PocketNester的c++源代码,很好的学习例子,仅供大家学习

				
				/////////////////////////////////////////////////////////////////////
				// Mapper 105
				void NES_mapper105::Reset()
				{
				  set_CPU_banks(0,1,2,3);
				
				  regs[0] = 0x0C;
				  regs[1] = 0x00;
				  regs[2] = 0x00;
				  regs[3] = 0x10;
				
				  bits = 0;
				  write_count = 0;
				
				  irq_counter = 0;
				  irq_enabled = 0;
				  init_state = 0;
				}
				
				void NES_mapper105::MemoryWrite(uint32 addr, uint8 data)
				{
				  uint32 reg_num = (addr & 0x7FFF) >> 13;
				
				  if (data & 0x80)
				  {
				    bits = write_count = 0;
				    if (reg_num == 0)
				    {
				      regs[reg_num] |= 0x0C;
				    }
				  }
				  else
				  {
				    bits |= (data & 1) 				    if (write_count == 5)
				    {
				      regs[reg_num] = bits & 0x1F;
				      bits = write_count = 0;
				    }
				  }
				
				  if(regs[0] & 0x02)
				  {
				    if(regs[0] & 0x01)
				    {
				      set_mirroring(NES_PPU::MIRROR_HORIZ);
				    }
				    else
				    {
				      set_mirroring(NES_PPU::MIRROR_VERT);
				    }
				  }
				  else
				  {
				    if(regs[0] & 0x01)
				    {
				      set_mirroring(1,1,1,1);
				    }
				    else
				    {
				      set_mirroring(0,0,0,0);
				    }
				  }
				
				  switch (init_state)
				  {
				    case 0:
				    case 1:
				      {
				        init_state++;
				      }
				      break;
				
				    case 2:
				      {
				        if(regs[1] & 0x08)
				        {
				          if (regs[0] & 0x08)
				          {
				            if (regs[0] & 0x04)
				            {
				              set_CPU_bank4((regs[3] & 0x07) * 2 + 16);
				              set_CPU_bank5((regs[3] & 0x07) * 2 + 17);
				              set_CPU_bank6(30);
				              set_CPU_bank7(31);
				            }
				            else
				            {
				              set_CPU_bank4(16);
				              set_CPU_bank5(17);
				              set_CPU_bank6((regs[3] & 0x07) * 2 + 16);
				              set_CPU_bank7((regs[3] & 0x07) * 2 + 17);
				            }
				          }
				          else
				          {
				            set_CPU_bank4((regs[3] & 0x06) * 2 + 16);
				            set_CPU_bank5((regs[3] & 0x06) * 2 + 17);
				            set_CPU_bank6((regs[3] & 0x06) * 2 + 18);
				            set_CPU_bank7((regs[3] & 0x06) * 2 + 19);
				          }
				        }
				        else
				        {
				          set_CPU_bank4((regs[1] & 0x06) * 2 + 0);
				          set_CPU_bank5((regs[1] & 0x06) * 2 + 1);
				          set_CPU_bank6((regs[1] & 0x06) * 2 + 2);
				          set_CPU_bank7((regs[1] & 0x06) * 2 + 3);
				        }
				
				        if(regs[1] & 0x10)
				        {
				          irq_counter = 0;
				          irq_enabled = 0;
				        }
				        else
				        {
				          irq_enabled = 1;
				        }
				      }
				      break;
				  }
				}
				
				void NES_mapper105::HSync(uint32 scanline)
				{
				  if(!scanline)
				  {
				    if(irq_enabled)
				    {
				      irq_counter += 29781;
				    }
				    if(((irq_counter | 0x21FFFFFF) & 0x3E000000) == 0x3E000000)
				    {
				      parent_NES->cpu->DoIRQ();
				    }
				  }
				}