From ffa53eda202b2a673b970b1ec8105566fff22d38 Mon Sep 17 00:00:00 2001
From: Lior Halphon <LIJI32@gmail.com>
Date: Fri, 14 Jan 2022 17:09:39 +0200
Subject: [PATCH] DMA during mode 3 emulation

---
 Core/display.c | 20 ++++++++++++++++----
 Core/memory.c  |  9 +++++----
 Core/timing.c  |  4 ++--
 3 files changed, 23 insertions(+), 10 deletions(-)

diff --git a/Core/display.c b/Core/display.c
index e89eb59..7ff1687 100644
--- a/Core/display.c
+++ b/Core/display.c
@@ -844,13 +844,13 @@ static void advance_fetcher_state_machine(GB_gameboy_t *gb)
     }
 }
 
-static uint8_t oam_read(GB_gameboy_t *gb, uint8_t addr)
+static inline uint8_t oam_read(GB_gameboy_t *gb, uint8_t addr)
 {
     if (unlikely(gb->oam_ppu_blocked)) {
         return 0xFF;
     }
-    if (unlikely(GB_is_dma_active(gb))) {
-        
+    if (unlikely(gb->dma_current_dest > 0 && gb->dma_current_dest <= 0xa0)) { // TODO: what happens in the last and first M cycles?
+       return gb->oam[((gb->dma_current_dest - 1) & ~1) | (addr & 1)];
     }
     return gb->oam[addr];
 }
@@ -1611,6 +1611,18 @@ void GB_display_run(GB_gameboy_t *gb, unsigned cycles, bool force)
                         goto abort_fetching_object;
                     }
                     
+                    if (unlikely(GB_is_dma_active(gb) || gb->dma_current_src == 0xFF)) {
+                        unsigned offset = cycles - gb->display_cycles; // Time passed in 8MHz ticks
+                        if (offset) {
+                            if (!gb->cgb_double_speed) {
+                                offset >>= 1; // Convert to T-cycles
+                            }
+                            unsigned old = gb->dma_cycles;
+                            gb->dma_cycles = offset;
+                            GB_dma_run(gb);
+                            gb->dma_cycles += old - offset;
+                        }
+                    }
                     
                     gb->object_low_line_address = get_object_line_address(gb,
                                                                           gb->objects_y[gb->n_visible_objs - 1],
@@ -1618,7 +1630,7 @@ void GB_display_run(GB_gameboy_t *gb, unsigned cycles, bool force)
                                                                           gb->object_flags = oam_read(gb, gb->visible_objs[gb->n_visible_objs - 1] * 4 + 3)
                                                                           );
                     
-                    gb->cycles_for_line++;
+                    gb->cycles_for_line += 1;
                     GB_SLEEP(gb, display, 39, 1);
                     if (gb->object_fetch_aborted) {
                         goto abort_fetching_object;
diff --git a/Core/memory.c b/Core/memory.c
index 5e23168..8409490 100644
--- a/Core/memory.c
+++ b/Core/memory.c
@@ -252,6 +252,7 @@ void GB_trigger_oam_bug_read(GB_gameboy_t *gb, uint16_t address)
 static bool is_addr_in_dma_use(GB_gameboy_t *gb, uint16_t addr)
 {
     if (!GB_is_dma_active(gb) || addr >= 0xfe00) return false;
+    if (gb->dma_current_dest == 0xFF) return false; // Warm up
     if (addr >= 0xfe00) return false;
     if (gb->dma_current_src == addr) return false; // Shortcut for DMA access flow
     if (gb->dma_current_src > 0xe000 && (gb->dma_current_src & ~0x2000) == addr) return false;
@@ -1459,8 +1460,8 @@ static void write_high_memory(GB_gameboy_t *gb, uint16_t addr, uint8_t value)
                 return;
 
             case GB_IO_DMA:
-                gb->dma_cycles = -3;
-                gb->dma_current_dest = 0;
+                gb->dma_cycles = 0;
+                gb->dma_current_dest = 0xFF;
                 gb->dma_current_src = value << 8;
                 gb->io_registers[GB_IO_DMA] = value;
                 return;
@@ -1681,12 +1682,12 @@ void GB_write_memory(GB_gameboy_t *gb, uint16_t addr, uint8_t value)
 
 bool GB_is_dma_active(GB_gameboy_t *gb)
 {
-    return gb->dma_current_dest < 0xa1;
+    return gb->dma_current_dest != 0xa1;
 }
 
 void GB_dma_run(GB_gameboy_t *gb)
 {
-    if (gb->dma_current_dest >= 0xa1) return;
+    if (gb->dma_current_dest == 0xa1) return;
     while (unlikely(gb->dma_cycles >= 4)) {
         gb->dma_cycles -= 4;
         if (gb->dma_current_dest >= 0xa0) {
diff --git a/Core/timing.c b/Core/timing.c
index c5d328f..e9b527c 100644
--- a/Core/timing.c
+++ b/Core/timing.c
@@ -428,12 +428,12 @@ void GB_advance_cycles(GB_gameboy_t *gb, uint8_t cycles)
     gb->rumble_on_cycles += gb->rumble_strength & 3;
     gb->rumble_off_cycles += (gb->rumble_strength & 3) ^ 3;
         
+    GB_apu_run(gb, false);
+    GB_display_run(gb, cycles, false);
     if (unlikely(!gb->stopped)) { // TODO: Verify what happens in STOP mode
         GB_dma_run(gb);
         GB_hdma_run(gb);
     }
-    GB_apu_run(gb, false);
-    GB_display_run(gb, cycles, false);
     ir_run(gb, cycles);
     rtc_run(gb, cycles);
 }