merge

this is a long time in the making. hello, memread and memwrite
byebye to mem[a] = v

scemu.c

@@ -14,14 +14,13 @@ enum {
 int		step(void);
 static	u16int	fetch16(void);
 
-u8int	mem[65536];
+u8int	mem[32768];
+u8int	prog[32768];
 u8int	rA, rS, rX, rY, rP;
 u16int	pc;
 
 int	irq, nmi;
 
-u8int	*prog;
-
 void
 usage(void)
 {
@@ -36,21 +35,18 @@ openprog(char *f, vlong *progsiz)
 	long n;
 	Dir *d;
 
-	prog = nil;
+	memset(prog, 0, sizeof prog);
 	if(f == nil)
 		f = "a.out";
 	fd = open(f, OREAD);
 	if(fd < 0)
-		return;
+		sysfatal("bad program: %r\n");
 	d = dirfstat(fd);
 	if(d->length > 32768)
-		sysfatal("bad program: bigger than 32K, please shrink it");
+		sysfatal("bad program: bigger than 32K and no banking support");
 	*progsiz = d->length;
 	free(d);
-	prog = malloc(*progsiz);
-	if(prog == nil)
-		sysfatal("bad malloc");
-	n = read(fd, prog, *progsiz);
+	n = read(fd, prog+32768-*progsiz, *progsiz);
 	if(n != *progsiz)
 		fprint(2, "tried to read %lld bytes, got only %ld bytes\n", *progsiz, n);
 	close(fd);
@@ -73,9 +69,6 @@ main(int argc, char **argv)
 		break;
 	}ARGEND
 	openprog(*argv, &progsiz);
-	if(prog == nil)
-		sysfatal("bad program: %r");
-	memmove(mem+0x8000, prog, progsiz);
 	rP = 0x34;
 	pc = 0xFFFC;
 	pc = fetch16();
@@ -94,49 +87,65 @@ main(int argc, char **argv)
 	}
 }
 
+u8int
+memread(u16int a)
+{
+	if(a < 0x8000)
+		return mem[a];
+	else
+		return prog[a-0x8000];
+}
+
+void
+memwrite(u16int a, u8int v)
+{
+	if(a < 0x8000)
+		mem[a] = v;
+}
+
 static void
 push8(u8int v)
 {
-	mem[0x100 | rS--] = v;
+	memwrite(0x100 | rS--, v);
 }
 
 static void
 push16(u16int v)
 {
-	mem[0x100 | rS--] = v >> 8;
-	mem[0x100 | rS--] = v&0xff;
+	memwrite(0x100 | rS--, v >> 8);
+	memwrite(0x100 | rS--, v);
 }
 
 static u8int
 pop8(void)
 {
-	return mem[0x100 | ++rS];
+	return memread(0x100 | ++rS);
 }
 
 static u16int
 pop16(void)
 {
 	u16int v;
-
-	v = mem[0x100 | ++rS];
-	v |= mem[0x100 | ++rS] << 8;
+	
+	v = memread(0x100 | ++rS);
+	v |= memread(0x100 | ++rS) << 8;
 	return v;
 }
 
 static u8int
 fetch8(void)
 {
-	return mem[pc++];
+	return memread(pc++);
 }
 
 static u16int
 fetch16(void)
 {
-	u16int v;
-
-	v = fetch8();
-	v |= fetch8() << 8;
-	return v;
+	u16int r;
+	
+	r = memread(pc++);
+	r |= memread(pc++) << 8;
+	return r;
 }
 
 static void
@@ -182,8 +191,8 @@ asl(u16int a)
 {
 	u8int v;
 
+	v = memread(a);
 	rP &= ~(Negative | Zero | Carry);
-	v = mem[a];
 	if(v & 0x80)
 		rP |= Carry;
 	v <<= 1;
@@ -191,7 +200,7 @@ asl(u16int a)
 		rP |= Zero;
 	if(v & 0x80)
 		rP |= Negative;
-	mem[a] = v;
+	memwrite(a, v);
 }
 
 static void
@@ -199,13 +208,13 @@ lsr(u16int a)
 {
 	u8int v;
 
-	v = mem[a];
+	v = memread(a);
 	rP &= ~(Negative | Zero | Carry);
 	rP |= v & 1;
 	v >>= 1;
 	if(v == 0) rP |= Zero;
 	if(v & 0x80) rP |= Negative;
-	mem[a] = v;
+	memwrite(a, v);
 }
 
 static void
@@ -213,14 +222,14 @@ rol(u16int a)
 {
 	u8int v, b;
 	
-	v = mem[a];
+	v = memread(a);
 	b = rP & Carry;
 	rP &= ~(Carry | Negative | Zero);
 	if(v & 0x80) rP |= Carry;
 	v = (v << 1) | b;
 	if(v & 0x80) rP |= Negative;
 	if(v == 0) rP |= Zero;
-	mem[a] = v;
+	memwrite(a, v);
 }
 
 static void
@@ -228,14 +237,14 @@ ror(u16int a)
 {
 	u8int v, b;
 	
-	v = mem[a];
+	v = memread(a);
 	b = rP & Carry;
 	rP &= ~(Carry | Negative | Zero);
 	rP |= v & 1;
 	v = (v >> 1) | (b << 7);
 	if(v & 0x80) rP |= Negative;
 	if(v == 0) rP |= Zero;
-	mem[a] = v;
+	memwrite(a, v);
 }
 
 static void
@@ -252,10 +261,10 @@ inc(u16int a)
 {
 	u8int v;
 
-	v = mem[a];
+	v = memread(a);
 	v++;
 	nz(v);
-	mem[a] = v;
+	memwrite(a, v);
 }
 
 static void
@@ -263,10 +272,10 @@ dec(u16int a)
 {
 	u8int v;
 
-	v = mem[a];
+	v = memread(a);
 	v--;
 	nz(v);
-	mem[a] = v;
+	memwrite(a, v);
 }
 
 static int
@@ -290,10 +299,10 @@ aindX(void)
 {
 	u8int r;
 	u16int b;
-
+	
 	r = fetch8() + rX;
-	b = mem[r++];
-	b |= mem[r] << 8;
+	b = memread(r++);
+	b |= memread(r) << 8;
 	return b;
 }
 
@@ -302,11 +311,11 @@ aindY(int *p)
 {
 	u8int r;
 	u16int b;
-
+	
 	r = fetch8();
-	b = mem[r++] + rY;
+	b = memread(r++) + rY;
 	*p = b > 0xFF;
-	b += mem[r] << 8;
+	b += memread(r) << 8;
 	return b;
 }
 
@@ -315,8 +324,8 @@ interrupt(int nmi, int brk)
 {
 	push16(pc);
 	push8(rP | 0x20 | (brk << 4));
-	pc = mem[0xFFFA | (!nmi << 2)];
-	pc |= mem[0xFFFB | (!nmi << 2)] << 8;
+	pc = memread(0xFFFA | (!nmi << 2));
+	pc |= memread(0xFFFB | (!nmi << 2)) << 8;
 	rP |= Interrupt;
 }