From 1b7b5106e24d1bad0776c97696f834209e30d900 Mon Sep 17 00:00:00 2001
From: CasualPokePlayer <50538166+CasualPokePlayer@users.noreply.github.com>
Date: Wed, 6 Dec 2023 00:03:53 -0800
Subject: FreeBIOS: Ensure upper 16 bits are cleared in the initial crc16
 value.

Fixes Castlevania: Dawn of Sorrow's checksumming which uses crc16 swi and has garbage in the upper 16 bits of r0.
The official BIOS would seem to implicitly clear these upper 16 bits.
---
 freebios/bios_common.S         |   3 +++
 freebios/drastic_bios_arm7.bin | Bin 16384 -> 16384 bytes
 freebios/drastic_bios_arm9.bin | Bin 4096 -> 4096 bytes
 3 files changed, 3 insertions(+)

(limited to 'freebios')

diff --git a/freebios/bios_common.S b/freebios/bios_common.S
index 56d349e..308d67c 100755
--- a/freebios/bios_common.S
+++ b/freebios/bios_common.S
@@ -517,6 +517,9 @@ swi_get_crc16:
   mov const_0x1E, #0x1E
   adr crc_table_ptr, crc_table
 
+  bic crc_value, crc_value, #0xFF000000
+  bic crc_value, crc_value, #0x00FF0000
+
   movs crc_length, crc_length, lsr #1
   beq 1f
 
diff --git a/freebios/drastic_bios_arm7.bin b/freebios/drastic_bios_arm7.bin
index e586eb9..adffb53 100755
Binary files a/freebios/drastic_bios_arm7.bin and b/freebios/drastic_bios_arm7.bin differ
diff --git a/freebios/drastic_bios_arm9.bin b/freebios/drastic_bios_arm9.bin
index 51a8282..95c330d 100755
Binary files a/freebios/drastic_bios_arm9.bin and b/freebios/drastic_bios_arm9.bin differ
-- 
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