Fix interrupts, implement halt mode and fix IME

src/bus.rs

@@ -5,7 +5,7 @@ use crate::utils::{
     join_bytes
 };
 use crate::rom::ROM;
-use crate::ppu::{PPU, LCDStatus, LCDStatusModeFlag};
+use crate::ppu::{PPU, LCDStatus, LCDStatusModeFlag, LCD_CONTROL_ADDRESS, LCD_Y_ADDRESS};
 use crate::cpu::{Interrupt};
 use crate::timer::{TIMER_DIVIDER_REGISTER_ADDRESS};
 
@@ -50,7 +50,7 @@ pub struct Bus {
 
 impl Bus {
     pub fn new() -> Self {
-        let game_rom = match ROM::load_file("ignore/tetris.gb".to_string()) {
+        let game_rom = match ROM::load_file("ignore/mario-land.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()) {
@@ -74,14 +74,11 @@ impl Bus {
     }
 
     pub fn read(&self, address: u16) -> u8 {
+        if address == 0xFF00 {
+            return 0xFF;
+        }
         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];
         }
         self.data[address as usize]
     }
@@ -106,10 +103,11 @@ 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) {
-            self.data[address as usize] = data;
         } else if address == TIMER_DIVIDER_REGISTER_ADDRESS {
             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 {
             self.data[address as usize] = data;
         }
@@ -121,12 +119,12 @@ impl Bus {
         self.write(address.wrapping_add(1), bytes[1]);
     }
 
-    pub fn set_interrupt_master(&mut self, interrupt: Interrupt, 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(&mut self, interrupt: Interrupt, val: bool) {
+    pub fn set_interrupt_flag(&mut self, interrupt: Interrupt, val: bool) {
         let byte = self.read(INTERRUPT_FLAG_ADDRESS);
         self.write(INTERRUPT_FLAG_ADDRESS, interrupt.set(byte, val));
     }

src/cpu.rs

@@ -841,6 +841,8 @@ pub struct CPU {
     cycles: Cycles,
     last_op_cycles: Cycles,
     exec_calls_count: usize,
+    is_halted: bool,
+    ime: bool, // Interrupt Master Enable
 }
 
 impl CPU {
@@ -850,6 +852,8 @@ impl CPU {
             cycles: Cycles(0),
             last_op_cycles: Cycles(0),
             exec_calls_count: 0,
+            is_halted: false,
+            ime: true,
         }
     }
 
@@ -905,8 +909,8 @@ impl CPU {
     }
 
     pub fn handle_interrupt(&mut self, bus: &mut Bus, interrupt: Interrupt) {
-        bus.set_interrupt_master(interrupt, false);
+        bus.set_interrupt_enable(interrupt, false);
-        bus.set_interrupt(interrupt, false);
+        bus.set_interrupt_flag(interrupt, false);
         let vector = interrupt.get_vector();
         self.exec(Opcode::CALL(OpcodeParameter::U16(vector)), bus);
         self.increment_cycles(Cycles(5));
@@ -914,6 +918,12 @@ impl CPU {
     }
 
     pub fn check_interrupts(&mut self, bus: &mut Bus) -> Option<Interrupt> {
+        if bus.read(INTERRUPT_ENABLE_ADDRESS) & bus.read(INTERRUPT_FLAG_ADDRESS) != 0 {
+            self.is_halted = false;
+        }
+        if !self.ime {
+            return None;
+        }
         if bus.get_interrupt(Interrupt::VBlank) {
             return Some(Interrupt::VBlank);
         } else if bus.get_interrupt(Interrupt::LCDSTAT) {
@@ -932,7 +942,7 @@ impl CPU {
         let cycles_start = self.get_cycles();
         if let Some(interrupt) = self.check_interrupts(bus) {
             self.handle_interrupt(bus, interrupt);
-        } else {
+        } 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();
@@ -941,6 +951,8 @@ impl CPU {
             }
             self.increment_cycles(cycles);
             self.exec(opcode, bus);
+        } else if self.is_halted {
+            self.increment_cycles(Cycles(1));
         }
         let cycles_end = self.get_cycles();
         self.set_last_op_cycles(cycles_start, cycles_end);
@@ -1767,21 +1779,24 @@ impl CPU {
             // Enable interrupts
             Opcode::EI => {
                 self.registers.increment(Register::PC, 1);
-                bus.write(INTERRUPT_ENABLE_ADDRESS, 0xFF); // Disable all interrupts
+                self.ime = true;
+                // bus.write(INTERRUPT_MASTER_ENABLE_ADDRESS, 0xFF); // Enable all interrupts
             },
             // Disable interrupts
             Opcode::DI => {
                 self.registers.increment(Register::PC, 1);
-                bus.write(INTERRUPT_ENABLE_ADDRESS, 0x00); // Disable all interrupts
+                self.ime = false;
+                // bus.write(INTERRUPT_MASTER_ENABLE_ADDRESS, 0x00); // Disable all interrupts
             },
             // 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);
@@ -1919,16 +1934,16 @@ 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);
+        cpu.exec(Opcode::LD(OpcodeParameter::FF00plusU8_Register(0x42, Register::A)), &mut bus);
-        assert_eq!(bus.read(addr + 4), 0xF1);
+        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);
+        bus.write(addr + 0x42, 0xF1);
-        cpu.exec(Opcode::LD(OpcodeParameter::Register_FF00plusU8(Register::A, 4)), &mut bus);
+        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

@@ -9,6 +9,7 @@ pub struct Emulator {
     cpu: CPU,
     ppu: PPU,
     bus: Bus,
+    timer: Timer,
 }
 
 impl Emulator {
@@ -17,6 +18,7 @@ impl Emulator {
             cpu: CPU::new(),
             ppu: PPU::new(),
             bus: Bus::new(),
+            timer: Timer::new(),
         }
     }
 
@@ -32,7 +34,7 @@ impl Emulator {
         while self.cpu.get_cycles().0 <= cpu_cycles.0 {
             self.cpu.run(&mut self.bus);
             self.ppu.do_cycles(&mut self.bus, self.cpu.get_last_op_cycles());
-            Timer::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/ppu.rs

@@ -19,7 +19,7 @@ enum Pixel {
 struct ColorPalette(u8, u8, u8, u8);
 
 pub enum LCDControl {
-    DisplayEnable,
+    LCDEnable,
     WindowTileMapAddress,
     WindowEnable,
     BackgroundWindowTileAddress,
@@ -51,20 +51,20 @@ 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;
+pub const LCD_CONTROL_ADDRESS: u16 = 0xFF40;
-const LCD_STATUS_ADDRESS: u16 = 0xFF41;
+pub const LCD_STATUS_ADDRESS: u16 = 0xFF41;
 
-const SCROLL_Y_ADDRESS: u16 = 0xFF42;
+pub const SCROLL_Y_ADDRESS: u16 = 0xFF42;
-const SCROLL_X_ADDRESS: u16 = 0xFF43;
+pub const SCROLL_X_ADDRESS: u16 = 0xFF43;
-const LCD_Y_ADDRESS: u16 = 0xFF44;
+pub const LCD_Y_ADDRESS: u16 = 0xFF44;
-const LCD_Y_COMPARE_ADDRESS: u16 = 0xFF45;
+pub const LCD_Y_COMPARE_ADDRESS: u16 = 0xFF45;
-const DMA_ADDRESS: u16 = 0xFF46;
+pub const DMA_ADDRESS: u16 = 0xFF46;
-const BACKGROUND_PALETTE_ADDRESS: u16 = 0xFF47;
+pub const BACKGROUND_PALETTE_ADDRESS: u16 = 0xFF47;
-const OBJECT_PALETTE_0_ADDRESS: u16 = 0xFF48;
+pub const OBJECT_PALETTE_0_ADDRESS: u16 = 0xFF48;
-const OBJECT_PALETTE_1_ADDRESS: u16 = 0xFF49;
+pub const OBJECT_PALETTE_1_ADDRESS: u16 = 0xFF49;
-const WINDOW_X_ADDRESS: u16 = 0xFF4A;
+pub const WINDOW_X_ADDRESS: u16 = 0xFF4A;
-const WINDOW_Y_ADDRESS: u16 = 0xFF4B;
+pub const WINDOW_Y_ADDRESS: u16 = 0xFF4B;
-const TILE_MAP_ADDRESS: u16 = 0x9800;
+pub const TILE_MAP_ADDRESS: u16 = 0x9800;
 
 pub struct PPU {
     cycles: Cycles,
@@ -96,30 +96,32 @@ impl PPU {
     }
 
     pub fn cycle(&mut self, bus: &mut Bus) {
-        // Mode 1 Vertical blank
+        self.increment_cycles(Cycles(1));
-        if PPU::get_lcd_y(bus) >= 144 {
+        if !PPU::get_lcd_control(bus, LCDControl::LCDEnable) {
-            if PPU::get_lcd_y(bus) == 144 {
+            return;
-                bus.set_interrupt(Interrupt::VBlank, true);
+        }
-                PPU::set_lcd_status(bus, LCDStatus::ModeFlag(LCDStatusModeFlag::VBlank), true);
+
-            }
+        if PPU::get_lcd_y(bus) < 144 {
-        } else {
             if self.cycles.0 == 0 {
                 // Mode 2 OAM scan
+                PPU::request_interrupt(bus, Interrupt::LCDSTAT);
                 PPU::set_lcd_status(bus, LCDStatus::ModeFlag(LCDStatusModeFlag::SearchingOAM), true);
             } else if self.cycles.0 == 80 + 1 {
                 // Mode 3 drawing pixel line. This could also last 289 cycles
-                bus.set_interrupt(Interrupt::LCDSTAT, true);
+                // PPU::request_interrupt(bus, Interrupt::LCDSTAT);
                 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_interrupt(Interrupt::LCDSTAT, true);
+                PPU::request_interrupt(bus, Interrupt::LCDSTAT);
                 PPU::set_lcd_status(bus, LCDStatus::ModeFlag(LCDStatusModeFlag::HBlank), true);
             }
+        } else if PPU::get_lcd_y(bus) == 144 && self.cycles.0 == 0 {
+            // Mode 1 Vertical blank
+            PPU::request_interrupt(bus, Interrupt::VBlank);
+            PPU::set_lcd_status(bus, LCDStatus::ModeFlag(LCDStatusModeFlag::VBlank), true);
         }
 
-        self.increment_cycles(Cycles(1));
-
         // Horizontal scan completed
         if self.cycles.0 > 456 {
             self.reset_cycles();
@@ -129,7 +131,7 @@ impl PPU {
             let lyc_compare = PPU::get_lcd_y(bus) == bus.read(LCD_Y_COMPARE_ADDRESS);
             if lyc_compare {
                 PPU::set_lcd_status(bus, LCDStatus::LYCInterrupt, lyc_compare);
-                bus.set_interrupt(Interrupt::LCDSTAT, true);
+                PPU::request_interrupt(bus, Interrupt::LCDSTAT);
             }
 
             // Frame completed
@@ -139,6 +141,14 @@ impl PPU {
         }
     }
 
+    fn request_interrupt(bus: &mut Bus, interrupt: Interrupt) {
+        if PPU::get_lcd_control(bus, LCDControl::LCDEnable) {
+            bus.set_interrupt_flag(interrupt, true);
+        } else {
+            println!("lcd off");
+        }
+    }
+
     fn get_lcd_y(bus: &Bus) -> u8 {
         bus.read(LCD_Y_ADDRESS)
     }
@@ -166,7 +176,7 @@ impl PPU {
     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::LCDEnable                   => 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),
@@ -180,7 +190,7 @@ impl PPU {
     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::LCDEnable                   => 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),

src/timer.rs

@@ -10,45 +10,66 @@ pub const TIMER_COUNTER_ADDRESS: u16          = 0xFF05;
 pub const TIMER_MODULO_ADDRESS: u16           = 0xFF06;
 pub const TIMER_CONTROL_ADDRESS: u16          = 0xFF07;
 
-pub struct Timer;
+pub struct Timer {
+    cycles: Cycles,
+}
 
 impl Timer {
 
-    pub fn do_cycles(bus: &mut Bus, cycles: Cycles) {
+    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() {
-            Timer::cycle(bus);
+            self.cycle(bus);
             count += 1;
         }
     }
 
-    fn cycle(bus: &mut Bus) {
+    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_increment = Timer::get_tima_increment(bus);
+            let tima_rate = Timer::get_tima_rate(bus);
-            if tima.checked_add(tima_increment) == None {
+            if self.cycles.0 >= tima_rate {
-                bus.write(TIMER_COUNTER_ADDRESS, bus.read(TIMER_MODULO_ADDRESS));
+                if tima.checked_add(1) == None {
-                bus.set_interrupt(Interrupt::Timer, true);
+                    bus.write(TIMER_COUNTER_ADDRESS, bus.read(TIMER_MODULO_ADDRESS));
-            } else {
+                    bus.set_interrupt_flag(Interrupt::Timer, true);
-                bus.write(TIMER_COUNTER_ADDRESS, tima.wrapping_add(tima_increment));
+                } 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_increment(bus: &Bus) -> u8 {
+    fn get_tima_rate(bus: &Bus) -> usize {
         let clock_select = bus.read(TIMER_CONTROL_ADDRESS) & 0b0000_0011;
         match clock_select {
-            0b00 => (4096 as u16 / 1026 as u16 / 4 as u16).to_be_bytes()[1],
+            0b00 => 16,
-            0b01 => (4096 as u16 /   16 as u16 / 4 as u16).to_be_bytes()[1],
+            0b01 => 64,
-            0b10 => (4096 as u16 /   64 as u16 / 4 as u16).to_be_bytes()[1],
+            0b10 => 256,
-            0b11 => (4096 as u16 /  256 as u16 / 4 as u16).to_be_bytes()[1],
+            0b11 => 1024,
             _ => 1,
         }
     }