Implement stepping

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 {