modbus-rtu-slave.rb

#!/usr/bin/ruby

SERIAL_DEVICE = '/dev/tty.usbserial-FTXYGCM5'
# On Windows, like SERIAL_DEVICE = 'COM4'

require 'rubygems'
require 'rmodbus'
# does not support 23 (0x17) Read/Write Multiple registers
#   according to https://github.com/flipback/rmodbus
require 'serialport'

# To prepare,
# $ gem environment
# $ gem install -V rmodbus serialport
# To clean-up,
# $ gem uninstall gserver rmodbus serialport

# Serial constants according to the master configuration
BAUD_RATE = 19_200
SERVER_ADDRESS = 50
SERIAL_OPTS = {
  :data_bit => 8,
  :stop_bits => 1,
  :parity => SerialPort::EVEN}
# FYI, default :read_timeout is 100 in SerialPort lib

# Modbus constants

HOLDING_REGISTER_OFFSET = 40001

IDX_WATCHDOG_COUNTER_M2S = 40501 - HOLDING_REGISTER_OFFSET
IDX_WATCHDOG_COUNTER_S2M = 40001 - HOLDING_REGISTER_OFFSET
WATCHDOG_COUNTER_MAX = 2 ** 8
IDX_DATA = 40510 - HOLDING_REGISTER_OFFSET
DATA_COUNTS = 28
INVALID_LENGTH_M2S = 0

# Constants for this implementation
DUMMY_BYTE = 0x00

class DummySlave < ModBus::RTUServer

  def initialize(*arvg)
    super

    @holding_registers = Array.new(1 + IDX_DATA + DATA_COUNTS * 2 + INVALID_LENGTH_M2S)
    @holding_registers[0..IDX_DATA] = [DUMMY_BYTE] * IDX_DATA
    # On 2015-09-11, the entire array was filled by DUMMY_BYTE and
    # it was why we could not find the error of the master,
    # which sends wrong 0x10 messages 2 bytes shorter than requite.
    # On 2015-09-15, changed not to fill the part of data from the master.

    @slave_watchdog_counter = 0
    holding_registers[IDX_WATCHDOG_COUNTER_S2M] = @slave_watchdog_counter
    @master_watchdog_counter = nil
  end

  def when_write
    timestamp = Time.now.utc.to_s
    if holding_registers[IDX_WATCHDOG_COUNTER_M2S] == @master_watchdog_counter
      warn "#{timestamp} Received a request to write holding registers with the same watchdog counter: #{@master_watchdog_counter}"
    else
      @master_watchdog_counter = holding_registers[IDX_WATCHDOG_COUNTER_M2S]
      @slave_watchdog_counter = (@slave_watchdog_counter + 1) % WATCHDOG_COUNTER_MAX
      holding_registers[IDX_WATCHDOG_COUNTER_S2M] = @slave_watchdog_counter
      $stderr.puts [timestamp,
#                    holding_registers[0, IDX_DATA],
                    holding_registers[IDX_WATCHDOG_COUNTER_S2M],
                    holding_registers[IDX_WATCHDOG_COUNTER_M2S],
                    holding_registers[IDX_DATA, DATA_COUNTS * 2].
                    each_slice(2).collect {|pair|
                      if pair.include? nil
                        '[' + pair.join(',') + ']'
                      else
                        sprintf('%.8e', pair.reverse.to_32f.first)
                      end
                    }#,
#                    holding_registers[IDX_DATA + DATA_COUNTS * 2, holding_registers.length]
                       ].flatten.join(',')
      # Array#to_32f is defined in rmodbus/ext.rb
      # The decimal digits of 32 bit float is 7.22
      #   according to https://en.wikipedia.org/wiki/IEEE_floating_point
    end
  end

  def parse_write_multiple_registers_func(req)
    ret_val = super
#     p ret_val
#     p quant = req[3,2].unpack('n')[0]
#     p addr = req[1,2].unpack('n')[0]
#     p @holding_registers.size
    when_write
    ret_val
  end

end

server = DummySlave.new(SERIAL_DEVICE, BAUD_RATE, SERVER_ADDRESS, SERIAL_OPTS)
server.debug = true
server.start
server.join