From b574e1b1bf76e3deb0377fea21a84eea5d1fdde8 Mon Sep 17 00:00:00 2001
From: Alex Janka <alex@alexjanka.com>
Date: Fri, 24 Feb 2023 11:53:44 +1100
Subject: [PATCH] interrupts work properly! and halt bug almost does

---
 src/processor/memory.rs            |  6 ++---
 src/processor/memory/interrupts.rs | 13 +++++++++--
 src/processor/mod.rs               | 36 ++++++++++++++++++++++++------
 src/processor/opcodes.rs           |  2 +-
 4 files changed, 44 insertions(+), 13 deletions(-)

diff --git a/src/processor/memory.rs b/src/processor/memory.rs
index 7a50f81..89e72ce 100644
--- a/src/processor/memory.rs
+++ b/src/processor/memory.rs
@@ -226,9 +226,9 @@ impl Cpu {
             self.memory.apu.div_apu_tick();
         }
 
-        self.memory
-            .interrupts
-            .set_interrupt(Interrupt::Timer, timer_return.timer_interrupt);
+        if timer_return.timer_interrupt {
+            self.memory.interrupts.set_interrupt(Interrupt::Timer, true);
+        }
 
         self.memory.apu.tick(steps);
 
diff --git a/src/processor/memory/interrupts.rs b/src/processor/memory/interrupts.rs
index cc7e531..9931f8c 100644
--- a/src/processor/memory/interrupts.rs
+++ b/src/processor/memory/interrupts.rs
@@ -1,6 +1,6 @@
 use crate::util::get_bit;
 
-#[derive(Default)]
+#[derive(Default, Debug)]
 struct InterruptRegister {
     vblank: bool,
     lcd_stat: bool,
@@ -31,6 +31,7 @@ fn bool_to_shifted(input: bool, shift: u8) -> u8 {
     (if input { 1 } else { 0 }) << shift
 }
 
+#[derive(Debug)]
 pub enum Interrupt {
     Vblank,
     LcdStat,
@@ -57,7 +58,7 @@ impl Interrupts {
     }
 
     pub(super) fn get_flag_register(&self) -> u8 {
-        self.flag_register.as_register()
+        0b11100000 | self.flag_register.as_register()
     }
 
     pub(super) fn set_flag_register(&mut self, data: u8) {
@@ -94,4 +95,12 @@ impl Interrupts {
             None
         }
     }
+
+    pub fn is_interrupt_queued(&self) -> bool {
+        (self.enable_register.vblank && self.flag_register.vblank)
+            || (self.enable_register.lcd_stat && self.flag_register.lcd_stat)
+            || (self.enable_register.timer && self.flag_register.timer)
+            || (self.enable_register.serial && self.flag_register.serial)
+            || (self.enable_register.joypad && self.flag_register.joypad)
+    }
 }
diff --git a/src/processor/mod.rs b/src/processor/mod.rs
index 7010177..2b4de46 100644
--- a/src/processor/mod.rs
+++ b/src/processor/mod.rs
@@ -26,6 +26,7 @@ pub struct Cpu {
     pub last_instruction: u8,
     last_instruction_addr: u16,
     halted: bool,
+    should_halt_bug: bool,
     gamepad_handler: Gilrs,
     cycle_start: Instant,
 }
@@ -41,6 +42,7 @@ impl Cpu {
             last_instruction: 0x0,
             last_instruction_addr: 0x0,
             halted: false,
+            should_halt_bug: false,
             gamepad_handler,
             cycle_start: Instant::now(),
         }
@@ -56,10 +58,6 @@ impl Cpu {
             return;
         }
 
-        self.last_instruction_addr = self.reg.pc;
-        let opcode = self.next_opcode();
-        self.last_instruction = opcode;
-
         if self.memory.ime_scheduled > 0 {
             self.memory.ime_scheduled = self.memory.ime_scheduled.saturating_sub(1);
             if self.memory.ime_scheduled == 0 {
@@ -67,13 +65,20 @@ impl Cpu {
             }
         }
 
+        self.last_instruction_addr = self.reg.pc;
+        let opcode = self.next_opcode();
+        if self.should_halt_bug {
+            self.reg.pc = self.reg.pc.wrapping_sub(0x1);
+            self.should_halt_bug = false;
+        }
+        self.last_instruction = opcode;
+
         verbose_println!(
             "exec {:#4X} from pc: {:#X}",
             opcode,
             self.last_instruction_addr
         );
-        let cycles = self.run_opcode(opcode);
-        self.increment_timers(cycles);
+        self.run_and_increment_timers(opcode);
     }
 
     fn next_opcode(&mut self) -> u8 {
@@ -82,8 +87,22 @@ impl Cpu {
         opcode
     }
 
+    fn run_and_increment_timers(&mut self, opcode: u8) {
+        let cycles = self.run_opcode(opcode);
+        self.increment_timers(cycles);
+    }
+
+    fn halt(&mut self) {
+        if !self.memory.ime && self.memory.interrupts.is_interrupt_queued() {
+            // halt bug
+            self.should_halt_bug = true;
+        } else {
+            self.halted = true;
+        }
+    }
+
     fn handle_interrupts(&mut self) -> u8 {
-        if self.memory.ime || self.halted {
+        if self.memory.ime {
             if let Some(interrupt) = self.memory.interrupts.get_next_interrupt() {
                 let interrupt_addr = match interrupt {
                     Interrupt::Vblank => 0x40,
@@ -98,6 +117,9 @@ impl Cpu {
                 0
             }
         } else {
+            if self.halted && self.memory.interrupts.is_interrupt_queued() {
+                self.halted = false;
+            }
             0
         }
     }
diff --git a/src/processor/opcodes.rs b/src/processor/opcodes.rs
index 3bc45de..4676661 100644
--- a/src/processor/opcodes.rs
+++ b/src/processor/opcodes.rs
@@ -554,7 +554,7 @@ impl Cpu {
                 2
             }
             0x76 => {
-                self.halted = true;
+                self.halt();
                 1
             }
             0x77 => {