c35e26f025
* changed signum for offset calculation * added error handling if a non-existent signal is to be removed from a message
116 lines
4.1 KiB
Python
116 lines
4.1 KiB
Python
# -*- coding: UTF-8 -*-
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'''
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Created on 06.07.2012
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@author: Christian Sültrop
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'''
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import array
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import sys
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class CanMessage(object):
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'''
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A CAN message.
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A CAN message is represented by an ID, a Length in bytes, a CycleTime in ms, an array of Signals, and Data.
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When calling the composeData() method, the data from all Signals is copied into the Data array of the message,
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with respect to the signal begin and length definitions from the CanSignal objects in Signals.
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'''
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def __init__(self, MessageId, MessageLength, MessageCycleTime, Label):
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'''
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Create a new CanMessage object.
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@param MessageId: The CAN ID. Valid range 0x00 to 0x7ff.
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@param MessageLength: The message length in bytes.
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@param messageCycleTime: Cycle time in ms.
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'''
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# Instance variables
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self.Signals = {}
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self.Data = array.array('B')
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# check message length for validity
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if MessageLength > 8:
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sys.exit('Invalid message MessageLength')
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# check message ID for validity
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if (MessageId < 0x000) or (MessageId > 0x7ff):
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sys.exit('Invalid MessageId')
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# assign the parameters
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self.Length = MessageLength
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self.Id = MessageId
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self.CycleTime = MessageCycleTime
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self.Label = Label
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# create an initial array of message data
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for i in range(0, self.Length):
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self.Data.append(0x00)
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def addSignal(self, CanSignal):
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'''
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Add a Signal of type CanSignal to the list of signals.
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@param CanSignal: The signal to add to the list of signals.
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'''
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self.Signals.update({CanSignal.Label: CanSignal})
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def removeSignal(self, CanSignalLabel):
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try:
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self.Signals.pop(CanSignalLabel)
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except:
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pass
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def clearSignals(self):
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self.Signals = {}
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def composeData(self):
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'''
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Takes the CanSignals from the list in self.Signals and copies
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the data that is stored in their Data fields into the Data field
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of the CanMessage object. The position where to copy the data
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is defined in the Begin and Length fields of the CanSignal objects.
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'''
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for sigKey in self.Signals:
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sig = self.Signals[sigKey]
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srcBegin = 0 # reading the source data (from the Signal definition) always starts at the first bit
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tgtBegin = sig.Begin # where the source data goes is defined in the Begin field of the CanSignal object
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srcByteNo = (srcBegin/8) # will be 0 if srcBegin == 0
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srcBitNo = (srcBegin%8) # will be 0 if srcBegin == 0
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tgtByteNo = (tgtBegin/8) # get the byte and bit numbers
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tgtBitNo = (tgtBegin%8) # for the target (the CanMessage object) array
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for i in range(0, sig.Length):
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# copy the source data bits to the target
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# OR # get srcBitNo from srcByteNo and shift it to tgtBitNo
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if tgtByteNo >= self.Length:
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sys.exit('Signal does not fit into message!')
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tmp = sig.Data[srcByteNo]
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tmp = tmp >> srcBitNo
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tmp = tmp & 0x01
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if tmp == 1: # the bit shall be set
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self.Data[tgtByteNo] |= (1 << tgtBitNo)
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else: # the bit shall be cleared
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self.Data[tgtByteNo] &= ~(1 << tgtBitNo)
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# increment the counters
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srcBitNo += 1
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if srcBitNo >= 8: # on bit counter overflow, increment the byte counter and reset the bit counter
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srcBitNo = 0
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srcByteNo += 1
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tgtBitNo += 1
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if tgtBitNo >= 8:
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tgtBitNo = 0
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tgtByteNo += 1
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