Add mapper 270

Author: negativeExponent

src/ines.c

@@ -821,6 +821,7 @@ INES_BOARD_BEGIN()
 	INES_BOARD( "8-in-1 JY-119",            267, Mapper267_Init         )
 	INES_BOARD( "COOLBOY/MINDKIDS",         268, Mapper268_Init         ) /* Submapper distinguishes between COOLBOY and MINDKIDS */
 	INES_BOARD( "Games Xplosion 121-in-1",  269, Mapper269_Init         )
+	INES_BOARD( "OneBus ($412C bankswitch)", 270, Mapper270_Init         )
 	INES_BOARD( "MGC-026",                  271, Mapper271_Init         )
 	INES_BOARD( "Akumajō Special: Boku Dracula-kun", 272, Mapper272_Init )
 	INES_BOARD( "80013-B",                  274, Mapper274_Init         )

src/ines.h

@@ -280,6 +280,7 @@ void Mapper266_Init(CartInfo *);
 void Mapper267_Init(CartInfo *);
 void Mapper268_Init(CartInfo *);
 void Mapper269_Init(CartInfo *);
+void Mapper270_Init(CartInfo *);
 void Mapper271_Init(CartInfo *);
 void Mapper272_Init(CartInfo *);
 void Mapper274_Init(CartInfo *);

src/mappers/mapper270.c

@@ -0,0 +1,107 @@
+/* FCEUmm - NES/Famicom Emulator
+ *
+ * Copyright notice for this file:
+ *  Copyright (C) 2025 negativeExponent
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ */
+
+/* NES 2.0 Mapper 270 denotes OneBus console multicarts that use the consoles'
+ * universal input/output (UIO) register $412C to bankswitch higher-order PRG
+ * address lines or several PRG chips, and select CHR-RAM via $4242.*/
+
+/* TODO: Family Pocket 638-in-1 freeze on jumper enable */
+
+#include "mapinc.h"
+#include "onebus.h"
+
+static uint8 reg4242;   /* $4242 */
+static uint8 dipsw; /* jumper */
+
+static void Sync(void) {
+	uint16 mblock = 0;
+	switch (iNESCart.submapper) {
+	case 1:
+		mblock |= (onebus.cpu41xx[0x2C] & 0x02) << 10; /* PRG/CHR A24 */
+		break;
+	case 2:
+		mblock |= (onebus.cpu41xx[0x2C] & 0x02) << 10; /* PRG/CHR A24 */
+		mblock |= (onebus.cpu41xx[0x2C] & 0x01) << 11; /* PRG/CHR A25 */
+		break;
+	case 3:
+		mblock |= (onebus.cpu41xx[0x2C] & 0x04) << 9; /* PRG/CHR A24 */
+		break;
+	case 0:
+	default:
+		mblock |= (onebus.cpu41xx[0x2C] & 0x02) << 10; /* PRG/CHR A24 */
+		mblock |= (onebus.cpu41xx[0x2C] & 0x04) <<  9; /* PRG/CHR A24 */
+		mblock |= (onebus.cpu41xx[0x2C] & 0x01) << 11; /* PRG/CHR A25 */
+		break;
+	}
+	OneBus_FixPRG(0x07FF, mblock);
+	if (reg4242 & 0x01) {
+		/* CHR-RAM enabled, use 8K unbancked CHR RAM */
+		setchr8(0);
+	} else {
+		OneBus_FixCHR(0x3FFF, mblock << 3);
+	}
+	OneBus_FixMIR();
+}
+
+static DECLFR(M270ReadJumperDetect) {
+	return dipsw << 3;
+}
+
+static DECLFW(M270WriteCHRRAMEnable) {
+	reg4242 = V;
+	if (CHRptr[0] && (reg4242 & 0x01)) {
+		SetupCartCHRMapping(0, CHRptr[0], CHRsize[0], TRUE);
+	} else {
+		SetupCartCHRMapping(0, PRGptr[0], PRGsize[0], FALSE);
+	}
+	Sync();
+}
+
+static void M270Power(void) {
+	dipsw = 0;
+	reg4242 = 0;
+	OneBus_Power();
+	SetReadHandler(0x412C, 0x412C, M270ReadJumperDetect);
+	SetWriteHandler(0x4242, 0x4242, M270WriteCHRRAMEnable);
+}
+
+static void M270Reset(void) {
+	SetupCartCHRMapping(0, PRGptr[0], PRGsize[0], FALSE);
+	dipsw = !dipsw; /* toggle jumper */
+	reg4242 = 0;
+	onebus.cpu41xx[0x2C] = 0;
+	OneBus_Reset();
+}
+
+void Mapper270_Init(CartInfo *info) {
+	int ws = (info->PRGRamSize + info->PRGRamSaveSize) / 1024;
+
+	if (!ws) {
+		ws = 8;
+	}
+
+	OneBus_Init(info, Sync, ws, info->battery);
+	info->Power = M270Power;
+	info->Reset = M270Reset;
+
+	AddExState(&reg4242, 1, 0, "CHRM");
+	AddExState(&dipsw, 1, 0, "DPSW");
+}