From 8c574fc47e9097fb892b467c4fe0f1a0eebd3bc0 Mon Sep 17 00:00:00 2001
From: Alex Janka <alex@alexjanka.com>
Date: Sat, 22 Apr 2023 21:39:46 +1000
Subject: [PATCH] double speed!!!! maybe there are edge cases but ive mostly
 got it

---
 lib/src/processor/memory.rs            | 18 ++++++++++---
 lib/src/processor/memory/mmio/timer.rs | 35 +++++++++++++-------------
 lib/src/processor/opcodes.rs           |  6 ++---
 3 files changed, 35 insertions(+), 24 deletions(-)

diff --git a/lib/src/processor/memory.rs b/lib/src/processor/memory.rs
index 2af22d0..336d60f 100644
--- a/lib/src/processor/memory.rs
+++ b/lib/src/processor/memory.rs
@@ -522,14 +522,26 @@ where
     C: PocketCamera + Send + 'static,
 {
     pub fn increment_timers(&mut self, machine_cycles: usize) {
+        self.increment_timers_div_optional(machine_cycles, true);
+    }
+
+    pub fn increment_timers_div_optional(&mut self, machine_cycles: usize, div: bool) {
         let steps = machine_cycles * 4;
+        let logical_steps = if self.memory.is_double_speed() {
+            steps / 2
+        } else {
+            steps
+        };
         self.cycle_count += steps;
 
         self.memory.oam_dma_tick(steps);
 
         self.memory.camera.lock().unwrap().tick(steps);
 
-        let timer_return = self.memory.timers.tick(steps);
+        let timer_return = self
+            .memory
+            .timers
+            .tick(steps, div, self.memory.is_double_speed());
 
         for _ in 0..timer_return.num_apu_ticks {
             self.memory.apu.div_apu_tick();
@@ -539,14 +551,14 @@ where
             self.memory.interrupts.set_interrupt(Interrupt::Timer, true);
         }
 
-        self.memory.apu.tick(steps);
+        self.memory.apu.tick(logical_steps);
 
         let serial_interrupt = self.memory.serial.tick(steps, self.memory.ime);
         self.memory
             .interrupts
             .set_interrupt(Interrupt::Serial, serial_interrupt);
 
-        let gpu_interrupts = self.memory.gpu.tick(steps);
+        let gpu_interrupts = self.memory.gpu.tick(logical_steps);
 
         self.memory
             .interrupts
diff --git a/lib/src/processor/memory/mmio/timer.rs b/lib/src/processor/memory/mmio/timer.rs
index 94409bf..0a91595 100644
--- a/lib/src/processor/memory/mmio/timer.rs
+++ b/lib/src/processor/memory/mmio/timer.rs
@@ -74,10 +74,6 @@ pub struct Timer {
     tima_counter: usize,
 }
 
-// this will need to change when cgb mode is implemented
-// as it uses bit 5 in double speed mode
-const AUDIO_BIT: u8 = 4;
-
 impl Timer {
     pub fn init() -> Self {
         Self {
@@ -90,24 +86,27 @@ impl Timer {
         }
     }
 
-    pub fn tick(&mut self, steps: usize) -> TimerReturn {
-        self.div_counter += steps;
-        let mut div_diff = (self.div_counter / 256) as u8;
-        let mut last_div = self.div;
+    pub fn tick(&mut self, steps: usize, with_div: bool, double_speed: bool) -> TimerReturn {
         let mut returning = TimerReturn::default();
-        while div_diff > 0 {
-            let div = last_div.wrapping_add(1);
+        if with_div {
+            let audio_bit = if double_speed { 5 } else { 4 };
+            self.div_counter += steps;
+            let mut div_diff = (self.div_counter / 256) as u8;
+            let mut last_div = self.div;
+            while div_diff > 0 {
+                let div = last_div.wrapping_add(1);
 
-            if (div & (1 << AUDIO_BIT)) < (last_div & (1 << AUDIO_BIT)) {
-                // trigger DIV-APU
-                returning.num_apu_ticks += 1;
+                if (div & (1 << audio_bit)) < (last_div & (1 << audio_bit)) {
+                    // trigger DIV-APU
+                    returning.num_apu_ticks += 1;
+                }
+
+                self.div = div;
+                last_div = div;
+                div_diff -= 1;
             }
-
-            self.div = div;
-            last_div = div;
-            div_diff -= 1;
+            self.div_counter %= 256;
         }
-        self.div_counter %= 256;
 
         if self.control.enable {
             self.tima_counter += steps;
diff --git a/lib/src/processor/opcodes.rs b/lib/src/processor/opcodes.rs
index 05011d3..140d469 100644
--- a/lib/src/processor/opcodes.rs
+++ b/lib/src/processor/opcodes.rs
@@ -94,11 +94,11 @@ where
                 // stop
                 // 1 cycle long
                 if self.memory.try_switch_speed() {
-                    2050
-                } else {
+                    self.increment_timers_div_optional(2050, false);
                     0
+                } else {
+                    1
                 }
-                // panic!("stop instruction");
             }
             0x11 => {
                 self.reg.de = self.ld_immediate_word();