0xFF02] = 0x7E;
         data[0xFF04] = 0x18;
@@ -97,12 +95,10 @@ impl Bus {
 
         data[0xFF4A] = 0x00;
         data[0xFF4B] = 0x00;
-        data[0xFFFF] = 0x00;
 
         Self {
             data,
             game_rom,
-            reset_timer: false,
         }
     }
 
@@ -122,10 +118,6 @@ impl Bus {
             // print!("{}", data as char); 
         }
 
-        if address == 0xFF06 {
-            println!("Writing {:02X} to modulo", data);
-        }
-
         if BANK_ZERO.in_range(address) || BANK_SWITCHABLE.in_range(address) {
             // println!("WRITING TO ROM");
         } else if WORK_RAM_1.in_range(address) || WORK_RAM_2.in_range(address) {
@@ -138,14 +130,13 @@ impl Bus {
             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 address == TIMER_DIVIDER_REGISTER_ADDRESS {
-            println!("bus timer reset");
-            self.reset_timer = true;
+            self.data[address as usize] = 0x00;
         } 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 {
             let byte = self.data[JOYPAD_ADDRESS as usize];
-            self.data[JOYPAD_ADDRESS as usize] = (data & 0b11110000) | (byte & 0b00001111);
+            self.data[JOYPAD_ADDRESS as usize] = (data & 0b00110000) | 0b11000000 | (byte & 0b00001111);
         } else {
             self.data[address as usize] = data;
         }

src/cpu.rs

@@ -843,7 +843,6 @@ pub struct CPU {
     exec_calls_count: usize,
     is_halted: bool,
     ime: bool, // Interrupt Master Enable
-    ei_delay: bool,
 }
 
 impl CPU {
@@ -854,7 +853,6 @@ impl CPU {
             last_op_cycles: Cycles(0),
             exec_calls_count: 0,
             is_halted: false,
-            ei_delay: false,
             ime: true,
         }
     }
@@ -911,16 +909,14 @@ impl CPU {
     }
 
     pub fn handle_interrupt(&mut self, bus: &mut Bus, interrupt: Interrupt) {
-        println!("Interrupt: {:?}", interrupt);
+        bus.set_interrupt_enable(interrupt, false);
         bus.set_interrupt_flag(interrupt, false);
-        self.ime = false;
-        self.exec(Opcode::CALL(OpcodeParameter::U16(interrupt.get_vector())), bus);
+        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> {
-        /* println!("IE {:08b}", bus.read(INTERRUPT_ENABLE_ADDRESS));
-        println!("IF {:08b}", bus.read(INTERRUPT_FLAG_ADDRESS));
-        println!("---"); */
         if !self.ime && !self.is_halted {
             return None;
         }
@@ -956,12 +952,6 @@ impl CPU {
             }
             self.increment_cycles(cycles);
             self.exec(opcode, bus);
-            if self.ei_delay && !self.ime {
-                println!("EI delay");
-                self.ei_delay = false;
-                self.run(bus);
-                self.ime = true;
-            }
         } else if self.is_halted {
             self.increment_cycles(Cycles(1));
         }
@@ -1791,20 +1781,25 @@ impl CPU {
             Opcode::EI => {
                 println!("EI");
                 self.registers.increment(Register::PC, 1);
-                self.ei_delay = true;
+                self.ime = true;
             },
             // Disable interrupts
             Opcode::DI => {
+                println!("DI");
                 self.registers.increment(Register::PC, 1);
                 self.ime = false;
             },
             // Same as enabling interrupts and then executing RET
             Opcode::RETI => {
+                println!("RETI");
+                let prev_pc = self.registers.get(Register::PC);
+                self.exec(Opcode::EI, bus);
                 self.exec(Opcode::RET(OpcodeParameter::NoParam), bus);
-                self.ime = true;
+                self.registers.set(Register::PC, prev_pc.wrapping_add(1));
             },
             // Don't execute instructions until an interrupt is requested
             Opcode::HALT => {
+                println!("HALT");
                 self.registers.increment(Register::PC, 1);
                 self.is_halted = true;
             },
@@ -1812,11 +1807,8 @@ impl CPU {
                 self.registers.increment(Register::PC, 2);
             },
             Opcode::NOP => self.registers.increment(Register::PC, 1),
-            Opcode::IllegalInstruction => {
-                println!("Illegal instruction!");
-                self.registers.increment(Register::PC, 1);
-            },
-            _ => unreachable!(),
+            Opcode::IllegalInstruction => {panic!("Illegal instruction");},
+            _ => {panic!("Illegal instruction");},
         };
     }
 }

src/emulator.rs

@@ -112,10 +112,6 @@ impl Emulator {
         self.cpu.reset_cycles();
         while self.cpu.get_cycles().0 <= cpu_cycles.0 {
             self.cpu.run(&mut self.bus);
-            if self.bus.reset_timer {
-                self.bus.reset_timer = false;
-                self.timer.reset(&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());
         }

src/joypad.rs

@@ -73,7 +73,8 @@ impl Joypad {
         let direction = !get_bit(byte, BitIndex::I4);
         let action = !get_bit(byte, BitIndex::I5);
 
-        let data = (byte & 0b11110000) |
+        let data = 0b11000000 |
+        (byte & 0b00110000) |
         (
             (!((direction && self.down) || (action && self.start)) as u8) << 3
         ) | (

src/ppu.rs

@@ -163,19 +163,16 @@ impl PPU {
             self.reset_cycles();
 
             PPU::set_lcd_y(bus, PPU::get_lcd_y(bus).wrapping_add(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);
             }
-            PPU::check_lyc(bus);
-        }
-    }
-
-    fn check_lyc(bus: &mut Bus) {
-        let lyc_compare = PPU::get_lcd_y(bus) == bus.read(LCD_Y_COMPARE_ADDRESS);
-        if PPU::get_lcd_status(bus, LCDStatus::LYCInterrupt) && lyc_compare {
-            PPU::set_lcd_status(bus, LCDStatus::LYCFlag, lyc_compare);
-            PPU::request_interrupt(bus, Interrupt::LCDSTAT);
         }
     }
 
@@ -338,17 +335,17 @@ impl PPU {
             0b01 => (palette_byte >> 2) & 0b11,
             0b10 => (palette_byte >> 4) & 0b11,
             0b11 => (palette_byte >> 6) & 0b11,
-            _ => unreachable!(),
+            _ => 0b00,
         }
     }
 
     fn get_pixel(two_bit_pixel: u8) -> Pixel {
         match two_bit_pixel {
-            0b00 => Pixel::White,
-            0b01 => Pixel::Light,
-            0b10 => Pixel::Dark,
-            0b11 => Pixel::Black,
-            _ => unreachable!(),
+            0x00 => Pixel::White,
+            0x01 => Pixel::Light,
+            0x10 => Pixel::Dark,
+            0x11 => Pixel::Black,
+            _ => Pixel::Black,
         }
     }
 

src/timer.rs

@@ -11,23 +11,23 @@ pub const TIMER_MODULO_ADDRESS: u16           = 0xFF06;
 pub const TIMER_CONTROL_ADDRESS: u16          = 0xFF07;
 
 pub struct Timer {
-    divider: u16,
-    prev_result: bool,
+    cycles: Cycles,
 }
 
 impl Timer {
 
     pub fn new() -> Self {
         Self {
-            divider: 0,
-            prev_result: false,
+            cycles: Cycles(0),
         }
     }
 
-    pub fn reset(&mut self, bus: &mut Bus) {
-        println!("timer reset");
-        self.divider = 0;
-        bus.force_write(TIMER_DIVIDER_REGISTER_ADDRESS, 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) {
@@ -39,37 +39,38 @@ impl Timer {
     }
 
     fn cycle(&mut self, bus: &mut Bus) {
-        self.divider = self.divider.wrapping_add(1);
-        bus.force_write(TIMER_DIVIDER_REGISTER_ADDRESS, self.divider.to_be_bytes()[0]);
+        let div = bus.read(TIMER_DIVIDER_REGISTER_ADDRESS);
+        bus.write(TIMER_DIVIDER_REGISTER_ADDRESS, div.wrapping_add(1));
 
-        let result = Timer::is_timer_enabled(bus) && self.get_tima_rate(bus);
-
-        if self.prev_result && !result {
-            let tima = bus.read(TIMER_COUNTER_ADDRESS).wrapping_add(1);
-            if tima == 0 {
+        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, true);
-                println!("Timer interrupt set");
+                    bus.set_interrupt_flag(Interrupt::Timer, false);
                 } else {
-                bus.write(TIMER_COUNTER_ADDRESS, tima);
+                    bus.write(TIMER_COUNTER_ADDRESS, tima.wrapping_add(1));
+                }
+                self.reset_cycles();
             }
         }
 
-        self.prev_result = result;
+        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(&self, bus: &Bus) -> bool {
+    fn get_tima_rate(bus: &Bus) -> usize {
         let clock_select = bus.read(TIMER_CONTROL_ADDRESS) & 0b0000_0011;
         match clock_select {
-            0b00 => ((self.divider >> 9) & 1) == 1,
-            0b01 => ((self.divider >> 3) & 1) == 1,
-            0b10 => ((self.divider >> 5) & 1) == 1,
-            0b11 => ((self.divider >> 7) & 1) == 1,
-            _ => unreachable!(),
+            0b00 => 16,
+            0b01 => 64,
+            0b10 => 256,
+            0b11 => 1024,
+            _ => 1,
         }
     }
 }