From bb4a67e9d2320670b14e6376bcd309c888e394c0 Mon Sep 17 00:00:00 2001
From: Vince Weaver <vincent.weaver@maine.edu>
Date: Fri, 12 Oct 2018 17:10:31 -0400
Subject: [PATCH] nibble_table: validating qkumba's DOS read nibble generation
 code

---
 gr-sim/6502_emulate.c | 75 +++++++++++++++++++++++++++++++++++++++++--
 gr-sim/6502_emulate.h |  5 +++
 gr-sim/dos/Makefile   | 31 ++++++++++++++++++
 gr-sim/dos/nibble.c   | 50 +++++++++++++++++++++++++++++
 4 files changed, 159 insertions(+), 2 deletions(-)
 create mode 100644 gr-sim/dos/Makefile
 create mode 100644 gr-sim/dos/nibble.c

diff --git a/gr-sim/6502_emulate.c b/gr-sim/6502_emulate.c
index 612f3287..c67fb919 100644
--- a/gr-sim/6502_emulate.c
+++ b/gr-sim/6502_emulate.c
@@ -207,9 +207,9 @@ void lsr(void) {
 
 	c=temp_a&0x1;
 	temp_a=temp_a>>1;
-	a=(temp_a&0xff);
+	a=(temp_a&0x7f);	// always shift 0 into top
 	z=(a==0);
-	n=!!(a&0x80);
+	n=!!(a&0x80);		// can this ever be 1?  no?
 //	printf("LSR A=%x\n",a);
 }
 
@@ -362,6 +362,21 @@ void bit(int value) {
 
 }
 
+	/* a is not modified */
+void bit_mem(int addr) {
+	int temp_a;
+
+	temp_a=a&ram[addr];
+	temp_a&=0xff;
+
+	z=(temp_a==0);
+
+	n=(ram[addr]&0x80);
+	v=(ram[addr]&0x40);
+
+}
+
+
 void lda(int addr) {
 
 	a=ram[addr];
@@ -441,6 +456,62 @@ void eor(int value) {
 
 }
 
+void ora(int value) {
+
+	int temp_a;
+	int temp_value;
+	int result;
+
+	temp_a=a&0xff;
+	temp_value=value&0xff;
+
+	result=(temp_a|temp_value);
+
+	n=(result&0x80)>>7;
+
+	a=result&0xff;
+	z=(a==0);
+
+}
+
+void ora_mem(int addr) {
+
+	int temp_a;
+	int temp_value;
+	int result;
+
+	temp_a=a&0xff;
+	temp_value=ram[addr]&0xff;
+
+	result=(temp_a|temp_value);
+
+	n=(result&0x80)>>7;
+
+	a=result&0xff;
+	z=(a==0);
+
+}
+
+void and(int value) {
+
+	int temp_a;
+	int temp_value;
+	int result;
+
+	temp_a=a&0xff;
+	temp_value=value&0xff;
+
+	result=(temp_a&temp_value);
+
+	n=(result&0x80)>>7;
+
+	a=result&0xff;
+	z=(a==0);
+
+}
+
+
+
 unsigned char high(int value) {
 	return (value>>8)&0xff;
 }
diff --git a/gr-sim/6502_emulate.h b/gr-sim/6502_emulate.h
index 4f116050..5fbd6253 100644
--- a/gr-sim/6502_emulate.h
+++ b/gr-sim/6502_emulate.h
@@ -8,7 +8,12 @@ unsigned short y_indirect(unsigned char base, unsigned char y);
 int init_6502(void);
 void adc(int value);
 void sbc(int value);
+void and(int value);
+void and_mem(int addr);
+void ora(int value);
+void ora_mem(int addr);
 void eor(int value);
+void eor_mem(int addr);
 void cmp(int value);
 void cpy(int value);
 void cpx(int value);
diff --git a/gr-sim/dos/Makefile b/gr-sim/dos/Makefile
new file mode 100644
index 00000000..e27edd16
--- /dev/null
+++ b/gr-sim/dos/Makefile
@@ -0,0 +1,31 @@
+CC = gcc
+CFLAGS = -Wall -O2 -I.. -g
+LFLAGS = -lm
+
+SDL_LIBS= `sdl-config --libs`
+SDL_INCLUDE= `sdl-config --cflags`
+GR_SIM = ../gr-sim.a
+
+all:	nibble
+
+####
+
+nibble:	nibble.o $(GR_SIM)
+	$(CC) $(LFLAGS) $(SDL_LIBS) -o nibble nibble.o $(GR_SIM)
+
+nibble.o:	nibble.c
+	$(CC) $(CFLAGS) -c nibble.c
+
+####
+
+nibble2:	nibble2.o $(GR_SIM)
+	$(CC) $(LFLAGS) $(SDL_LIBS) -o nibble2 nibble2.o $(GR_SIM)
+
+nibble2.o:	nibble2.c
+	$(CC) $(CFLAGS) -c nibble2.c
+
+
+####
+
+clean:	
+	rm -f *~ *.o nibble nibble2
diff --git a/gr-sim/dos/nibble.c b/gr-sim/dos/nibble.c
new file mode 100644
index 00000000..22645129
--- /dev/null
+++ b/gr-sim/dos/nibble.c
@@ -0,0 +1,50 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+
+#include <math.h>
+
+#include "gr-sim.h"
+#include "tfv_utils.h"
+#include "tfv_zp.h"
+#include "6502_emulate.h"
+
+int main(int argc, char **argv) {
+
+	int yy;
+
+	grsim_init();
+	gr();
+
+	yy=0;
+	printf("****yy=%d\n",yy);
+
+	y=yy;			// ldy	   #0
+	x=3;			// ldx     #3
+L1:
+	ram[0x3c]=x;		// stx     $3c
+	a=x;			// txa
+	asl();			// asl
+	bit_mem(0x3c);		// bit     $3c
+	if (z==1) goto L3;	// beq     L3
+	ora_mem(0x3c);		// ora     $3c
+	eor(0xff);		// eor     #$ff
+	and(0x7e);		// and     #$7e
+L2:
+	if (c==1) goto L3;	// bcs     L3
+	lsr();			// lsr
+	if (z==0) goto L2;	// bne     L2
+
+	a=y;			// tya
+	printf("%x=%x\n",x,a);	// sta     nibtbl, x
+	y++;			// iny
+L3:
+	x++;			// inx
+	if (!(x&0x80)) goto L1;	// bpl     L1
+
+
+
+	return 0;
+}
+