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games/snes: made cpu timing slightly more accurate

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

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

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

 extern u8int dma, nmi, irq;

 extern u32int hdma;

 extern int trace;

+extern int memcyc;

 extern uchar *prg, *sram;

 extern int nprg, nsram, hirom;

@@ -66,6 +67,7 @@

 	OVERSCAN = 1<<2,

 	AUTOJOY = 1,

 	NMITIMEN = 0x4200,

+	MEMSEL = 0x420d,

 	RDNMI = 0x4210,

 	VBLANK = 1<<7,

 	VCNTIRQ = 1<<5,

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

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

@@ -10,6 +10,7 @@

 u16int cgram[256];

 u16int oamaddr, vramlatch;

 u32int keylatch, lastkeys;

+int memcyc;

 enum {

 	OAMLATCH,

 	CGLATCH,

@@ -373,11 +374,18 @@

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

 			return regread(al);

 		}

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

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

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

+				memcyc += 2;

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

+		}

 	}

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

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

+		memcyc += 2;

 		return 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];

@@ -391,8 +399,10 @@

 	al = a;

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

-	if(b >= 0x7e && a < 0x800000)

+	if(b >= 0x7e && a < 0x800000){

+		memcyc += 2;

 		mem[a - 0x7e0000] = v;

+	}

 	if(al < 0x8000){

 		if(b < 0x40){

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

@@ -405,6 +415,8 @@

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

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

 		save:

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

+				memcyc += 2;	

 			if(saveclock == 0)

 				saveclock = SAVEFREQ;

 			return;

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

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

@@ -255,7 +255,12 @@

 			qlock(&pauselock);

 			qunlock(&pauselock);

 		}

-		t = cpustep() * 8;

+		memcyc = 0;

+		t = cpustep();

+		if(curpc == -1)

+			t *= 8;

+		else

+			t = t * 6 + memcyc;

 		spcclock -= t;

 		stimerclock += t;

 		ppuclock += t;