I try to write a ModbusTCP server software connected wıth a database. I used pyModbus library for that task. That library has an Updating Server Example. By using that code, I wrote my code as :
'''
Pymodbus Server With Updating Thread
--------------------------------------------------------------------------
This is an example of having a background thread updating the
context while the server is operating. This can also be done with
a python thread::
from threading import Thread
thread = Thread(target=updating_writer, args=(context,))
thread.start()
'''
#---------------------------------------------------------------------------#
# import the modbus libraries we need
#---------------------------------------------------------------------------#
from pymodbus.server.async import StartTcpServer
from pymodbus.device import ModbusDeviceIdentification
from pymodbus.datastore import ModbusSequentialDataBlock
from pymodbus.datastore import ModbusSlaveContext, ModbusServerContext
from pymodbus.transaction import ModbusRtuFramer, ModbusAsciiFramer
#---------------------------------------------------------------------------#
# import the twisted libraries we need
#---------------------------------------------------------------------------#
from twisted.internet.task import LoopingCall
#---------------------------------------------------------------------------#
# configure the service logging
#---------------------------------------------------------------------------#
import logging
logging.basicConfig()
log = logging.getLogger()
log.setLevel(logging.DEBUG)
#---------------------------------------------------------------------------#
# for database reading
#---------------------------------------------------------------------------#
import sqlite3
import sys
sqlite_file = 'ModbusTable.db'
thermostats = 25
registers_per_thermostat = 3
global total_registers
total_registers = thermostats * registers_per_thermostat
#---------------------------------------------------------------------------#
# define your callback process
#---------------------------------------------------------------------------#
def updating_writer(a):
''' A worker process that runs every so often and
updates live values of the context. It should be noted
that there is a race condition for the update.
:param arguments: The input arguments to the call
'''
log.debug("updating the context")
context = a[0]
functioncode = 3
slave_id = 0x01 # slave address
address = 0x10 # start register : 400017
values = []
# Connecting to the database file
conn = sqlite3.connect(sqlite_file)
c1 = conn.cursor()
c1.execute("""SELECT ID, SetPoint, ActualTemp FROM ModbusData""")
registers = c1.fetchall()
c1.close()
for register in registers:
for value in register:
values.append(value)
log.debug("values from database: " + str(values))
context[slave_id].setValues(functioncode, address, values)
values = context[slave_id].getValues(functioncode, address, count=total_registers)
log.debug("values to be written to database: " + str(values))
c2 = conn.cursor()
for index in range(len(values)):
if (index+2)<len(values):
column1 = values[index]
column2 = values[index+1]
column3 = values[index+2]
c2.execute("""UPDATE ModbusData set SetPoint = ?, ActualTemp = ? where ID=?""",[column2, column3, column1])
# Committing changes and closing the connection to the database file
c2.close()
conn.close()
#---------------------------------------------------------------------------#
# initialize your data store
#---------------------------------------------------------------------------#
store = ModbusSlaveContext(
di = ModbusSequentialDataBlock(0, [17]*total_registers),
co = ModbusSequentialDataBlock(0, [17]*total_registers),
hr = ModbusSequentialDataBlock(0, [17]*total_registers),
ir = ModbusSequentialDataBlock(0, [17]*total_registers))
context = ModbusServerContext(slaves=store, single=True)
#---------------------------------------------------------------------------#
# initialize the server information
#---------------------------------------------------------------------------#
identity = ModbusDeviceIdentification()
identity.VendorName = 'pymodbus'
identity.ProductCode = 'PM'
identity.VendorUrl = 'http://github.com/bashwork/pymodbus/'
identity.ProductName = 'pymodbus Server'
identity.ModelName = 'pymodbus Server'
identity.MajorMinorRevision = '1.0'
#---------------------------------------------------------------------------#
# run the server you want
#---------------------------------------------------------------------------#
time = 5 # 5 seconds delay
loop = LoopingCall(f=updating_writer, a=(context,))
loop.start(time, now=False) # initially delay by time
StartTcpServer(context, identity=identity, address=("", 5007))
Basically, what i try to achieve is that server context is synced with database. I try to read values from database to context and then last updated context values to database. I am successful at getting data from database to context. Because when I request values with a modbus client located on another lan computer , I successfuly get requested data there. However, I cant write to database through TCP server. With the same modbus client on another lan computer, I send request to write to some registers in server context and then write it to database. At this point I fail. I cant write the latest updated situation of server context to database. I thought, I could possibly benefit from "Database Datastore Example" located in pymodbus documentation but I could not figure out how to do it. So I need your ideas about this task.
