[Python-Dev] Python vs. chat (conversation with modem) (original) (raw)

Bertram Scharpf b.scharpf at tesionmail.de
Wed Apr 7 15:46:14 EDT 2004

Hi,

in simple serial communication, I found a problem that doesn't arise, when I'm doing exactly the same with the `chat' program.

I admit my hardware is a little bit special and may have problems itself. It is an ISDN telephone, Elmeg C200d at ta. With a normal modem, everything works fine.

For a speech call, my telephone wants me to send a command 'at&b30' before dialing (otherwise the modem functionality is dialing).

When I send the commands with `chat', the device is dialing, but when I send them from a Python script, the communication hangs.

My code is (simplified):

class Modem: def init( self, device = '/dev/ttyS0'): self.modem = open( device, 'w+') self.command( 'atz')

def send( self, cmd):
    print >>self.modem, cmd + '\r'

def expect( self, patt):
    import select
    ...

def command( self, cmd):
    self.send( cmd)
    self.expect( 'OK')

def dial_orig( self, nr):
    self.command( 'at&b30')
    # On this request, the modem won't send an answer.
    self.command( 'atdt,%s;h0z' % nr)
    self.command( 'at&b31')

def dial_chat( self, nr):
    "That's working!?"
    script += [ repr( ''), 'atz',
                'OK',      r'at\&b30dt,\\T\;h0z',
                'OK',      r'\\c']
    chatcmd = '/usr/sbin/chat -vs -T %s %s <%s >%s' % \
        (nr, ' '.join( script), self.modem.name, self.modem.name)
    import os
    os.system( chatcmd)

dial = dial_chat

(The full script is available at `http://www.bertram-scharpf.de/dial.py'.)

On the 'atz' an answer of 'OK' is sent back, but not on the 'at&b30' request. `chat' receives an OK. Setting the termcaps exactly to what chat would have chosen didn't help.

I have found this behaviour in the versions 2.1, 2.2 and 2.3.

$ uname -srmp Linux 2.4.18-bs1 i586 unknown

Do I have any chance to find out what happens?

Bertram

-- Bertram Scharpf Stuttgart, Deutschland/Germany http://www.bertram-scharpf.de

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