popen problem

[Gandalf]

  Hi All!

I don't know if this is a Python problem or not. Here is a snippet:

import os
TERM='\n\r\n\r'
cmd = 'cu -l /dev/cuaa0 -s9600'
pop = os.popen4(cmd,1)
pop[0].write('AT'+TERM) # Ping modem

def readln():
    buffer = ''
    while True:
        c = pop[1].read(1)
        if c == '\n':
            return buffer
        elif (c != '\r') and not (c in TERM):
            buffer += c

pop[1].readln()
pop[1].readln()
pop[1].readln()

Here is the problem: on FreeBSD, this works fine. The last readln() 
calls  will print this:

'Connected.'
''
'OK'

But if I try to do the same on Linux (with /dev/ttyS0 instead of 
/dev/cuaa0) I get this:

1. The first read blocks.
2. When I do 'killall cu' in another shell, it starts to read this:

'\0x7Connected.'
'cu: Got interrupt signal'

It seems that the first line ('Connected.') if buffered somewhere. I 
guess 'OK' is also buffered but it is not read because of the interrup.
Is it a problem with Linux of Python? Or is it a big difference between 
/dev/ttyS0 and /dev/cuaa0?

Thanks in advance,

    G