Refactor MBCs

src/bus.rs

@@ -2,7 +2,7 @@ use std::ops::RangeInclusive;
 use crate::utils::{
     join_bytes
 };
-use crate::rom::ROM;
+use crate::rom::{ROM, load_rom};
 use crate::ppu::{
     PPU,
     DMA_ADDRESS,
@@ -27,7 +27,7 @@ pub const INTERRUPT_ENABLE_ADDRESS: u16 = 0xFFFF;
 pub const INTERRUPT_FLAG_ADDRESS: u16 = 0xFF0F;
 
 pub struct Bus {
-    game_rom: ROM,
+    game_rom: Box<dyn ROM>,
     data: [u8; 0x10000],
     pub ppu: PPU,
     pub joypad: Joypad,
@@ -41,7 +41,7 @@ impl Bus {
             println!("Please, specify a ROM file");
             std::process::exit(1);
         }
-        let game_rom = match ROM::load_file(&args[1]) {
+        let game_rom = match load_rom(&args[1]) {
             Ok(rom) => rom,
             Err(err) => {
                 println!("Could not read ROM: {}", err);

src/rom.rs

@@ -14,10 +14,17 @@ pub const RAM_SIZE_ADDRESS: u16 = 0x0149;
 pub const ROM_SIZE_ADDRESS: u16 = 0x0148;
 pub const DESTINATION_CODE_ADDRESS: u16 = 0x014A;
 
-#[derive(Debug)]
-enum Region {
-    Japanese,
-    NonJapanese,
+pub fn load_rom(filename: &str) -> std::io::Result<Box<dyn ROM>> {
+    let mut file = File::open(filename)?;
+    let mut data = vec![];
+    file.read_to_end(&mut data)?;
+    let info = ROMInfo::from_bytes(&data);
+
+    Ok(match info.mbc {
+        MBC::NoMBC => Box::new(NoMBC::new(data, info)),
+        MBC::MBC1 => Box::new(MBC1::new(data, info)),
+        _ => unimplemented!(),
+    })
 }
 
 #[derive(Debug, Copy, Clone)]
@@ -36,6 +43,12 @@ enum MBC {
     BandaiTIMA5,
 }
 
+#[derive(Debug)]
+enum Region {
+    Japanese,
+    NonJapanese,
+}
+
 #[derive(Debug)]
 enum BankingMode {
     Simple,
@@ -144,7 +157,41 @@ impl ROMInfo {
     }
 }
 
-pub struct ROM {
+pub trait ROM {
+    fn read(&self, address: u16) -> u8;
+    fn write(&mut self, address: u16, data: u8);
+}
+
+pub struct NoMBC {
+    data: Vec<u8>,
+    info: ROMInfo,
+}
+
+impl NoMBC {
+    pub fn new(data: Vec<u8>, info: ROMInfo) -> Self {
+        let rom = Self {
+            data,
+            info,
+        };
+        println!("MBC {:?}", rom.info.mbc);
+        println!("Region {:?}", rom.info.region);
+
+        rom
+    }
+}
+
+impl ROM for NoMBC {
+    fn read(&self, address: u16) -> u8 {
+        match self.data.get(address as usize) {
+            Some(byte) => *byte,
+            None => 0xFF,
+        }
+    }
+
+    fn write(&mut self, _address: u16, _data: u8) {}
+}
+
+pub struct MBC1 {
     data: Vec<u8>,
     info: ROMInfo,
     ram: Vec<u8>,
@@ -154,21 +201,15 @@ pub struct ROM {
     banking_mode: BankingMode,
 }
 
-impl ROM {
-    pub fn load_file(filename: &str) -> std::io::Result<Self> {
-        let mut file = File::open(filename)?;
-        let mut data = vec![];
-        file.read_to_end(&mut data)?;
-
-        let info = ROMInfo::from_bytes(&data);
+impl MBC1 {
+    fn new(data: Vec<u8>, info: ROMInfo) -> Self {
         println!("MBC {:?}", info.mbc);
+        println!("Region {:?}", info.region);
         println!("Has RAM {}", info.has_ram);
         println!("ROM banks {}", info.rom_banks);
         println!("RAM banks {}", info.ram_banks);
-        println!("Region {:?}", info.region);
         let ram = Vec::with_capacity(info.ram_size() as usize);
-
-        Ok(Self {
+        Self {
             data,
             info,
             ram,
@@ -176,18 +217,22 @@ impl ROM {
             ram_bank: 0,
             ram_enable: false,
             banking_mode: BankingMode::Simple,
-        })
+        }
     }
 
-    pub fn read(&self, address: u16) -> u8 {
-        match self.info.mbc {
-            MBC::NoMBC => {
-                return match self.data.get(address as usize) {
-                    Some(data) => *data,
-                    None => 0xFF,
-                };
-            },
-            MBC::MBC1 => {
+    fn switch_rom_bank(&mut self, bank: u16) {
+        self.rom_bank = bank;
+        if self.rom_bank > self.info.rom_banks.saturating_sub(1) {
+            self.rom_bank = self.info.rom_banks.saturating_sub(1);
+        }
+        if self.rom_bank == 0 {
+            self.rom_bank = 1;
+        }
+    }
+}
+
+impl ROM for MBC1 {
+    fn read(&self, address: u16) -> u8 {
         if BANK_ZERO.contains(&address) {
             return self.data[address as usize];
         } else if BANK_SWITCHABLE.contains(&address) {
@@ -202,15 +247,9 @@ impl ROM {
             };
         }
         unreachable!("ROM read: Address {} not valid", address);
-            },
-            _ => unimplemented!(),
-        }
     }
 
-    pub fn write(&mut self, address: u16, data: u8) {
-        match self.info.mbc {
-            MBC::NoMBC => {},
-            MBC::MBC1 => {
+    fn write(&mut self, address: u16, data: u8) {
         if address <= 0x1FFF { // RAM enable register
             if !self.info.has_ram {
                 return;
@@ -242,18 +281,5 @@ impl ROM {
             }
             self.switch_rom_bank(self.rom_bank + (data as u16 >> 5));
         }
-            },
-            _ => unimplemented!(),
-        }
-    }
-
-    pub fn switch_rom_bank(&mut self, bank: u16) {
-        self.rom_bank = bank;
-        if self.rom_bank > self.info.rom_banks.saturating_sub(1) {
-            self.rom_bank = self.info.rom_banks.saturating_sub(1);
-        }
-        if self.rom_bank == 0 {
-            self.rom_bank = 1;
-        }
     }
 }