implement call & return instructions

src/display.rs

@@ -1,8 +1,8 @@
-use ratatui::DefaultTerminal;
-use ratatui::style::{Color, Style};
+use ratatui::style::Color;
 use ratatui::symbols::Marker;
-use ratatui::widgets::{Block, Borders, Paragraph};
 use ratatui::widgets::canvas::Canvas;
+use ratatui::widgets::{Block, Borders};
+use ratatui::DefaultTerminal;
 
 /// Represents the display's width in pixels.
 const DISPLAY_WIDTH: usize = 64;
@@ -19,8 +19,7 @@ pub trait Display {
 }
 
 /// Simple terminal display for the Chip8's emulator.
-pub struct TerminalDisplay {
-}
+pub struct TerminalDisplay {}
 
 impl TerminalDisplay {
     pub fn new() -> TerminalDisplay {
@@ -52,13 +51,13 @@ impl Display for TerminalDisplay {
 
 /// Ratatui based TUI display.
 pub struct RatatuiDisplay {
-    terminal: DefaultTerminal
+    terminal: DefaultTerminal,
 }
 
 impl RatatuiDisplay {
     pub fn new() -> RatatuiDisplay {
         RatatuiDisplay {
-            terminal:  ratatui::init()
+            terminal: ratatui::init(),
         }
     }
 }
@@ -69,9 +68,14 @@ impl Display for RatatuiDisplay {
     }
 
     fn render(&mut self, display_data: &[bool; DISPLAY_WIDTH * DISPLAY_HEIGHT]) {
-        self.terminal.draw(|frame| {
+        self.terminal
+            .draw(|frame| {
                 let canvas = Canvas::default()
-                .block(Block::default().title("Chip8 Emulator by nuculabs.dev").borders(Borders::ALL))
+                    .block(
+                        Block::default()
+                            .title("Chip8 Emulator by nuculabs.dev")
+                            .borders(Borders::ALL),
+                    )
                     .marker(Marker::Bar)
                     .paint(|ctx| {
                         for row in 0..DISPLAY_HEIGHT {
@@ -92,9 +96,8 @@ impl Display for RatatuiDisplay {
                     .y_bounds([0.0, DISPLAY_HEIGHT as f64]);
 
                 // Render the canvas widget
-
-            // Center the paragraph in the terminal
                 frame.render_widget(canvas, frame.area());
-        }).expect("failed to draw");
+            })
+            .expect("failed to draw");
     }
 }

src/emulator.rs

@@ -149,9 +149,11 @@ where
             ProcessorInstruction::SetIndexRegister(data) => {
                 trace!("Set index register to data {:04x}", data);
                 self.index_register = data;
-            },
+            }
             ProcessorInstruction::Draw(vx_register, vy_register, num_rows) => {
-                trace!("Draw vx_register={vx_register} vy_register={vy_register} pixels={num_rows}");
+                trace!(
+                    "Draw vx_register={vx_register} vy_register={vy_register} pixels={num_rows}"
+                );
                 let x_coordinate = self.registers[vx_register as usize];
                 let y_coordinate = self.registers[vy_register as usize];
 
@@ -188,6 +190,18 @@ where
 
                 self.display.render(&self.display_data);
             }
+            ProcessorInstruction::Return => {
+                let value = self.stack.pop().unwrap();
+                trace!("Return to {value:04x}");
+                self.program_counter = value;
+            }
+            ProcessorInstruction::Call(address) => {
+                trace!("Call {address:04x}");
+                // Save PC to the stack
+                self.stack.push(self.program_counter);
+                // Set PC to subroutine address
+                self.program_counter = address;
+            }
             ProcessorInstruction::UnknownInstruction => {
                 warn!("Unknown instruction: {:04x}, skipping.", instruction);
             }

src/instruction.rs

@@ -26,6 +26,10 @@ pub enum ProcessorInstruction {
     SetIndexRegister(u16),
     /// Draws to the screen.
     Draw(u8, u8, u8),
+    /// Call sets PC to the address and saves the return address on the stack
+    Call(u16),
+    /// Pops the stack and sets the PC
+    Return,
     /// Unknown instruction
     UnknownInstruction,
 }
@@ -86,9 +90,7 @@ impl Instruction {
                 )
             }
             // Set index register
-            (0xA, _, _, _) => {
-                ProcessorInstruction::SetIndexRegister(Self::grab_inner_data(data))
-            },
+            (0xA, _, _, _) => ProcessorInstruction::SetIndexRegister(Self::grab_inner_data(data)),
             // Draw on screen
             (0xD, _, _, _) => {
                 // DXYN
@@ -98,6 +100,18 @@ impl Instruction {
                     Self::grab_last_nibble(data),
                 )
             }
+            /*
+            00EE and 2NNN:
+
+            2NNN calls the subroutine at memory location NNN. In other words, just like 1NNN,
+            you should set PC to NNN. However, the difference between a jump and a call is that
+            this instruction should first push the current PC to the stack, so the subroutine can return later.
+
+            Returning from a subroutine is done with 00EE, and it does this by removing
+            (“popping”) the last address from the stack and setting the PC to it.
+             */
+            (0x0, 0x0, 0xE, 0xE) => ProcessorInstruction::Return,
+            (0x2, _, _, _) => ProcessorInstruction::Call(Self::grab_inner_data(data)),
             // Unknown instruction
             _ => ProcessorInstruction::UnknownInstruction,
         }
@@ -118,7 +132,6 @@ impl Instruction {
         ((data & 0xF000) >> 12) as u8
     }
 
-
     /// Grabs the first nibble from the data.
     fn grab_first_nibble(data: u16) -> u8 {
         ((data & 0x0F00) >> 8) as u8

src/main.rs

@@ -1,4 +1,4 @@
-use crate::display::{RatatuiDisplay};
+use crate::display::RatatuiDisplay;
 use crate::emulator::Emulator;
 use env_logger;