1 files changed, 38 insertions, 0 deletions
diff --git a/agbx/source/gfx/vsync.s b/agbx/source/gfx/vsync.s
new file mode 100644
index 0000000..5bfbe06
--- /dev/null
+++ b/agbx/source/gfx/vsync.s
@@ -0,0 +1,38 @@
+@ Copyright 2022 Gabriel Jensen.
+@ This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
+@ If a copy of the MPL was not distributed with this file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+.syntax unified
+
+.cpu arm7tdmi
+.thumb
+
+.globl agbx_vsync
+
+.func
+
+.thumb_func
+
+agbx_vsync:
+	@ Set the constants:
+	ldr r0,.scancnt @ Address of the scanline counter register.
+	movs r1,0xA0 @ Number of horizontal lines;
+	
+.loop:
+	@ Check the scanline counter:
+	ldr r2,[r0] @ Load the counter.
+	cmp r2,r1 @ Check if it has reached the bottom.
+	beq .ret @ Return if so.
+
+.ret:
+	@ Return:
+	bx lr
+
+.endfunc
+
+.align
+
+.scancnt:
+	.long 0x4000000
+
+.align