A class for getting events from a Griffin PowerMate

power_mate.rb

#!/usr/bin/env ruby
# Ruby interface for Griffin PowerMate

require 'usb'

class PowerMate
  VENDOR_ID = 0x077d
  PRODUCT_ID_NEW = 0x0410
  PRODUCT_ID_OLD = 0x04AA

  EVENT_UNIT = 256 # interval at which values will fall
  EVENT_SIZE = 16 # how many bytes to read per event
  EVENT_KEEP = 4 # number of events to keep for debouncing
  EVENT_TIME = 0.25 # maximum time to keep events

  attr_reader :handle, :dev

  def self.find_dev
    USB.devices.each do |dev|
      if dev.idVendor == VENDOR_ID &&
          (dev.idProduct == PRODUCT_ID_NEW || dev.idProduct == PRODUCT_ID_OLD)
        return dev
      end
    end
  end

  def initialize(dev = nil)
    @dev  = dev || self.class.find_dev
    @last = []
    @time = Time.now.to_f
  end

  def connect
    return false if connected?
    @handle = dev.open
    @handle.usb_claim_interface(0)
  end

  def disconnect
    return false unless connected?
    @handle.usb_close
    @handle = nil
  end

  def connected?
    not @handle.nil?
  end

  def button_press &block
    @button_press = block
  end

  def dial_rotate &block
    @dial_rotate = block
  end

  def process_input_events
    connect unless connected?
    loop do
      buffer = '0' * EVENT_SIZE
      epaddr = dev.endpoints.first.bEndpointAddress
      nbytes = handle.usb_bulk_read(epaddr, buffer, 0)
      next unless nbytes > 0
      event = buffer.unpack("ldsxx")
      handle_event event[2]
    end
  end

  private

  def handle_event code
    time = Time.now.to_f

    if time - @time > EVENT_TIME
      @last.clear
    end

    if code == 0 || code == 1
      if @last.empty?
        @last << nil
        @button_press.call
      end
    else
      value = code / EVENT_UNIT
      press = code % EVENT_UNIT == 1

      @last << (code > 0)
      @last.shift if @last.size > EVENT_KEEP

      if @last.empty? || @last.uniq.size == 1
        @dial_rotate.call value, press
      end
    end

    @time = time
  end
end

if __FILE__ == $0
  trap :INT do
    exit
  end

  pm = PowerMate.new

  pm.button_press do
    puts 'BUTTON PRESS'
  end

  pm.dial_rotate do |value, press|
    print press ? 'PRESS' : 'FREE'
    print ' ROTATE '
    print value > 0 ? 'RIGHT' : 'LEFT'
    print ' SPEED '
    puts value.abs
  end

  pm.process_input_events
end