GBC: Added BIOS support

Author: ducalex

gnuboy-go/components/gnuboy/cpu.c

@@ -280,14 +280,12 @@ void cpu_reset(bool hard)
 	IME = 0;
 	IMA = 0;
 
-	PC = 0x0100;
+	PC = hw.bios ? 0x0000 : 0x0100;
 	SP = 0xFFFE;
-	AF = 0x01B0;
+	AF = hw.cgb ? 0x11B0 : 0x01B0;
 	BC = 0x0013;
 	DE = 0x00D8;
 	HL = 0x014D;
-
-	if (hw.cgb) A = 0x11;
 }
 
 /* cnt - time to emulate, expressed in real clock cycles */

gnuboy-go/components/gnuboy/hw.h

@@ -28,6 +28,7 @@ typedef struct
 	un32 cgb;
 	n32 hdma;
 	n32 serial;
+	un8 *bios;
 } hw_t;
 
 

gnuboy-go/components/gnuboy/loader.c

@@ -170,7 +170,7 @@ int rom_loadbank(int bank)
 
 int rom_load(const char *file)
 {
-    MESSAGE_INFO("Loading file: '%s'\n", file);
+	MESSAGE_INFO("Loading file: '%s'\n", file);
 
 	fpRomFile = fopen(file, "rb");
 	if (fpRomFile == NULL)
@@ -565,6 +565,9 @@ int state_load(const char *file)
 	fclose(fp);
 	free(buf);
 
+	// Disable BIOS. This is a hack to support old saves
+	R_BIOS = 0x1;
+
 	pal_dirty();
 	sound_dirty();
 	mem_updatemap();
@@ -577,3 +580,29 @@ int state_load(const char *file)
 
 	return -1;
 }
+
+
+int bios_load(const char *file)
+{
+	MESSAGE_INFO("Loading BIOS file: '%s'\n", file);
+
+	FILE *fpBiosFile = fopen(file, "rb");
+	if (fpBiosFile == NULL)
+	{
+		MESSAGE_ERROR("BIOS fopen failed");
+		return -1;
+	}
+
+	hw.bios = malloc(0x900);
+	if (!hw.bios)
+		emu_die("Out of memory");
+
+	if (fread(hw.bios, 1, 0x900, fpBiosFile) >= 0x100)
+	{
+		MESSAGE_INFO("BIOS loaded\n");
+	}
+
+	fclose(fpBiosFile);
+
+	return 0;
+}

gnuboy-go/components/gnuboy/loader.h

@@ -4,6 +4,8 @@
 int rom_loadbank(int);
 int rom_load(const char *file);
 void rom_unload(void);
+int bios_load(const char *file);
+void bios_unload(void);
 
 int sram_load(const char *file);
 int sram_save(const char *file);

gnuboy-go/components/gnuboy/mem.c

@@ -44,6 +44,12 @@ void IRAM_ATTR mem_updatemap()
 	mbc.rmap[0x2] = rom.bank[0];
 	mbc.rmap[0x3] = rom.bank[0];
 
+	// Force bios to go through mem_read (speed doesn't really matter here)
+	if (hw.bios && (R_BIOS & 1) == 0)
+	{
+		mbc.rmap[0x0] = NULL;
+	}
+
 	if (mbc.rombank < mbc.romsize)
 	{
 		mbc.rmap[0x4] = rom.bank[mbc.rombank] - 0x4000;
@@ -198,6 +204,10 @@ static inline void ioreg_write(byte r, byte b)
 	case RI_KEY1:
 		REG(r) = (REG(r) & 0x80) | (b & 0x01);
 		break;
+	case RI_BIOS:
+		REG(r) = b;
+		mem_updatemap();
+		break;
 	case RI_HDMA1:
 	case RI_HDMA2:
 	case RI_HDMA3:
@@ -250,6 +260,7 @@ static inline byte ioreg_read(byte r)
 	case RI_OCPD:
 	case RI_SVBK:
 	case RI_KEY1:
+	case RI_BIOS:
 	case RI_HDMA1:
 	case RI_HDMA2:
 	case RI_HDMA3:
@@ -514,6 +525,14 @@ byte IRAM_ATTR mem_read(addr_t a)
 	switch (ha)
 	{
 	case 0x0:
+		if (a < 0x900 && (R_BIOS & 1) == 0)
+		{
+			if (a < 0x100)
+				return hw.bios[a];
+			if (hw.cgb && a >= 0x200)
+				return hw.bios[a];
+		}
+		// fall through
 	case 0x2:
 		return rom.bank[0][a & 0x3fff];
 

gnuboy-go/components/gnuboy/regs.h

@@ -45,6 +45,8 @@
 
 #define RI_VBK   0x4F
 
+#define RI_BIOS  0x50
+
 #define RI_HDMA1 0x51
 #define RI_HDMA2 0x52
 #define RI_HDMA3 0x53
@@ -128,6 +130,8 @@
 #define R_WY    REG(RI_WY)
 #define R_WX    REG(RI_WX)
 
+#define R_BIOS  REG(RI_BIOS)
+
 #define R_VBK   REG(RI_VBK)
 
 #define R_HDMA1 REG(RI_HDMA1)

gnuboy-go/main/main.c

@@ -254,6 +254,12 @@ void app_main(void)
     // Load ROM
     rom_load(app->romPath);
 
+    // Load BIOS
+    if (hw.cgb)
+        bios_load(RG_BASE_PATH "/bios/gbc_bios.bin");
+    else
+        bios_load(RG_BASE_PATH "/bios/gb_bios.bin");
+
     // Set palette for non-gbc games (must be after rom_load)
     pal_set_dmg(rg_settings_get_app_int32(SETTING_PALETTE, 0));