Callback Server Example

#!/usr/bin/env python
'''
Pymodbus Server With Callbacks
--------------------------------------------------------------------------

This is an example of adding callbacks to a running modbus server
when a value is written to it. In order for this to work, it needs
a device-mapping file.
'''
#---------------------------------------------------------------------------# 
# import the modbus libraries we need
#---------------------------------------------------------------------------# 
from pymodbus.server.async import StartTcpServer
from pymodbus.device import ModbusDeviceIdentification
from pymodbus.datastore import ModbusSparseDataBlock
from pymodbus.datastore import ModbusSlaveContext, ModbusServerContext
from pymodbus.transaction import ModbusRtuFramer, ModbusAsciiFramer

#---------------------------------------------------------------------------# 
# import the python libraries we need
#---------------------------------------------------------------------------# 
from multiprocessing import Queue, Process

#---------------------------------------------------------------------------# 
# configure the service logging
#---------------------------------------------------------------------------# 
import logging
logging.basicConfig()
log = logging.getLogger()
log.setLevel(logging.DEBUG)

#---------------------------------------------------------------------------# 
# create your custom data block with callbacks
#---------------------------------------------------------------------------# 
class CallbackDataBlock(ModbusSparseDataBlock):
    ''' A datablock that stores the new value in memory
    and passes the operation to a message queue for further
    processing.
    '''

    def __init__(self, devices, queue):
        '''
        '''
        self.devices = devices
        self.queue = queue

        values = {k:0 for k in devices.iterkeys()}
        values[0xbeef] = len(values) # the number of devices
        super(CallbackDataBlock, self).__init__(values)

    def setValues(self, address, value):
        ''' Sets the requested values of the datastore

        :param address: The starting address
        :param values: The new values to be set
        '''
        super(CallbackDataBlock, self).setValues(address, value)
        self.queue.put((self.devices.get(address, None), value))

#---------------------------------------------------------------------------# 
# define your callback process
#---------------------------------------------------------------------------# 
def rescale_value(value):
    ''' Rescale the input value from the range
    of 0..100 to -3200..3200.

    :param value: The input value to scale
    :returns: The rescaled value
    '''
    s = 1 if value >= 50 else -1
    c = value if value < 50 else (value - 50)
    return s * (c * 64)

def device_writer(queue):
    ''' A worker process that processes new messages
    from a queue to write to device outputs

    :param queue: The queue to get new messages from
    '''
    while True:
        device, value = queue.get()
        scaled = rescale_value(value[0])
        log.debug("Write(%s) = %s" % (device, value))
        if not device: continue
        # do any logic here to update your devices

#---------------------------------------------------------------------------# 
# initialize your device map
#---------------------------------------------------------------------------# 
def read_device_map(path):
    ''' A helper method to read the device
    path to address mapping from file::

       0x0001,/dev/device1 
       0x0002,/dev/device2 

    :param path: The path to the input file
    :returns: The input mapping file
    '''
    devices = {}
    with open(path, 'r') as stream:
        for line in stream:
            piece = line.strip().split(',')
            devices[int(piece[0], 16)] = piece[1]
    return devices

#---------------------------------------------------------------------------# 
# initialize your data store
#---------------------------------------------------------------------------# 
queue   = Queue()
devices = read_device_map("device-mapping")
block   = CallbackDataBlock(devices, queue)
store   = ModbusSlaveContext(di=block, co=block, hr=block, ir=block)
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
#---------------------------------------------------------------------------# 
p = Process(target=device_writer, args=(queue,))
p.start()
StartTcpServer(context, identity=identity, address=("localhost", 5020))