Leo, I like your tuple idea. I will implement it. The ack and nak both have the same format, namely: "Id Ack" or "Id Nak"
rob On Dec 15, 4:34 pm, "Leo Kislov" <[EMAIL PROTECTED]> wrote: > Rob wrote: > > Hi all, > > > I am fairly new to python, but not programming and embedded. I am > > having an issue which I believe is related to the hardware, triggered > > by the software read I am doing in pySerial. I am sending a short > > message to a group of embedded boxes daisy chained via the serial port. > > When I send a 'global' message, all the connected units should reply > > with their Id and Ack in this format '0 Ack' To be certain that I > > didn't miss a packet, and hence a unit, I do the procedure three times, > > sending the message and waiting for a timeout before I run through the > > next iteration. Frequently I get through the first two iterations > > without a problem, but the third hangs up and crashes, requiring me to > > remove the Belkin USB to serial adapter, and then reconnect it. Here > > is the code: > > > import sys, os > > import serial > > import sret > > import time > > > from serial.serialutil import SerialException > > #################################################################### > > #### GetAck Procedure > > #################################################################### > > def GetAck(p): > > response = "" > > > try: > > response = p.readline() > > except SerialException: > > print ">>>>>Timed out<<<<<" > > return -1 > > res = response.split() > > > #look for ack in the return message > > reslen = len(response) > > if reslen > 5: > > if res[1] == 'Ack': > > return res[0] > > elif res[1] == 'Nak': > > return 0x7F > > else: > > return -1 > > > >>>>> Snip <<<<<< > > #################################################################### > > #### GetNumLanes Procedure > > #################################################################### > > def GetNumLanes(Lanes): > > print "Looking for connected units" > > # give a turn command and wait for responses > > msg = ".g t 0 336\n" > > > for i in range(3): > > port = OpenPort() > > time.sleep(3) > > print port.isOpen() > > print "Request #%d" % (i+1) > > try: > > port.writelines(msg) > > except OSError: > > print "Serial port failure. Power cycle units" > > port.close() > > sys.exit(1) > > > done = False > > # Run first connection check > > #Loop through getting responses until we get a -1 from GetAck > > while done == False: > > # lane will either be -1 (timeout), 0x7F (Nak), > > # or the lane number that responded with an Ack > > lane = GetAck(port) > > if lane >= '0':Your GetAck returns either string or number and > > then you compare it > with a string. If you compare string with a number python currently > returns result you probably don't expect > > >>> -1 >= '0' > False > >>> 0x7f >= '0'False > > This is a wart and it will be fixed in python 3.0 (it will raise > exception) I think you should rewrite GetAck to return a tuple (state, > lane) > > def GetAck(p): > response = "" > > try: > response = p.readline() > except SerialException: > print ">>>>>Timed out<<<<<" > return 'Timeout', 'NoID' > res = response.split() > > #look for ack in the return message > reslen = len(response) > if reslen > 5: > if res[1] == 'Ack': > return 'Ack', res[0] > elif res[1] == 'Nak': > return 'Nak', Does Nak response contain lane id? > else: > return 'Unknown', 'NoID' > > And then instead of > > lane = GetAck(port) > if lane >= '0': > > use > > state, lane = GetAck(port) > if state == 'Ack': > > -- Leo -- http://mail.python.org/mailman/listinfo/python-list
