diff --git a/Makefile b/Makefile
index 4f4b9184d..4dea321dd 100644
--- a/Makefile
+++ b/Makefile
@@ -75,6 +75,7 @@ $(B_DIR)/lib/ultra/io/contpfs.o: LOOPUNROLL :=
 $(B_DIR)/lib/ultra/io/contramread.o: LOOPUNROLL :=
 $(B_DIR)/lib/ultra/io/contramwrite.o: LOOPUNROLL :=
 $(B_DIR)/lib/ultra/io/gbpakgetstatus.o: LOOPUNROLL :=
+$(B_DIR)/lib/ultra/io/gbpakreadid.o: LOOPUNROLL :=
 $(B_DIR)/lib/ultra/io/motor.o: LOOPUNROLL :=
 $(B_DIR)/lib/ultra/io/pfschecker.o: LOOPUNROLL :=
 $(B_DIR)/lib/ultra/io/pfsfreeblocks.o: LOOPUNROLL :=
diff --git a/src/include/data.h b/src/include/data.h
index 531d5d76d..48634cc80 100644
--- a/src/include/data.h
+++ b/src/include/data.h
@@ -126,8 +126,6 @@ extern u32 var800609a0;
 extern u32 var800609c4;
 extern u32 var800609f0;
 extern u32 var800611ec;
-extern u32 var800611f0;
-extern u32 var80061220;
 extern OSViMode osViModePalLan1;
 extern OSViMode osViModeMpalLan1;
 extern OSViMode osViModeNtscLan1;
diff --git a/src/lib/ultra/io/gbpakreadid.c b/src/lib/ultra/io/gbpakreadid.c
index cc2a73710..bbd08cce7 100644
--- a/src/lib/ultra/io/gbpakreadid.c
+++ b/src/lib/ultra/io/gbpakreadid.c
@@ -2,153 +2,91 @@
 #include "libultra_internal.h"
 #include "constants.h"
 #include "bss.h"
-#include "lib/lib_4b170.h"
-#include "lib/lib_4e090.h"
 #include "data.h"
 #include "types.h"
 
-u32 var800611f0 = 0xceed6666;
-u32 var800611f4 = 0xcc0d000b;
-u32 var800611f8 = 0x03730083;
-u32 var800611fc = 0x000c000d;
-u32 var80061200 = 0x0008111f;
-u32 var80061204 = 0x8889000e;
-u32 var80061208 = 0xdccc6ee6;
-u32 var8006120c = 0xddddd999;
-u32 var80061210 = 0xbbbb6763;
-u32 var80061214 = 0x6e0eeccc;
-u32 var80061218 = 0xdddc999f;
-u32 var8006121c = 0xbbb9333e;
+u32 g_OsGbNintendoData[] = {
+	0xceed6666, 0xcc0d000b, 0x03730083, 0x000c000d,
+	0x0008111f, 0x8889000e, 0xdccc6ee6, 0xddddd999,
+	0xbbbb6763, 0x6e0eeccc, 0xdddc999f, 0xbbb9333e,
+};
 
-u32 var80061220 = 0x00010101;
-u32 var80061224 = 0xff0202ff;
-u32 var80061228 = 0x0000ffff;
-u32 var8006122c = 0xffffff03;
-u32 var80061230 = 0x03030303;
+u8 g_OsGbCartVersions[] = {
+	0x00, 0x01, 0x01, 0x01,
+	0xff, 0x02, 0x02, 0xff,
+	0x00, 0x00, 0xff, 0xff,
+	0xff, 0xff, 0xff, 0x03,
+	0x03, 0x03, 0x03, 0x03,
+};
 
-GLOBAL_ASM(
-glabel osGbpakReadId
-/*    50d60:	27bdff70 */ 	addiu	$sp,$sp,-144
-/*    50d64:	afbf001c */ 	sw	$ra,0x1c($sp)
-/*    50d68:	afa50094 */ 	sw	$a1,0x94($sp)
-/*    50d6c:	afa40090 */ 	sw	$a0,0x90($sp)
-/*    50d70:	afa60098 */ 	sw	$a2,0x98($sp)
-/*    50d74:	0c0142f8 */ 	jal	osGbpakGetStatus
-/*    50d78:	00c02825 */ 	or	$a1,$a2,$zero
-/*    50d7c:	2401000d */ 	addiu	$at,$zero,0xd
-/*    50d80:	14410005 */ 	bne	$v0,$at,.L00050d98
-/*    50d84:	00403825 */ 	or	$a3,$v0,$zero
-/*    50d88:	8fa40090 */ 	lw	$a0,0x90($sp)
-/*    50d8c:	0c0142f8 */ 	jal	osGbpakGetStatus
-/*    50d90:	8fa50098 */ 	lw	$a1,0x98($sp)
-/*    50d94:	00403825 */ 	or	$a3,$v0,$zero
-.L00050d98:
-/*    50d98:	2401000d */ 	addiu	$at,$zero,0xd
-/*    50d9c:	14410003 */ 	bne	$v0,$at,.L00050dac
-/*    50da0:	00000000 */ 	nop
-/*    50da4:	10000058 */ 	b	.L00050f08
-/*    50da8:	24020004 */ 	addiu	$v0,$zero,0x4
-.L00050dac:
-/*    50dac:	14400055 */ 	bnez	$v0,.L00050f04
-/*    50db0:	8fae0098 */ 	lw	$t6,0x98($sp)
-/*    50db4:	91cf0000 */ 	lbu	$t7,0x0($t6)
-/*    50db8:	8fa40090 */ 	lw	$a0,0x90($sp)
-/*    50dbc:	31f80001 */ 	andi	$t8,$t7,0x1
-/*    50dc0:	57000008 */ 	bnezl	$t8,.L00050de4
-/*    50dc4:	24190060 */ 	addiu	$t9,$zero,0x60
-/*    50dc8:	0c0018cc */ 	jal	osGbpakPower
-/*    50dcc:	24050001 */ 	addiu	$a1,$zero,0x1
-/*    50dd0:	50400004 */ 	beqzl	$v0,.L00050de4
-/*    50dd4:	24190060 */ 	addiu	$t9,$zero,0x60
-/*    50dd8:	1000004c */ 	b	.L00050f0c
-/*    50ddc:	8fbf001c */ 	lw	$ra,0x1c($sp)
-/*    50de0:	24190060 */ 	addiu	$t9,$zero,0x60
-.L00050de4:
-/*    50de4:	afb90010 */ 	sw	$t9,0x10($sp)
-/*    50de8:	8fa40090 */ 	lw	$a0,0x90($sp)
-/*    50dec:	00002825 */ 	or	$a1,$zero,$zero
-/*    50df0:	24060100 */ 	addiu	$a2,$zero,0x100
-/*    50df4:	0c0144ec */ 	jal	osGbpakReadWrite
-/*    50df8:	27a70024 */ 	addiu	$a3,$sp,0x24
-/*    50dfc:	10400003 */ 	beqz	$v0,.L00050e0c
-/*    50e00:	8fa40090 */ 	lw	$a0,0x90($sp)
-/*    50e04:	10000041 */ 	b	.L00050f0c
-/*    50e08:	8fbf001c */ 	lw	$ra,0x1c($sp)
-.L00050e0c:
-/*    50e0c:	0c0142f8 */ 	jal	osGbpakGetStatus
-/*    50e10:	8fa50098 */ 	lw	$a1,0x98($sp)
-/*    50e14:	2401000d */ 	addiu	$at,$zero,0xd
-/*    50e18:	14410002 */ 	bne	$v0,$at,.L00050e24
-/*    50e1c:	00403825 */ 	or	$a3,$v0,$zero
-/*    50e20:	24070004 */ 	addiu	$a3,$zero,0x4
-.L00050e24:
-/*    50e24:	10e00003 */ 	beqz	$a3,.L00050e34
-/*    50e28:	3c048006 */ 	lui	$a0,%hi(var800611f0)
-/*    50e2c:	10000036 */ 	b	.L00050f08
-/*    50e30:	00e01025 */ 	or	$v0,$a3,$zero
-.L00050e34:
-/*    50e34:	248411f0 */ 	addiu	$a0,$a0,%lo(var800611f0)
-/*    50e38:	27a50028 */ 	addiu	$a1,$sp,0x28
-/*    50e3c:	24060030 */ 	addiu	$a2,$zero,0x30
-/*    50e40:	0c013824 */ 	jal	bcmp
-/*    50e44:	afa70088 */ 	sw	$a3,0x88($sp)
-/*    50e48:	10400003 */ 	beqz	$v0,.L00050e58
-/*    50e4c:	8fa70088 */ 	lw	$a3,0x88($sp)
-/*    50e50:	1000002d */ 	b	.L00050f08
-/*    50e54:	24020004 */ 	addiu	$v0,$zero,0x4
-.L00050e58:
-/*    50e58:	93a20058 */ 	lbu	$v0,0x58($sp)
-/*    50e5c:	93a80059 */ 	lbu	$t0,0x59($sp)
-/*    50e60:	27a3005a */ 	addiu	$v1,$sp,0x5a
-/*    50e64:	27a40072 */ 	addiu	$a0,$sp,0x72
-/*    50e68:	00481021 */ 	addu	$v0,$v0,$t0
-/*    50e6c:	304900ff */ 	andi	$t1,$v0,0xff
-/*    50e70:	01201025 */ 	or	$v0,$t1,$zero
-.L00050e74:
-/*    50e74:	906a0000 */ 	lbu	$t2,0x0($v1)
-/*    50e78:	906c0001 */ 	lbu	$t4,0x1($v1)
-/*    50e7c:	906e0002 */ 	lbu	$t6,0x2($v1)
-/*    50e80:	90780003 */ 	lbu	$t8,0x3($v1)
-/*    50e84:	004a5821 */ 	addu	$t3,$v0,$t2
-/*    50e88:	016c6821 */ 	addu	$t5,$t3,$t4
-/*    50e8c:	01ae7821 */ 	addu	$t7,$t5,$t6
-/*    50e90:	01f81021 */ 	addu	$v0,$t7,$t8
-/*    50e94:	305900ff */ 	andi	$t9,$v0,0xff
-/*    50e98:	24630004 */ 	addiu	$v1,$v1,0x4
-/*    50e9c:	1464fff5 */ 	bne	$v1,$a0,.L00050e74
-/*    50ea0:	03201025 */ 	or	$v0,$t9,$zero
-/*    50ea4:	27280019 */ 	addiu	$t0,$t9,0x19
-/*    50ea8:	310900ff */ 	andi	$t1,$t0,0xff
-/*    50eac:	11200003 */ 	beqz	$t1,.L00050ebc
-/*    50eb0:	27a40024 */ 	addiu	$a0,$sp,0x24
-/*    50eb4:	10000014 */ 	b	.L00050f08
-/*    50eb8:	24020004 */ 	addiu	$v0,$zero,0x4
-.L00050ebc:
-/*    50ebc:	8fa50094 */ 	lw	$a1,0x94($sp)
-/*    50ec0:	24060050 */ 	addiu	$a2,$zero,0x50
-/*    50ec4:	0c012c5c */ 	jal	bcopy
-/*    50ec8:	afa70088 */ 	sw	$a3,0x88($sp)
-/*    50ecc:	8faa0094 */ 	lw	$t2,0x94($sp)
-/*    50ed0:	3c0b8006 */ 	lui	$t3,%hi(var80061220)
-/*    50ed4:	8fa70088 */ 	lw	$a3,0x88($sp)
-/*    50ed8:	91420047 */ 	lbu	$v0,0x47($t2)
-/*    50edc:	8fac0090 */ 	lw	$t4,0x90($sp)
-/*    50ee0:	28410014 */ 	slti	$at,$v0,0x14
-/*    50ee4:	10200003 */ 	beqz	$at,.L00050ef4
-/*    50ee8:	01625821 */ 	addu	$t3,$t3,$v0
-/*    50eec:	916b1220 */ 	lbu	$t3,%lo(var80061220)($t3)
-/*    50ef0:	ad8b004c */ 	sw	$t3,0x4c($t4)
-.L00050ef4:
-/*    50ef4:	8fad0094 */ 	lw	$t5,0x94($sp)
-/*    50ef8:	8faf0090 */ 	lw	$t7,0x90($sp)
-/*    50efc:	91ae0049 */ 	lbu	$t6,0x49($t5)
-/*    50f00:	adee0050 */ 	sw	$t6,0x50($t7)
-.L00050f04:
-/*    50f04:	00e01025 */ 	or	$v0,$a3,$zero
-.L00050f08:
-/*    50f08:	8fbf001c */ 	lw	$ra,0x1c($sp)
-.L00050f0c:
-/*    50f0c:	27bd0090 */ 	addiu	$sp,$sp,0x90
-/*    50f10:	03e00008 */ 	jr	$ra
-/*    50f14:	00000000 */ 	nop
-);
+s32 osGbpakReadId(OSPfs *pfs, OSGbpakId *id, u8 *status)
+{
+	s32 i;
+	s32 ret;
+	u8 sum;
+	u8 buffer[0x60];
+
+	ret = osGbpakGetStatus(pfs, status);
+
+	if (ret == PFS_ERR_NEW_GBCART) {
+		ret = osGbpakGetStatus(pfs, status);
+	}
+
+	if (ret == PFS_ERR_NEW_GBCART) {
+		return PFS_ERR_CONTRFAIL;
+	}
+
+	if (ret == 0) {
+		if ((*status & OS_GBPAK_POWER) == 0) {
+			ret = osGbpakPower(pfs, OS_GBPAK_POWER_ON);
+
+			if (ret != 0) {
+				return ret;
+			}
+		}
+
+		ret = osGbpakReadWrite(pfs, PFS_READ, 0x100, buffer, 0x60);
+
+		if (ret != 0) {
+			return ret;
+		}
+
+		ret = osGbpakGetStatus(pfs, status);
+
+		if (ret == PFS_ERR_NEW_GBCART) {
+			ret = PFS_ERR_CONTRFAIL;
+		}
+
+		if (ret != 0) {
+			return ret;
+		}
+
+		// Compare id->nintendo_chr with expected data
+		if (bcmp(g_OsGbNintendoData, &buffer[4], sizeof(id->nintendo_chr)) != 0) {
+			return PFS_ERR_CONTRFAIL;
+		}
+
+		// Sum game_title through to isum
+		sum = 0;
+
+		for (i = 0x34; i < 0x4e; i++) {
+			sum += buffer[i];
+		}
+
+		sum = (sum + 25) & 0xff;
+
+		if (sum != 0) {
+			return PFS_ERR_CONTRFAIL;
+		}
+
+		bcopy(buffer, id, sizeof(OSGbpakId));
+
+		if (id->cart_type < 20) {
+			pfs->version = g_OsGbCartVersions[id->cart_type];
+		}
+
+		pfs->dir_size = id->ram_size;
+	}
+
+	return ret;
+}