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games/gb: store sram in save state as well

Some games (notably Polished Crystal rom hack) use parts of sram
as extended wram.

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

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

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

 extern Var cpuvars[], ppuvars[], memvars[], apuvars[], evvars[];

 extern Event *events[NEVENT], *elist;

+extern u8int *back;

+extern int nback;

 static Biobuf *bp;

 Var apuvars[] = {{nil, 0, 0}};

@@ -128,6 +130,8 @@

 void

 savestate(char *file)

 {

+	u16int nsram;

+

 	flushback();

 	bp = Bopen(file, OWRITE);

 	if(bp == nil){

@@ -141,6 +145,12 @@

 	putvars(evvars);

 	putevents();

 	mapper(SAVE, 0);

+

+	nsram = nback;

+	Bputc(bp, nsram);

+	Bputc(bp, nsram>>8);

+	if(nsram > 0)

+		Bwrite(bp, back, nback);

 	Bterm(bp);

 }

@@ -147,6 +157,9 @@

 void

 loadstate(char *file)

 {

+	uchar buf[2];

+	u16int nsram;

+

 	bp = Bopen(file, OREAD);

 	if(bp == nil){

 		print("open: %r\n");

@@ -159,6 +172,14 @@

 	getvars(evvars);

 	getevents();

 	mapper(RSTR, 0);

+	if(Bread(bp, buf, 2) == 2){

+		nsram = buf[0] | (buf[1]<<8);

+		if(nback == nsram){

+			if(Bread(bp, back, nback) != nback)

+				sysfatal("truncated sram in save state");

+		} else

+			fprint(2, "sram count in save state (%ud) does match detected size from rom (%d)\n", nsram, nback);

+	}

 	memload();

 	Bterm(bp);

 }

-- 

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