mirror of
https://git.do.srb2.org/STJr/SRB2.git
synced 2024-12-21 02:10:39 +00:00
114 lines
3.1 KiB
C++
114 lines
3.1 KiB
C++
// NES 6502 CPU emulator
|
|
|
|
// Game_Music_Emu 0.6.0
|
|
#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
|