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games/nes: SUROM support, subtle NMI timing bug fixed

--- a/sys/src/games/nes/cpu.c

+++ b/sys/src/games/nes/cpu.c

@@ -244,11 +244,12 @@

 	u16int a, v;

 	int c;

-	if(nmi){

-		interrupt(1, 0);

-		nmi = 0;

-		return 7;

-	}

+	if(nmi)

+		if(--nmi == 0){

+			interrupt(1, 0);

+			nmi = 0;

+			return 7;

+		}

 	if(irq && (rP & 4) == 0){

 		interrupt(0, 0);

 		return 7;

@@ -256,7 +257,7 @@

 	curpc = pc;

 	op = fetch8();

 	if(trace)

-		print("%x %x %x %x %x %x %x %x\n", curpc, op, rA, rX, rY, rS, rP, memread(0x2c));

+		print("%x %x %x %x %x %x %x\n", curpc, op, rA, rX, rY, rS, rP);

 	switch(op){

 	case 0x00: pc++; interrupt(0, 1); return 7;

 	case 0x01: nz(rA |= indX()); return 6;

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

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

@@ -54,6 +54,8 @@

 	if(v < 0){

 		switch(v){

 		case INIT:

+			if(nprg > 32)

+				sysfatal("bad rom, too much prg rom for mmc1");

 			mode = 0x0C;

 			prgsh = 14;

 			chrsh = 12;

@@ -99,6 +101,10 @@

 		mirr = mirrs[mode & 3];

 		break;

 	case 0xA000:

+		if(nprg > 16){

+			pr = s & 0x10 | pr & 0x0f;

+			pr %= nprg;

+		}

 		c0 = s & 0x1f;

 		c0 %= 2*nchr;

 		break;

@@ -107,7 +113,7 @@

 		c1 %= 2*nchr;

 		break;

 	case 0xE000:

-		pr = s & 0x0f;

+		pr = pr & 0x10 | s & 0x0f;

 		pr %= nprg;

 		break;

 	}

@@ -121,7 +127,7 @@

 		break;

 	case 0x0C:

 		prgb[0] = prg + pr * 0x4000;

-		prgb[1] = prg + (0x0f % nprg) * 0x4000;

+		prgb[1] = prg + ((pr & 0x10 | 0x0f) % nprg) * 0x4000;

 		break;

 	default:

 		prgb[0] = prg + (pr & 0xfe) * 0x4000;

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

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

@@ -93,7 +93,7 @@

 		if(readn(fd, chr, nchr * CHRSZ) < nchr * CHRSZ)

 			sysfatal("read: %r");

 	}else{

-		nchr = 16;

+		nchr = 1;

 		chr = malloc(nchr * CHRSZ);

 		if(chr == nil)

 			sysfatal("malloc: %r");

--- a/sys/src/games/nes/ppu.c

+++ b/sys/src/games/nes/ppu.c

@@ -326,7 +326,7 @@

 		if(ppux == 1){

 			mem[PPUSTATUS] |= PPUVBLANK;

 			if((mem[PPUCTRL] & PPUNMI) != 0)

-				nmi = 1;

+				nmi = 2;

 			flush();

 		}

 	}