M include/mgba/internal/gb/video.h → include/mgba/internal/gb/video.h

@@ -167,6 +167,7 @@ void GBVideoWriteLYC(struct GBVideo* video, uint8_t value);
 void GBVideoWritePalette(struct GBVideo* video, uint16_t address, uint8_t value);
 void GBVideoSwitchBank(struct GBVideo* video, uint8_t value);
 
+void GBVideoDisableCGB(struct GBVideo* video);
 void GBVideoSetPalette(struct GBVideo* video, unsigned index, uint32_t color);
 
 void GBVideoWriteSGBPacket(struct GBVideo* video, uint8_t* data);

M src/gb/io.c → src/gb/io.c

@@ -424,6 +424,10 @@ if (gb->memory.romBase < gb->memory.rom || gb->memory.romBase > &gb->memory.rom[gb->memory.romSize - 1]) {
 			free(gb->memory.romBase);
 			gb->memory.romBase = gb->memory.rom;
 		}
+		if (gb->model >= GB_MODEL_CGB && gb->memory.io[0x6C]) {
+			gb->model = GB_MODEL_DMG;
+			GBVideoDisableCGB(&gb->video);
+		}
 		break;
 	case REG_IE:
 		gb->memory.ie = value;

M src/gb/video.c → src/gb/video.c

@@ -561,6 +561,23 @@ }
 	video->dmgPalette[index] = M_RGB8_TO_RGB5(color);
 }
 
+void GBVideoDisableCGB(struct GBVideo* video) {
+	video->dmgPalette[0] = video->palette[0];
+	video->dmgPalette[1] = video->palette[1];
+	video->dmgPalette[2] = video->palette[2];
+	video->dmgPalette[3] = video->palette[3];
+	video->dmgPalette[4] = video->palette[8 * 4 + 0];
+	video->dmgPalette[5] = video->palette[8 * 4 + 1];
+	video->dmgPalette[6] = video->palette[8 * 4 + 2];
+	video->dmgPalette[7] = video->palette[8 * 4 + 3];
+	video->dmgPalette[8] = video->palette[9 * 4 + 0];
+	video->dmgPalette[9] = video->palette[9 * 4 + 1];
+	video->dmgPalette[10] = video->palette[9 * 4 + 2];
+	video->dmgPalette[11] = video->palette[9 * 4 + 3];
+	video->renderer->deinit(video->renderer);
+	video->renderer->init(video->renderer, video->p->model, video->sgbBorders);
+}
+
 void GBVideoWriteSGBPacket(struct GBVideo* video, uint8_t* data) {
 	int i;
 	if (!(video->sgbCommandHeader & 7)) {