e6502/e6502.h

#include <stdint.h>


typedef enum {
    e6502_Status_C = 0b00000001,
    e6502_Status_Z = 0b00000010,
    e6502_Status_I = 0b00000100,
    e6502_Status_D = 0b00001000,
    e6502_Status_B = 0b00010000,
    e6502_Status_1 = 0b00100000,
    e6502_Status_V = 0b01000000,
    e6502_Status_N = 0b10000000,
} e6502_Status_Flag;

typedef enum __attribute__ ((__packed__)) {
    e6502_Pin_NMI = 0b01,
    e6502_Pin_IRQ = 0b10,

    e6502_NMI_Serviced = 0b10000000
} e6502_Pin;

typedef struct __attribute__ ((__packed__)) {
    uint16_t PC;
    uint8_t  S;
    uint8_t  A;
    uint8_t  X;
    uint8_t  Y;
    uint8_t  P;
} e6502_Registers;

typedef uint16_t e6502_Mem_Addr;

#ifndef E6502_POLL_MEM
typedef uint8_t(e6502_Read)(void*, e6502_Mem_Addr);
typedef void(e6502_Write)(void*, e6502_Mem_Addr, uint8_t);
#endif

typedef struct {
    e6502_Registers registers;
    e6502_Pin       pins;
#ifdef E6502_POLL_MEM
    uint8_t memory[65536];
#else
    e6502_Read*  bus_read;
    e6502_Write* bus_write;
    void*        bus_context;
#endif
    int cycle;
} e6502_Core;

#define e6502_Memory_Stack  (0x0100U)

#define e6502_IRQ_Vec   (0xFFFEU)
#define e6502_Reset_Vec (0xFFFCU)
#define e6502_NMI_Vec   (0xFFFAU)

#ifdef E6502_POLL_MEM

static inline uint8_t e6502_r8(e6502_Core* core,
                               e6502_Mem_Addr adr) {
    return core->memory[adr];
}

static inline void e6502_w8(e6502_Core* core,
                            e6502_Mem_Addr adr,
                            uint8_t val) {
    core->memory[adr] = val;
}

#else

static inline uint8_t e6502_r8(e6502_Core* core,
                               e6502_Mem_Addr adr) {
    return core->bus_read(core->bus_context, adr);
}

static inline void e6502_w8(e6502_Core* core,
                            e6502_Mem_Addr adr,
                            uint8_t val) {
    return core->bus_write(core->bus_context, adr, val);
}

#endif

static inline uint16_t e6502_r16(e6502_Core* core,
                                 e6502_Mem_Addr adr) {
    return e6502_r8(core, adr) |
           ((uint16_t)e6502_r8(core, adr + 1) << 8);
}

static inline void e6502_w16(e6502_Core* core,
                             e6502_Mem_Addr adr,
                             uint16_t val) {
    e6502_w8(core, adr, val);
    e6502_w8(core, adr + 1, val >> 8);
}

static inline void e6502_push8(e6502_Core* core, uint8_t val) {
    e6502_w8(core, e6502_Memory_Stack + core->registers.S--, val);
}

static inline void e6502_push16(e6502_Core* core, uint16_t val) {
    e6502_push8(core, val >> 8);
    e6502_push8(core, val & 0xFF);
}

static inline uint8_t e6502_pop8(e6502_Core* core) {
    return e6502_r8(core, e6502_Memory_Stack +
                          ++core->registers.S);
}

static inline uint16_t e6502_pop16(e6502_Core* core) {
    return (e6502_pop8(core) | ((uint16_t)e6502_pop8(core) << 8));
}


#ifdef E6502_POLL_MEM
void e6502_init(e6502_Core*);
#else
void e6502_init(e6502_Core*, e6502_Read, e6502_Write, void*);
#endif

int e6502_step(e6502_Core* core);
int e6502_run(e6502_Core* core,
              int remaining,
              int* run,
              int instructions);

void e6502_reset(e6502_Core* core);

void e6502_set_irq(e6502_Core* core, int active);

void e6502_set_nmi(e6502_Core* core, int active);