From 92855bf6b92b5d2c287a6a5c3694f71b63723904 Mon Sep 17 00:00:00 2001
From: Kevin Hamacher <kevin.hamacher@ruhr-uni-bochum.de>
Date: Mon, 17 Feb 2020 19:23:16 +0100
Subject: [PATCH] Implement proper shutdown

---
 src/cpu.rs          | 23 ++++++++++++++++++-----
 src/interconnect.rs | 11 +++++++++--
 src/main.rs         |  4 +---
 3 files changed, 28 insertions(+), 10 deletions(-)

diff --git a/src/cpu.rs b/src/cpu.rs
index 0f75062..e652e5e 100644
--- a/src/cpu.rs
+++ b/src/cpu.rs
@@ -21,6 +21,12 @@ const FLAG_N: u8 = 1 << 6;
 const FLAG_H: u8 = 1 << 5;
 const FLAG_C: u8 = 1 << 4;
 
+use interconnect::TickResult;
+enum CpuTickResult {
+    Continue { cycles_executed: usize },
+    Shutdown { cycles_executed: usize },
+}
+
 pub struct CPU {
     // Registers: B, C, D, E, H, L, A
     regs: [u8; 7],
@@ -904,9 +910,13 @@ impl CPU {
             // The gameboy has a freq of 4.194304MHz
             // This means it takes it 238.418569ns to execute a single
             // cycle.
-            let expected_cycles = start.elapsed().as_nanos() / 238;
+            let expected_cycles = start.elapsed().as_nanos() / (238 / 2);
             while cycles_executed < expected_cycles {
-                cycles_executed += self.run_instruction() as u128;
+                if let CpuTickResult::Continue { cycles_executed: x, .. } = self.run_instruction() {
+                    cycles_executed += x as u128;
+                } else {
+                    return;
+                }
             }
             sleep(Duration::new(0, 10 * 238));
         }
@@ -951,7 +961,7 @@ impl CPU {
         false
     }
 
-    pub fn run_instruction(&mut self) -> u8 {
+    pub fn run_instruction(&mut self) -> CpuTickResult {
         // self.debug = !self.interconnect.is_boot_rom();
         if !self.trigger_once && !self.interconnect.is_boot_rom() {
             self.trigger_once = true;
@@ -1745,7 +1755,10 @@ impl CPU {
                 _ => panic!("Unknown instruction: {:02x}", instruction),
             };
         }
-        self.interconnect.tick(cycles);
-        cycles
+
+        if self.interconnect.tick(cycles) == TickResult::Shutdown {
+            return CpuTickResult::Shutdown { cycles_executed: cycles as usize }
+        }
+        CpuTickResult::Continue { cycles_executed: cycles as usize }
     }
 }
diff --git a/src/interconnect.rs b/src/interconnect.rs
index 6e21e7c..edc6ec3 100644
--- a/src/interconnect.rs
+++ b/src/interconnect.rs
@@ -32,6 +32,12 @@ extern crate sdl2;
 use self::sdl2::event::Event;
 use self::sdl2::keyboard::Keycode;
 
+#[derive(Debug, Copy, Clone, PartialEq)]
+pub enum TickResult {
+    Continue,
+    Shutdown,
+}
+
 #[derive(Debug)]
 enum Key {
     UP,
@@ -137,7 +143,7 @@ impl Interconnect {
     }
 
     // Somehow we need different timers for this.
-    pub fn tick(&mut self, cycles: u8) {
+    pub fn tick(&mut self, cycles: u8) -> TickResult {
         self.display.tick(cycles as u16);
         self.timer.tick(cycles as u16);
 
@@ -168,7 +174,7 @@ impl Interconnect {
                             ..
                         } => {
                             self.cartridge.save();
-                            panic!("TODO: Proper shutdown");
+                            return TickResult::Shutdown;
                         }
                         Event::KeyDown {
                             keycode: Some(Keycode::Left),
@@ -245,6 +251,7 @@ impl Interconnect {
         } else {
             self.cycles += cycles as u16;
         }
+        TickResult::Continue
     }
 
     #[inline]
diff --git a/src/main.rs b/src/main.rs
index 503d2e2..74d6fd2 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -36,9 +36,7 @@ fn main() {
         let interconnect = interconnect::Interconnect::new(bios, rom, save_file);
         let mut cpu = cpu::CPU::new(interconnect);
 
-        loop {
-            cpu.run();
-        }
+        cpu.run();
     }
 }