From cedb13b522a3d439a652647e1afcfa946e8b35db Mon Sep 17 00:00:00 2001
From: Jonathan Balls <jonathanballs@protonmail.com>
Date: Tue, 10 Sep 2024 15:10:46 +0100
Subject: [PATCH] fix mbc1 rom addressing and support 0x9000 addressing for
 rendering

---
 src/cartridge/mbc1.rs   |  6 ++++--
 src/gameboy/debugger.rs |  2 ++
 src/mmu/mod.rs          |  2 --
 src/mmu/ppu.rs          | 10 ++++++++--
 src/renderer.rs         |  4 ++--
 5 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/src/cartridge/mbc1.rs b/src/cartridge/mbc1.rs
index 993f617..2d4887d 100644
--- a/src/cartridge/mbc1.rs
+++ b/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],
             _ => {
diff --git a/src/gameboy/debugger.rs b/src/gameboy/debugger.rs
index 94e3462..bd8cbf7 100644
--- a/src/gameboy/debugger.rs
+++ b/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();
diff --git a/src/mmu/mod.rs b/src/mmu/mod.rs
index 06ed72c..9fa5d14 100644
--- a/src/mmu/mod.rs
+++ b/src/mmu/mod.rs
@@ -83,8 +83,6 @@ impl MMU {
 
             // Interrupt enable
             0xFFFF => self.ie,
-
-            _ => unreachable!(),
         }
     }
 
diff --git a/src/mmu/ppu.rs b/src/mmu/ppu.rs
index 4ac2f82..4b84420 100644
--- a/src/mmu/ppu.rs
+++ b/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 {
diff --git a/src/renderer.rs b/src/renderer.rs
index bac7354..c85ca65 100644
--- a/src/renderer.rs
+++ b/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,