From 90a943d05a007155d67f6528fd260718e0e7582d Mon Sep 17 00:00:00 2001
From: Lior Halphon <LIJI32@gmail.com>
Date: Sun, 25 Feb 2018 22:32:41 +0200
Subject: [PATCH] Emulate an HDMA quirk required to properly emulate Aevilia

---
 Core/display.c | 2 ++
 Core/gb.h      | 3 ++-
 Core/memory.c  | 6 +++++-
 Core/z80_cpu.c | 4 ++--
 4 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/Core/display.c b/Core/display.c
index 41f85bf..dda9fab 100755
--- a/Core/display.c
+++ b/Core/display.c
@@ -527,6 +527,8 @@ static void update_display_state(GB_gameboy_t *gb, uint8_t cycles)
                 gb->vram_read_blocked = false;
                 gb->oam_write_blocked = false;
                 gb->vram_write_blocked = false;
+            }
+            else if (position_in_line == MODE2_LENGTH + MODE3_LENGTH + stat_delay + scx_delay + 16) {
                 if (gb->hdma_on_hblank) {
                     gb->hdma_on = true;
                     gb->hdma_cycles = 0;
diff --git a/Core/gb.h b/Core/gb.h
index 3dea996..c93aa3d 100644
--- a/Core/gb.h
+++ b/Core/gb.h
@@ -254,7 +254,7 @@ struct GB_gameboy_internal_s {
         bool halted;
         bool stopped;
         bool boot_rom_finished;
-        bool ime_toggle; /* ei (and di in CGB) have delayed effects.*/
+        bool ime_toggle; /* ei has delayed a effect.*/
         bool halt_bug;
 
         /* Misc state */
@@ -275,6 +275,7 @@ struct GB_gameboy_internal_s {
         uint16_t dma_current_src;
         int16_t dma_cycles;
         bool is_dma_restarting;
+        uint8_t last_opcode_read; /* Required to emulte HDMA reads from Exxx */
     );
     
     /* MBC */
diff --git a/Core/memory.c b/Core/memory.c
index ef2f007..dca92aa 100644
--- a/Core/memory.c
+++ b/Core/memory.c
@@ -111,6 +111,9 @@ static uint8_t read_high_memory(GB_gameboy_t *gb, uint16_t addr)
 {
 
     if (addr < 0xFE00) {
+        if (gb->hdma_on) {
+            return gb->last_opcode_read;
+        }
         return gb->ram[addr & 0x0FFF];
     }
 
@@ -122,7 +125,8 @@ static uint8_t read_high_memory(GB_gameboy_t *gb, uint16_t addr)
     }
 
     if (addr < 0xFF00) {
-        /* Unusable. CGB results are verified, but DMG results were tested on a SGB2  */
+        /* Unusable. CGB results are verified, but DMG results were tested on a SGB2 */
+        /* Also, writes to this area are not emulated */
         if ((gb->io_registers[GB_IO_STAT] & 0x3) >= 2) { /* Seems to be disabled in Modes 2 and 3 */
             return 0xFF;
         }
diff --git a/Core/z80_cpu.c b/Core/z80_cpu.c
index 16dbd08..4794df5 100644
--- a/Core/z80_cpu.c
+++ b/Core/z80_cpu.c
@@ -1392,12 +1392,12 @@ void GB_cpu_run(GB_gameboy_t *gb)
         GB_debugger_call_hook(gb, call_addr);
     }
     else if(!gb->halted && !gb->stopped) {
-        uint8_t opcode = GB_read_memory(gb, gb->pc++);
+        gb->last_opcode_read = GB_read_memory(gb, gb->pc++);
         if (gb->halt_bug) {
             gb->pc--;
             gb->halt_bug = false;
         }
-        opcodes[opcode](gb, opcode);
+        opcodes[gb->last_opcode_read](gb, gb->last_opcode_read);
     }
     else {
         GB_advance_cycles(gb, 4);