dos33fsprogs/gr-sim/6502_emulate.c

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C
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#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include "6502_emulate.h"
/* 128kB of RAM */
#define RAMSIZE 128*1024
unsigned char ram[RAMSIZE];
/* Registers */
unsigned char a,y,x;
unsigned short sp;
/* Flags */
unsigned int n,z,c,v;
int init_6502(void) {
a=0;
y=0;
x=0;
sp=0x1ff;
n=0; z=0; c=0; v=0;
return 0;
}
unsigned short y_indirect(unsigned char base, unsigned char y) {
unsigned short addr;
addr=(((short)(ram[base+1]))<<8) | (short)ram[base];
//if (debug) printf("Address=%x\n",addr+y);
return addr+y;
}
void adc(int value) {
int temp_a;
int temp_value;
int result;
temp_a=a&0xff;
temp_value=value&0xff;
result=(temp_a+temp_value+c);
c=(result&0x100)>>8;
n=(result&0x80)>>7;
v=!!((a^result)&(value^result)&0x80);
a=result&0xff;
z=(a==0);
}
void sbc(int value) {
int temp_a;
int result;
int temp_value;
temp_a=a&0xff;
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temp_value=(~value)&0xff;
result=temp_a+temp_value+c;
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// printf("SBC: %x - %x (%x) = %x\n",a,value,c,result);
c=(result&0x100)>>8;
n=(result&0x80)>>7;
v=!!((a^result)&((255-value)^result)&0x80);
a=result&0xff;
z=(a==0);
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}
void cmp(int value) {
int temp_a;
int temp_value;
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int result;
temp_a=a&0xff;
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temp_value=(~value)&0xff;
result=temp_a+temp_value+1;
c=(result&0x100)>>8;
result&=0xff;
n=(result&0x80)>>7;
z=(result==0);
}
void pha(void) {
sp--;
ram[sp]=a;
}
void pla(void) {
a=ram[sp];
sp++;
}
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void lsr(void) {
int temp_a;
temp_a=a;
temp_a&=0xff;
temp_a=temp_a>>1;
a=(temp_a&0xff);
// printf("LSR A=%x\n",a);
}
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unsigned char high(int value) {
return (value>>8)&0xff;
}
unsigned char low(int value) {
return (value&0xff);
}