Implement frame advance

src/emulator.rs

@@ -291,6 +291,26 @@ impl Emulator {
         );
     }
 
+    fn frame_advance(&mut self) {
+        if self
+            .state
+            .compare_exchange(
+                EmulatorState::Paused,
+                EmulatorState::Stepping,
+                Ordering::AcqRel,
+                Ordering::Acquire,
+            )
+            .is_err_and(|s| s == EmulatorState::Running)
+        {
+            let _ = self.state.compare_exchange(
+                EmulatorState::Running,
+                EmulatorState::Stepping,
+                Ordering::AcqRel,
+                Ordering::Relaxed,
+            );
+        }
+    }
+
     fn save_sram(&mut self, sim_id: SimId) -> Result<()> {
         let sim = self.sims.get_mut(sim_id.to_index());
         let cart = self.carts[sim_id.to_index()].as_mut();
@@ -366,6 +386,7 @@ impl Emulator {
         debugger.stop_reason = None;
         true
     }
+
     fn debug_step(&mut self, sim_id: SimId) {
         if self.debug_continue(sim_id) {
             let Some(sim) = self.sims.get_mut(sim_id.to_index()) else {
@@ -428,7 +449,7 @@ impl Emulator {
         // Don't emulate if the state is "paused", or if any sim is paused in the debugger
         let running = match state {
             EmulatorState::Paused => false,
-            EmulatorState::Running => true,
+            EmulatorState::Running | EmulatorState::Stepping => true,
             EmulatorState::Debugging => self.debuggers.values().all(|d| d.stop_reason.is_none()),
         };
         let p1_running = running && p1_state == SimState::Ready;
@@ -442,6 +463,10 @@ impl Emulator {
             self.sims[SimId::Player2.to_index()].emulate();
         }
 
+        if state == EmulatorState::Stepping {
+            self.state.store(EmulatorState::Paused, Ordering::Release);
+        }
+
         // Debug state
         if state == EmulatorState::Debugging {
             for sim_id in SimId::values() {
@@ -539,6 +564,9 @@ impl Emulator {
             EmulatorCommand::Resume => {
                 self.resume_sims();
             }
+            EmulatorCommand::FrameAdvance => {
+                self.frame_advance();
+            }
             EmulatorCommand::StartDebugging(sim_id, debugger) => {
                 self.start_debugging(sim_id, debugger);
             }
@@ -665,6 +693,7 @@ pub enum EmulatorCommand {
     StopSecondSim,
     Pause,
     Resume,
+    FrameAdvance,
     StartDebugging(SimId, DebugSender),
     StopDebugging(SimId),
     DebugInterrupt(SimId),
@@ -700,6 +729,7 @@ pub enum SimState {
 pub enum EmulatorState {
     Paused,
     Running,
+    Stepping,
     Debugging,
 }