Module: Beaglebone::PWM

Defined in:
lib/beaglebone/pwm.rb

Overview

PWM

procedural methods for PWM control

Summary

#start is called to enable a PWM pin

Constant Summary collapse

POLARITIES =

Polarity hash

{ :NORMAL => 0, :INVERTED => 1 }

Class Method Summary collapse

Class Method Details

.cleanup ⇒ Object

reset all PWM pins we’ve used to IN and unexport them



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# File 'lib/beaglebone/pwm.rb', line 285

def cleanup
  get_pwm_pins.each { |x| disable_pwm_pin(x) }
end

.disable_pwm_pin(pin) ⇒ Object

Disable a PWM pin

Parameters:

  • pin —

    should be a symbol representing the header pin



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# File 'lib/beaglebone/pwm.rb', line 302

def disable_pwm_pin(pin)
  Beaglebone::check_valid_pin(pin, :pwm)
  Beaglebone::delete_pin_status(pin) if Beaglebone::device_tree_unload("#{TREES[:PWM][:pin]}#{pin}")
end

.enabled?(pin) ⇒ Boolean

Returns true if specified pin is enabled in PWM mode, else false

Returns:

  • (Boolean) 


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# File 'lib/beaglebone/pwm.rb', line 74

def enabled?(pin)
  return true if Beaglebone::get_pin_status(pin, :type) == :pwm

  return false unless valid?(pin)
  if Dir.exists?(pwm_directory(pin))

    start(pin, nil, nil, nil, false)
    return true
  end
  false
end

.get_pwm_pins ⇒ Array<Symbol>

Return an array of PWM pins in use

Examples:

PWM.get_pwm_pins => [:P9_13, :P9_14]

Returns:

  • (Array<Symbol>) 


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# File 'lib/beaglebone/pwm.rb', line 295

def get_pwm_pins
  Beaglebone.pinstatus.clone.select { |x,y| x if y[:type] == :pwm}.keys
end

.run(pin) ⇒ Object

Start PWM output on specified pin. Pin must have been previously started

Parameters:

  • pin —

    should be a symbol representing the header pin

Raises:

  • (StandardError) 


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# File 'lib/beaglebone/pwm.rb', line 110

def run(pin)
  Beaglebone::check_valid_pin(pin, :pwm)

  return false unless enabled?(pin)

  raise StandardError, "Pin is not PWM enabled: #{pin}" unless Beaglebone::get_pin_status(pin, :type) == :pwm

  run_fd = Beaglebone::get_pin_status(pin, :fd_run)

  raise StandardError, "Pin is not PWM enabled: #{pin}" unless run_fd

  run_fd.write('1')
  run_fd.flush

  raise StandardError, "Could not start PWM: #{pin}" unless read_run_value(pin) == 1
  true

end

.set_duty_cycle(pin, duty, newperiod = nil) ⇒ Object

Set duty cycle of specified pin in percentage

Examples:

PWM.set_duty_cycle(:P9_14, 25)

Parameters:

  • pin —

    should be a symbol representing the header pin

  • duty —

    should specify the duty cycle in percentage

Raises:

  • (ArgumentError) 


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# File 'lib/beaglebone/pwm.rb', line 155

def set_duty_cycle(pin, duty, newperiod=nil)

  raise ArgumentError, "Duty cycle must be >= 0 and <= 100, #{duty} invalid" if duty < 0 || duty > 100
  check_pwm_enabled(pin)


  fd = Beaglebone::get_pin_status(pin, :fd_duty)
  raise StandardError, "Pin is not PWM enabled: #{pin}" unless fd

  period = newperiod || Beaglebone::get_pin_status(pin, :period)

  value = ((duty * period) / 100).to_i

  fd.write(value.to_s)
  fd.flush

  raise StandardError, "Could not set duty cycle: #{pin} (#{value})" unless read_duty_value(pin) == value

  value

end

.set_duty_cycle_ns(pin, duty) ⇒ Object

Set duty cycle of specified pin in nanoseconds

Examples:

PWM.set_duty_cycle_ns(:P9_14, 2500000)

Parameters:

  • pin —

    should be a symbol representing the header pin

  • duty —

    should specify the duty cycle in nanoseconds

Raises:

  • (StandardError) 


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# File 'lib/beaglebone/pwm.rb', line 184

def set_duty_cycle_ns(pin, duty)

  check_pwm_enabled(pin)

  fd = Beaglebone::get_pin_status(pin, :fd_duty)
  raise StandardError, "Pin is not PWM enabled: #{pin}" unless fd

  period = Beaglebone::get_pin_status(pin, :period)

  duty = duty.to_i

  if duty < 0 || duty > period
    raise ArgumentError, "Duty cycle ns must be >= 0 and <= #{period} (current period), #{duty} invalid"
  end

  value = duty

  fd.write(value.to_s)
  fd.flush

  raise StandardError, "Could not set duty cycle: #{pin} (#{value})" unless read_duty_value(pin) == value

  value
end

.set_frequency(pin, frequency) ⇒ Object

Set frequency of specified pin in cycles per second

Examples:

PWM.set_frequency(:P9_14, 100)

Parameters:

  • pin —

    should be a symbol representing the header pin

  • frequency —

    should specify the frequency in cycles per second

Raises:

  • (ArgumentError) 


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# File 'lib/beaglebone/pwm.rb', line 215

def set_frequency(pin, frequency)
  frequency = frequency.to_i
  raise ArgumentError, "Frequency must be > 0 and <= 1000000000, #{frequency} invalid" if frequency < 1 || frequency > 1000000000
  check_pwm_enabled(pin)

  fd = Beaglebone::get_pin_status(pin, :fd_period)
  raise StandardError, "Pin is not PWM enabled: #{pin}" unless fd

  duty_ns = Beaglebone::get_pin_status(pin, :duty)
  duty_pct = Beaglebone::get_pin_status(pin, :duty_pct)

  value = (1000000000 / frequency).to_i

  #we can't set the frequency lower than the previous duty cycle
  #adjust if necessary
  if duty_ns > value
    set_duty_cycle(pin, Beaglebone::get_pin_status(pin, :duty_pct), value)
  end

  fd.write(value.to_s)
  fd.flush

  raise StandardError, "Could not set frequency: #{pin} (#{value})" unless read_period_value(pin) == value

  #adjust the duty cycle if we haven't already
  if duty_ns <= value
    set_duty_cycle(pin, duty_pct, value)
  end

  value
end

.set_period_ns(pin, period) ⇒ Object

Set frequency of specified pin based on period duration

Examples:

PWM.set_frequency_ns(:P9_14, 100000000)

Parameters:

  • pin —

    should be a symbol representing the header pin

  • period —

    should specify the length of a cycle in nanoseconds

Raises:

  • (ArgumentError) 


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# File 'lib/beaglebone/pwm.rb', line 254

def set_period_ns(pin, period)
  period = period.to_i
  raise ArgumentError, "period must be > 0 and <= 1000000000, #{period} invalid" if period < 1 || period > 1000000000
  check_pwm_enabled(pin)

  fd = Beaglebone::get_pin_status(pin, :fd_period)
  raise StandardError, "Pin is not PWM enabled: #{pin}" unless fd

  duty_ns = Beaglebone::get_pin_status(pin, :duty)
  value = period.to_i

  #we can't set the frequency lower than the previous duty cycle
  #adjust if necessary
  if duty_ns > value
    set_duty_cycle(pin, Beaglebone::get_pin_status(pin, :duty_pct), value)
  end

  fd.write(value.to_s)
  fd.flush

  raise StandardError, "Could not set period: #{pin} (#{value})" unless read_period_value(pin) == value

  #adjust the duty cycle if we haven't already
  if duty_ns <= value
    set_duty_cycle(pin, Beaglebone::get_pin_status(pin, :duty_pct), value)
  end

  value
end

.set_polarity(pin, polarity) ⇒ Object

Set polarity on specified pin

Examples:

PWM.set_polarity(:P9_14, :INVERTED)

Parameters:

  • pin —

    should be a symbol representing the header pin

  • polarity —

    should specify the polarity, :NORMAL or :INVERTED

Raises:

  • (StandardError) 


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# File 'lib/beaglebone/pwm.rb', line 135

def set_polarity(pin, polarity)
  check_valid_polarity(polarity)
  check_pwm_enabled(pin)

  polarity_fd = Beaglebone::get_pin_status(pin, :fd_polarity)
  raise StandardError, "Pin is not PWM enabled: #{pin}" unless polarity_fd

  polarity_fd.write(POLARITIES[polarity.to_sym].to_s)
  polarity_fd.flush

  raise StandardError, "Could not set polarity: #{pin}" unless read_polarity_value(pin) == POLARITIES[polarity.to_sym]

end

.start(pin, duty = nil, frequency = nil, polarity = nil, run = true) ⇒ Object

Initialize a PWM pin

Examples:

PWM.start(:P9_14, 90, 10, :NORMAL)

Parameters:

  • pin —

    should be a symbol representing the header pin

  • duty (defaults to: nil) —

    should specify the duty cycle

  • frequency (defaults to: nil) —

    should specify cycles per second

  • polarity (defaults to: nil) —

    optional, should specify the polarity, :NORMAL or :INVERTED

  • run (defaults to: true) —

    optional, if false, pin will be configured but will not run

Raises:

  • (StandardError) 


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# File 'lib/beaglebone/pwm.rb', line 25

def start(pin, duty=nil, frequency=nil, polarity=nil, run=true)
  #make sure the pwm controller dtb is loaded
  Beaglebone::device_tree_load(TREES[:PWM][:global])

  Beaglebone::check_valid_pin(pin, :pwm)

  #if pin is enabled for something else, disable it
  if Beaglebone::get_pin_status(pin) && Beaglebone::get_pin_status(pin, :type) != :pwm
    Beaglebone::disable_pin(pin)
  end

  #load device tree for pin if not already loaded
  unless Beaglebone::get_pin_status(pin, :type) == :pwm
    Beaglebone::device_tree_load("#{TREES[:PWM][:pin]}#{pin}")
    Beaglebone::set_pin_status(pin, :type, :pwm)
  end

  duty_fd = File.open("#{pwm_directory(pin)}/duty", 'r+')
  period_fd = File.open("#{pwm_directory(pin)}/period", 'r+')
  polarity_fd = File.open("#{pwm_directory(pin)}/polarity", 'r+')
  run_fd = File.open("#{pwm_directory(pin)}/run", 'r+')

  Beaglebone::set_pin_status(pin, :fd_duty, duty_fd)
  Beaglebone::set_pin_status(pin, :fd_period, period_fd)
  Beaglebone::set_pin_status(pin, :fd_polarity, polarity_fd)
  Beaglebone::set_pin_status(pin, :fd_run, run_fd)


  read_period_value(pin)
  read_duty_value(pin)
  read_polarity_value(pin)

  run_fd.write('0')
  run_fd.flush

  set_polarity(pin, polarity) if polarity
  set_frequency(pin, frequency) if frequency
  set_duty_cycle(pin, duty) if duty

  if run
    run_fd.write('1')
    run_fd.flush
  end

  raise StandardError, "Could not start PWM: #{pin}" unless read_run_value(pin) == 1
  true
end

.stop(pin) ⇒ Object

Stop PWM output on specified pin

Parameters:

  • pin —

    should be a symbol representing the header pin

Raises:

  • (StandardError) 


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# File 'lib/beaglebone/pwm.rb', line 89

def stop(pin)
  Beaglebone::check_valid_pin(pin, :pwm)

  return false unless enabled?(pin)

  raise StandardError, "Pin is not PWM enabled: #{pin}" unless Beaglebone::get_pin_status(pin, :type) == :pwm

  run_fd = Beaglebone::get_pin_status(pin, :fd_run)

  raise StandardError, "Pin is not PWM enabled: #{pin}" unless run_fd

  run_fd.write('0')
  run_fd.flush

  raise StandardError, "Could not stop PWM: #{pin}" unless read_run_value(pin) == 0
  true
end