From 1e90400916031b5f5d95fe377019cd53a8069fd8 Mon Sep 17 00:00:00 2001
From: Lior Halphon <LIJI32@gmail.com>
Date: Sat, 9 Sep 2017 13:32:12 +0300
Subject: [PATCH] Reimplemented delayed/future interrupts, currently correct
 only for CGB.

---
 Core/display.c | 17 +++++++++++++++--
 Core/gb.h      |  5 ++---
 Core/memory.c  |  5 +++--
 Core/timing.c  |  9 +++------
 Core/z80_cpu.c |  4 ++++
 5 files changed, 27 insertions(+), 13 deletions(-)

diff --git a/Core/display.c b/Core/display.c
index c0f385fc..38897177 100755
--- a/Core/display.c
+++ b/Core/display.c
@@ -305,6 +305,9 @@ static void update_display_state(GB_gameboy_t *gb, uint8_t cycles)
     uint8_t vram_blocking_rush = gb->is_cgb? 0 : 4;
     
     for (; cycles; cycles -= atomic_increase) {
+        gb->io_registers[GB_IO_IF] |= gb->future_interrupts & 3;
+        gb->future_interrupts &= ~3;
+        
         bool previous_stat_interrupt_line = gb->stat_interrupt_line;
         gb->stat_interrupt_line = false;
         
@@ -351,7 +354,12 @@ static void update_display_state(GB_gameboy_t *gb, uint8_t cycles)
         else if (gb->display_cycles == LINES * LINE_LENGTH + stat_delay) {
             gb->io_registers[GB_IO_STAT] &= ~3;
             gb->io_registers[GB_IO_STAT] |= 1;
-            gb->io_registers[GB_IO_IF] |= 1;
+            if (gb->is_cgb) {
+                gb->future_interrupts |= 1;
+            }
+            else {
+                gb->io_registers[GB_IO_IF] |= 1;
+            }
             
             /* Entering VBlank state triggers the OAM interrupt. In CGB, it happens 4 cycles earlier */
             if (gb->io_registers[GB_IO_STAT] & 0x20 && !gb->is_cgb) {
@@ -573,7 +581,12 @@ static void update_display_state(GB_gameboy_t *gb, uint8_t cycles)
         }
         
         if (gb->stat_interrupt_line && !previous_stat_interrupt_line) {
-            gb->io_registers[GB_IO_IF] |= 2;
+            if (gb->is_cgb) {
+                gb->future_interrupts |= 2;
+            }
+            else {
+                gb->io_registers[GB_IO_IF] |= 2;
+            }
         }
     }
     
diff --git a/Core/gb.h b/Core/gb.h
index c18bf304..37dada46 100644
--- a/Core/gb.h
+++ b/Core/gb.h
@@ -332,9 +332,8 @@ struct GB_gameboy_internal_s {
         GB_PADDING(uint16_t, serial_cycles);
         uint16_t serial_cycles; /* This field changed its meaning in v0.10 */
         uint16_t serial_length;
-        bool dont_delay_timer_interrupt; /* If the timer glitch causes a TIMA overflow, it causes the timer to overflow
-                                            with different timing, so the triggered interrupt is not delayed.
-                                            Todo: needs test ROM. */
+        uint8_t future_interrupts; /* Interrupts can occur in any T-cycle. Some timings result in different interrupt
+                                     timing when the CPU is in halt mode, and might also affect the DI instruction. */
     );
 
     /* APU */
diff --git a/Core/memory.c b/Core/memory.c
index d8f7df7e..4fbd1f1d 100644
--- a/Core/memory.c
+++ b/Core/memory.c
@@ -136,7 +136,7 @@ static uint8_t read_high_memory(GB_gameboy_t *gb, uint16_t addr)
     if (addr < 0xFF80) {
         switch (addr & 0xFF) {
             case GB_IO_IF:
-                return gb->io_registers[GB_IO_IF] | 0xE0;
+                return gb->io_registers[GB_IO_IF] | 0xE0 | gb->future_interrupts;
             case GB_IO_TAC:
                 return gb->io_registers[GB_IO_TAC] | 0xF8;
             case GB_IO_STAT:
@@ -416,8 +416,9 @@ static void write_high_memory(GB_gameboy_t *gb, uint16_t addr, uint8_t value)
             case GB_IO_WX:
                 GB_window_related_write(gb, addr & 0xFF, value);
                 break;
-            case GB_IO_SCX:
             case GB_IO_IF:
+                gb->future_interrupts = 0;
+            case GB_IO_SCX:
             case GB_IO_SCY:
             case GB_IO_LYC:
             case GB_IO_BGP:
diff --git a/Core/timing.c b/Core/timing.c
index e5ac7882..9a96f595 100644
--- a/Core/timing.c
+++ b/Core/timing.c
@@ -82,14 +82,13 @@ static void GB_ir_run(GB_gameboy_t *gb)
 
 static void advance_tima_state_machine(GB_gameboy_t *gb)
 {
+    gb->io_registers[GB_IO_IF] |= gb->future_interrupts & 4;
+    gb->future_interrupts &= ~4;
     if (gb->tima_reload_state == GB_TIMA_RELOADED) {
         gb->tima_reload_state = GB_TIMA_RUNNING;
     }
     else if (gb->tima_reload_state == GB_TIMA_RELOADING) {
-        gb->io_registers[GB_IO_IF] |= 4;
-        if (!gb->dont_delay_timer_interrupt) {
-            // Todo
-        }
+        gb->future_interrupts |= 4;
         gb->tima_reload_state = GB_TIMA_RELOADED;
     }
 }
@@ -157,7 +156,6 @@ static void increase_tima(GB_gameboy_t *gb)
 {
     gb->io_registers[GB_IO_TIMA]++;
     if (gb->io_registers[GB_IO_TIMA] == 0) {
-        gb->dont_delay_timer_interrupt = false;
         gb->io_registers[GB_IO_TIMA] = gb->io_registers[GB_IO_TMA];
         gb->tima_reload_state = GB_TIMA_RELOADING;
     }
@@ -197,7 +195,6 @@ void GB_emulate_timer_glitch(GB_gameboy_t *gb, uint8_t old_tac, uint8_t new_tac)
         /* And now either the timer must be disabled, or the new bit used for overflow testing be 0. */
         if (!(new_tac & 4) || gb->div_cycles & (new_clocks >> 1)) {
             increase_tima(gb);
-            gb->dont_delay_timer_interrupt = true;
         }
     }
 }
diff --git a/Core/z80_cpu.c b/Core/z80_cpu.c
index ce30d551..878358da 100644
--- a/Core/z80_cpu.c
+++ b/Core/z80_cpu.c
@@ -1338,6 +1338,10 @@ void GB_cpu_run(GB_gameboy_t *gb)
 {
     gb->vblank_just_occured = false;
     uint8_t interrupt_queue = gb->interrupt_enable & gb->io_registers[GB_IO_IF] & 0x1F;
+    if (!gb->halted) {
+        interrupt_queue |= gb->future_interrupts & gb->interrupt_enable;
+    }
+    
 
     if (interrupt_queue) {
         gb->halted = false;