chip8 emu

chip-8.rb

require 'curses'
require 'io/console'
class Chip
  FONTSET = [
    0xF0, 0x90, 0x90, 0x90, 0xF0,#0
    0x20, 0x60, 0x20, 0x20, 0x70,#1
    0xF0, 0x10, 0xF0, 0x80, 0xF0,#2
    0xF0, 0x10, 0xF0, 0x10, 0xF0,#3
    0x90, 0x90, 0xF0, 0x10, 0x10,#4
    0xF0, 0x80, 0xF0, 0x10, 0xF0,#5
    0xF0, 0x80, 0xF0, 0x90, 0xF0,#6
    0xF0, 0x10, 0x20, 0x40, 0x40,#7
    0xF0, 0x90, 0xF0, 0x90, 0xF0,#8
    0xF0, 0x90, 0xF0, 0x10, 0xF0,#9
    0xF0, 0x90, 0xF0, 0x90, 0x90,#A
    0xE0, 0x90, 0xE0, 0x90, 0xE0,#B
    0xF0, 0x80, 0x80, 0x80, 0xF0,#C
    0xE0, 0x90, 0x90, 0x90, 0xE0,#D
    0xF0, 0x80, 0xF0, 0x80, 0xF0,#E
    0xF0, 0x80, 0xF0, 0x80, 0x80#F
  ]
  def initialize
    # initialize registers and memory
    @memory = Array.new(4096, 0)
    @v = Array.new(16, 0)
    @i = 0
    @pc = 0x200
    @gfx = Array.new(64*32, 0)
    @delay_timer = 0
    @sound_timer = 0
    @opcode = 0
    @stack = Array.new(16, 0)
    @sp = -1
#   @key = Array.new(16,0)
    @memory[0..(FONTSET.length - 1)] = FONTSET[0..(FONTSET.length - 1)]
    @window = Curses::Window.new(35, 64, 0, 0)
    @drawflag = 0
  end

  def loadgame(rom)
    buffer = File.binread(rom)
    buffer.each_byte.with_index do |val, index|
      @memory[0x200 + index] = val.ord
    end
  end

  def nread_key
    key = (STDIN.read_nonblock(1) rescue nil)
    case key
    when "1"
      return 1
    when "2"
      return 2
    when "3"
      return 3
    when "4"
      return 0xC
    when "q"
      return 4
    when "w"
      return 5
    when "e"
      return 6
    when "r"
      return 0xD
    when "a"
      return 7
    when "s"
      return 8
    when "d"
      return 9
    when "f"
      return 0xE
    when "z"
      return 0xA
    when "x"
      return 0
    when "c"
      return 0xB
    when "v"
      return 0xF
    end
   end

  def read_key
    key = STDIN.readchar
    case key
    when "1"
      return 1
    when "2"
      return 2
    when "3"
      return 3
    when "4"
      return 0xC
    when "q"
      return 4
    when "w"
      return 5
    when "e"
      return 6
    when "r"
      return 0xD
    when "a"
      return 7
    when "s"
      return 8
    when "d"
      return 9
    when "f"
      return 0xE
    when "z"
      return 0xA
    when "x"
      return 0
    when "c"
      return 0xB
    when "v"
      return 0xF
    end
  end

  def emulate_cycle
    # fetch opcode
    @opcode = (@memory[@pc].ord << 8) | @memory[@pc + 1].ord
    # decode opcode
    nnn = @opcode & 0x0FFF
    kk = @opcode & 0x00FF
    n = @opcode & 0x000F
    x = (@opcode & 0x0F00)>> 8
    y = (@opcode & 0x00F0)>> 4

    case @opcode & 0xF000
    when 0x0000
      case @opcode & 0x000F
      when 0x0000
        @gfx.clear
        @gfx = Array.new(64*32, 0)
        @pc += 2
      when 0x000E
        @pc = @stack[@sp]
        @sp -=1
        @pc += 2
      end
    when 0x1000
      @pc = nnn
    when 0x2000
      @sp += 1
      @stack[@sp] = @pc
      @pc = nnn
    when 0x3000
      if @v[x] == kk
        @pc += 4
      else
        @pc += 2
      end
    when 0x4000
      if @v[x] != kk
        @pc += 4
      else
        @pc += 2
      end
    when 0x5000
      if @v[x] == @v[y]
        @pc += 4
      else
        @pc += 2
      end
    when 0x6000
      @v[x] = kk
      @pc += 2
    when 0x7000
      @v[x] = @v[x] + kk
      @v[x] &= 0xFF
      @pc += 2
    when 0x8000
      case n
      when 0x0000
        @v[x] = @v[y]
        @pc += 2
      when 0x0001
        @v[x] |= @v[y]
        @pc += 2
      when 0x0002
        @v[x] &= @v[y]
        @pc += 2
      when 0x0003
        @v[x] ^= @v[y]
        @pc += 2
      when 0x0004
        @v[x] += @v[y]
        if @v[x] > 0xFF
          @v[0xF] = 1
        else
          @v[0xF] = 0
        end
          @v[x] &= 0xFF
        @pc += 2
      when 0x0005
        if @v[x] >= @v[y]
          @v[0xF] = 1
        else
          @v[0xF] = 0
        end
        @v[x] -= @v[y]
        @v[x] &= 0xFF
        @pc += 2
      when 0x0006
        if @v[x] & 0x01 == 1
          @v[0xF] = 1
        else
          @v[0xF] = 0
        end
        @v[x] = (@v[x] >> 1) & 0xFF
        @pc += 2
      when 0x0007
        if @v[y] > @v[x]
          @v[0xF] = 1
        else
          @v[0xF] = 0
        end
        @v[x] = (@v[y] - @v[x])
        @v[x] &= 0xFF
        @pc += 2
      when 0x000E
        if ((@v[x] & 0x80) >> 7) == 1
          @v[0xF] = 1
        else
          @v[0xF] = 0
        end
        @v[x] = (@v[x] << 1) & 0xFF
        @pc += 2
      end
    when 0x9000
      if @v[x] != @v[y]
        @pc += 4
      else
        @pc += 2
      end
    when 0xA000
      @i = nnn
      @pc += 2
    when 0xB000
      @pc = nnn + @v[0]
    when 0xC000
      @v[x] = rand(0xFF) & kk
      @pc += 2
    when 0xD000
      # sprite display
      for yline in 0..(n - 1)
        pixel = @memory[@i + yline]
        for xline in 0..7
          if (pixel & (0x80 >> xline)) != 0
            if (@gfx[@v[x] + xline + ((@v[y] + yline) * 64)] == 1)
              @v[0xF] = 1
            else
              @v[0xF] = 0
            end
            @gfx[@v[x] + xline + ((@v[y] + yline) * 64)] ^= 1
          end
        end
      end
      @drawflag = 1
      @pc += 2
    when 0xE000
      case kk
      when 0x009E
        if nread_key == @v[x]
          @pc += 4
        else
          @pc += 2
        end
#       self.debug
#       sleep(1)
      when 0x00A1
        if nread_key != @v[x]
          @pc += 4
        else
          @pc += 2
        end
#       self.debug
#       sleep(1)
      end
    when 0xF000
      case kk
      when 0x07
        @v[x] = @delay_timer
        @pc += 2
      when 0x0A
        @v[x] = read_key
        @pc += 2
      when 0x15
        @delay_timer = @v[x]
        @pc += 2
      when 0x18
        @sound_timer = @v[x]
        @pc += 2
      when 0x1E
        @i = @i + @v[x]
        @pc += 2
      when 0x29
        @i = @v[x] * 5
        @pc += 2
      when 0x33
        @memory[@i] = @v[x] / 100
        @memory[@i + 1] = (@v[x] / 10) % 10
        @memory[@i + 2] = (@v[x] % 100) % 10
        @pc += 2
      when 0x55
        for idx in 0..x
          @memory[@i] = @v[idx]
          @i += 1
        end
        @pc += 2
      when 0x65
        for idx in 0..x
          @v[idx] = @memory[@i]
          @i += 1
        end
        @pc += 2
      end
    else
      puts "unknown opcode #{@opcode.to_s(16)}"
      @pc += 2
    end
#   @window.getch
#   STDIN.readchar
  end

  def tick_timers
    if @delay_timer > 0
      @delay_timer -= 1
    end

    if @sound_timer > 0
      @sound_timer -= 1
    end
  end

  def drawflag
    return @drawflag
  end

  def draw_graphics
    @window.clear
    @gfx.each.with_index do |pix, index|
      x = index % 64
      y = index / 64 #/
      if pix != 0
        @window.setpos(y, x)
        @window << "X"
      end
    end
    @window.setpos(0, 0)
    @window.refresh
    @drawflag = 0
  end

  def debug
    @window.setpos(32, 0)
    @window.addstr("                                                                ")
    @window.setpos(33, 0)
    @window.addstr("                                                                ")
    @window.setpos(34, 0)
    @window.addstr("                                                                ")
    @window.setpos(32, 0)
    @window.addstr("opcode: #{@opcode.to_s(16)} PC: #{@pc.to_s(16)} I: #{@i.to_s(16)} *I: #{@memory[@i].to_s(16)}")
    @window.setpos(33, 0)
    @window.addstr("reg: #{@v[0].to_s(16)} #{@v[1].to_s(16)} #{@v[2].to_s(16)} #{@v[3].to_s(16)} #{@v[4].to_s(16)} #{@v[5].to_s(16)} #{@v[6].to_s(16)} #{@v[7].to_s(16)} #{@v[8].to_s(16)} #{@v[9].to_s(16)} #{@v[10].to_s(16)} #{@v[11].to_s(16)} #{@v[12].to_s(16)} #{@v[13].to_s(16)} #{@v[14].to_s(16)} #{@v[0xF]}")
    @window.setpos(34, 0)
    @window.addstr("SP: #{@sp.to_s(16)} stack: #{@stack[0].to_s(16)} #{@stack[1].to_s(16)} #{@stack[2].to_s(16)} #{@stack[3].to_s(16)} #{@stack[4].to_s(16)} #{@stack[5].to_s(16)} #{@stack[6].to_s(16)} #{@stack[7].to_s(16)} #{@stack[8].to_s(16)} #{@stack[9].to_s(16)} #{@stack[10].to_s(16)} #{@stack[11].to_s(16)} #{@stack[12].to_s(16)} #{@stack[13].to_s(16)} #{@stack[14].to_s(16)} #{@stack[15].to_s(16)}")
    @window.setpos(0, 0)
    @window.refresh
  end
end

begin
  Curses.init_screen
  Curses.noecho
  chip8 = Chip.new

  chip8.loadgame(ARGV[0])

  loop do
    chip8.emulate_cycle
    chip8.tick_timers
    if chip8.drawflag != 0
      chip8.draw_graphics
    end
    chip8.debug
    sleep(0.001)
  end
ensure
  Curses.close_screen
end