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
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