Implement CGB-mode TILE_SEL mixing, fixes cgb-acid-hell and m3_lcdc_tile_sel_change2, closes #308

Core/display.c

@@ -430,6 +430,23 @@ static void add_object_from_index(GB_gameboy_t *gb, unsigned index)
     }
 }
 
+static uint8_t data_for_tile_sel_glitch(GB_gameboy_t *gb, bool *should_use)
+{
+    /*
+     Based on Matt Currie's research here:
+     https://github.com/mattcurrie/mealybug-tearoom-tests/blob/master/the-comprehensive-game-boy-ppu-documentation.md#tile_sel-bit-4
+    */
+        
+    *should_use = true;
+    if (gb->io_registers[GB_IO_LCDC] & 0x10) {
+        *should_use = !(gb->current_tile & 0x80);
+        /* if (gb->model != GB_MODEL_CGB_D) */ return gb->current_tile;
+        // TODO: CGB D behaves differently
+    }
+    return gb->data_for_sel_glitch;
+}
+
+
 static void render_pixel_if_possible(GB_gameboy_t *gb)
 {
     GB_fifo_item_t *fifo_item = NULL;
@@ -621,6 +638,10 @@ static void advance_fetcher_state_machine(GB_gameboy_t *gb)
         break;
             
         case GB_FETCHER_GET_TILE_DATA_LOWER: {
+            bool use_glitched = false;
+            if (gb->tile_sel_glitch) {
+                gb->current_tile_data[0] = data_for_tile_sel_glitch(gb, &use_glitched);
+            }
             uint8_t y_flip = 0;
             uint16_t tile_address = 0;
             uint8_t y = gb->model > GB_MODEL_CGB_C ? gb->fetcher_y : fetcher_y(gb);
@@ -638,20 +659,32 @@ static void advance_fetcher_state_machine(GB_gameboy_t *gb)
             if (gb->current_tile_attributes & 0x40) {
                 y_flip = 0x7;
             }
-            gb->current_tile_data[0] =
+            if (!use_glitched) {
+                gb->current_tile_data[0] =
+                    gb->vram[tile_address + ((y & 7) ^ y_flip) * 2];
+                if (gb->vram_ppu_blocked) {
+                    gb->current_tile_data[0] = 0xFF;
+                }
+            }
+            else {
+                gb->data_for_sel_glitch =
                 gb->vram[tile_address + ((y & 7) ^ y_flip) * 2];
-            if (gb->vram_ppu_blocked) {
+                if (gb->vram_ppu_blocked) {
-                gb->current_tile_data[0] = 0xFF;
+                    gb->data_for_sel_glitch = 0xFF;
+                }
             }
         }
         gb->fetcher_state++;
         break;
             
         case GB_FETCHER_GET_TILE_DATA_HIGH: {
-            /* Todo: Verified for DMG (Tested: SGB2), CGB timing is wrong.
+            /* Todo: Verified for DMG (Tested: SGB2), CGB timing is wrong. */
-             Additionally, on CGB-D and newer mixing two tiles by changing the tileset
+            
-             bit mid-fetching causes a glitched mixing of the two, in comparison to the
+            bool use_glitched = false;
-             more logical DMG version. */
+            if (gb->tile_sel_glitch) {
+                gb->current_tile_data[1] = data_for_tile_sel_glitch(gb, &use_glitched);
+            }
+
             uint16_t tile_address = 0;
             uint8_t y = gb->model > GB_MODEL_CGB_C ? gb->fetcher_y : fetcher_y(gb);
             
@@ -669,10 +702,20 @@ static void advance_fetcher_state_machine(GB_gameboy_t *gb)
                 y_flip = 0x7;
             }
             gb->last_tile_data_address = tile_address +  ((y & 7) ^ y_flip) * 2 + 1;
-            gb->current_tile_data[1] =
+            if (!use_glitched) {
-                gb->vram[gb->last_tile_data_address];
+                gb->current_tile_data[1] =
-            if (gb->vram_ppu_blocked) {
+                    gb->vram[gb->last_tile_data_address];
-                gb->current_tile_data[1] = 0xFF;
+                if (gb->vram_ppu_blocked) {
+                    gb->current_tile_data[1] = 0xFF;
+                }
+            }
+            else {
+                if ((gb->io_registers[GB_IO_LCDC] & 0x10) && gb->tile_sel_glitch) {
+                    gb->data_for_sel_glitch = gb->vram[gb->last_tile_data_address];
+                    if (gb->vram_ppu_blocked) {
+                        gb->data_for_sel_glitch = 0xFF;
+                    }
+                }
             }
         }
         if (gb->wx_triggered) {
@@ -1112,7 +1155,8 @@ void GB_display_run(GB_gameboy_t *gb, uint8_t cycles)
                                             object->flags & 0x80,
                                             gb->object_priority == GB_OBJECT_PRIORITY_INDEX? gb->visible_objs[gb->n_visible_objs - 1] : 0,
                                             object->flags & 0x20);
-                    
+
+                    gb->data_for_sel_glitch = gb->vram_ppu_blocked? 0xFF : gb->vram[line_address + 1];
                     gb->n_visible_objs--;
                 }
                 
@@ -1128,6 +1172,14 @@ abort_fetching_object:
                 GB_SLEEP(gb, display, 21, 1);
             }
             
+            /* TODO: Verify */
+            if (gb->fetcher_state == 4 || gb->fetcher_state == 5) {
+                gb->data_for_sel_glitch = gb->current_tile_data[0];
+            }
+            else {
+                gb->data_for_sel_glitch = gb->current_tile_data[1];
+            }
+            
             while (gb->lcd_x != 160 && !gb->disable_rendering && gb->screen && !gb->sgb) {
                 /* Oh no! The PPU and LCD desynced! Fill the rest of the line whith white. */
                 uint32_t *dest = NULL;

Core/gb.h

@@ -548,6 +548,7 @@ struct GB_gameboy_internal_s {
         uint16_t last_tile_data_address;
         uint16_t last_tile_index_address;
         bool cgb_repeated_a_frame;
+        uint8_t data_for_sel_glitch;
     );
 
     /* Unsaved data. This includes all pointers, as well as everything that shouldn't be on a save state */
@@ -692,6 +693,7 @@ struct GB_gameboy_internal_s {
                
         /* Temporary state */
         bool wx_just_changed;
+        bool tile_sel_glitch;
    );
 };
     

Core/sm83_cpu.c

@@ -21,10 +21,12 @@ typedef enum {
     GB_CONFLICT_DMG_LCDC,
     GB_CONFLICT_SGB_LCDC,
     GB_CONFLICT_WX,
+    GB_CONFLICT_CGB_LCDC,
 } GB_conflict_t;
 
 /* Todo: How does double speed mode affect these? */
 static const GB_conflict_t cgb_conflict_map[0x80] = {
+    [GB_IO_LCDC] = GB_CONFLICT_CGB_LCDC,
     [GB_IO_IF] = GB_CONFLICT_WRITE_CPU,
     [GB_IO_LYC] = GB_CONFLICT_WRITE_CPU,
     [GB_IO_STAT] = GB_CONFLICT_STAT_CGB,
@@ -241,6 +243,34 @@ static void cycle_write(GB_gameboy_t *gb, uint16_t addr, uint8_t value)
             gb->wx_just_changed = false;
             gb->pending_cycles = 3;
             return;
+            
+        case GB_CONFLICT_CGB_LCDC:
+            if ((value ^ gb->io_registers[GB_IO_LCDC]) & 0x10) {
+                // Todo: This is difference is because my timing is off in one of the models
+                if (gb->model > GB_MODEL_CGB_C) {
+                    GB_advance_cycles(gb, gb->pending_cycles);
+                    gb->tile_sel_glitch = true;
+                    GB_advance_cycles(gb, 1);
+                    gb->tile_sel_glitch = false;
+                    GB_write_memory(gb, addr, value);
+                    gb->pending_cycles = 3;
+                }
+                else {
+                    GB_advance_cycles(gb, gb->pending_cycles - 1);
+                    gb->tile_sel_glitch = true;
+                    GB_advance_cycles(gb, 1);
+                    gb->tile_sel_glitch = false;
+                    GB_write_memory(gb, addr, value);
+                    gb->pending_cycles = 4;
+                }
+            }
+            else {
+                GB_advance_cycles(gb, gb->pending_cycles);
+                GB_write_memory(gb, addr, value);
+                gb->pending_cycles = 4;
+            }
+            return;
+
     }
 }