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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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