From 3dce1726a8c9723516c44e35cc463d9b8cd210dc Mon Sep 17 00:00:00 2001
From: Isaac Marovitz <isaacryu@icloud.com>
Date: Thu, 14 Dec 2023 00:38:43 -0500
Subject: [PATCH] Make boot rom optional

---
 src/cpu.rs       |  4 ++--
 src/main.rs      | 21 ++++++++++++++-------
 src/registers.rs |  6 +++---
 3 files changed, 19 insertions(+), 12 deletions(-)

diff --git a/src/cpu.rs b/src/cpu.rs
index 3d5a9a6..94a6db7 100644
--- a/src/cpu.rs
+++ b/src/cpu.rs
@@ -11,9 +11,9 @@ pub struct CPU {
 }
 
 impl CPU {
-    pub fn new(mode: GBMode, rom: Vec<u8>) -> Self {
+    pub fn new(mode: GBMode, rom: Vec<u8>, booting: bool) -> Self {
         Self {
-            reg: Registers::new(mode),
+            reg: Registers::new(mode, booting),
             mem: MMU::new(mode, rom),
             halted: false,
             ime: false
diff --git a/src/main.rs b/src/main.rs
index a12ef32..967f005 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -29,22 +29,29 @@ pub const STEP_CYCLES: u32 = (STEP_TIME as f64 / (1000_f64 / CLOCK_FREQUENCY as
 #[derive(Parser)]
 struct Args {
     rom_path: String,
-    boot_rom: String
+    boot_rom: Option<String>
 }
 
 #[tokio::main]
 async fn main() -> Result<(), impl std::error::Error> {
     let args = Args::parse();
     let mut file = File::open(args.rom_path).expect("No ROM found!");
-    let mut boot = File::open(args.boot_rom).expect("No Boot ROM found!");
     let mut buffer = Vec::new();
-    let mut boot_rom = Vec::new();
+    let mut booting = true;
 
     file.read_to_end(&mut buffer).expect("Failed to read ROM!");
-    boot.read_to_end(&mut boot_rom).expect("Failed to read Boot ROM!");
 
-    // Display Nintendo Logo
-    buffer[0..=0x00FF].copy_from_slice(boot_rom.as_slice());
+    match args.boot_rom {
+        Some(path) => {
+            let mut boot_rom = Vec::new();
+            let mut boot = File::open(path).expect("No Boot ROM found!");
+            boot.read_to_end(&mut boot_rom).expect("Failed to read Boot ROM!");
+
+            // Display Nintendo Logo
+            buffer[0..=0x00FF].copy_from_slice(boot_rom.as_slice());
+        },
+        None => booting = false
+    }
 
     // Get game name
     let name_data = &buffer[0x0134..=0x0143];
@@ -73,7 +80,7 @@ async fn main() -> Result<(), impl std::error::Error> {
         let context = Arc::clone(&context);
         // Start CPU
         tokio::spawn(async move {
-            let mut cpu = CPU::new(GBMode::Classic, buffer);
+            let mut cpu = CPU::new(GBMode::Classic, buffer, booting);
             let mut step_cycles = 0;
             let mut step_zero = Instant::now();
 
diff --git a/src/registers.rs b/src/registers.rs
index 1f128ab..78a0304 100644
--- a/src/registers.rs
+++ b/src/registers.rs
@@ -81,7 +81,7 @@ impl Registers {
         }
     }
 
-    pub fn new(mode: GBMode) -> Registers {
+    pub fn new(mode: GBMode, booting: bool) -> Registers {
         match mode {
             GBMode::Classic => {
                 Registers {
@@ -93,7 +93,7 @@ impl Registers {
                     e: 0xD8,
                     h: 0x01,
                     l: 0x4D,
-                    pc: 0x0000,
+                    pc: if booting { 0x0000 } else { 0x0100 },
                     sp: 0xFFFE
                 }
             },
@@ -107,7 +107,7 @@ impl Registers {
                     e: 0x56,
                     h: 0x00,
                     l: 0x0D,
-                    pc: 0x0100,
+                    pc: if booting { 0x0000 } else { 0x0100 },
                     sp: 0xFFFE
                 }
             }