Class: Rubyboy::ApuChannels::Channel3

Inherits:
Object
  • Object
show all
Defined in:
lib/rubyboy/apu_channels/channel3.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 ⇒ Channel3

Returns a new instance of Channel3.



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# File 'lib/rubyboy/apu_channels/channel3.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

  @output_level = 0
  @volume_shift = 0
  @wave_ram = Array.new(16, 0)
end

Instance Attribute Details

#enabled ⇒ Object

Returns the value of attribute enabled.



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# File 'lib/rubyboy/apu_channels/channel3.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/channel3.rb', line 6

def wave_duty_position
  @wave_duty_position
end

#wave_ram ⇒ Object

Returns the value of attribute wave_ram.



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# File 'lib/rubyboy/apu_channels/channel3.rb', line 6

def wave_ram
  @wave_ram
end

Instance Method Details

#calculate_frequency ⇒ Object 



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# File 'lib/rubyboy/apu_channels/channel3.rb', line 64

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/channel3.rb', line 76

def dac_output
  return 0.0 unless @dac_enabled && @enabled

  ret = ((0xf & (
    @wave_ram[@wave_duty_position >> 1] >> ((@wave_duty_position & 0x01) << 2)
  ))) >> @volume_shift

  (ret / 7.5) - 1.0
end

#length ⇒ Object 



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# File 'lib/rubyboy/apu_channels/channel3.rb', line 57

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

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

#read_nr3x(x) ⇒ Object 



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# File 'lib/rubyboy/apu_channels/channel3.rb', line 86

def read_nr3x(x)
  case x
  when 0 then ((@dac_enabled ? 0x80 : 0x00) | 0x7f)
  when 1 then 0xff
  when 2 then (@output_level << 5) | 0x9f
  when 3 then 0xff
  when 4 then (@length_enabled ? 0x40 : 0x00) | 0xbf
  else 0xff
  end
end

#step(cycles) ⇒ Object 



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# File 'lib/rubyboy/apu_channels/channel3.rb', line 43

def step(cycles)
  @cycles += cycles

  return if @cycles < @frequency_timer

  @cycles -= @frequency_timer
  @frequency_timer = (2048 - @frequency) * 2
  @wave_duty_position = (@wave_duty_position + 1) % 32
end

#step_fs(fs) ⇒ Object 



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# File 'lib/rubyboy/apu_channels/channel3.rb', line 53

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

#write_nr3x(x, val) ⇒ Object 



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# File 'lib/rubyboy/apu_channels/channel3.rb', line 97

def write_nr3x(x, val)
  case x
  when 0
    @dac_enabled = val & 0x80 > 0
    @enabled &= @dac_enabled
  when 1
    @length_timer = 256 - val
  when 2
    @output_level = (val >> 5) & 0x03
  when 3
    @frequency = (@frequency & 0x700) | val
  when 4
    @frequency = (@frequency & 0xff) | ((val & 0x07) << 8)
    @length_enabled = val & 0x40 > 0
    @length_timer = 256 if @length_timer == 0
    @enabled = true if (val & 0x80) > 0 && @dac_enabled
  end
end