diff options
Diffstat (limited to 'gme/Nes_Cpu.h')
-rw-r--r-- | gme/Nes_Cpu.h | 114 |
1 files changed, 114 insertions, 0 deletions
diff --git a/gme/Nes_Cpu.h b/gme/Nes_Cpu.h new file mode 100644 index 00000000..d303b57c --- /dev/null +++ b/gme/Nes_Cpu.h @@ -0,0 +1,114 @@ +// NES 6502 CPU emulator + +// Game_Music_Emu 0.5.2 +#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 = LONG_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 |