Class: OpenC3::LengthProtocol

Inherits:
BurstProtocol show all
Defined in:
lib/openc3/interfaces/protocols/length_protocol.rb

Overview

Protocol which delineates packets using a length field at a fixed location in each packet.

Instance Attribute Summary

Attributes inherited from Protocol

#allow_empty_data, #extra, #interface

Instance Method Summary collapse

Methods inherited from BurstProtocol

#handle_sync_pattern, #log_discard, #read_data, #reset

Methods inherited from Protocol

#connect_reset, #disconnect_reset, #post_write_interface, #protocol_cmd, #read_data, #read_packet, #reset

Constructor Details

#initialize(length_bit_offset = 0, length_bit_size = 16, length_value_offset = 0, length_bytes_per_count = 1, length_endianness = 'BIG_ENDIAN', discard_leading_bytes = 0, sync_pattern = nil, max_length = nil, fill_length_and_sync_pattern = false, allow_empty_data = nil) ⇒ LengthProtocol 



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# File 'lib/openc3/interfaces/protocols/length_protocol.rb', line 49

def initialize(
  length_bit_offset = 0,
  length_bit_size = 16,
  length_value_offset = 0,
  length_bytes_per_count = 1,
  length_endianness = 'BIG_ENDIAN',
  discard_leading_bytes = 0,
  sync_pattern = nil,
  max_length = nil,
  fill_length_and_sync_pattern = false,
  allow_empty_data = nil
)
  super(discard_leading_bytes, sync_pattern, fill_length_and_sync_pattern, allow_empty_data)

  # Save length field attributes
  @length_bit_offset = Integer(length_bit_offset)
  @length_bit_size = Integer(length_bit_size)
  @length_value_offset = Integer(length_value_offset)
  @length_bytes_per_count = Integer(length_bytes_per_count)

  # Save endianness
  if length_endianness.to_s.upcase == 'LITTLE_ENDIAN'
    @length_endianness = :LITTLE_ENDIAN
  else
    @length_endianness = :BIG_ENDIAN
  end

  # Derive number of bytes required to contain entire length field
  if @length_endianness == :BIG_ENDIAN or ((@length_bit_offset % 8) == 0)
    length_bits_needed = @length_bit_offset + @length_bit_size
    length_bits_needed += 8 if (length_bits_needed % 8) != 0
    @length_bytes_needed = ((length_bits_needed - 1) / 8) + 1
  else
    @length_bytes_needed = (length_bit_offset / 8) + 1
  end

  # Save max length setting
  @max_length = ConfigParser.handle_nil(max_length)
  @max_length = Integer(@max_length) if @max_length
end

Instance Method Details

#write_data(data, extra = nil) ⇒ String

Called to perform modifications on write data before making it into a packet



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# File 'lib/openc3/interfaces/protocols/length_protocol.rb', line 115

def write_data(data, extra = nil)
  data, extra = super(data, extra)
  if @fill_fields
    # If the start of the length field is before what we discard, then the
    # length field is outside the packet
    if @length_bit_offset < (@discard_leading_bytes * 8)
      BinaryAccessor.write(calculate_length(data.length), @length_bit_offset, @length_bit_size, :UINT,
                           data, @length_endianness, :ERROR)
    end
  end
  return data, extra
end

#write_packet(packet) ⇒ Packet

Called to perform modifications on a command packet before it is send



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# File 'lib/openc3/interfaces/protocols/length_protocol.rb', line 94

def write_packet(packet)
  if @fill_fields
    # If the start of the length field is past what we discard, then the
    # length field is inside the packet
    if @length_bit_offset >= (@discard_leading_bytes * 8)
      length = calculate_length(packet.buffer(false).length + @discard_leading_bytes)
      # Subtract off the discarded bytes since they haven't been added yet
      # Adding bytes happens in the write_data method
      offset = @length_bit_offset - (@discard_leading_bytes * 8)
      # Directly write the packet buffer and fill in the length
      BinaryAccessor.write(length, offset, @length_bit_size, :UINT,
                           packet.buffer(false), @length_endianness, :ERROR)
    end
  end
  return super(packet) # Allow burst_protocol to set the sync if needed
end