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"""
Modbus Modicon Payload Builder
-----------------------------------------------------------
This is an example of building a custom payload builder
that can be used in the pymodbus library. Below is a
simple modicon encoded builder and decoder.
"""
from struct import pack, unpack
from pymodbus.constants import Endian
from pymodbus.interfaces import IPayloadBuilder
from pymodbus.utilities import pack_bitstring
from pymodbus.utilities import unpack_bitstring
from pymodbus.exceptions import ParameterException
class ModiconPayloadBuilder(IPayloadBuilder):
"""
A utility that helps build modicon encoded payload
messages to be written with the various modbus messages.
example::
builder = ModiconPayloadBuilder()
builder.add_8bit_uint(1)
builder.add_16bit_uint(2)
payload = builder.build()
"""
def __init__(self, payload=None, endian=Endian.Little):
""" Initialize a new instance of the payload builder
:param payload: Raw payload data to initialize with
:param endian: The endianess of the payload
"""
self._payload = payload or []
self._endian = endian
def __str__(self):
""" Return the payload buffer as a string
:returns: The payload buffer as a string
"""
return ''.join(self._payload)
def reset(self):
""" Reset the payload buffer
"""
self._payload = []
def build(self):
""" Return the payload buffer as a list
This list is two bytes per element and can
thus be treated as a list of registers.
:returns: The payload buffer as a list
"""
string = str(self)
length = len(string)
string = string + ('\x00' * (length % 2))
return [string[i:i+2] for i in range(0, length, 2)]
def add_bits(self, values):
""" Adds a collection of bits to be encoded
If these are less than a multiple of eight,
they will be left padded with 0 bits to make
it so.
:param values: The value to add to the buffer
"""
value = pack_bitstring(values)
self._payload.append(value)
def add_8bit_uint(self, value):
""" Adds a 8 bit unsigned int to the buffer
:param value: The value to add to the buffer
"""
fstring = self._endian + 'B'
self._payload.append(pack(fstring, value))
def add_16bit_uint(self, value):
""" Adds a 16 bit unsigned int to the buffer
:param value: The value to add to the buffer
"""
fstring = self._endian + 'H'
self._payload.append(pack(fstring, value))
def add_32bit_uint(self, value):
""" Adds a 32 bit unsigned int to the buffer
:param value: The value to add to the buffer
"""
fstring = self._endian + 'I'
handle = pack(fstring, value)
handle = handle[2:] + handle[:2]
self._payload.append(handle)
def add_8bit_int(self, value):
""" Adds a 8 bit signed int to the buffer
:param value: The value to add to the buffer
"""
fstring = self._endian + 'b'
self._payload.append(pack(fstring, value))
def add_16bit_int(self, value):
""" Adds a 16 bit signed int to the buffer
:param value: The value to add to the buffer
"""
fstring = self._endian + 'h'
self._payload.append(pack(fstring, value))
def add_32bit_int(self, value):
""" Adds a 32 bit signed int to the buffer
:param value: The value to add to the buffer
"""
fstring = self._endian + 'i'
handle = pack(fstring, value)
handle = handle[2:] + handle[:2]
self._payload.append(handle)
def add_32bit_float(self, value):
""" Adds a 32 bit float to the buffer
:param value: The value to add to the buffer
"""
fstring = self._endian + 'f'
handle = pack(fstring, value)
handle = handle[2:] + handle[:2]
self._payload.append(handle)
def add_string(self, value):
""" Adds a string to the buffer
:param value: The value to add to the buffer
"""
fstring = self._endian + 's'
for c in value:
self._payload.append(pack(fstring, c))
class ModiconPayloadDecoder(object):
"""
A utility that helps decode modicon encoded payload
messages from a modbus reponse message. What follows is
a simple example::
decoder = ModiconPayloadDecoder(payload)
first = decoder.decode_8bit_uint()
second = decoder.decode_16bit_uint()
"""
def __init__(self, payload, endian):
""" Initialize a new payload decoder
:param payload: The payload to decode with
"""
self._payload = payload
self._pointer = 0x00
self._endian = endian
@staticmethod
def from_registers(registers, endian=Endian.Little):
""" Initialize a payload decoder with the result of
reading a collection of registers from a modbus device.
The registers are treated as a list of 2 byte values.
We have to do this because of how the data has already
been decoded by the rest of the library.
:param registers: The register results to initialize with
:param endian: The endianess of the payload
:returns: An initialized PayloadDecoder
"""
if isinstance(registers, list): # repack into flat binary
payload = ''.join(pack('>H', x) for x in registers)
return ModiconPayloadDecoder(payload, endian)
raise ParameterException('Invalid collection of registers supplied')
@staticmethod
def from_coils(coils, endian=Endian.Little):
""" Initialize a payload decoder with the result of
reading a collection of coils from a modbus device.
The coils are treated as a list of bit(boolean) values.
:param coils: The coil results to initialize with
:param endian: The endianess of the payload
:returns: An initialized PayloadDecoder
"""
if isinstance(coils, list):
payload = pack_bitstring(coils)
return ModiconPayloadDecoder(payload, endian)
raise ParameterException('Invalid collection of coils supplied')
def reset(self):
""" Reset the decoder pointer back to the start
"""
self._pointer = 0x00
def decode_8bit_uint(self):
""" Decodes a 8 bit unsigned int from the buffer
"""
self._pointer += 1
fstring = self._endian + 'B'
handle = self._payload[self._pointer - 1:self._pointer]
return unpack(fstring, handle)[0]
def decode_16bit_uint(self):
""" Decodes a 16 bit unsigned int from the buffer
"""
self._pointer += 2
fstring = self._endian + 'H'
handle = self._payload[self._pointer - 2:self._pointer]
return unpack(fstring, handle)[0]
def decode_32bit_uint(self):
""" Decodes a 32 bit unsigned int from the buffer
"""
self._pointer += 4
fstring = self._endian + 'I'
handle = self._payload[self._pointer - 4:self._pointer]
handle = handle[2:] + handle[:2]
return unpack(fstring, handle)[0]
def decode_8bit_int(self):
""" Decodes a 8 bit signed int from the buffer
"""
self._pointer += 1
fstring = self._endian + 'b'
handle = self._payload[self._pointer - 1:self._pointer]
return unpack(fstring, handle)[0]
def decode_16bit_int(self):
""" Decodes a 16 bit signed int from the buffer
"""
self._pointer += 2
fstring = self._endian + 'h'
handle = self._payload[self._pointer - 2:self._pointer]
return unpack(fstring, handle)[0]
def decode_32bit_int(self):
""" Decodes a 32 bit signed int from the buffer
"""
self._pointer += 4
fstring = self._endian + 'i'
handle = self._payload[self._pointer - 4:self._pointer]
handle = handle[2:] + handle[:2]
return unpack(fstring, handle)[0]
def decode_32bit_float(self, size=1):
""" Decodes a float from the buffer
"""
self._pointer += 4
fstring = self._endian + 'f'
handle = self._payload[self._pointer - 4:self._pointer]
handle = handle[2:] + handle[:2]
return unpack(fstring, handle)[0]
def decode_bits(self):
""" Decodes a byte worth of bits from the buffer
"""
self._pointer += 1
handle = self._payload[self._pointer - 1:self._pointer]
return unpack_bitstring(handle)
def decode_string(self, size=1):
""" Decodes a string from the buffer
:param size: The size of the string to decode
"""
self._pointer += size
return self._payload[self._pointer - size:self._pointer]
# -------------------------------------------------------------------------- #
# Exported Identifiers
# -------------------------------------------------------------------------- #
__all__ = ["ModiconPayloadBuilder", "ModiconPayloadDecoder"]
|
