71 lines
1.0 KiB
C
71 lines
1.0 KiB
C
#include <stdint.h>
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#define CPU_FREQ 4000000
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#define STEP_DURATION 10000000 // 10ms
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#define ONE_SECOND 1e9
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#define NUM_MODES 13
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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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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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void * readAddr;
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void * writeAddr;
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struct StatusBits{
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int carry:1; // bit 0
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int zero:1;
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int interrupt:1;
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int decimal:1;
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int brk:1; // "break" is a reserved word :(
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int unused:1;
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int overflow:1;
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int 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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union StatusReg SR;
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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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} Mode;
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typedef struct {
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char * mnemonic;
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void (*function)();
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Mode mode;
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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();
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int load_rom(char * filename);
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void step_cpu();
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