path: root/agbx/source/gfx/flip.s

@ 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

.extern __ax_getvbnk

.globl ax_flip

.func
.thumb_func

ax_flip:
	@ Get the current value of dispcnt:
	ldr r0,.dispcntaddr @ ax_i20 dispcntaddr = 0x4000000u;
	ldrh r1,[r0]        @ ax_i10 dispcnt = *(ax_i10 *)dispcntaddr;

	@ XOR bit five:
	movs r2,0b10000
	eors r1,r2          @ dispcnt ^= 0b10000u;

	@ Save dispcnt:
	strh r1,[r0]        @ *(ax_i10 *)dispcntaddr = dispcnt;

	@ Get the address of the video bank:
	b __ax_getvbnk    @ ax_i20 vaddr = __ax_getvbnk();
	
	bx lr               @ return vaddr;

.endfunc

.align

.dispcntaddr:
	.long 0x4000000