From 9ca2d514b76d255b65c97643bb38690dc6699a77 Mon Sep 17 00:00:00 2001
From: 0kmg <9137159+0kmg@users.noreply.github.com>
Date: Sat, 25 Sep 2021 11:42:28 -0800
Subject: [PATCH] bus/nes: Fixed hardwired 4-screen mirroring for MMC3 games.
 (#8620)

- Fixes most graphics glitches in Rad Racer II and unlicensed Jurassic Boy 2, Rocman X carts.
---
 hash/nes.xml                 | 5 ++++-
 src/devices/bus/nes/mmc3.cpp | 3 ++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/hash/nes.xml b/hash/nes.xml
index b03f6a8d6da..909f15cb5a0 100644
--- a/hash/nes.xml
+++ b/hash/nes.xml
@@ -30488,7 +30488,7 @@ license:CC0
 		</part>
 	</software>
 
-	<software name="radracr2" supported="partial">
+	<software name="radracr2">
 		<description>Rad Racer II (USA)</description>
 		<year>1990</year>
 		<publisher>Square</publisher>
@@ -53095,6 +53095,7 @@ preliminary proto for the PAL version, still running on NTSC systems) or the gfx
 		<part name="cart" interface="nes_cart">
 			<feature name="slot" value="txrom" />
 			<feature name="pcb" value="NES-TLROM" />
+			<feature name="mirroring" value="4screen" />
 			<dataarea name="chr" size="131072">
 				<rom name="jurassic boy 2 (asia) (unl).chr" size="131072" crc="6f043956" sha1="30b107c995edd9b986a496d54d7581f5a6e187ce" offset="00000" status="baddump" />
 			</dataarea>
@@ -53129,6 +53130,7 @@ preliminary proto for the PAL version, still running on NTSC systems) or the gfx
 		<part name="cart" interface="nes_cart">
 			<feature name="slot" value="txrom" />
 			<feature name="pcb" value="NES-TLROM" />
+			<feature name="mirroring" value="4screen" />
 			<dataarea name="chr" size="262144">
 				<rom name="rocman x (asia) (unl).chr" size="262144" crc="dcb06887" sha1="5e846b18a5caf16b1fb384a08b13b2e08d7a45e6" offset="00000" status="baddump" />
 			</dataarea>
@@ -53146,6 +53148,7 @@ preliminary proto for the PAL version, still running on NTSC systems) or the gfx
 		<part name="cart" interface="nes_cart">
 			<feature name="slot" value="txrom" />
 			<feature name="pcb" value="NES-TLROM" />
+			<feature name="mirroring" value="4screen" />
 			<dataarea name="chr" size="262144">
 				<rom name="rocman x (sachen) (japan).chr" size="262144" crc="5da2317a" sha1="ba45052ed4a2d8dc1320e6ec0ade293493322c4a" offset="00000" status="baddump" />
 			</dataarea>
diff --git a/src/devices/bus/nes/mmc3.cpp b/src/devices/bus/nes/mmc3.cpp
index d6f7f37dc4a..dfc57f59b71 100644
--- a/src/devices/bus/nes/mmc3.cpp
+++ b/src/devices/bus/nes/mmc3.cpp
@@ -283,7 +283,8 @@ void nes_txrom_device::txrom_write(offs_t offset, uint8_t data)
 			break;
 
 		case 0x2000:
-			set_nt_mirroring(BIT(data, 0) ? PPU_MIRROR_HORZ : PPU_MIRROR_VERT);
+			if (m_mirroring != PPU_MIRROR_4SCREEN)
+				set_nt_mirroring(BIT(data, 0) ? PPU_MIRROR_HORZ : PPU_MIRROR_VERT);
 			break;
 
 		case 0x2001: