Hes_Cpu.h

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// PC Engine CPU emulator for use with HES music files
 
// Game_Music_Emu https://bitbucket.org/mpyne/game-music-emu/
#ifndef HES_CPU_H
#define HES_CPU_H
 
#include "blargg_common.h"
 
typedef blargg_long hes_time_t; // clock cycle count
typedef unsigned hes_addr_t; // 16-bit address
enum { future_hes_time = INT_MAX / 2 + 1 };
 
class Hes_Cpu {
public:
        void reset();
        
        enum { page_size = 0x2000 };
        enum { page_shift = 13 };
        enum { page_count = 8 };
        void set_mmr( int reg, int bank );
        
        uint8_t const* get_code( hes_addr_t );
        
        uint8_t ram [page_size];
        
        // not kept updated during a call to run()
        struct registers_t {
                uint16_t pc;
                uint8_t a;
                uint8_t x;
                uint8_t y;
                uint8_t status;
                uint8_t sp;
        };
        registers_t r;
        
        // page mapping registers
        uint8_t mmr [page_count + 1];
        
        // Set end_time and run CPU from current time. Returns true if any illegal
        // instructions were encountered.
        bool run( hes_time_t end_time );
        
        // Time of beginning of next instruction to be executed
        hes_time_t time() const             { return state->time + state->base; }
        void set_time( hes_time_t t )       { state->time = t - state->base; }
        void adjust_time( int delta )       { state->time += delta; }
        
        hes_time_t irq_time() const         { return irq_time_; }
        void set_irq_time( hes_time_t );
        
        hes_time_t end_time() const         { return end_time_; }
        void set_end_time( hes_time_t );
        
        void end_frame( hes_time_t );
        
        // Attempt to execute instruction here results in CPU advancing time to
        // lesser of irq_time() and end_time() (or end_time() if IRQs are
        // disabled)
        enum { idle_addr = 0x1FFF };
        
        // Can read this many bytes past end of a page
        enum { cpu_padding = 8 };
        
public:
        Hes_Cpu() { state = &state_; }
        enum { irq_inhibit = 0x04 };
private:
        // noncopyable
        Hes_Cpu( const Hes_Cpu& );
        Hes_Cpu& operator = ( const Hes_Cpu& );
        
        struct state_t {
                uint8_t const* code_map [page_count + 1];
                hes_time_t base;
                blargg_long time;
        };
        state_t* state; // points to state_ or a local copy within run()
        state_t state_;
        hes_time_t irq_time_;
        hes_time_t end_time_;
        
        void set_code_page( int, void const* );
        inline int update_end_time( hes_time_t end, hes_time_t irq );
};
 
inline uint8_t const* Hes_Cpu::get_code( hes_addr_t addr )
{
        return state->code_map [addr >> page_shift] + addr
        #if !BLARGG_NONPORTABLE
                % (unsigned) page_size
        #endif
        ;
}
 
inline int Hes_Cpu::update_end_time( hes_time_t t, hes_time_t irq )
{
        if ( irq < t && !(r.status & irq_inhibit) ) t = irq;
        int delta = state->base - t;
        state->base = t;
        return delta;
}
 
inline void Hes_Cpu::set_irq_time( hes_time_t t )
{
        state->time += update_end_time( end_time_, (irq_time_ = t) );
}
 
inline void Hes_Cpu::set_end_time( hes_time_t t )
{
        state->time += update_end_time( (end_time_ = t), irq_time_ );
}
 
inline void Hes_Cpu::end_frame( hes_time_t t )
{
        assert( state == &state_ );
        state_.base -= t;
        if ( irq_time_ < future_hes_time ) irq_time_ -= t;
        if ( end_time_ < future_hes_time ) end_time_ -= t;
}
 
#endif