fix mbc1 rom addressing and support 0x9000 addressing for rendering

src/cartridge/mbc1.rs

@@ -21,13 +21,15 @@ impl MBC for MBC1 {
         match addr {
             0x0..=0x3FFF => self.rom[addr as usize],
             0x4000..=0x7FFF => {
-                let bank_number: u16 = if self.rom_bank == 0 {
+                let bank: u16 = if self.rom_bank == 0 {
                     1
                 } else {
                     self.rom_bank as u16
                 };
 
-                return self.rom[(bank_number * 0x4000 | addr) as usize];
+                let idx = bank * 0x4000 | (addr & 0x3FFF);
+
+                return self.rom[idx as usize];
             }
             0xA000..=0xBFFF => self.ram[addr as usize - 0xA000],
             _ => {

src/gameboy/debugger.rs

@@ -45,6 +45,8 @@ impl GameBoy {
 
                 "d" | "debug" => println!("{:#?}", &self),
 
+                "ppu" => println!("{:#?}", &self.mmu.ppu),
+
                 "f" | "flush" => {
                     //pub fn flush(&self) {
                     //    self.tx.send(self.clone()).unwrap();

src/mmu/mod.rs

@@ -83,8 +83,6 @@ impl MMU {
 
             // Interrupt enable
             0xFFFF => self.ie,
-
-            _ => unreachable!(),
         }
     }
 

src/mmu/ppu.rs

@@ -165,8 +165,14 @@ impl PPU {
         return result;
     }
 
-    pub fn get_tile(&self, tile_index: usize) -> Tile {
-        let start_address = 0x8000 + (tile_index * 16) as u16;
+    pub fn get_tile(&self, tile_index: u8) -> Tile {
+        let start_address = if self.lcdc & 0x10 > 0 {
+            0x8000 + ((tile_index as u16) * 16) as u16
+        } else {
+            let offset = ((tile_index as i8) as i16) * 16;
+            0x9000_u16.wrapping_add(offset as u16)
+        };
+
         let mut ret = [[0u8; 8]; 8];
 
         for i in 0..8 {

src/renderer.rs

@@ -77,7 +77,7 @@ pub fn window_loop(rx: Receiver<PPU>, tx: Sender<(bool, Key)>, game_title: &Stri
                 let tile_index = ppu.get_byte(0x9800 + i);
 
                 render_tile(
-                    ppu.get_tile(tile_index as usize),
+                    ppu.get_tile(tile_index),
                     &mut buffer,
                     (i as usize * 8) % 256,
                     ((i as usize / 32) * 8).wrapping_sub(ppu.scy as usize),
@@ -94,7 +94,7 @@ pub fn window_loop(rx: Receiver<PPU>, tx: Sender<(bool, Key)>, game_title: &Stri
                 //let flags = ppu.get_byte(start_position + 3);
 
                 render_tile(
-                    ppu.get_tile(tile_index as usize),
+                    ppu.get_tile(tile_index),
                     &mut buffer,
                     x_position.wrapping_sub(8) as usize,
                     y_position.wrapping_sub(16) as usize,