Class: Amaterasu::GameBoy::Bus

Inherits:
Object
  • Object
show all
Defined in:
lib/amaterasu/game_boy/bus.rb,
sig/akane/game_boy/bus.rbs

Overview

| 0x0000-0x7FFF | 32 KiB | Cartridge ROM | Bank 0 fixed, Bank N switchable | | 0x8000-0x9FFF | 8 KiB | Video RAM (VRAM) | Tile data + tile maps | | 0xA000-0xBFFF | 8 KiB | External RAM | Cartridge RAM, battery-backed | | 0xC000-0xDFFF | 8 KiB | Work RAM (WRAM) | General purpose | | 0xE000-0xFDFF | ~8 KiB | Echo RAM | Mirror of WRAM (0xC000-0xDDFF) | | 0xFE00-0xFE9F | 160 B | OAM | Sprite attribute table | | 0xFEA0-0xFEFF | 96 B | Unusable | Prohibited area | | 0xFF00-0xFF7F | 128 B | I/O Registers | Hardware control | | 0xFF80-0xFFFE | 127 B | High RAM (HRAM) | Fast RAM, accessible during DMA | | 0xFFFF | 1 B | IE Register | Interrupt Enable |

Instance Method Summary collapse

Constructor Details

#initialize ⇒ Object 



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# File 'sig/akane/game_boy/bus.rbs', line 4

def initialize: (

Instance Method Details

#read_byte(address:, caller: nil) ⇒ Integer

Delegates the read to the proper component based on the address and returns the 8-bit value that was stored there.

Parameters:

  • address: (Integer)

Returns:

  • (Integer) 


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# File 'lib/amaterasu/game_boy/bus.rb', line 42

def read_byte(address:, caller: nil)
  return 0xFF if @dma.active?
    && caller.is_a?(Cpu)
    && address < 0xFF00

  if address <= 0x7FFF
    @cartridge.read_rom(address)
  elsif address <= 0x9FFF
    @ppu.read_vram(address:)
  elsif address <= 0xBFFF
    @cartridge.read_ram(address)
  elsif address <= 0xDFFF
    @wram.read_byte(address:)
  elsif address <= 0xFDFF
    @wram.read_byte(address: address - 0x2000)
  elsif address <= 0xFE9F
    @ppu.read_oam(address:)
  elsif address <= 0xFEFF
    0xFF
  elsif address <= 0xFF7F
    read_io(address)
  elsif address <= 0xFFFE
    @hram.read_byte(address:)
  elsif address == 0xFFFF
    @interrupts.ie_register
  else
    raise "Not implemented bus read at $#{address.to_s(16)}"
  end
end

#read_io(address) ⇒ Integer

Extracts the IO registers read logic for organization.

Parameters:

  • address (Integer)

Returns:

  • (Integer) 


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# File 'lib/amaterasu/game_boy/bus.rb', line 107

def read_io(address)
  case address
  when 0xFF00 then @joypad.p1
  when 0xFF01 then @serial.sb
  when 0xFF02 then @serial.sc
  when 0xFF04 then @timer.div
  when 0xFF05 then @timer.tima
  when 0xFF06 then @timer.tma
  when 0xFF07 then @timer.tac
  when 0xFF0F then @interrupts.if_register
  when 0xFF40 then @ppu.registers.lcdc.value
  when 0xFF41 then @ppu.registers.stat.value
  when 0xFF42 then @ppu.registers.scy
  when 0xFF43 then @ppu.registers.scx
  when 0xFF44 then @ppu.registers.ly
  when 0xFF45 then @ppu.registers.lyc
  when 0xFF46 then @dma.internal_latch
  when 0xFF47 then @ppu.registers.bgp
  when 0xFF48 then @ppu.registers.obp0
  when 0xFF49 then @ppu.registers.obp1
  when 0xFF4A then @ppu.registers.wy
  when 0xFF4B then @ppu.registers.wx
  else
    0xFF
  end
end

#wire_components(cartridge:, ppu:, wram:, hram:, interrupts:, apu:, timer:, serial:, joypad:, dma:) ⇒ Object 



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# File 'lib/amaterasu/game_boy/bus.rb', line 16

def wire_components(
  cartridge:,
  ppu:,
  wram:,
  hram:,
  interrupts:,
  apu:,
  timer:,
  serial:,
  joypad:,
  dma:
)
  @cartridge = cartridge
  @ppu = ppu
  @wram = wram
  @hram = hram
  @interrupts = interrupts
  @apu = apu
  @timer = timer
  @serial = serial
  @joypad = joypad
  @dma = dma
end

#write_byte(address:, value:, caller: nil) ⇒ void

This method returns an undefined value.

Delegates the write to the proper component based on the address and stores a 8-bit value at that location.

Parameters:

  • address: (Integer)
  • value: (Integer) 


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# File 'lib/amaterasu/game_boy/bus.rb', line 74

def write_byte(address:, value:, caller: nil)
  return if @dma.active?
    && caller.is_a?(Cpu)
    && address < 0xFF00

  if address <= 0x7FFF
    @cartridge.write_rom(address, value)
  elsif address <= 0x9FFF
    @ppu.write_vram(address:, value:)
  elsif address <= 0xBFFF
    @cartridge.write_ram(address - 0xA000, value)
  elsif address <= 0xDFFF
    @wram.write_byte(address:, value:)
  elsif address <= 0xFDFF
    @wram.write_byte(address: address - 0x2000, value:)
  elsif address <= 0xFE9F
    @ppu.write_oam(address:, value:)
  elsif address <= 0xFEFF
    nil
  elsif address <= 0xFF7F
    write_io(address, value)
  elsif address <= 0xFFFE
    @hram.write_byte(address:, value:)
  elsif address == 0xFFFF
    @interrupts.ie_register = value
  else
    raise "Not implemented bus write at $#{address.to_s(16)}"
  end
end

#write_io(address, value) ⇒ void

This method returns an undefined value.

Extracts the IO registers write logic for organization.

Parameters:

  • address (Integer)
  • value (Integer) 


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# File 'lib/amaterasu/game_boy/bus.rb', line 135

def write_io(address, value)
  case address
  when 0xFF00 then @joypad.p1 = value
  when 0xFF01 then @serial.sb = value
  when 0xFF02 then @serial.sc = value
  when 0xFF04 then @timer.div = value
  when 0xFF05 then @timer.tima = value
  when 0xFF06 then @timer.tma = value
  when 0xFF07 then @timer.tac = value
  when 0xFF0F then @interrupts.if_register = value
  when 0xFF40 then @ppu.registers.lcdc = value
  when 0xFF41 then @ppu.registers.stat = value
  when 0xFF42 then @ppu.registers.scy = value
  when 0xFF43 then @ppu.registers.scx = value
  when 0xFF44 then nil # @ppu.registers.ly = value -> read-only
  when 0xFF45 then @ppu.registers.lyc = value
  when 0xFF46 then @dma.request_transfer(source_value: value)
  when 0xFF47 then @ppu.registers.bgp = value
  when 0xFF48 then @ppu.registers.obp0 = value
  when 0xFF49 then @ppu.registers.obp1 = value
  when 0xFF4A then @ppu.registers.wy = value
  when 0xFF4B then @ppu.registers.wx = value
  end
end