mirror of
https://github.com/DavidBuchanan314/6502-emu.git
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2d30a08daf
* note: this is not multithreading; it simply allows a program to step through more than one CPU in the same process
82 lines
1.4 KiB
C
82 lines
1.4 KiB
C
#include <stdint.h>
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#include <stdbool.h>
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#define CPU_FREQ 4e6 // 4Mhz
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#define STEP_DURATION 10e6 // 10ms
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#define ONE_SECOND 1e9
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#define NUM_MODES 14
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#define NMI_VEC 0xFFFA
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#define RST_VEC 0xFFFC
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#define IRQ_VEC 0xFFFE
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struct StatusBits{
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bool carry:1; // bit 0
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bool zero:1;
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bool interrupt:1;
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bool decimal:1;
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bool brk:1; // "break" is a reserved word :(
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bool unused:1;
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bool overflow:1;
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bool sign:1; // bit 7
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};
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union StatusReg { // this means we can access the status register as a byte, or as individual bits.
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struct StatusBits bits;
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uint8_t byte;
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};
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typedef struct {
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uint8_t memory[1<<16];
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uint8_t A;
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uint8_t X;
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uint8_t Y;
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uint16_t PC;
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uint8_t SP; // points to first empty stack location
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uint8_t extra_cycles;
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uint64_t total_cycles;
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union StatusReg SR;
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void * read_addr;
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void * write_addr;
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int jumping; // used to check that we don't need to increment the PC after a jump
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} CPU;
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typedef enum {
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ACC,
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ABS,
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ABSX,
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ABSY,
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IMM,
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IMPL,
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IND,
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XIND,
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INDY,
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REL,
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ZP,
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ZPX,
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ZPY,
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JMP_IND_BUG,
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} Mode;
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typedef struct {
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char * mnemonic;
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void (*function)(CPU *);
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Mode mode;
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uint8_t cycles;
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} Instruction;
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Instruction instructions[0x100];
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void init_tables();
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void reset_cpu(CPU *cpu, int _a, int _x, int _y, int _sp, int _sr, int _pc);
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int load_rom(CPU *cpu, char * filename, int load_addr);
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int step_cpu(CPU *cpu, int verbose);
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void save_memory(CPU *cpu, char * filename);
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CPU * create_cpu();
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