mirror of
https://github.com/deater/dos33fsprogs.git
synced 2024-07-01 18:29:27 +00:00
138 lines
1.6 KiB
C
138 lines
1.6 KiB
C
#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include "6502_emulate.h"
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/* 128kB of RAM */
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#define RAMSIZE 128*1024
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unsigned char ram[RAMSIZE];
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/* Registers */
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unsigned char a,y,x;
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unsigned short sp;
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/* Flags */
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unsigned int n,z,c,v;
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int init_6502(void) {
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a=0;
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y=0;
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x=0;
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sp=0x1ff;
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n=0; z=0; c=0; v=0;
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return 0;
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}
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unsigned short y_indirect(unsigned char base, unsigned char y) {
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unsigned short addr;
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addr=(((short)(ram[base+1]))<<8) | (short)ram[base];
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//if (debug) printf("Address=%x\n",addr+y);
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return addr+y;
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}
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void adc(int value) {
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int temp_a;
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int temp_value;
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int result;
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temp_a=a&0xff;
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temp_value=value&0xff;
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result=(temp_a+temp_value+c);
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c=(result&0x100)>>8;
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n=(result&0x80)>>7;
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v=!!((a^result)&(value^result)&0x80);
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a=result&0xff;
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z=(a==0);
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}
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void sbc(int value) {
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int temp_a;
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int result;
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int temp_value;
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temp_a=a&0xff;
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temp_value=(~value)&0xff;
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result=temp_a+temp_value+c;
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// printf("SBC: %x - %x (%x) = %x\n",a,value,c,result);
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c=(result&0x100)>>8;
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n=(result&0x80)>>7;
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v=!!((a^result)&((255-value)^result)&0x80);
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a=result&0xff;
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z=(a==0);
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}
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void cmp(int value) {
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int temp_a;
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int temp_value;
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int result;
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temp_a=a&0xff;
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temp_value=(~value)&0xff;
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result=temp_a+temp_value+1;
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c=(result&0x100)>>8;
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result&=0xff;
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n=(result&0x80)>>7;
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z=(result==0);
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}
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void pha(void) {
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sp--;
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ram[sp]=a;
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}
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void pla(void) {
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a=ram[sp];
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sp++;
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}
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void lsr(void) {
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int temp_a;
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temp_a=a;
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temp_a&=0xff;
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temp_a=temp_a>>1;
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a=(temp_a&0xff);
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// printf("LSR A=%x\n",a);
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}
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unsigned char high(int value) {
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return (value>>8)&0xff;
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}
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unsigned char low(int value) {
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return (value&0xff);
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}
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