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games/snes: added open bus emulation

--- a/sys/src/games/snes/dat.h

+++ b/sys/src/games/snes/dat.h

@@ -12,6 +12,7 @@

 extern u32int keys, keylatch, lastkeys;

 extern u8int reg[32768], mem[131072], spcmem[65536], vram[65536], oam[544];

 extern u16int cgram[256], vramlatch;

+extern u8int mdr, mdr1, mdr2;

 extern int ppux, ppuy, rx;

 extern u16int vtime, htime, subcolor, oamaddr;

--- a/sys/src/games/snes/mem.c

+++ b/sys/src/games/snes/mem.c

@@ -22,6 +22,8 @@

 	OPVCTH,

 };

+u8int mdr, mdr1, mdr2;

+

 extern void calc7(void);

 static u16int

@@ -120,11 +122,11 @@

 	switch(p){

 	case 0x2134: case 0x2135: case 0x2136:

 		r = ((signed short)m7[0] * (signed char)reg[0x211c]) & 0xffffff;

-		return r >> 8 * (p - 0x2134);

+		return mdr1 = r >> 8 * (p - 0x2134);

 	case 0x2137:

 		if((reg[0x4201] & 0x80) != 0)

 			hvlatch();

-		return 0;

+		return mdr;

 	case 0x2138:

 		if(oamaddr < 0x200)

 			v = oam[oamaddr];

@@ -131,33 +133,36 @@

 		else

 			v = oam[oamaddr & 0x21f];

 		oamaddr = (oamaddr + 1) & 0x3ff;

-		return v;

+		return mdr1 = v;

 	case 0x2139:

 		v = vramlatch;

 		incvram(0, 1);

-		return v;

+		return mdr1 = v;

 	case 0x213a:

 		v = vramlatch >> 8;

 		incvram(1, 1);

-		return v;

+		return mdr1 = v;

 	case 0x213b:

 		a = swaprb(cgram[reg[0x2121]]);

 		if(reg[CGLH] != 0){

 			a >>= 8;

+			a |= mdr2 & 0x80;

 			reg[0x2121]++;

 		}

 		reg[CGLH] ^= 1;

-		return a;

+		return mdr2 = a;

 	case 0x213c:

 		reg[OPCTLATCH] ^= 1;

 		if((reg[OPCTLATCH] & 1) == 0)

-			return reg[OPHCTH];

-		break;

+			return mdr2 = reg[OPHCTH] | mdr2 & 0xfe;

+		return mdr2 = reg[p];

 	case 0x213d:

 		reg[OPCTLATCH] ^= 2;

 		if((reg[OPCTLATCH] & 2) == 0)

-			return reg[OPVCTH];

-		break;

+			return reg[OPVCTH] | mdr2 & 0xfe;

+		return mdr2 = reg[p];

+	case 0x213e:

+		return (mdr1 = reg[p]) | mdr & 0x10;

 	case 0x213f:

 		v = 2 | reg[OPCTLATCH] & 0x40;

 		if((reg[0x4201] & 0x80) != 0)

@@ -164,7 +169,7 @@

 			reg[OPCTLATCH] &= ~0x43;

 		else

 			reg[OPCTLATCH] &= ~3;

-		return v;

+		return mdr2 = v | mdr2 & 0x20;

 	case 0x2180:

 		v = memread(0x7e0000 | reg[0x2181] | reg[0x2182] << 8 | (reg[0x2183] & 1) << 16);

 		incwram();

@@ -180,13 +185,15 @@

 		}

 		v = keylatch >> 31;

 		keylatch = (keylatch << 1) | 1;

-		return v;

+		return v | mdr & 0xfc;

 	case 0x4017:

-		return 0;

+		return 0x1f | mdr & 0xe0;

+	case 0x4210:

+		return reg[p] | mdr & 0x70;

 	case 0x4211:

 		v = irq;

 		irq &= ~IRQPPU;

-		return v;

+		return v | mdr & 0x7f;

 	case 0x4212:

 		v = 0;

 		if(ppux >= 274 || ppux == 0)

@@ -197,11 +204,17 @@

 			if(ppuy <= a + 2 && (reg[NMITIMEN] & AUTOJOY) != 0)

 				v |= 1;

 		}

-		return v;

+		return v | mdr & 0x3e;

+	case 0x4214: case 0x4215: case 0x4216: case 0x4217: case 0x4218:

+	case 0x4219: case 0x421a: case 0x421b: case 0x421c: case 0x421d:

+	case 0x421e: case 0x421f:

+		return reg[p];

 	}

-	if((p & 0xff40) == 0x2140)

+	if((p & 0xff80) == 0x4300)

+		return reg[p];

+	if((p & 0xffc0) == 0x2140)

 		return spcmem[0xf4 | p & 3];

-	return reg[p];

+	return mdr;

 }

 void

@@ -381,25 +394,28 @@

 	b = (a>>16) & 0x7f;

 	if(al < 0x8000){

 		if(b < 0x40){

-			if(hirom && al >= 0x6000 && nsram != 0)

-				return sram[(b << 13 | al & 0x1ffff) & (nsram - 1)];

-			return regread(al);

+			if(hirom && al >= 0x6000 && nsram != 0){

+				if(a < 0x800000 || (reg[MEMSEL] & 1) == 0)

+					memcyc += 2;

+				return mdr = sram[(b << 13 | al & 0x1ffff) & (nsram - 1)];

+			}

+			return mdr = regread(al);

 		}

 		if(!hirom && (b & 0xf8) == 0x70 && nsram != 0){

 			if(a < 0x800000 || (reg[MEMSEL] & 1) == 0)

 				memcyc += 2;

-			return sram[a & 0x07ffff & (nsram - 1)];

+			return mdr = sram[a & 0x07ffff & (nsram - 1)];

 		}

 	}

 	if(b >= 0x7e && (a & (1<<23)) == 0){

 		memcyc += 2;

-		return mem[a - 0x7e0000];

+		return mdr = mem[a - 0x7e0000];

 	}

 	if(a < 0x800000 || (reg[MEMSEL] & 1) == 0)

 		memcyc += 2;

 	if(hirom)

-		return prg[((b & 0x3f) % nprg) << 16 | al];

-	return prg[(b%nprg) << 15 | al & 0x7fff];

+		return mdr = prg[((b & 0x3f) % nprg) << 16 | al];

+	return mdr = prg[(b%nprg) << 15 | al & 0x7fff];

 }

 void

--- a/sys/src/games/snes/state.c

+++ b/sys/src/games/snes/state.c

@@ -106,6 +106,9 @@

 	dma = get8();

 	hdma = get32();

 	wai = get8();

+	mdr = get8();

+	mdr1 = get8();

+	mdr2 = get8();

 	oamaddr = get16();

 	vramlatch = get16();

 	keylatch = get32();

@@ -163,6 +166,9 @@

 	put8(dma);

 	put32(hdma);

 	put8(wai);

+	put8(mdr);

+	put8(mdr1);

+	put8(mdr2);

 	put16(oamaddr);

 	put16(vramlatch);

 	put32(keylatch);