Reworked the sync function to reduce input-lag by one frame and changed confusing documentation.

Cargo.lock

@@ -539,7 +539,7 @@ checksum = "7da8b5736845d9f2fcb837ea5d9e2628564b3b043a70948a3f0b778838c5fb4f"
 
 [[package]]
 name = "svc16"
-version = "0.9.0"
+version = "0.9.1"
 dependencies = [
  "anyhow",
  "clap",

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "svc16"
-version = "0.9.0"
+version = "0.9.1"
 edition = "2021"
 authors = ["Jan Neuendorf"]
 description = "An emulator for a simple virtual computer"

specification/specification.typ

@@ -104,7 +104,7 @@ These keys are supposed to represent the face buttons of an NES controller.
 The codes for the *A* and *B* keys also represent the left and right mouse buttons.
 
 On synchronization the new input is loaded into the input-buffer.
-Before the first synchronization, both input codes are zero.
+Before the first synchronization, the input codes are not accessible.
 
 The *position code* is the index of the pixel, the mouse is currently on. 
 It follows the same convention as the screen index explained in @screen.

src/engine.rs

@@ -25,8 +25,8 @@ pub struct Engine {
     screen_buffer: [u16; MEMSIZE],
     utility_buffer: [u16; MEMSIZE],
     instruction_pointer: u16,
-    pos_code: u16,
-    key_code: u16,
+    pos_code_dest: u16,
+    key_code_dest: u16,
     sync_called: bool,
     expansion_triggered: bool,
 }
@@ -62,8 +62,8 @@ impl Engine {
             screen_buffer: [0; MEMSIZE],
             utility_buffer: [0; MEMSIZE],
             instruction_pointer: 0,
-            pos_code: 0,
-            key_code: 0,
+            pos_code_dest: 0,
+            key_code_dest: 0,
             sync_called: false,
             expansion_triggered: false,
         }
@@ -72,8 +72,8 @@ impl Engine {
         return self.sync_called;
     }
     pub fn set_input(&mut self, pos_code: u16, key_code: u16) {
-        self.pos_code = pos_code;
-        self.key_code = key_code;
+        self.set(self.pos_code_dest, pos_code);
+        self.set(self.key_code_dest, key_code);
     }
     pub fn perform_sync(
         &mut self,
@@ -81,9 +81,9 @@ impl Engine {
         key_code: u16,
         buffer: &mut [u16; MEMSIZE],
     ) -> () {
-        self.set_input(pos_code, key_code);
         self.sync_called = false;
         *buffer = self.screen_buffer;
+        self.set_input(pos_code, key_code);
         if self.expansion_triggered {
             self.expansion_triggered = false;
             self.utility_buffer = [0; MEMSIZE];
@@ -216,8 +216,8 @@ impl Engine {
             }
             SYNC => {
                 self.sync_called = true;
-                self.set(arg1, self.pos_code);
-                self.set(arg2, self.key_code);
+                self.pos_code_dest = arg1;
+                self.key_code_dest = arg2;
                 if arg3 > 0 {
                     self.expansion_triggered = true;
                 }

src/main.rs

@@ -87,7 +87,6 @@ async fn main() -> Result<()> {
                 }
                 ipf += 1;
             }
-
             #[cfg(feature = "gamepad")]
             while let Some(event) = gilrs.next_event() {
                 gilrs.update(&event);