[Tutor] question about serial coms

[Bennett, Joe]

I have been working with pyserial. One question I have
is this. I have a loop that writes to the serial port
and then waits about 500ms and then reads from the
serial port. The first thing read from the serial port
is ALWAYS the data written to the serial port... I
must be missing something obvious, but I thuoght the
two buffers were separate...

Here is the code I'm using if that helps:

while i == 0:
  line = parmfile.readline()
  line = string.rstrip(line)
  #print line
  if line == "":
    i = 1
    break
  
  else:
    
    ser.write(line + "\r")
    #ser.write("\r\n")
    print "Sending: " + line

    
   
    time.sleep(1)
    data_in = ser.read(100)
    print "Response: " + data_in
    time.sleep(.2)
    
    
print "Closing Serial Port\n"    
ser.close()



-Joe


--- nephish <nephish at xit.net> wrote:

> ok, i think i got it. Thanks so much. 
> let you know how it turns out.
> shawn
> 
> 
> On Tue, 2005-11-15 at 11:27 +1300, Hans
> Dushanthakumar wrote:
> > Lock() is provided by the threading module.
> > see
> > http://docs.python.org/lib/module-threading.html 
> > &
> > http://docs.python.org/lib/lock-objects.html
> > 
> > Cheers
> > Hans
> > 
> > 
> > -----Original Message-----
> > From: nephish [mailto:nephish at xit.net] 
> > Sent: Tuesday, 15 November 2005 11:23 a.m.
> > To: Hans Dushanthakumar
> > Cc: Hugo González Monteverde; tutor
> > Subject: RE: [Tutor] question about serial coms
> > 
> > ok, lock is something you wrote yourself ?
> > i can't find it in the docs. However, i think i
> can essentially build the same thing. 
> > the serial module i use is pyserial.
> pyserial.sourceforge.net.
> > the docs are a wee bit on the sparce side. But i
> think i can pull it off. Thanks for your help. 
> > 
> > shawn
> > 
> > 
> > On Tue, 2005-11-15 at 10:58 +1300, Hans
> Dushanthakumar wrote:
> > > I believe that the drivers take care of that,
> however, I did use locks to make sure that there
> were no conflicts.
> > > 
> > > In the listener thread I had something along the
> lines of:
> > > 
> > >  Acquire lock
> > >  readline() from the ser port
> > >  Release lock
> > > 
> > > And in the sender thread,
> > > 
> > >  Acquire lock
> > >  send msg over ser port
> > >  Release lock
> > > 
> > > Cheers
> > > Hans
> > > 
> > > -----Original Message-----
> > > From: nephish [mailto:nephish at xit.net]
> > > Sent: Tuesday, 15 November 2005 10:47 a.m.
> > > To: Hans Dushanthakumar
> > > Cc: Hugo González Monteverde; tutor
> > > Subject: RE: [Tutor] question about serial coms
> > > 
> > > well thats encouraging, did you have to do
> anything special to prevent an error when trying to
> read or write at the same time ?
> > > 
> > > thanks
> > > sk
> > > 
> > > 
> > > On Tue, 2005-11-15 at 09:29 +1300, Hans
> Dushanthakumar wrote:
> > > > Ive worked on a similar application. I used
> one thread to read from the serial port and another
> one to handle the writes. 
> > > > 
> > > > -----Original Message-----
> > > > From: tutor-bounces at python.org
> [mailto:tutor-bounces at python.org] On 
> > > > Behalf Of Hugo González Monteverde
> > > > Sent: Tuesday, 15 November 2005 7:36 a.m.
> > > > To: nephish
> > > > Cc: tutor
> > > > Subject: Re: [Tutor] question about serial
> coms
> > > > 
> > > > Hi Nephish,
> > > > 
> > > > Are you using pyserial or rolling your own?
> Normally you can write and read to the /dev/ttySXX
> file at the same time; since they're special files,
> not ordinary files, the driver handles that.
> > > > 
> > > > Handling both writing and reading in your
> program's flow control is a wholly different matter,
> though. You might  need to use select()  to avoid
> blocking.
> > > > 
> > > > Are you using two completely different scripts
> for reding and writing?
> > > > 
> > > > There is some valuable info, if not about
> python, in the Serial Programming howto, at:
> > > > 
> > > >
> http://www.tldp.org/HOWTO/Serial-Programming-HOWTO/
> > > > 
> > > > 
> > > > Hugo
> > > > 
> > > > nephish wrote:
> > > > > Hey there,
> > > > > 	i am developing on a linux computer with
> the serial module. Now, 
> > > > > i already am able to recieve info from a
> serial RS232 device and 
> > > > > process everything ok. What i need to do now
> is write to the 
> > > > > serial device, but i also need to be able to
> not interrupt the 
> > > > > script that is reading from it.
> > > > > 	I guess my question is, do i have to
> interrupt the reading script 
> > > > > to write to the same RS232 device ?
> > > > > 	and if so, how do i do that?
> > > > > 
> > > > > 	thanks,
> > > > > 	shawn
> > > > > 
> > > > >
> _______________________________________________
> > > > > Tutor maillist  -  Tutor at python.org 
> > > > >
> http://mail.python.org/mailman/listinfo/tutor
> > > > > 
> > > >
> _______________________________________________
> > > > Tutor maillist  -  Tutor at python.org
> > > > http://mail.python.org/mailman/listinfo/tutor
> > > 
> > 
> 
> _______________________________________________
> Tutor maillist  -  Tutor at python.org
> http://mail.python.org/mailman/listinfo/tutor
>