Class: Rubyboy::ApuChannels::Channel4

Inherits:
Object
  • Object
show all
Defined in:
lib/rubyboy/apu_channels/channel4.rb

Constant Summary collapse

WAVE_DUTY = 
[
  [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1.0], # 12.5%
  [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1.0, 1.0], # 25%
  [0.0, 0.0, 0.0, 0.0, 1.0, 1.0, 1.0, 1.0], # 50%
  [0.0, 0.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0]  # 75%
].freeze

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize ⇒ Channel4

Returns a new instance of Channel4.



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# File 'lib/rubyboy/apu_channels/channel4.rb', line 15

def initialize
  @cycles = 0
  @frequency = 0
  @frequency_timer = 0
  @wave_duty_position = 0

  @enabled = false
  @dac_enabled = false
  @length_enabled = false
  @is_upwards = false
  @is_decrementing = false
  @sweep_enabled = false
  @sweep_period = 0
  @sweep_shift = 0
  @period = 0
  @period_timer = 0
  @current_volume = 0
  @initial_volume = 0
  @shadow_frequency = 0
  @sweep_timer = 0
  @length_timer = 0
  @wave_duty_pattern = 0

  @lfsr = 0x7fff
  @width_mode = false
  @shift_amount = 0
  @divisor_code = 0
end

Instance Attribute Details

#enabled ⇒ Object

Returns the value of attribute enabled.



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# File 'lib/rubyboy/apu_channels/channel4.rb', line 6

def enabled
  @enabled
end

#wave_duty_position ⇒ Object

Returns the value of attribute wave_duty_position.



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# File 'lib/rubyboy/apu_channels/channel4.rb', line 6

def wave_duty_position
  @wave_duty_position
end

Instance Method Details

#calculate_frequency ⇒ Object 



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# File 'lib/rubyboy/apu_channels/channel4.rb', line 88

def calculate_frequency
  if @is_decrementing
    if @shadow_frequency >= (@shadow_frequency >> @sweep_shift)
      @shadow_frequency - (@shadow_frequency >> @sweep_shift)
    else
      0
    end
  else
    [0x3ff, @shadow_frequency + (@shadow_frequency >> @sweep_shift)].min
  end
end

#dac_output ⇒ Object 



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# File 'lib/rubyboy/apu_channels/channel4.rb', line 100

def dac_output
  return 0.0 unless @dac_enabled && @enabled

  ret = (@lfsr & 0x01) * @current_volume
  (ret / 7.5) - 1.0
end

#envelope ⇒ Object 



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# File 'lib/rubyboy/apu_channels/channel4.rb', line 72

def envelope
  return if @period == 0

  @period_timer -= 1 if @period_timer > 0

  return if @period_timer != 0

  @period_timer = @period

  if @current_volume < 15 && @is_upwards
    @current_volume += 1
  elsif @current_volume > 0 && !@is_upwards
    @current_volume -= 1
  end
end

#length ⇒ Object 



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# File 'lib/rubyboy/apu_channels/channel4.rb', line 65

def length
  return unless @length_enabled && @length_timer > 0

  @length_timer -= 1
  @enabled &= @length_timer > 0
end

#read_nr4x(x) ⇒ Object 



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# File 'lib/rubyboy/apu_channels/channel4.rb', line 107

def read_nr4x(x)
  case x
  when 0 then 0xff
  when 1 then 0xff
  when 2 then (@initial_volume << 4) | (@is_upwards ? 0x08 : 0x00) | @period
  when 3 then (@shift_amount << 4) | (@width_mode ? 0x08 : 0x00) | @divisor_code
  when 4 then (@length_enabled ? 0x40 : 0x00) | 0xbf
  else 0xff
  end
end

#step(cycles) ⇒ Object 



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# File 'lib/rubyboy/apu_channels/channel4.rb', line 44

def step(cycles)
  @cycles += cycles

  return if @cycles < @frequency_timer

  @cycles -= @frequency_timer
  @frequency_timer = [8, @divisor_code << 4].max << @shift_amount

  xor = (@lfsr & 0x01) ^ ((@lfsr & 0b10) >> 1)
  @lfsr = (@lfsr >> 1) | (xor << 14)
  return unless @width_mode

  @lfsr &= ~(1 << 6)
  @lfsr |= xor << 6
end

#step_fs(fs) ⇒ Object 



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# File 'lib/rubyboy/apu_channels/channel4.rb', line 60

def step_fs(fs)
  length if fs & 0x01 == 0
  envelope if fs == 7
end

#write_nr4x(x, val) ⇒ Object 



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# File 'lib/rubyboy/apu_channels/channel4.rb', line 118

def write_nr4x(x, val)
  case x
  when 0
    # nop
  when 1
    @length_timer = 64 - (val & 0x3f)
  when 2
    @is_upwards = (val & 0x08) > 0
    @initial_volume = val >> 4
    @period = val & 0x07
    @dac_enabled = val & 0xf8 > 0
    @enabled &= @dac_enabled
  when 3
    @shift_amount = (val >> 4) & 0x0f
    @width_mode = (val & 0x08) > 0
    @divisor_code = val & 0x07
  when 4
    @length_enabled = (val & 0x40) > 0
    @length_timer = 64 if @length_timer == 0
    return unless (val & 0x80) > 0

    @enabled = true if @dac_enabled

    @lfsr = 0x7fff
    @period_timer = @period
    @current_volume = @initial_volume
  end
end