From ec6a7d02b22a03066db19afbdbef64617263f170 Mon Sep 17 00:00:00 2001
From: Alex Janka <alex@alexjanka.com>
Date: Sat, 22 Apr 2023 19:09:33 +1000
Subject: [PATCH] pretends to go double speed

---
 lib/src/processor/memory.rs                       |  2 +-
 lib/src/processor/memory/mmio/cgb/double_speed.rs |  4 +++-
 lib/src/processor/mod.rs                          | 14 ++++----------
 lib/src/processor/opcodes.rs                      | 13 +++++++++----
 4 files changed, 17 insertions(+), 16 deletions(-)

diff --git a/lib/src/processor/memory.rs b/lib/src/processor/memory.rs
index fd5604b..625db34 100644
--- a/lib/src/processor/memory.rs
+++ b/lib/src/processor/memory.rs
@@ -521,7 +521,7 @@ where
     R: Renderer<ColourFormat>,
     C: PocketCamera + Send + 'static,
 {
-    pub fn increment_timers(&mut self, machine_cycles: u8) {
+    pub fn increment_timers(&mut self, machine_cycles: usize) {
         let steps = (machine_cycles as usize) * 4;
         self.cycle_count += steps;
 
diff --git a/lib/src/processor/memory/mmio/cgb/double_speed.rs b/lib/src/processor/memory/mmio/cgb/double_speed.rs
index 951ac55..79d103c 100644
--- a/lib/src/processor/memory/mmio/cgb/double_speed.rs
+++ b/lib/src/processor/memory/mmio/cgb/double_speed.rs
@@ -32,14 +32,16 @@ where
             .map_or(false, |v| v.double_speed.current)
     }
 
-    pub(crate) fn should_switch_speed(&mut self) -> bool {
+    pub(crate) fn try_switch_speed(&mut self) -> bool {
         if let Some(cgb_peripherals) = &mut self.cgb_peripherals {
             if cgb_peripherals.double_speed.prepared && !cgb_peripherals.double_speed.current {
+                println!("switching to double speed");
                 cgb_peripherals.double_speed.current = true;
                 cgb_peripherals.double_speed.prepared = false;
                 return true;
             } else if cgb_peripherals.double_speed.prepared && cgb_peripherals.double_speed.current
             {
+                println!("switching to normal speed");
                 cgb_peripherals.double_speed.current = false;
                 cgb_peripherals.double_speed.prepared = false;
                 return true;
diff --git a/lib/src/processor/mod.rs b/lib/src/processor/mod.rs
index e5d0321..2a0e6d0 100644
--- a/lib/src/processor/mod.rs
+++ b/lib/src/processor/mod.rs
@@ -98,15 +98,9 @@ where
         }
 
         // double this if in double speed mode
-        let mut vram_dma_cycles = self.memory.vram_dma_tick();
-        while vram_dma_cycles > 0 {
-            let cycles = if vram_dma_cycles > 0xFF {
-                0xFF
-            } else {
-                vram_dma_cycles as u8
-            };
-            vram_dma_cycles -= cycles as usize;
-            self.increment_timers(cycles);
+        let vram_dma_cycles = self.memory.vram_dma_tick();
+        if vram_dma_cycles > 0 {
+            self.increment_timers(vram_dma_cycles);
             let interrupt_cycles = self.handle_interrupts();
             self.increment_timers(interrupt_cycles);
         }
@@ -152,7 +146,7 @@ where
         }
     }
 
-    fn handle_interrupts(&mut self) -> u8 {
+    fn handle_interrupts(&mut self) -> usize {
         if self.memory.ime {
             if let Some(interrupt) = self.memory.interrupts.get_next_interrupt() {
                 // if interrupt != Interrupt::Vblank {
diff --git a/lib/src/processor/opcodes.rs b/lib/src/processor/opcodes.rs
index 8574a9f..05011d3 100644
--- a/lib/src/processor/opcodes.rs
+++ b/lib/src/processor/opcodes.rs
@@ -15,7 +15,7 @@ where
     R: Renderer<ColourFormat>,
     C: PocketCamera + Send + 'static,
 {
-    pub fn run_opcode(&mut self, opcode: u8) -> u8 {
+    pub fn run_opcode(&mut self, opcode: u8) -> usize {
         match opcode {
             0x00 => {
                 // noop
@@ -93,7 +93,12 @@ where
             0x10 => {
                 // stop
                 // 1 cycle long
-                panic!("stop instruction");
+                if self.memory.try_switch_speed() {
+                    2050
+                } else {
+                    0
+                }
+                // panic!("stop instruction");
             }
             0x11 => {
                 self.reg.de = self.ld_immediate_word();
@@ -1231,7 +1236,7 @@ where
         }
     }
 
-    fn cb_subop(&mut self, subop: u8) -> u8 {
+    fn cb_subop(&mut self, subop: u8) -> usize {
         match subop {
             0x00 => {
                 let val = self.rlc(self.reg.get_8(Reg8::B));
@@ -2453,6 +2458,6 @@ where
     }
 }
 
-fn undefined(opcode: u8) -> u8 {
+fn undefined(opcode: u8) -> usize {
     panic!("Undefined behaviour: opcode {opcode:#X}");
 }