src/emulator.rs

@@ -315,7 +315,7 @@ impl Emulator {
 
     fn stop_debugging(&mut self, sim_id: SimId) {
         if let Some(sim) = self.sims.get_mut(sim_id.to_index()) {
-            sim.clear_breakpoints();
+            sim.clear_debug_state();
         }
         self.debuggers.remove(&sim_id);
         if self.debuggers.is_empty() {
@@ -345,12 +345,21 @@ impl Emulator {
         }
     }
 
-    fn debug_continue(&mut self, sim_id: SimId) {
+    fn debug_continue(&mut self, sim_id: SimId) -> bool {
         let Some(debugger) = self.debuggers.get_mut(&sim_id) else {
             self.stop_debugging(sim_id);
-            return;
+            return false;
         };
         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 {
+                return;
+            };
+            sim.step();
+        }
     }
 
     pub fn run(&mut self) {
@@ -412,6 +421,7 @@ impl Emulator {
                 };
                 if let Some(reason) = sim.stop_reason() {
                     let stop_reason = match reason {
+                        StopReason::Stepped => DebugStopReason::Trace,
                         StopReason::Breakpoint => DebugStopReason::Breakpoint,
                     };
                     self.debug_stop(sim_id, stop_reason);
@@ -509,6 +519,9 @@ impl Emulator {
             EmulatorCommand::DebugContinue(sim_id) => {
                 self.debug_continue(sim_id);
             }
+            EmulatorCommand::DebugStep(sim_id) => {
+                self.debug_step(sim_id);
+            }
             EmulatorCommand::ReadRegister(sim_id, register, done) => {
                 let Some(sim) = self.sims.get_mut(sim_id.to_index()) else {
                     return;
@@ -596,6 +609,7 @@ pub enum EmulatorCommand {
     StopDebugging(SimId),
     DebugInterrupt(SimId),
     DebugContinue(SimId),
+    DebugStep(SimId),
     ReadRegister(SimId, VBRegister, oneshot::Sender<u32>),
     ReadMemory(SimId, Range<u32>, Vec<u8>, oneshot::Sender<Vec<u8>>),
     AddBreakpoint(SimId, u32),
@@ -628,6 +642,8 @@ type DebugSender = tokio::sync::mpsc::UnboundedSender<DebugEvent>;
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub enum DebugStopReason {
+    // We are stepping
+    Trace,
     // We hit a breakpoint
     Breakpoint,
     // The debugger told us to pause

src/emulator/shrooms_vb_core.rs

@@ -147,12 +147,18 @@ extern "C" fn on_execute(sim: *mut VB, address: u32, _code: *const u16, _length:
     // There is no way for the userdata to be null or otherwise invalid.
     let data: &mut VBState = unsafe { &mut *vb_get_user_data(sim).cast() };
 
-    if data.breakpoints.binary_search(&address).is_err() {
-        return 0;
+    let mut stopped = 0;
+    if data.step_from.is_some_and(|s| s != address) {
+        data.step_from = None;
+        data.stop_reason = Some(StopReason::Stepped);
+        stopped = 1;
+    }
+    if data.breakpoints.binary_search(&address).is_ok() {
+        data.stop_reason = Some(StopReason::Breakpoint);
+        stopped = 1;
     }
 
-    data.stop_reason = Some(StopReason::Breakpoint);
-    1
+    stopped
 }
 
 const AUDIO_CAPACITY_SAMPLES: usize = 834 * 4;
@@ -162,6 +168,7 @@ pub const EXPECTED_FRAME_SIZE: usize = 834 * 2;
 struct VBState {
     frame_seen: bool,
     stop_reason: Option<StopReason>,
+    step_from: Option<u32>,
     breakpoints: Vec<u32>,
 }
 
@@ -172,6 +179,7 @@ pub struct Sim {
 
 pub enum StopReason {
     Breakpoint,
+    Stepped,
 }
 
 impl Sim {
@@ -183,12 +191,14 @@ impl Sim {
         let sim: *mut VB = Box::into_raw(memory.into_boxed_slice()).cast();
         unsafe { vb_init(sim) };
         unsafe { vb_set_option(sim, VBOption::PseudoHalt, 1) };
+        unsafe { vb_set_keys(sim, VBKey::SGN.bits()) };
         unsafe { vb_reset(sim) };
 
         // set up userdata
         let state = VBState {
             frame_seen: false,
             stop_reason: None,
+            step_from: None,
             breakpoints: vec![],
         };
         unsafe { vb_set_user_data(sim, Box::into_raw(Box::new(state)).cast()) };
@@ -361,21 +371,35 @@ impl Sim {
         let data = self.get_state();
         if let Ok(index) = data.breakpoints.binary_search(&address) {
             data.breakpoints.remove(index);
-            if data.breakpoints.is_empty() {
+            if data.step_from.is_none() && data.breakpoints.is_empty() {
                 unsafe { vb_set_execute_callback(self.sim, None) };
             }
         }
     }
 
-    pub fn clear_breakpoints(&mut self) {
+    pub fn step(&mut self) {
+        let current_pc = unsafe { vb_get_program_counter(self.sim) };
         let data = self.get_state();
+        data.step_from = Some(current_pc);
+        unsafe {
+            vb_set_execute_callback(self.sim, Some(on_execute));
+        }
+    }
+
+    pub fn clear_debug_state(&mut self) {
+        let data = self.get_state();
+        data.step_from = None;
         data.breakpoints.clear();
         unsafe { vb_set_execute_callback(self.sim, None) };
     }
 
     pub fn stop_reason(&mut self) -> Option<StopReason> {
         let data = self.get_state();
-        data.stop_reason.take()
+        let reason = data.stop_reason.take();
+        if data.step_from.is_none() && data.breakpoints.is_empty() {
+            unsafe { vb_set_execute_callback(self.sim, None) };
+        }
+        reason
     }
 
     fn get_state(&mut self) -> &mut VBState {

src/gdbserver.rs

@@ -258,6 +258,12 @@ impl GdbConnection {
             self.stop_reason = None;
             // Don't send a response until we hit a breakpoint or get interrupted
             return Ok(None);
+        } else if req.match_str("s") {
+            self.client
+                .send_command(EmulatorCommand::DebugStep(self.sim_id));
+            self.stop_reason = None;
+            // Don't send a response until we hit a breakpoint or get interrupted
+            return Ok(None);
         } else if req.match_str("p") {
             let mut read_register = || {
                 let register_index = req.match_hex::<usize>()?;
@@ -348,7 +354,8 @@ impl Drop for GdbConnection {
 
 fn debug_stop_reason_string(reason: Option<DebugStopReason>) -> &'static str {
     match reason {
-        Some(DebugStopReason::Breakpoint) => "T05;thread:p1.t1;threads;p1.t1;reason:breakpoint",
+        Some(DebugStopReason::Trace) => "T05;thread:p1.t1;threads:p1.t1;reason:trace;",
+        Some(DebugStopReason::Breakpoint) => "T05;thread:p1.t1;threads:p1.t1;reason:breakpoint;",
         Some(DebugStopReason::Trapped) => "T05;swbreak;thread:p1.t1;threads:p1.t1;reason:trap;",
         None => "T00;thread:p1.t1;threads:p1.t1;",
     }