erc-c/include/mos6502.h

#ifndef _MOS6502_H_
#define _MOS6502_H_

#include "vm_bits.h"
#include "vm_segment.h"

#define MOS6502_MEMSIZE     65536

#define SET_ARITH_STATUS(v) \
    cpu->P &= ~NEGATIVE; \
    cpu->P &= ~ZERO; \
    cpu->P &= ~CARRY; \
    if ((v) == 0) cpu->P |= ZERO; \
    if ((v) > 0) cpu->P |= CARRY; \
    if ((v) & 0x80) cpu->P |= NEGATIVE

#define SET_PC_BYTE(cpu, off, byte) \
    vm_segment_set(cpu->memory, cpu->PC + off, byte)

#define INIT_ADDR_MODE() \
    mos6502 *cpu; \
    cpu = mos6502_create()

#define END_ADDR_MODE() \
    mos6502_free(cpu)

#define START_CPU_TEST(t) \
    t *cpu; \
    cpu = t##_create()

#define END_CPU_TEST(t) \
    t##_free(cpu)

#define DEFINE_INST(inst) \
    void mos6502_handle_##inst (mos6502 *cpu, vm_8bit oper)

typedef struct {
    // Our memory.
    vm_segment *memory;

    // This contains the last _effective_ address we've resolved in one
    // of our address modes. In absolute mode, this would be the literal
    // operand we read from memory; in indirect mode, this will be the
    // address we _find_ after dereferencing the operand we read from
    // memory. Another way of thinking of this is, this address is where
    // we found the value we care about.
    vm_16bit last_addr;

    /*
     * This field contains the number of CPU cycles that the last
     * instruction handled should consume. In order to accurately
     * emulate any architecture, we must model the type of "wait" time
     * each instruction would cause.
     *
     * It should also be pointed out that the number of cycles is both
     * informed by the instruction _and_ the address mode. For example,
     * an instruction executed in zero-page address mode would consume
     * fewer cycles than one executed in absolute address mode, because
     * in the latter, the CPU would have to read ahead to discover a
     * 16-bit operand vs. the 8-bit operand in the former.
     */
    int cycles;

    // Our program counter register; this is what we'll use to determine
    // where we're "at" in memory while executing opcodes. We use a
    // 16-bit register because our memory is 64k large.
    vm_16bit PC;

    // This is the accumulator register. It's used in most arithmetic
    // operations, and anything like that which you need to do will end
    // up storing the value here.
    vm_8bit A;

    // The X and Y registers are our index registers. They're provided
    // to aid looping over tables, but they can also be used for other
    // purposes.
    vm_8bit X, Y;

    // The P register is our status flag register. (I presume 'P' means
    // 'predicate'.) Each bit stands for some kind of status.
    vm_8bit P;

    // The S register is our stack counter register. It indicates how
    // far into the stack we've gone.
    vm_8bit S;
} mos6502;

/*
 * This is a small convenience so that we don't need to expose the
 * somewhat regrettable syntax for function pointers to any main source
 * file
 */
typedef vm_8bit (*mos6502_address_resolver)(mos6502 *);

extern mos6502 *mos6502_create();
extern void mos6502_free(mos6502 *);
extern vm_8bit mos6502_next_byte(mos6502 *);
extern void mos6502_push_stack(mos6502 *, vm_16bit);
extern vm_16bit mos6502_pop_stack(mos6502 *);
extern void mos6502_set_status(mos6502 *, vm_8bit);
extern void mos6502_modify_status(mos6502 *, vm_8bit, vm_8bit);
extern int mos6502_cycles(mos6502 *, vm_8bit);
extern int mos6502_instruction(vm_8bit);

/*
 * Below are some functions that are defined in mos6502.addr.c
 */
extern int mos6502_addr_mode(vm_8bit);
extern mos6502_address_resolver mos6502_get_address_resolver(int);

/*
 * In some address mode resolution, we must factor the carry bit into
 * the arithmetic we perform. In all those cases, if the carry bit is
 * set, we must only add 1 to the addition. The carry variable is,
 * therefore, the literal value we are adding, rather than a boolean
 * signifier.
 */
#define CARRY_BIT() \
    vm_8bit carry = 0; \
    if (cpu->P & CARRY) carry = 1

/*
 * A uniform way of declaring resolve functions for address modes, which
 * is useful in the event that we need to change the function signature.
 */
#define DECL_ADDR_MODE(x) \
    extern vm_8bit mos6502_resolve_##x (mos6502 *)

/*
 * Similarly, a uniform way of declaring instruction handler functions,
 * for the same reasons.
 */
#define DECL_INST(x) \
    extern void mos6502_handle_##x (mos6502 *, vm_8bit)

/*
 * All of our address modes
 */
DECL_ADDR_MODE(acc);
DECL_ADDR_MODE(abs);
DECL_ADDR_MODE(abx);
DECL_ADDR_MODE(aby);
DECL_ADDR_MODE(imm);
DECL_ADDR_MODE(ind);
DECL_ADDR_MODE(idx);
DECL_ADDR_MODE(idy);
DECL_ADDR_MODE(rel);
DECL_ADDR_MODE(zpg);
DECL_ADDR_MODE(zpx);
DECL_ADDR_MODE(zpy);

/*
 * And now, our instruction handlers; held generally in mos6502.*.c
 * (excepting mos6502.addr.c).
 */
DECL_INST(adc);
DECL_INST(and);
DECL_INST(asl);
DECL_INST(bcc);
DECL_INST(bcs);
DECL_INST(beq);
DECL_INST(bit);
DECL_INST(bmi);
DECL_INST(bne);
DECL_INST(bpl);
DECL_INST(brk);
DECL_INST(bvc);
DECL_INST(bvs);
DECL_INST(clc);
DECL_INST(cld);
DECL_INST(cli);
DECL_INST(clv);
DECL_INST(cmp);
DECL_INST(cpx);
DECL_INST(cpy);
DECL_INST(dec);
DECL_INST(dex);
DECL_INST(dey);
DECL_INST(eor);
DECL_INST(inc);
DECL_INST(inx);
DECL_INST(iny);
DECL_INST(jmp);
DECL_INST(jsr);
DECL_INST(lda);
DECL_INST(ldx);
DECL_INST(ldy);
DECL_INST(lsr);
DECL_INST(nop);
DECL_INST(ora);
DECL_INST(pha);
DECL_INST(php);
DECL_INST(pla);
DECL_INST(plp);
DECL_INST(rol);
DECL_INST(ror);
DECL_INST(rti);
DECL_INST(rts);
DECL_INST(sbc);
DECL_INST(sec);
DECL_INST(sed);
DECL_INST(sei);
DECL_INST(sta);
DECL_INST(stx);
DECL_INST(sty);
DECL_INST(tax);
DECL_INST(tay);
DECL_INST(tsx);
DECL_INST(txa);
DECL_INST(txs);
DECL_INST(tya);

#endif