Class: Cosmos::CrcProtocol

Inherits:
Protocol show all
Defined in:
lib/cosmos/interfaces/protocols/crc_protocol.rb

Overview

Creates a CRC on write and verifies a CRC on read

Constant Summary collapse

ERROR =

on CRC mismatch

"ERROR"
DISCONNECT =

on CRC mismatch

"DISCONNECT"

Instance Attribute Summary

Attributes inherited from Protocol

#allow_empty_data, #interface

Instance Method Summary collapse

Methods inherited from Protocol

#connect_reset, #disconnect_reset, #post_write_interface, #read_packet, #reset

Constructor Details

#initialize(write_item_name = nil, strip_crc = false, bad_strategy = "ERROR", bit_offset = -32,, bit_size = 32, endianness = 'BIG_ENDIAN', poly = nil, seed = nil, xor = nil, reflect = nil, allow_empty_data = nil) ⇒ CrcProtocol

Returns a new instance of CrcProtocol.

Parameters:

  • write_item_name (String/nil) (defaults to: nil) —

    Item to fill with calculated CRC value for outgoing packets (nil = don't fill)

  • strip_crc (Boolean) (defaults to: false) —

    Whether or not to remove the CRC from incoming packets

  • bad_strategy (ERROR/DISCONNECT) (defaults to: "ERROR") —

    How to handle CRC errors on incoming packets. ERROR = Just log the error, DISCONNECT = Disconnect interface

  • bit_offset (Integer) (defaults to: -32,) —

    Bit offset of the CRC in the data. Can be negative to indicate distance from end of packet

  • bit_size (Integer) (defaults to: 32) —

    Bit size of the CRC - Must be 16, 32, or 64

  • endianness (BIG_ENDIAN/LITTLE_ENDIAN) (defaults to: 'BIG_ENDIAN') —

    Endianness of the CRC

  • poly (Integer) (defaults to: nil) —

    Polynomial to use when calculating the CRC

  • seed (Integer) (defaults to: nil) —

    Seed value to start the calculation

  • xor (Boolean) (defaults to: nil) —

    Whether to XOR the CRC result with 0xFFFF

  • reflect (Boolean) (defaults to: nil) —

    Whether to bit reverse each byte of data before calculating the CRC

  • allow_empty_data (true/false/nil) (defaults to: nil) —

    See Protocol#initialize



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# File 'lib/cosmos/interfaces/protocols/crc_protocol.rb', line 42

def initialize(
  write_item_name = nil,
  strip_crc = false,
  bad_strategy = "ERROR",
  bit_offset = -32,
  bit_size = 32,
  endianness = 'BIG_ENDIAN',
  poly = nil,
  seed = nil,
  xor = nil,
  reflect = nil,
  allow_empty_data = nil
)
  super(allow_empty_data)
  @write_item_name = ConfigParser.handle_nil(write_item_name)
  @strip_crc = ConfigParser.handle_true_false(strip_crc)
  raise "Invalid strip CRC of '#{strip_crc}'. Must be TRUE or FALSE." unless !!@strip_crc == @strip_crc

  case bad_strategy
  when ERROR, DISCONNECT
    @bad_strategy = bad_strategy
  else
    raise "Invalid bad CRC strategy of #{bad_strategy}. Must be ERROR or DISCONNECT."
  end

  case endianness.to_s.upcase
  when 'BIG_ENDIAN'
    @endianness = :BIG_ENDIAN # Convert to symbol for use in BinaryAccessor.write
  when 'LITTLE_ENDIAN'
    @endianness = :LITTLE_ENDIAN # Convert to symbol for use in BinaryAccessor.write
  else
    raise "Invalid endianness '#{endianness}'. Must be BIG_ENDIAN or LITTLE_ENDIAN."
  end

  begin
    @bit_offset = Integer(bit_offset)
  rescue
    raise "Invalid bit offset of #{bit_offset}. Must be a number."
  end
  raise "Invalid bit offset of #{bit_offset}. Must be divisible by 8." if @bit_offset % 8 != 0

  poly = ConfigParser.handle_nil(poly)
  begin
    poly = Integer(poly) if poly
  rescue
    raise "Invalid polynomial of #{poly}. Must be a number."
  end

  seed = ConfigParser.handle_nil(seed)
  begin
    seed = Integer(seed) if seed
  rescue
    raise "Invalid seed of #{seed}. Must be a number."
  end

  xor = ConfigParser.handle_true_false_nil(xor)
  raise "Invalid XOR value of '#{xor}'. Must be TRUE or FALSE." if xor && !!xor != xor

  reflect = ConfigParser.handle_true_false_nil(reflect) if reflect
  raise "Invalid reflect value of '#{reflect}'. Must be TRUE or FALSE." if reflect && !!reflect != reflect

  # Built the CRC arguments array. All subsequent arguments are dependent
  # on the previous ones so we build it up incrementally.
  args = []
  if poly
    args << poly
    if seed
      args << seed
      unless xor.nil? # Can't check raw variable because it could be false
        args << xor
        unless reflect.nil? # Can't check raw variable because it could be false
          args << reflect
        end
      end
    end
  end

  @bit_size = bit_size.to_i
  case @bit_size
  when 16
    @pack = (@endianness == :BIG_ENDIAN) ? 'n' : 'v'
    if args.empty?
      @crc = Crc16.new
    else
      @crc = Crc16.new(*args)
    end
  when 32
    @pack = (@endianness == :BIG_ENDIAN) ? 'N' : 'V'
    if args.empty?
      @crc = Crc32.new
    else
      @crc = Crc32.new(*args)
    end
  when 64
    @pack = (@endianness == :BIG_ENDIAN) ? 'N' : 'V'
    if args.empty?
      @crc = Crc64.new
    else
      @crc = Crc64.new(*args)
    end
  else
    raise "Invalid bit size of #{bit_size}. Must be 16, 32, or 64."
  end
end

Instance Method Details

#read_data(data) ⇒ Object 



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# File 'lib/cosmos/interfaces/protocols/crc_protocol.rb', line 147

def read_data(data)
  return super(data) if data.length <= 0

  crc = BinaryAccessor.read(@bit_offset, @bit_size, :UINT, data, @endianness)
  calculated_crc = @crc.calc(data[0...(@bit_offset / 8)])
  if calculated_crc != crc
    Logger.error "#{@interface ? @interface.name : ""}: Invalid CRC detected! Calculated 0x#{calculated_crc.to_s(16).upcase} vs found 0x#{crc.to_s(16).upcase}."
    if @bad_strategy == DISCONNECT
      return :DISCONNECT
    end
  end
  if @strip_crc
    new_data = data.dup
    new_data = new_data[0...(@bit_offset / 8)]
    end_range = (@bit_offset + @bit_size) / 8
    new_data << data[end_range..-1] if end_range != 0
    return new_data
  end
  return data
end

#write_data(data) ⇒ Object 



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# File 'lib/cosmos/interfaces/protocols/crc_protocol.rb', line 177

def write_data(data)
  unless @write_item_name
    if @bit_size == 64
      crc = @crc.calc(data)
      data << ("\x00" * 8)
      BinaryAccessor.write((crc >> 32), -64, 32, :UINT, data, @endianness, :ERROR)
      BinaryAccessor.write((crc & 0xFFFFFFFF), -32, 32, :UINT, data, @endianness, :ERROR)
    else
      crc = @crc.calc(data)
      data << ("\x00" * (@bit_size / 8))
      BinaryAccessor.write(crc, -@bit_size, @bit_size, :UINT, data, @endianness, :ERROR)
    end
  end
  data
end

#write_packet(packet) ⇒ Object 



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# File 'lib/cosmos/interfaces/protocols/crc_protocol.rb', line 168

def write_packet(packet)
  if @write_item_name
    end_range = packet.get_item(@write_item_name).bit_offset / 8
    crc = @crc.calc(packet.buffer(false)[0...end_range])
    packet.write(@write_item_name, crc)
  end
  packet
end