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718112a8fe
Currently none of these is being used, but eventually they will, once more code gets ported over. So it's better to have them right away and avoid editing the project file too much, only to revert that later.
112 lines
3.1 KiB
C++
112 lines
3.1 KiB
C++
// NES 6502 CPU emulator
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// Game_Music_Emu https://bitbucket.org/mpyne/game-music-emu/
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#ifndef NES_CPU_H
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#define NES_CPU_H
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#include "blargg_common.h"
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typedef blargg_long nes_time_t; // clock cycle count
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typedef unsigned nes_addr_t; // 16-bit address
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enum { future_nes_time = INT_MAX / 2 + 1 };
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class Nes_Cpu {
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public:
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// Clear registers, map low memory and its three mirrors to address 0,
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// and mirror unmapped_page in remaining memory
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void reset( void const* unmapped_page = 0 );
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// Map code memory (memory accessed via the program counter). Start and size
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// must be multiple of page_size. If mirror is true, repeats code page
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// throughout address range.
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enum { page_size = 0x800 };
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void map_code( nes_addr_t start, unsigned size, void const* code, bool mirror = false );
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// Access emulated memory as CPU does
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uint8_t const* get_code( nes_addr_t );
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// 2KB of RAM at address 0
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uint8_t low_mem [0x800];
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// NES 6502 registers. Not kept updated during a call to run().
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struct registers_t {
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uint16_t pc;
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uint8_t a;
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uint8_t x;
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uint8_t y;
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uint8_t status;
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uint8_t sp;
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};
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registers_t r;
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// Set end_time and run CPU from current time. Returns true if execution
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// stopped due to encountering bad_opcode.
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bool run( nes_time_t end_time );
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// Time of beginning of next instruction to be executed
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nes_time_t time() const { return state->time + state->base; }
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void set_time( nes_time_t t ) { state->time = t - state->base; }
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void adjust_time( int delta ) { state->time += delta; }
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nes_time_t irq_time() const { return irq_time_; }
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void set_irq_time( nes_time_t );
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nes_time_t end_time() const { return end_time_; }
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void set_end_time( nes_time_t );
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// Number of undefined instructions encountered and skipped
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void clear_error_count() { error_count_ = 0; }
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unsigned long error_count() const { return error_count_; }
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// CPU invokes bad opcode handler if it encounters this
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enum { bad_opcode = 0xF2 };
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public:
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Nes_Cpu() { state = &state_; }
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enum { page_bits = 11 };
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enum { page_count = 0x10000 >> page_bits };
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enum { irq_inhibit = 0x04 };
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private:
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struct state_t {
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uint8_t const* code_map [page_count + 1];
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nes_time_t base;
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int time;
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};
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state_t* state; // points to state_ or a local copy within run()
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state_t state_;
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nes_time_t irq_time_;
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nes_time_t end_time_;
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unsigned long error_count_;
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void set_code_page( int, void const* );
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inline int update_end_time( nes_time_t end, nes_time_t irq );
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};
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inline uint8_t const* Nes_Cpu::get_code( nes_addr_t addr )
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{
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return state->code_map [addr >> page_bits] + addr
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#if !BLARGG_NONPORTABLE
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% (unsigned) page_size
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#endif
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;
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}
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inline int Nes_Cpu::update_end_time( nes_time_t t, nes_time_t irq )
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{
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if ( irq < t && !(r.status & irq_inhibit) ) t = irq;
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int delta = state->base - t;
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state->base = t;
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return delta;
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}
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inline void Nes_Cpu::set_irq_time( nes_time_t t )
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{
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state->time += update_end_time( end_time_, (irq_time_ = t) );
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}
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inline void Nes_Cpu::set_end_time( nes_time_t t )
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{
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state->time += update_end_time( (end_time_ = t), irq_time_ );
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}
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#endif
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