implement timer logic

src/emulator.rs

@@ -7,6 +7,7 @@ use rand::Rng;
 use std::fs::File;
 use std::io::Read;
 use std::path::Path;
+use std::time::Instant;
 use std::{thread, time};
 
 /// Represents the display's width in pixels.
@@ -110,9 +111,12 @@ where
 
     /// Emulation loop executes the fetch -> decode -> execute pipeline
     fn emulation_loop<T>(&mut self) -> Result<(), anyhow::Error> {
+        let mut start_time = Instant::now();
         let mut last_program_counter = self.program_counter;
         loop {
-            // fetch instruction
+            self.handle_timers(&mut start_time);
+
+            // fetch instruction & decode it
             let instruction = self.fetch_instruction()?;
             self.program_counter += 2;
 
@@ -121,7 +125,7 @@ where
             }
             last_program_counter = self.program_counter;
 
-            // decode & execute
+            // execute
             self.execute_instruction(instruction)?;
 
             // insert some delay
@@ -129,6 +133,30 @@ where
         }
     }
 
+    /// Handles the timers logic.
+    fn handle_timers(&mut self, start_time: &mut Instant) {
+        // Handle 60hz timers
+        let elapsed_time = start_time.elapsed().as_micros();
+        // 16667 us which is 1/60 of a second
+        if elapsed_time > 16667 {
+            if self.delay_timer > 0 {
+                self.delay_timer -= 1
+            }
+            if self.sound_timer > 0 {
+                self.delay_timer -= 1
+            } else {
+                self.do_beep()
+            }
+            *start_time = Instant::now()
+        }
+    }
+
+    /// Should make an audible beep.
+    fn do_beep(&mut self) {
+        // beep, for now
+    }
+
+    /// Executes the instruction
     fn execute_instruction(&mut self, instruction: Instruction) -> Result<(), anyhow::Error> {
         match instruction.processor_instruction() {
             ProcessorInstruction::ClearScreen => {

src/input.rs

@@ -1 +1 @@
-// TODO: grab keyboard keys and interrupt emulation cycle
+// TODO: grab keyboard keys and interrupt emulation cycle

src/instruction.rs

@@ -138,16 +138,6 @@ 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)),
             (0x8, _, _, 0x0) => ProcessorInstruction::Set(
@@ -207,15 +197,15 @@ impl Instruction {
                 Self::grab_first_nibble(data),
                 Self::grab_middle_nibble(data),
             ),
-            (0xF, _, 0x0, 0x7) => ProcessorInstruction::SetVXToDelayTimer(
-                Self::grab_first_nibble(data)
-            ),
-            (0xF, _, 0x1, 0x5) => ProcessorInstruction::SetDelayTimer(
-                Self::grab_first_nibble(data)
-            ),
-            (0xF, _, 0x1, 0x8) => ProcessorInstruction::SetSoundTimer(
-                Self::grab_first_nibble(data)
-            ),
+            (0xF, _, 0x0, 0x7) => {
+                ProcessorInstruction::SetVXToDelayTimer(Self::grab_first_nibble(data))
+            }
+            (0xF, _, 0x1, 0x5) => {
+                ProcessorInstruction::SetDelayTimer(Self::grab_first_nibble(data))
+            }
+            (0xF, _, 0x1, 0x8) => {
+                ProcessorInstruction::SetSoundTimer(Self::grab_first_nibble(data))
+            }
             // Unknown instruction
             _ => ProcessorInstruction::UnknownInstruction,
         }

src/main.rs

@@ -4,16 +4,16 @@ use env_logger;
 
 mod display;
 mod emulator;
+mod input;
 mod instruction;
 mod stack;
-mod input;
 
 fn main() -> Result<(), anyhow::Error> {
     env_logger::init();
 
     let mut emulator = Emulator::new(RatatuiDisplay::new());
 
-    emulator.emulate(String::from("./roms/3-corax+.ch8"))?;
+    emulator.emulate(String::from("./roms/ibm-logo.ch8"))?;
 
     Ok(())
 }