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packetSerial.py
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packetSerial.py
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'''
Basic packet format
STX
LEN
FSEP
DATA[LEN]
FSEP
CRC
ETX
'''
import serial
from time import sleep
import binascii
LOG_DEBUG=False
LOG_WARNING=False
def logDebug( msg ):
if (LOG_DEBUG==True):
print msg
def logWarning( msg ):
if (LOG_WARNING==True):
print msg
class PacketSerial:
STX = '<'
FSEP = ','
ETX = '>'
RX_STATE_READING_STX = 1
RX_STATE_READING_LEN_DATA = 2
RX_STATE_READING_DATA = 3
RX_STATE_READING_CRC = 4
RX_STATE_READING_ETX = 5
def __init__( self, serial):
'''
'''
self.serial = serial
self.data = []
self.dataAvailable = False
self.resetToStartState()
def resetToStartState( self ):
'''
'''
self.receiveState = self.RX_STATE_READING_STX
self.receiveBuffer = ""
self.receiveDataLen = None
self.receiveData = None
def sendData( self, data ):
'''
'''
# build packet and calculate CRC
content = ''
# length of data element
content += str( len(data) )
content += self.FSEP
# data element
content += data
# CRC
crc = str ( self.calcCRC(data) )
packet = self.STX
packet += content
packet += self.FSEP
packet += crc
packet += self.ETX
logDebug("Sending: %s" % packet)
# The Arduino only has a serial ring buffer of 64 bytes
# When sending large packets of data this can result in dropped
# characters so here we limit the size of the chunks we send
# and add a small gap in between them to work around this limitation
MAX_CHUNK_SIZE = 48
INTER_CHUNK_DELAY = 0.2
if (len(packet)<=MAX_CHUNK_SIZE):
self.serial.write(packet)
self.serial.flush()
else:
def chunks(l, n):
n = max(1, n)
return (l[i:i+n] for i in xrange(0, len(l), n))
for chunk in chunks(packet, MAX_CHUNK_SIZE):
self.serial.write(chunk)
self.serial.flush()
sleep(INTER_CHUNK_DELAY)
def getData( self ):
'''
'''
if (self.dataAvailable==True):
rc = self.data
self.dataAvailable = False
self.data = []
return rc
else:
self.processIncoming()
return None
def processIncoming( self ):
'''
Read all incoming characters until we have read a packet or buffer is empty
'''
rxChar = self.getNextChar()
# loop until we have read a packet or there are no incoming chars left
while ((self.dataAvailable==False) and (rxChar is not None)):
if (rxChar is not None):
# *****************************************************
# STX waiting for packet start
# *****************************************************
if (self.receiveState==self.RX_STATE_READING_STX):
logDebug('RX_STATE_READING_STX:%s' % rxChar)
if (rxChar==self.STX):
# found packet start
self.receiveBuffer=""
self.receiveState=self.RX_STATE_READING_LEN_DATA
else:
# not packet start so ignore the char
# maybe we started reading mid packet
logWarning('RX_STATE_READING_STX: Encountered unexpected char in stream: [%s]' % rxChar)
# *****************************************************
# reading data len
# *****************************************************
elif (self.receiveState==self.RX_STATE_READING_LEN_DATA):
logDebug('RX_STATE_READING_LEN_DATA:%s' % rxChar)
if (rxChar!=self.FSEP):
nums = [ str(x) for x in xrange(0,10) ]
if (rxChar in nums):
self.receiveBuffer += rxChar
else:
logWarning('RX_STATE_READING_LEN_DATA: Encountered unexpected char in stream: [%s]' % rxChar)
self.resetToStartState()
else:
self.receiveDataLen = int(self.receiveBuffer)
self.receiveData = []
self.receiveBuffer = ""
self.receiveState = self.RX_STATE_READING_DATA
# *****************************************************
# reading data
# *****************************************************
elif (self.receiveState==self.RX_STATE_READING_DATA):
logDebug('RX_STATE_READING_DATA:%s' % rxChar)
if (len(self.receiveBuffer)< self.receiveDataLen):
self.receiveBuffer += rxChar
else:
# should be field seperator after data element
if (rxChar==self.FSEP):
self.receiveData = self.receiveBuffer
self.receiveBuffer = ""
self.receiveState=self.RX_STATE_READING_CRC
else:
# was expecting field seperator after data block
logWarning('RX_STATE_READING_DATA: Encountered unexpected char in stream: [%s]' % rxChar)
self.resetToStartState()
# *****************************************************
# reading CRC
# *****************************************************
elif (self.receiveState==self.RX_STATE_READING_CRC):
logDebug('RX_STATE_READING_CRC:%s' % rxChar)
# read all numbers into CRC
nums = [ str(x) for x in xrange(0,10) ]
if (rxChar in nums):
self.receiveBuffer += rxChar
# until we hit ETX
elif (rxChar==self.ETX):
receiveCRC = int(self.receiveBuffer)
self.receiveBuffer = ""
if ( self.checkCRC(self.receiveData, receiveCRC) == True):
self.data = self.receiveData
self.dataAvailable = True
self.resetToStartState()
else:
logWarning('RX_STATE_READING_CRC: CRC check failed')
self.resetToStartState()
else:
logWarning('RX_STATE_READING_CRC: Encountered unexpected char in stream: [%s]' % rxChar)
self.resetToStartState()
else:
pass
rxChar = self.getNextChar()
def getNextChar( self ):
'''
'''
rc = None
if (self.serial.inWaiting() > 0):
rc = self.serial.read(1)
return rc
def calcCRC( self, content ):
# Override this to implement your CRC mechanism
return 0
def checkCRC( self, content, crc ):
calcCRC = self.calcCRC( content )
if (calcCRC != crc ):
return False
else:
return True
import sys
def run():
'''
Send a packet every N seconds
Receives packets and prints to console
Note that ps.getData() must be called repeatedly as it pulls individual characters from the
incoming stream and executes the FSM. Once a packet has been received ps.getData() will return the data
but until then it will return None
'''
if (len(sys.argv)!=2):
print "Error: comPortNumber missing"
print "Usage: packetSerial.py <comPort>"
print " e.g. packetSerial.py COM4"
return 1
portName = sys.argv[1]
print 'Using port %s' % portName
serialPort = serial.Serial( portName, 57600 )
ps = PacketSerial(serialPort)
# Send a packet every 2 seconds
payloadCount = 0
loopCount = 0
sendPeriodInSecs = 2
loopDelayInSecs = 0.01
countPerSendPeriod= sendPeriodInSecs / loopDelayInSecs
while (True):
loopCount+=1
if ((loopCount % countPerSendPeriod)==0):
payload = "Hello %s" % payloadCount
print "TX Packet [%s]" % payload
ps.sendData(payload)
loopCount=0
payloadCount += 1
# Call FSM to process incoming chars and see if a packet has been received
rxData = ps.getData()
while (rxData is not None):
print "RX Packet [%s]" % rxData
rxData = ps.getData()
sleep(loopDelayInSecs)
if __name__ == '__main__':
#LOG_DEBUG=True
#LOG_WARNING=True
run()