src/emulator.rs

@@ -305,6 +305,10 @@ impl Emulator {
     }
 
     fn start_debugging(&mut self, sim_id: SimId, sender: DebugSender) {
+        if self.sim_state[sim_id.to_index()].load(Ordering::Acquire) != SimState::Ready {
+            // Can't debug unless a game is connected
+            return;
+        }
         let debug = DebugInfo {
             sender,
             stop_reason: Some(DebugStopReason::Trapped),

src/gdbserver.rs

@@ -9,7 +9,7 @@ use std::{
 use tokio::{
     io::{AsyncWriteExt as _, BufReader},
     net::{TcpListener, TcpStream},
-    select,
+    pin, select,
     sync::{mpsc, oneshot},
 };
 use tracing::{debug, enabled, error, info, Level};
@@ -57,8 +57,9 @@ impl GdbServer {
                 .unwrap()
                 .block_on(async move {
                     select! {
-                        _ = run_server(sim_id, client, port, &status) => {}
+                        _ = run_server(sim_id, client.clone(), port, &status) => {}
                         _ = rx => {
+                            client.send_command(EmulatorCommand::StopDebugging(sim_id));
                             *status.lock().unwrap() = GdbServerStatus::Stopped;
                         }
                     }
@@ -73,19 +74,46 @@ impl GdbServer {
     }
 }
 
+impl Drop for GdbServer {
+    fn drop(&mut self) {
+        self.stop();
+    }
+}
+
 async fn run_server(
     sim_id: SimId,
     client: EmulatorClient,
     port: u16,
     status: &Mutex<GdbServerStatus>,
 ) {
+    let (debug_sink, mut debug_source) = mpsc::unbounded_channel();
+    client.send_command(EmulatorCommand::StartDebugging(sim_id, debug_sink));
+
     info!("Connecting to debugger on port {port}...");
-    let Some(stream) = try_connect(port, status).await else {
-        return;
+    let connect_future = try_connect(port, status);
+    pin!(connect_future);
+
+    let stream = loop {
+        select! {
+            stream = &mut connect_future => {
+                if let Some(stream) = stream {
+                    break stream;
+                } else {
+                    return;
+                }
+            }
+            event = debug_source.recv() => {
+                if event.is_none() {
+                    // The sim has stopped (or was never started)
+                    *status.lock().unwrap() = GdbServerStatus::Stopped;
+                    return;
+                }
+            }
+        }
     };
     info!("Connected!");
     let mut connection = GdbConnection::new(sim_id, client);
-    match connection.run(stream).await {
+    match connection.run(stream, debug_source).await {
         Ok(()) => {
             info!("Finished debugging.");
             *status.lock().unwrap() = GdbServerStatus::Stopped;
@@ -154,12 +182,13 @@ impl GdbConnection {
             memory_buf: None,
         }
     }
-    async fn run(&mut self, stream: TcpStream) -> Result<()> {
-        let (debug_sink, mut debug_source) = mpsc::unbounded_channel();
+    async fn run(
+        &mut self,
+        stream: TcpStream,
+        mut debug_source: mpsc::UnboundedReceiver<DebugEvent>,
+    ) -> Result<()> {
         let (rx, mut tx) = stream.into_split();
         let mut request_source = RequestSource::new(BufReader::new(rx));
-        self.client
-            .send_command(EmulatorCommand::StartDebugging(self.sim_id, debug_sink));
         loop {
             let response = select! {
                 maybe_event = debug_source.recv() => {

src/main.rs

@@ -3,7 +3,7 @@
 
 use std::{path::PathBuf, process, time::SystemTime};
 
-use anyhow::Result;
+use anyhow::{bail, Result};
 use app::Application;
 use clap::Parser;
 use emulator::EmulatorBuilder;
@@ -95,10 +95,13 @@ fn main() -> Result<()> {
     let args = Args::parse();
 
     let (mut builder, client) = EmulatorBuilder::new();
-    if let Some(path) = args.rom {
-        builder = builder.with_rom(&path);
+    if let Some(path) = &args.rom {
+        builder = builder.with_rom(path);
     }
     if args.debug_port.is_some() {
+        if args.rom.is_none() {
+            bail!("to start debugging, please select a game.");
+        }
         builder = builder.start_paused(true);
     }
 

src/window/gdb.rs

@@ -3,7 +3,7 @@ use winit::event_loop::EventLoopProxy;
 
 use crate::{
     app::UserEvent,
-    emulator::{EmulatorClient, SimId},
+    emulator::{EmulatorClient, SimId, SimState},
     gdbserver::{GdbServer, GdbServerStatus},
 };
 
@@ -11,6 +11,7 @@ use super::AppWindow;
 
 pub struct GdbServerWindow {
     sim_id: SimId,
+    client: EmulatorClient,
     port_str: String,
     connected: bool,
     quit_on_disconnect: bool,
@@ -22,6 +23,7 @@ impl GdbServerWindow {
     pub fn new(sim_id: SimId, client: EmulatorClient, proxy: EventLoopProxy<UserEvent>) -> Self {
         Self {
             sim_id,
+            client: client.clone(),
             port_str: (8080 + sim_id.to_index()).to_string(),
             connected: false,
             quit_on_disconnect: false,
@@ -78,7 +80,9 @@ impl AppWindow for GdbServerWindow {
                     self.connected = false;
                 }
                 let start_button = Button::new("Start");
-                if ui.add_enabled(port_num.is_some(), start_button).clicked() {
+                let can_start =
+                    port_num.is_some() && self.client.sim_state(self.sim_id) == SimState::Ready;
+                if ui.add_enabled(can_start, start_button).clicked() {
                     let port = port_num.unwrap();
                     self.server.start(port);
                     self.connected = true;