move apu to use Int16 rather than Float32 samples

src/crab/apu.cr

@@ -22,7 +22,7 @@ class APU
   @sound_enabled : Bool = false
   @soundbias = Reg::SOUNDBIAS.new 0
 
-  @buffer = Slice(Float32).new BUFFER_SIZE
+  @buffer = Slice(Int16).new BUFFER_SIZE
   @buffer_pos = 0
   @frame_sequencer_stage = 0
   getter first_half_of_length_period = false
@@ -35,7 +35,7 @@ class APU
   def initialize(@gba : GBA)
     @audiospec = LibSDL::AudioSpec.new
     @audiospec.freq = SAMPLE_RATE
-    @audiospec.format = LibSDL::AUDIO_F32SYS
+    @audiospec.format = LibSDL::AUDIO_S16
     @audiospec.channels = CHANNELS
     @audiospec.samples = BUFFER_SIZE
     @audiospec.callback = nil
@@ -101,48 +101,41 @@ class APU
 
   def get_sample : Nil
     abort "Prohibited sound 1-4 volume #{@soundcnt_h.sound_volume}" if @soundcnt_h.sound_volume >= 3
-    psg_master_volume = ((100 >> (2 - @soundcnt_h.sound_volume)) / 100).to_f32
+    # Puts PSGs on scale of 0...0x40
     psg_sound = ((@channel1.get_amplitude * @soundcnt_l.channel_1_left) +
                  (@channel2.get_amplitude * @soundcnt_l.channel_2_left) +
                  (@channel3.get_amplitude * @soundcnt_l.channel_3_left) +
-                 (@channel4.get_amplitude * @soundcnt_l.channel_4_left)) / 4
-    psg_left = psg_master_volume *
-               (@soundcnt_l.left_volume / 7) *
-               psg_sound
-    psg_right = psg_master_volume *
-                (@soundcnt_l.right_volume / 7) *
-                psg_sound
+                 (@channel4.get_amplitude * @soundcnt_l.channel_4_left))# * 2 - 0x80
+    # Puts PSGs on scale of 0...0x200
+    psg_left = (psg_sound * @soundcnt_l.left_volume) >> (2 - @soundcnt_h.sound_volume)
+    psg_right = (psg_sound * @soundcnt_l.right_volume) >> (2 - @soundcnt_h.sound_volume)
 
+    # Gets DMAs on scale of -0x100...0x100
     dma_a, dma_b = @dma_channels.get_amplitude
-    vol_a = ((100 >> (1 - @soundcnt_h.dma_sound_a_volume)) / 100).to_f32
-    vol_b = ((100 >> (1 - @soundcnt_h.dma_sound_b_volume)) / 100).to_f32
-    dma_left = ((dma_a * @soundcnt_h.dma_sound_a_left * vol_a) +
-                (dma_b * @soundcnt_h.dma_sound_b_left * vol_b)) / 2
-    dma_right = ((dma_a * @soundcnt_h.dma_sound_a_right * vol_a) +
-                 (dma_b * @soundcnt_h.dma_sound_b_right * vol_b)) / 2
+    dma_a <<= 1
+    dma_b <<= 1
+    # Puts DMAs on scale of -0x200...0x200
+    dma_a <<= @soundcnt_h.dma_sound_a_volume
+    dma_b <<= @soundcnt_h.dma_sound_b_volume
+    dma_left = dma_a * @soundcnt_h.dma_sound_a_left + dma_b * @soundcnt_h.dma_sound_b_left
+    dma_right = dma_a * @soundcnt_h.dma_sound_a_right + dma_b * @soundcnt_h.dma_sound_b_right
 
-    @buffer[@buffer_pos] = (psg_left + 2*dma_left) / 3
-    @buffer[@buffer_pos + 1] = (psg_right + 2*dma_right) / 3
+    bias = 0x200
 
-    if @buffer[@buffer_pos].abs > 1 || @buffer[@buffer_pos + 1].abs > 1
-      STDERR.puts "Left:  #{@buffer[@buffer_pos]}"
-      STDERR.puts "  PSG: #{psg_left}"
-      STDERR.puts "  DMA: #{dma_right}"
-      STDERR.puts "Right: #{@buffer[@buffer_pos + 1]}"
-      STDERR.puts "  PSG: #{psg_right}"
-      STDERR.puts "  DMA: #{dma_right}"
-      exit 1
-    end
+    total_left = (psg_left + dma_left + bias).clamp(0_i16..0x3FF_i16)
+    total_right = (psg_right + dma_right + bias).clamp(0_i16..0x3FF_i16)
 
+    @buffer[@buffer_pos] = total_left * 32
+    @buffer[@buffer_pos + 1] = total_right * 32
     @buffer_pos += 2
 
     # push to SDL if buffer is full
     if @buffer_pos >= BUFFER_SIZE
       LibSDL.clear_queued_audio 1 unless @sync
-      while LibSDL.get_queued_audio_size(1) > BUFFER_SIZE * sizeof(Float32) * 2
+      while LibSDL.get_queued_audio_size(1) > BUFFER_SIZE * sizeof(Int16) * 2
         LibSDL.delay(1)
       end
-      LibSDL.queue_audio 1, @buffer, BUFFER_SIZE * sizeof(Float32)
+      LibSDL.queue_audio 1, @buffer, BUFFER_SIZE * sizeof(Int16)
       @buffer_pos = 0
     end
 

src/crab/apu/abstract_channels.cr

@@ -39,7 +39,7 @@ abstract class SoundChannel
   # Called when @period reaches 0
   abstract def step_wave_generation : Nil
 
-  abstract def get_amplitude : Float32
+  abstract def get_amplitude : Int16
 
   abstract def read_io(index : Int) : UInt8
   abstract def write_io(index : Int, value : UInt8) : Nil

src/crab/apu/channel1.cr

@@ -57,14 +57,13 @@ class Channel1 < VolumeEnvelopeChannel
     end
   end
 
-  def get_amplitude : Float32
+  # Outputs a value 0..0xF
+  def get_amplitude : Int16
     if @enabled && @dac_enabled
-      dac_input = WAVE_DUTY[@duty][@wave_duty_position] * @current_volume
-      dac_output = (dac_input / 7.5) - 1
-      dac_output
+      WAVE_DUTY[@duty][@wave_duty_position].to_i16 * @current_volume
     else
-      0
-    end.to_f32
+      0_i16
+    end
   end
 
   # Calculate the new shadow frequency, disable channel if overflow 11 bits

src/crab/apu/channel2.cr

@@ -33,14 +33,13 @@ class Channel2 < VolumeEnvelopeChannel
     @gba.scheduler.schedule frequency_timer, ->step, Scheduler::EventType::APUChannel2
   end
 
-  def get_amplitude : Float32
+  # Outputs a value 0..0xF
+  def get_amplitude : Int16
     if @enabled && @dac_enabled
-      dac_input = WAVE_DUTY[@duty][@wave_duty_position] * @current_volume
-      dac_output = (dac_input / 7.5) - 1
-      dac_output
+      WAVE_DUTY[@duty][@wave_duty_position].to_i16 * @current_volume
     else
-      0
-    end.to_f32
+      0_i16
+    end
   end
 
   def read_io(index : Int) : UInt8

src/crab/apu/channel3.cr

@@ -8,7 +8,7 @@ class Channel3 < SoundChannel
 
   @wave_ram = Array(Bytes).new 2, Bytes.new(WAVE_RAM_RANGE.size) { |idx| idx & 1 == 0 ? 0x00_u8 : 0xFF_u8 }
   @wave_ram_position : UInt8 = 0
-  @wave_ram_sample_buffer : UInt8 = 0x00
+  @wave_ram_sample_buffer : Int16 = 0x00
 
   # NR30
   @wave_ram_dimension : Bool = false
@@ -21,15 +21,13 @@ class Channel3 < SoundChannel
   @volume_code : UInt8 = 0x00
   @volume_force : Bool = false
 
-  @volume_multiplier : Float32 = 0
-
   # NR33 / NR34
   @frequency : UInt16 = 0x00
 
   def step_wave_generation : Nil
     @wave_ram_position = (@wave_ram_position + 1) % (WAVE_RAM_RANGE.size * 2)
     @wave_ram_bank ^= 1 if @wave_ram_position == 0 && @wave_ram_dimension
-    @wave_ram_sample_buffer = @wave_ram[@wave_ram_bank][@wave_ram_position // 2]
+    @wave_ram_sample_buffer = @wave_ram[@wave_ram_bank][@wave_ram_position // 2].to_i16
   end
 
   def frequency_timer : UInt32
@@ -40,14 +38,14 @@ class Channel3 < SoundChannel
     @gba.scheduler.schedule frequency_timer, ->step, Scheduler::EventType::APUChannel3
   end
 
-  def get_amplitude : Float32
+  # Outputs a value 0..0xF
+  def get_amplitude : Int16
     if @enabled && @dac_enabled
-      dac_input = @volume_multiplier * ((@wave_ram_sample_buffer >> (@wave_ram_position & 1 == 0 ? 4 : 0)) & 0x0F)
-      dac_output = (dac_input / 7.5) - 1
-      dac_output
+      volume_shift = (-1 + @volume_code) % 4
+      (((@wave_ram_sample_buffer >> (@wave_ram_position & 1 == 0 ? 4 : 0)) & 0x0F) >> volume_shift)
     else
-      0
-    end.to_f32
+      0_i16
+    end
   end
 
   def read_io(index : Int) : UInt8
@@ -82,15 +80,6 @@ class Channel3 < SoundChannel
     when 0x73
       @volume_code = (value & 0x60) >> 5
       @volume_force = bit?(value, 7)
-      # Internal values
-      @volume_multiplier = case {@volume_force, @volume_code}
-                           when {true, _} then 0.75_f32
-                           when {_, 0b00} then 0_f32
-                           when {_, 0b01} then 1_f32
-                           when {_, 0b10} then 0.5_f32
-                           when {_, 0b11} then 0.25_f32
-                           else                raise "Impossible volume code #{@volume_code}"
-                           end
     when 0x74
       @frequency = (@frequency & 0x0700) | value
     when 0x75

src/crab/apu/channel4.cr

@@ -33,14 +33,13 @@ class Channel4 < VolumeEnvelopeChannel
     @gba.scheduler.schedule frequency_timer, ->step, Scheduler::EventType::APUChannel4
   end
 
-  def get_amplitude : Float32
+  # Outputs a value 0..0xF
+  def get_amplitude : Int16
     if @enabled && @dac_enabled
-      dac_input = (~@lfsr & 1) * @current_volume
-      dac_output = (dac_input / 7.5) - 1
-      dac_output
+      ((~@lfsr & 1) * @current_volume).to_i16
     else
-      0
-    end.to_f32
+      0_i16
+    end
   end
 
   def read_io(index : Int) : UInt8

src/crab/apu/dma_channels.cr

@@ -5,7 +5,7 @@ class DMAChannels
   @positions = Array(Int32).new 2, 0
   @sizes = Array(Int32).new 2, 0
   @timers : Array(Proc(UInt16))
-  @latches = Array(Float32).new 2, 0
+  @latches = Array(Int16).new 2, 0
 
   def ===(value) : Bool
     value.is_a?(Int) && RANGE.includes?(value)
@@ -21,7 +21,7 @@ class DMAChannels
   def read_io(index : Int) : UInt8
     0_u8
   end
-
+  
   def write_io(index : Int, value : Byte) : Nil
     channel = bit?(index, 2).to_unsafe
     if @sizes[channel] < 32
@@ -37,7 +37,7 @@ class DMAChannels
       if timer == @timers[channel].call
         if @sizes[channel] > 0
           log "Timer overflow good; channel:#{channel}, timer:#{timer}".colorize.fore(:yellow)
-          @latches[channel] = (@fifos[channel][@positions[channel]] / 128).to_f32
+          @latches[channel] = @fifos[channel][@positions[channel]].to_i16
           @positions[channel] = (@positions[channel] + 1) % 32
           @sizes[channel] -= 1
         else
@@ -49,7 +49,8 @@ class DMAChannels
     end
   end
 
-  def get_amplitude : Tuple(Float32, Float32)
+  # Outputs a value -0x100...0x100
+  def get_amplitude : Tuple(Int16, Int16)
     {@latches[0], @latches[1]}
   end
 end