Sap_Cpu.h

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// Atari 6502 CPU emulator
 
// Game_Music_Emu https://bitbucket.org/mpyne/game-music-emu/
#ifndef SAP_CPU_H
#define SAP_CPU_H
 
#include "blargg_common.h"
 
typedef blargg_long sap_time_t; // clock cycle count
typedef unsigned sap_addr_t; // 16-bit address
enum { future_sap_time = INT_MAX / 2 + 1 };
 
class Sap_Cpu {
public:
        // Clear all registers and keep pointer to 64K memory passed in
        void reset( void* mem_64k );
        
        // Run until specified time is reached. Returns true if suspicious/unsupported
        // instruction was encountered at any point during run.
        bool run( sap_time_t end_time );
        
        // Registers are not updated until run() returns (except I flag in status)
        struct registers_t {
                uint16_t pc;
                uint8_t a;
                uint8_t x;
                uint8_t y;
                uint8_t status;
                uint8_t sp;
        };
        registers_t r;
        
        enum { idle_addr = 0xFEFF };
        
        // Time of beginning of next instruction to be executed
        sap_time_t time() const             { return state->time + state->base; }
        void set_time( sap_time_t t )       { state->time = t - state->base; }
        void adjust_time( int delta )       { state->time += delta; }
        
        sap_time_t irq_time() const         { return irq_time_; }
        void set_irq_time( sap_time_t );
        
        sap_time_t end_time() const         { return end_time_; }
        void set_end_time( sap_time_t );
        
public:
        Sap_Cpu() { state = &state_; }
        enum { irq_inhibit = 0x04 };
private:
        struct state_t {
                sap_time_t base;
                sap_time_t time;
        };
        state_t* state; // points to state_ or a local copy within run()
        state_t state_;
        sap_time_t irq_time_;
        sap_time_t end_time_;
        uint8_t* mem;
        
        inline sap_time_t update_end_time( sap_time_t end, sap_time_t irq );
};
 
inline sap_time_t Sap_Cpu::update_end_time( sap_time_t t, sap_time_t irq )
{
        if ( irq < t && !(r.status & irq_inhibit) ) t = irq;
        sap_time_t delta = state->base - t;
        state->base = t;
        return delta;
}
 
inline void Sap_Cpu::set_irq_time( sap_time_t t )
{
        state->time += update_end_time( end_time_, (irq_time_ = t) );
}
 
inline void Sap_Cpu::set_end_time( sap_time_t t )
{
        state->time += update_end_time( (end_time_ = t), irq_time_ );
}
 
#endif