From 593e7c125bb3451b25699bff8fe618337b97bd8e Mon Sep 17 00:00:00 2001
From: CasualPokePlayer <50538166+CasualPokePlayer@users.noreply.github.com>
Date: Fri, 18 Oct 2024 13:46:25 -0700
Subject: [PATCH] force real bios file usage if an encrypted DS rom is used

---
 .../Consoles/Nintendo/NDS/MelonDS.cs                  | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/src/BizHawk.Emulation.Cores/Consoles/Nintendo/NDS/MelonDS.cs b/src/BizHawk.Emulation.Cores/Consoles/Nintendo/NDS/MelonDS.cs
index 2743732d3f..7c43369b9b 100644
--- a/src/BizHawk.Emulation.Cores/Consoles/Nintendo/NDS/MelonDS.cs
+++ b/src/BizHawk.Emulation.Cores/Consoles/Nintendo/NDS/MelonDS.cs
@@ -190,6 +190,17 @@ namespace BizHawk.Emulation.Cores.Consoles.Nintendo.NDS
 
 				_activeSyncSettings.UseRealBIOS |= IsDSi;
 
+				if (!_activeSyncSettings.UseRealBIOS)
+				{
+					// check if the user is using an encrypted rom
+					// if they are, they need to be using real bios files
+					Span<byte> decryptedBytePattern = stackalloc byte[] { 0xFF, 0xDE, 0xFF, 0xE7, 0xFF, 0xDE, 0xFF, 0xE7 };
+					if (!roms[0].AsSpan(0x4000, 8).SequenceEqual(decryptedBytePattern))
+					{
+						_activeSyncSettings.UseRealBIOS = true;
+					}
+				}
+
 				byte[] bios9 = null, bios7 = null, firmware = null;
 				if (_activeSyncSettings.UseRealBIOS)
 				{