Beginner question about updating registers

[jonty oxford]

Hello,

I am trying to set up a simple TCP server with a self updating temperature measurement. At the moment I am taking the processor temp reading but will swap for an external temperature sensor once the hardware arrives. 

I plugged this into the updating server example, and the server starts without error, and debug gives periodic updated values (see below) but when I send a request using:

client.read_holding_registers(0,10,unit=0)

from another device, the register hasn't been updated:

ReadRegisterResponse (10)

[0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

I assume I am doing something very stupid but would be greatful for any pointers.

See code below.

Debug of running server:

INFO:pymodbus.server.async:Starting Modbus TCP Server on 192.168.1.87:5020

DEBUG:root:updating the context

DEBUG:root:new values: 33.6

DEBUG:pymodbus.datastore.context:setValues[1] 17:4

DEBUG:root:updating the context

DEBUG:root:new values: 32.6

DEBUG:pymodbus.datastore.context:setValues[1] 17:4

DEBUG:root:updating the context

DEBUG:root:new values: 32.6

server code:

#!/usr/bin/env python

'''

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

#---------------------------------------------------------------------------#

import os

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)

#---------------------------------------------------------------------------#

# 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]

    register = 1

    slave_id = 0x00

    address  = 0x10

    CPUtemp  = os.popen('vcgencmd measure_temp').readline()

    values   = (CPUtemp.replace("temp=","").replace("'C\n",""))

    log.debug("new values: " + str(values))

    context[slave_id].setValues(register, address, values)

#---------------------------------------------------------------------------#

# initialize your data store

#---------------------------------------------------------------------------#

store = ModbusSlaveContext(

    di = ModbusSequentialDataBlock(0, [0]*100),

    co = ModbusSequentialDataBlock(0, [0]*100),

    hr = ModbusSequentialDataBlock(0, [0]*100),

    ir = ModbusSequentialDataBlock(0, [0]*100))

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=("192.168.1.87", 5020))

[zuababa]

Did you solve the issue? I was trying this now out and what I wonder is how the setValues function knows this should be stored to the holding registers. Maybe it stores it somewhere else? And you are reading just the 0s which are initialized in the context at the beginning.
Then I saw that the arguments are:

setValues(fx, address, values)

Your example has fx=1 which is for coils. I think fx=3 is for holding registers.

Does that help?

[zuababa]

First of all register should indeed be 3 for holding registers at the server.

    register = 1

Next, I noticed that in your code you have: 

    values   = (CPUtemp.replace("temp=","").replace("'C\n",""))

So, values is a string. Later when attempting to read that one with the client I used:

    client.read_holding_registers(0x10, 1, unit=0)

It was giving a 'ModbusIOException'. On the server side I saw that a struct function could not create an Integer from the obtained value. This meant that the value stored in the context was not right. I think the values _have to_ be an integer if you use the setValues() function. So I gave only the number via setValues and saw on the server side:

    _logger.debug("setValues[%d] %d:%d" % (fx, address, len(values)))
    exceptions.TypeError: object of type 'int' has no len()

So I changed the line 85 in datastore/context.py to 

    _logger.debug("setValues[%d] %d:%d" % (fx, address, len(str(values))))

now it works:)