diff --git a/src/lib/ultra/os/writebackdcache.c b/src/lib/ultra/os/writebackdcache.c
deleted file mode 100644
index 011fc9139..000000000
--- a/src/lib/ultra/os/writebackdcache.c
+++ /dev/null
@@ -1,39 +0,0 @@
-#include <libultra_internal.h>
-#include "data.h"
-
-GLOBAL_ASM(
-glabel osWritebackDCache
-/*    4ad80:	18a00011 */ 	blez	$a1,.L0004adc8
-/*    4ad84:	00000000 */ 	nop
-/*    4ad88:	240b2000 */ 	addiu	$t3,$zero,0x2000
-/*    4ad8c:	00ab082b */ 	sltu	$at,$a1,$t3
-/*    4ad90:	1020000f */ 	beqz	$at,.L0004add0
-/*    4ad94:	00000000 */ 	nop
-/*    4ad98:	00804025 */ 	or	$t0,$a0,$zero
-/*    4ad9c:	00854821 */ 	addu	$t1,$a0,$a1
-/*    4ada0:	0109082b */ 	sltu	$at,$t0,$t1
-/*    4ada4:	10200008 */ 	beqz	$at,.L0004adc8
-/*    4ada8:	00000000 */ 	nop
-/*    4adac:	310a000f */ 	andi	$t2,$t0,0xf
-/*    4adb0:	2529fff0 */ 	addiu	$t1,$t1,-16
-/*    4adb4:	010a4023 */ 	subu	$t0,$t0,$t2
-.L0004adb8:
-/*    4adb8:	bd190000 */ 	cache	0x19,0x0($t0)
-/*    4adbc:	0109082b */ 	sltu	$at,$t0,$t1
-/*    4adc0:	1420fffd */ 	bnez	$at,.L0004adb8
-/*    4adc4:	25080010 */ 	addiu	$t0,$t0,0x10
-.L0004adc8:
-/*    4adc8:	03e00008 */ 	jr	$ra
-/*    4adcc:	00000000 */ 	nop
-.L0004add0:
-/*    4add0:	3c088000 */ 	lui	$t0,0x8000
-/*    4add4:	010b4821 */ 	addu	$t1,$t0,$t3
-/*    4add8:	2529fff0 */ 	addiu	$t1,$t1,-16
-.L0004addc:
-/*    4addc:	bd010000 */ 	cache	0x1,0x0($t0)
-/*    4ade0:	0109082b */ 	sltu	$at,$t0,$t1
-/*    4ade4:	1420fffd */ 	bnez	$at,.L0004addc
-/*    4ade8:	25080010 */ 	addiu	$t0,$t0,0x10
-/*    4adec:	03e00008 */ 	jr	$ra
-/*    4adf0:	00000000 */ 	nop
-);
diff --git a/src/lib/ultra/os/writebackdcache.s b/src/lib/ultra/os/writebackdcache.s
new file mode 100644
index 000000000..9f0c09d2c
--- /dev/null
+++ b/src/lib/ultra/os/writebackdcache.s
@@ -0,0 +1,40 @@
+#include "macros.inc"
+.set noat
+.set noreorder
+
+.section .text
+
+glabel osWritebackDCache
+	blez  $a1, .L0004adc8
+ 	nop
+	addiu $t3, $zero, 0x2000
+	sltu  $at, $a1, $t3
+	beqz  $at, .L0004add0
+ 	nop
+	move  $t0, $a0
+	addu  $t1, $a0, $a1
+	sltu  $at, $t0, $t1
+	beqz  $at, .L0004adc8
+ 	nop
+	andi  $t2, $t0, 0xf
+	addiu $t1, $t1, -16
+	subu  $t0, $t0, $t2
+.L0004adb8:
+	cache 0x19, 0x0($t0)
+	sltu  $at, $t0, $t1
+	bnez  $at, .L0004adb8
+	addiu $t0, $t0, 0x10
+.L0004adc8:
+	jr    $ra
+ 	nop
+.L0004add0:
+	lui   $t0, 0x8000
+	addu  $t1, $t0, $t3
+	addiu $t1, $t1, -16
+.L0004addc:
+	cache 0x1, 0x0($t0)
+	sltu  $at, $t0, $t1
+	bnez  $at, .L0004addc
+	addiu $t0, $t0, 0x10
+	jr    $ra
+ 	nop