ccsds_cadu_to_transfer_frames_protocol.rb

# encoding: ascii-8bit

# Copyright 2018 Fredrik Persson <u.fredrik.persson@gmail.com>
#                Martin Erik Werner <martinerikwerner@gmail.com>
#
# This program is free software; you can modify and/or redistribute it
# under the terms of the GNU General Public License
# as published by the Free Software Foundation; version 3 with
# attribution addendums as found in the LICENSE.txt

require 'cosmos/config/config_parser'
require 'cosmos/interfaces/protocols/protocol'
require 'thread'

module Cosmos
  # Make ccsds transfer frames from from stream of ccsds channel access data units ("cadu").
  class CcsdsCaduToTransferFramesProtocol < Protocol
    CCSDS_SYNC_MARKER_LEN = 4

    # @param transfer_frame_size [Integer] Size of transfer frame in bytes
    # @param reed_solomon_size [Integer] Size of Reed-Solomon coding field in bytes
    # @param allow_empty_data [true/false/nil] See Protocol#initialize
    def initialize(
      transfer_frame_size,
      reed_solomon_size,
      allow_empty_data = nil)
      super(allow_empty_data)

      @reed_solomon_size = Integer(reed_solomon_size)
      @cadu_size = CCSDS_SYNC_MARKER_LEN + Integer(transfer_frame_size) + @reed_solomon_size
    end

    def reset
      super()
      @data = ''
    end

    def read_data(data)
      @data << data

      packet_data = reduce_to_single_transfer_frame()

      # Potentially allow blank string to be sent to other protocols if no packet is ready in this one
      if Symbol === packet_data
        if (data.length <= 0) and packet_data == :STOP
          return super(data)
        else
          return packet_data
        end
      end

      return packet_data
    end

    def write_data(data)
      return data
    end

    def reduce_to_single_transfer_frame
      return :STOP if (@data.length < @cadu_size)

      cadu = @data.slice!(0...@cadu_size)
      transfer_frame = cadu[CCSDS_SYNC_MARKER_LEN..-(@reed_solomon_size + 1)]
      return transfer_frame
    end
  end
end