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// NES 6502 CPU emulator
// Game_Music_Emu 0.5.5
#ifndef NES_CPU_H
#define NES_CPU_H
#include "blargg_common.h"
typedef blargg_long nes_time_t; // clock cycle count
typedef unsigned nes_addr_t; // 16-bit address
enum { future_nes_time = INT_MAX / 2 + 1 };
class Nes_Cpu {
public:
typedef BOOST::uint8_t uint8_t;
// Clear registers, map low memory and its three mirrors to address 0,
// and mirror unmapped_page in remaining memory
void reset( void const* unmapped_page = 0 );
// Map code memory (memory accessed via the program counter). Start and size
// must be multiple of page_size. If mirror is true, repeats code page
// throughout address range.
enum { page_size = 0x800 };
void map_code( nes_addr_t start, unsigned size, void const* code, bool mirror = false );
// Access emulated memory as CPU does
uint8_t const* get_code( nes_addr_t );
// 2KB of RAM at address 0
uint8_t low_mem [0x800];
// NES 6502 registers. Not kept updated during a call to run().
struct registers_t {
BOOST::uint16_t pc;
BOOST::uint8_t a;
BOOST::uint8_t x;
BOOST::uint8_t y;
BOOST::uint8_t status;
BOOST::uint8_t sp;
};
registers_t r;
// Set end_time and run CPU from current time. Returns true if execution
// stopped due to encountering bad_opcode.
bool run( nes_time_t end_time );
// Time of beginning of next instruction to be executed
nes_time_t time() const { return state->time + state->base; }
void set_time( nes_time_t t ) { state->time = t - state->base; }
void adjust_time( int delta ) { state->time += delta; }
nes_time_t irq_time() const { return irq_time_; }
void set_irq_time( nes_time_t );
nes_time_t end_time() const { return end_time_; }
void set_end_time( nes_time_t );
// Number of undefined instructions encountered and skipped
void clear_error_count() { error_count_ = 0; }
unsigned long error_count() const { return error_count_; }
// CPU invokes bad opcode handler if it encounters this
enum { bad_opcode = 0xF2 };
public:
Nes_Cpu() { state = &state_; }
enum { page_bits = 11 };
enum { page_count = 0x10000 >> page_bits };
enum { irq_inhibit = 0x04 };
private:
struct state_t {
uint8_t const* code_map [page_count + 1];
nes_time_t base;
int time;
};
state_t* state; // points to state_ or a local copy within run()
state_t state_;
nes_time_t irq_time_;
nes_time_t end_time_;
unsigned long error_count_;
void set_code_page( int, void const* );
inline int update_end_time( nes_time_t end, nes_time_t irq );
};
inline BOOST::uint8_t const* Nes_Cpu::get_code( nes_addr_t addr )
{
return state->code_map [addr >> page_bits] + addr
#if !BLARGG_NONPORTABLE
% (unsigned) page_size
#endif
;
}
inline int Nes_Cpu::update_end_time( nes_time_t t, nes_time_t irq )
{
if ( irq < t && !(r.status & irq_inhibit) ) t = irq;
int delta = state->base - t;
state->base = t;
return delta;
}
inline void Nes_Cpu::set_irq_time( nes_time_t t )
{
state->time += update_end_time( end_time_, (irq_time_ = t) );
}
inline void Nes_Cpu::set_end_time( nes_time_t t )
{
state->time += update_end_time( (end_time_ = t), irq_time_ );
}
#endif
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