Add MBC2 implementation

src/cartridge.rs

@@ -27,7 +27,7 @@ impl Cartridge {
         let mbc_type: MemoryBankControllerType = match rom[0x0147] {
             0x00 | 0x08 ... 0x09 => MemoryBankControllerType::None,
             0x01 ... 0x03 => MemoryBankControllerType::MBC1,
-            // 0x05 ... 0x06 => MemoryBankControllerType::MBC2,
+            0x05 ... 0x06 => MemoryBankControllerType::MBC2,
             0x0F ... 0x13 => MemoryBankControllerType::MBC3,
             // 0xFF => MemoryBankControllerType::HuC1,
             _ => panic!("Unsupported MBC type: {:02X}", rom[0x0147]),
@@ -65,6 +65,7 @@ impl Cartridge {
         let mbc: Box<super::mbc::mbc::MBC> = match mbc_type {
             MemoryBankControllerType::None => Box::new(super::mbc::mbc::NoMBC::new(rom, ram)),
             MemoryBankControllerType::MBC1 => Box::new(super::mbc::mbc1::MBC1::new(rom, ram)),
+            MemoryBankControllerType::MBC2 => Box::new(super::mbc::mbc2::MBC2::new(rom, ram)),
             MemoryBankControllerType::MBC3 => Box::new(super::mbc::mbc3::MBC3::new(rom, ram)),
             _ => panic!("{:?} not implemented", mbc_type),
         };

src/mbc/mbc1.rs

@@ -58,7 +58,7 @@ impl MBC for MBC1 {
                 self.ram[self.active_ram_bank() as usize * 0x2000 + addr as usize]
             }
             _ => {
-                panic!("Cartride: Unable to read from {:04X}", addr);
+                panic!("MBC1: Unable to read from {:04X}", addr);
             }
         }
     }
@@ -73,12 +73,12 @@ impl MBC for MBC1 {
                 }
             },
             0x2000 ... 0x3FFF => {
-                println!("Selecting bank {:02X}", self.rom_bank_no);
                 if val != 0 {
                     self.rom_bank_no = val & 0x1F;
                 } else {
                     self.rom_bank_no = 1; // 0x00 -> 0x01, 0x20 -> 0x21 etc
                 }
+                println!("MBC1: Selecting bank {:02X}", self.rom_bank_no);
             }
             0x4000 ... 0x5FFF => {
                 // Upper ROM bank / RAM bank select

src/mbc/mbc2.rs

@@ -0,0 +1,70 @@
+use super::mbc::MBC;
+
+pub struct MBC2 {
+    rom: Box<[u8]>,
+    ram: Box<[u8]>,
+    rom_bank_no: u8,
+    ram_enable: bool,
+}
+
+impl MBC2 {
+    pub fn new(rom: Box<[u8]>, ram: Box<[u8]>) -> MBC2 {
+        MBC2 {
+            rom: rom,
+            ram: ram,
+            rom_bank_no: 0,
+            ram_enable: false,
+        }
+    }
+
+    fn active_rom_bank(&self) -> u8 {
+        self.rom_bank_no
+    }
+ }
+
+impl MBC for MBC2 {
+    fn read_byte(&self, addr: u16) -> u8 {
+        match addr {
+            0x0000 ... 0x3FFF => self.rom[addr as usize],
+            0x4000 ... 0x7FFF => {
+                let addr = addr - 0x4000;
+                let abs_addr: usize = addr as usize + self.active_rom_bank() as usize * 0x4000;
+                let val: u8 = self.rom[abs_addr];
+                val
+            },
+            0xA000 ... 0xA1FF => {
+                let addr = addr - 0xA000;
+                self.ram[addr as usize] & 0x0F
+            }
+            _ => {
+                panic!("MBC2: Unable to read from {:04X}", addr);
+            }
+        }
+    }
+
+    fn write_byte(&mut self, addr: u16, val: u8) {
+        match addr {
+            0x0000 ... 0x1FFF => {
+                // To enable the ram, the LSB of the higher byte must be 0
+                if val & 0x0100 == 0 {
+                    match val {
+                        0x0A => self.ram_enable = true,
+                        0x00 => self.ram_enable = false,
+                        _ => println!("Unknown MBC2 value {:02X} for {:04X}", val, addr)
+                    }
+                } else {
+                    println!("MBC2: Write {:02X} to {:04X} has no effect", val, addr);
+                }
+            },
+            0x2000 ... 0x3FFF => {
+                if val & 0x0100 == 1 {
+                    self.rom_bank_no = val & 0x0F;
+                    println!("MBC2: Selecting bank {:02X}", self.rom_bank_no);
+                } else {
+                    println!("MBC2: Write {:02X} to {:04X} has no effect", val, addr);
+                }
+            }
+            _ => panic!("MBC2: Writing {:02X} to {:04X} not supported", val, addr),
+        }
+    }
+}

src/mbc/mod.rs

@@ -1,3 +1,4 @@
 pub mod mbc;
 pub mod mbc1;
+pub mod mbc2;
 pub mod mbc3;