Class: PSX::Timers::Timer

Inherits:
Object
  • Object
show all
Defined in:
lib/psx/timers.rb

Overview

Overflow occurred (bit 12)

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize ⇒ Timer

Returns a new instance of Timer.



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# File 'lib/psx/timers.rb', line 27

def initialize
  @counter = 0
  @mode = 0
  @target = 0
  @irq_fired = false
end

Instance Attribute Details

#counter ⇒ Object

Returns the value of attribute counter.



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# File 'lib/psx/timers.rb', line 25

def counter
  @counter
end

#mode ⇒ Object

Returns the value of attribute mode.



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# File 'lib/psx/timers.rb', line 25

def mode
  @mode
end

#target ⇒ Object

Returns the value of attribute target.



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# File 'lib/psx/timers.rb', line 25

def target
  @target
end

Instance Method Details

#read_counter ⇒ Object 



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# File 'lib/psx/timers.rb', line 34

def read_counter
  @counter
end

#read_mode ⇒ Object 



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# File 'lib/psx/timers.rb', line 42

def read_mode
  # Return mode and clear flags
  result = @mode
  @mode &= ~(MODE_TARGET_REACHED | MODE_OVERFLOW)
  result
end

#read_target ⇒ Object 



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# File 'lib/psx/timers.rb', line 55

def read_target
  @target
end

#tick(cycles = 1) ⇒ Object

Increment counter, returns true if IRQ should fire Optimized to avoid per-cycle loop



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# File 'lib/psx/timers.rb', line 65

def tick(cycles = 1)
  return false if cycles <= 0

  irq = false
  new_counter = @counter + cycles

  # Check for target hit (if target is set and reset-on-target is enabled)
  if @target > 0 && (@mode & MODE_RESET_TARGET) != 0
    # Will we cross the target?
    if @counter < @target && new_counter >= @target
      @mode |= MODE_TARGET_REACHED
      if (@mode & MODE_IRQ_TARGET) != 0
        irq = true if !@irq_fired || (@mode & MODE_IRQ_REPEAT) != 0
      end
      # Reset and continue counting from target
      new_counter = (new_counter - @target) % (@target > 0 ? @target : 0x10000)
    end
  elsif @target > 0 && @counter < @target && new_counter >= @target
    # Target without reset - just set flag
    @mode |= MODE_TARGET_REACHED
    if (@mode & MODE_IRQ_TARGET) != 0
      irq = true if !@irq_fired || (@mode & MODE_IRQ_REPEAT) != 0
    end
  end

  # Check for overflow
  if new_counter > 0xFFFF
    @mode |= MODE_OVERFLOW
    if (@mode & MODE_IRQ_OVERFLOW) != 0
      irq = true if !@irq_fired || (@mode & MODE_IRQ_REPEAT) != 0
    end
    new_counter &= 0xFFFF
  end

  @counter = new_counter
  @irq_fired = true if irq && (@mode & MODE_IRQ_REPEAT) == 0
  irq
end

#write_counter(value) ⇒ Object 



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# File 'lib/psx/timers.rb', line 38

def write_counter(value)
  @counter = value & 0xFFFF
end

#write_mode(value) ⇒ Object 



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# File 'lib/psx/timers.rb', line 49

def write_mode(value)
  @mode = value & 0x03FF  # Writable bits
  @counter = 0  # Writing to mode resets counter
  @irq_fired = false
end

#write_target(value) ⇒ Object 



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# File 'lib/psx/timers.rb', line 59

def write_target(value)
  @target = value & 0xFFFF
end