chore: imrpove private and public APIs

Cargo.lock

@@ -810,6 +810,7 @@ dependencies = [
  "pollster",
  "rodio",
  "rtrb",
+ "thiserror",
  "tracing",
  "tracing-subscriber",
  "wgpu",

Cargo.toml

@@ -22,6 +22,7 @@ rtrb = "0.2"
 directories-next = "2.0"
 tracing = "0.1"
 tracing-subscriber = { version = "0.3", features = ["std", "env-filter"] }
+thiserror = "1.0.30"
 
 [profile.release]
 debug = true

src/apu.rs

@@ -30,7 +30,7 @@ pub struct Apu {
     fs: FrameSequencer,
     div_prev: Option<u16>,
 
-    prod: Option<SampleProducer<f32>>,
+    pub(crate) prod: Option<SampleProducer<f32>>,
     sample_counter: u64,
 
     cap: f32,
@@ -188,10 +188,6 @@ impl Apu {
         }
     }
 
-    pub fn attach_producer(&mut self, prod: SampleProducer<f32>) {
-        self.prod = Some(prod);
-    }
-
     fn reset(&mut self) {
         self.ch1.sweep = Default::default();
         self.ch1.duty = Default::default();

src/bus.rs

@@ -51,14 +51,6 @@ impl Bus {
         }
     }
 
-    pub(crate) fn load_cart(&mut self, rom: Vec<u8>) {
-        self.cart = Some(Cartridge::new(rom));
-    }
-
-    pub(crate) fn cart_title(&self) -> Option<&str> {
-        self.cart.as_ref()?.title()
-    }
-
     #[allow(dead_code)]
     pub(crate) fn boot_mapped(&self) -> bool {
         self.boot.is_some()

src/cartridge.rs

@@ -13,7 +13,7 @@ const ROM_TITLE_MAX_SIZE: usize = 16;
 #[derive(Debug, Default)]
 pub(crate) struct Cartridge {
     memory: Vec<u8>,
-    title: Option<String>,
+    pub(crate) title: Option<String>,
     mbc: Box<dyn MBCIo>,
 }
 
@@ -80,10 +80,6 @@ impl Cartridge {
         }
     }
 
-    pub(crate) fn title(&self) -> Option<&str> {
-        self.title.as_deref()
-    }
-
     fn detect_ram_info(memory: &[u8]) -> RamSize {
         let id = memory[RAM_SIZE_ADDRESS];
         id.into()

src/emu.rs

@@ -1,5 +1,6 @@
 use crate::apu::gen::SampleProducer;
 use crate::bus::BOOT_SIZE;
+use crate::cartridge::Cartridge;
 use crate::cpu::Cpu;
 use crate::{Cycle, GB_HEIGHT, GB_WIDTH};
 use clap::crate_name;
@@ -8,7 +9,9 @@ use std::fs::File;
 use std::io::{Read, Write};
 use std::path::{Path, PathBuf};
 use std::time::Duration;
+use thiserror::Error;
 use winit::event::KeyboardInput;
+use winit::event_loop::ControlFlow;
 
 pub const SM83_CYCLE_TIME: Duration = Duration::from_nanos(1_000_000_000 / SM83_CLOCK_SPEED);
 pub const CYCLES_IN_FRAME: Cycle = 456 * 154; // 456 Cycles times 154 scanlines
@@ -30,6 +33,12 @@ pub fn run_frame(cpu: &mut Cpu, gamepad: &mut Gilrs, key: KeyboardInput) -> Cycl
     elapsed
 }
 
+pub fn save_and_exit(cpu: &Cpu, control_flow: &mut ControlFlow) {
+    write_save(cpu);
+    *control_flow = ControlFlow::Exit;
+}
+
+#[inline]
 pub fn pixel_buf(cpu: &Cpu) -> &[u8; GB_HEIGHT * GB_WIDTH * 4] {
     cpu.bus.ppu.frame_buf.as_ref()
 }
@@ -39,50 +48,82 @@ pub fn from_boot_rom<P: AsRef<Path>>(path: P) -> std::io::Result<Cpu> {
 }
 
 pub fn read_game_rom<P: AsRef<Path>>(cpu: &mut Cpu, path: P) -> std::io::Result<()> {
-    Ok(cpu.bus.load_cart(std::fs::read(path.as_ref())?))
+    cpu.bus.cart = Some(Cartridge::new(std::fs::read(path.as_ref())?));
+    Ok(())
 }
 
-pub fn set_audio_producer(cpu: &mut Cpu, producer: SampleProducer<f32>) {
-    cpu.bus.apu.attach_producer(producer);
+pub fn set_audio_prod(cpu: &mut Cpu, prod: SampleProducer<f32>) {
+    cpu.bus.apu.prod = Some(prod);
 }
 
 pub fn rom_title(cpu: &Cpu) -> &str {
-    cpu.bus.cart_title().unwrap_or(DEFAULT_TITLE)
+    cpu.bus
+        .cart
+        .as_ref()
+        .map(|c| c.title.as_deref())
+        .flatten()
+        .unwrap_or(DEFAULT_TITLE)
 }
 
-pub fn write_save(cpu: &Cpu) -> std::io::Result<()> {
-    if let Some(ext_ram) = cpu.bus.cart.as_ref().map(|c| c.ext_ram()).flatten() {
-        if let Some(title) = cpu.bus.cart_title() {
+pub fn write_save(cpu: &Cpu) {
+    match cpu.bus.cart.as_ref() {
+        Some(cart) => match write_save_to_file(cart) {
+            Ok(path) => tracing::info!("Wrote to save at {:?}", path),
+            Err(err @ SaveError::NotApplicable) => tracing::warn!("Unable to Save: {:?}", err),
+            Err(SaveError::Io(err)) => tracing::error!("{:?}", err),
+        },
+        None => tracing::error!("No cartridge is currently present"),
+    }
+}
+
+pub fn load_save(cpu: &mut Cpu) {
+    match cpu.bus.cart.as_mut() {
+        Some(cart) => match read_save_from_file(cart) {
+            Ok(path) => tracing::info!("Loaded save from {:?}", path),
+            Err(err @ SaveError::NotApplicable) => tracing::warn!("Unable to load save: {:?}", err),
+            Err(SaveError::Io(err)) => match err.kind() {
+                std::io::ErrorKind::NotFound => tracing::warn!("Save not found"),
+                _ => tracing::error!("{:?}", err),
+            },
+        },
+        None => tracing::error!("No cartridge is currently present"),
+    }
+}
+
+fn write_save_to_file(cart: &Cartridge) -> Result<PathBuf, SaveError> {
+    match cart.title.as_ref().zip(cart.ext_ram()) {
+        Some((title, ram)) => {
             let mut save_path = data_path().unwrap_or_else(|| PathBuf::from("."));
             save_path.push(title);
             save_path.set_extension("sav");
 
-            let mut file = File::create(save_path)?;
-            file.write_all(ext_ram)?;
+            let mut file = File::create(&save_path)?;
+            file.write_all(ram)?;
+            Ok(save_path)
         }
+        None => Err(SaveError::NotApplicable),
     }
-
-    Ok(())
 }
 
-pub fn load_save(cpu: &mut Cpu) -> std::io::Result<()> {
-    if let Some(cart) = &mut cpu.bus.cart {
-        if let Some(title) = cart.title() {
+fn read_save_from_file(cart: &mut Cartridge) -> Result<PathBuf, SaveError> {
+    match cart.title.as_deref() {
+        Some(title) => {
             let mut save_path = data_path().unwrap_or_else(|| PathBuf::from("."));
             save_path.push(title);
             save_path.set_extension("sav");
 
-            if let Ok(mut file) = File::open(&save_path) {
-                tracing::info!("Load {:?}", save_path);
+            let mut file = File::open(&save_path)?;
+            let mut memory = Vec::new();
+            file.read_to_end(&mut memory)?;
 
-                let mut memory = Vec::new();
-                file.read_to_end(&mut memory)?;
-                cart.write_ext_ram(memory);
-            }
+            // FIXME: We call this whether we can write to Ext RAM or not.
+            // We should add a check that ensures that by this point we know whether
+            // the cartridge has external RAM or not.
+            cart.write_ext_ram(memory);
+            Ok(save_path)
         }
+        None => Err(SaveError::NotApplicable),
     }
-
-    Ok(())
 }
 
 fn read_boot<P: AsRef<Path>>(path: P) -> std::io::Result<[u8; BOOT_SIZE]> {
@@ -103,3 +144,11 @@ fn data_path() -> Option<PathBuf> {
         None => None,
     }
 }
+
+#[derive(Debug, Error)]
+pub enum SaveError {
+    #[error("cartridge lacks title and/or external ram")]
+    NotApplicable,
+    #[error(transparent)]
+    Io(#[from] std::io::Error),
+}

src/main.rs

@@ -8,7 +8,7 @@ use gilrs::Gilrs;
 use rodio::{OutputStream, Sink};
 use tracing_subscriber::EnvFilter;
 use winit::event::{Event, WindowEvent};
-use winit::event_loop::{ControlFlow, EventLoop};
+use winit::event_loop::EventLoop;
 
 const AUDIO_ENABLED: bool = true;
 
@@ -86,9 +86,8 @@ fn main() {
         emu::read_game_rom(&mut cpu, path).expect("read game rom from path");
     }
 
-    // Load Save File if it exists
-    // FIXME: Shouldn't the API be better than this?
-    emu::load_save(&mut cpu).expect("Load save if exists");
+    emu::load_save(&mut cpu);
+
     let rom_title = emu::rom_title(&cpu).to_string();
 
     tracing::info!("Initialize Gamepad");
@@ -106,7 +105,7 @@ fn main() {
             s
         };
 
-        emu::set_audio_producer(&mut cpu, prod);
+        emu::set_audio_prod(&mut cpu, prod);
 
         tracing::info!("Spawn Audio Thread");
         std::thread::spawn(move || {
@@ -127,7 +126,7 @@ fn main() {
         match event {
             Event::MainEventsCleared => {
                 if app.quit {
-                    *control_flow = ControlFlow::Exit;
+                    emu::save_and_exit(&cpu, control_flow);
                 }
 
                 gb::emu::run_frame(&mut cpu, &mut gamepad, last_key);
@@ -187,7 +186,7 @@ fn main() {
                     surface.configure(&device, &config);
                 }
                 WindowEvent::CloseRequested => {
-                    *control_flow = ControlFlow::Exit;
+                    emu::save_and_exit(&cpu, control_flow);
                 }
                 WindowEvent::KeyboardInput { input, .. } => last_key = input,
                 _ => {}