mode7 doc: add code that proves the Woz free DRAM refresh actually works

mode7_demo/docs/address.c

@@ -0,0 +1,119 @@
+#include <stdio.h>
+
+int main(int argc, char **argv) {
+
+	int h[7],hpe;
+	int sum_a3,sum_a4,sum_a5,sum_a6;
+	int v[5],va,vb,vc;
+	int a[16],addr,i;
+	// hbl = horizontal blanking gate
+	int text=1,page1=1,page2=0,hbl=0;
+	int vcount=0;
+	int vline=0;
+	int refresh[128],ra[7],ras,refresh_cycles=0;
+
+	for(i=0;i<128;i++) refresh[i]=0;
+
+	while(1) {
+		h[0]=(vcount>>0)&1;
+		h[1]=(vcount>>1)&1;
+		h[2]=(vcount>>2)&1;
+		h[3]=(vcount>>3)&1;
+		h[4]=(vcount>>4)&1;
+		h[5]=(vcount>>5)&1;
+		hpe=(vcount>>6)&1;
+		va=(vcount>>7)&1;
+		vb=(vcount>>8)&1;
+		vc=(vcount>>9)&1;
+		v[0]=(vcount>>10)&1;
+		v[1]=(vcount>>11)&1;
+		v[2]=(vcount>>12)&1;
+		v[3]=(vcount>>13)&1;
+		v[4]=(vcount>>14)&1;
+		v[5]=(vcount>>15)&1;
+
+
+		/* First 25 cycles */
+		hbl=!h[5]&&(!h[3]||!h[4]);
+
+		int x,y,z,sum;
+		x=0xd;	// 1101
+		y=(h[5]<<2)|(h[4]<<1)|(h[3]);
+		z=(v[4]<<3)|(v[3]<<2)|(v[4]<<1)|(v[3]);
+		sum=x+y+z;
+
+		sum_a6=(sum>>3)&1;
+		sum_a5=(sum>>2)&1;
+		sum_a4=(sum>>1)&1;
+		sum_a3=(sum)&1;
+
+		a[0]=h[0];
+		a[1]=h[1];
+		a[2]=h[2];
+		a[3]=sum_a3;
+		a[4]=sum_a4;
+		a[5]=sum_a5;
+		a[6]=sum_a6;
+		a[7]=v[0];
+		a[8]=v[1];
+		a[9]=v[2];
+		a[10]=text&page1;
+		a[11]=text&page2;
+		a[12]=text&hbl;
+		a[13]=0;
+		a[14]=0;
+		a[15]=0;
+
+		ra[0]=v[0];
+		ra[1]=h[2];
+		ra[2]=h[0];
+		ra[3]=v[1];
+		ra[4]=sum_a3;	// sum0?
+		ra[5]=h[1];
+		ra[6]=hbl;
+
+		ras=0;
+		for(i=0;i<7;i++) ras|=(ra[i]<<i);
+//		printf("RAS: %d\n",ras);
+
+		refresh[ras]=1;
+
+		int refreshed=0;
+		for(i=0;i<128;i++) refreshed+=refresh[i];
+//		printf("REFRESHED= %d\n",refreshed);
+
+		if (refreshed==128) {
+			printf("*** DONE REFRESHING %d ***\n",
+				refresh_cycles);
+			for(i=0;i<128;i++) refresh[i]=0;
+			refresh_cycles=0;
+		}
+
+		addr=0;
+		for(i=0;i<15;i++) addr|=(a[i]<<i);
+		printf("%04x ",addr);
+
+		/* horizontal divide by 65 counter */
+		/* values are 000.0000 and 100.0000-111.1111 */
+		if ((vcount&0x7f)==0) {
+			vcount|=0x40;
+			printf("\nRestart H, V=%d\n",vline);
+			vline++;
+		}
+		else {
+			vcount++;
+		}
+
+		/* vertical divide by 262 */
+		if ((vcount&0xff80)==0) {
+			vcount|=0x7d00; // 0.1111.1010
+					// 0111.1101.0000.0000
+			vline=0;
+			printf("Restart V\n");
+		}
+
+		refresh_cycles++;
+	}
+
+	return 0;
+}