more roms

gemma/src/chip8/computer.rs

@@ -96,6 +96,7 @@ impl Chip8Computer {
             Chip8CpuStates::WaitingForInstruction => {
                 self.sound_timer.tick();
                 self.delay_timer.tick();
+                self.video_memory.tick();
             }
             Chip8CpuStates::WaitingForKey => {
                 println!("waiting for a key press...");

gemma/src/chip8/instructions.rs

@@ -695,7 +695,7 @@ impl Chip8CpuInstructions {
 
                 debug!("PPOOSSTT -> CHIP8CPUINSTRUCTION:DRAWVXNIBBLE -> {}", input.video_memory.format_as_string());
 
-                let mut did_change: bool = false;
+                let mut did_change: bool = input.video_memory.has_frame_changed;
 
                 if did_change {
                     input.registers.poke(0xf, 1u8);

gemma/src/chip8/video.rs

@@ -42,22 +42,22 @@ impl Chip8Video {
     }
 
     pub fn poke(&mut self, address: u16, new_value: bool) -> Self {
-        trace!("OFFSET: {address} - POKING {new_value}");
+        // println!("OFFSET: {address} - POKING {new_value}");
+
+        // Loop the address
         let effective_address = if address >= 2048 {
             address - 2048
         } else {
             address
         };
-        let old_value = self.memory[effective_address as usize];
-        let value_to_poke = new_value ^ old_value;
 
-        if old_value != value_to_poke {
-            trace!("**VIDEO** TOGGLING");
-            self.has_frame_changed = true;
-        } else {
-            trace!("NOT TOGGLING");
-        }
-        self.memory[effective_address as usize] = new_value ^ old_value;
+        let old_value = self.memory[effective_address as usize];
+        let xored_value = new_value ^ old_value;       // XOR of the video
+        let value_changed = old_value != xored_value;  // From True to False is a change.
+
+        self.has_frame_changed = if xored_value && value_changed { false } else { true };
+
+        self.memory[effective_address as usize] = xored_value;
         self.to_owned()
     }
 
@@ -369,6 +369,7 @@ mod test {
     fn verify_change_registered() {
         let mut v = Chip8Video::default();
         v.poke(0x01, true);
+        v.poke(0x01, true);
         assert!(v.has_frame_changed);
 
         v.start_frame();
@@ -423,4 +424,34 @@ mod test {
         x = x.reset();
         assert_eq!(x.format_as_string(), read_test_result("test_reset_clears_video.asc"));
     }
+
+    #[test]
+    fn collision_test() {
+        // Setup: Set 0xFF to 0x00 with a new frame ready
+        // Action: Run Poke to the same area
+        // Test: Verify the 'changed' flag is tripped
+        let mut x = Chip8Video::default();
+        x.poke_byte(0x00, 0xff);
+        x.tick();
+        // set the cell thats already set...
+        x.poke(0x00, true);
+        // it becomes unset and theres a frame changed
+        assert_eq!(false, x.peek(0x00));
+
+        assert_eq!(true, x.has_frame_changed);
+    }
+
+    #[test]
+    fn collision_test2() {
+        let mut x = Chip8Video::default();
+        x.poke_byte(0x00, 0b11110000);
+        assert_eq!(true, x.has_frame_changed);
+        x.tick();
+        assert_eq!(false, x.has_frame_changed);
+        // clear the 'has changed' flag
+
+        // now set a no-collision value
+        x.poke_byte(0x00, 0b00001111);
+        assert_eq!(false, x.has_frame_changed);
+    }
 }