getting an external trigger from parallel port

I'm trying to use the parallel port get an external trigger to wake up 
my software. When I use subdevice 3, and prepare a command with 
scan_begin_src=TRIG_EXT (as in ledclock.c), I get an error:
comedi_command: Command not supported

It looks like I have the comedi_parport driver properly setup. info reports
the following:

overall info:
  version code: 0x000742
  driver name: comedi_parport
  board name: parport
  number of subdevices: 4
subdevice 0:
  type: 5 (digital I/O)
  number of channels: 8
  max data value: 1
  ranges:
    all chans: [0,5]
  command:
    not supported
subdevice 1:
  type: 3 (digital input)
  number of channels: 5
  max data value: 1
  ranges:
    all chans: [0,5]
  command:
    not supported
subdevice 2:
  type: 4 (digital output)
  number of channels: 4
  max data value: 1
  ranges:
    all chans: [0,5]
  command:
    not supported
subdevice 3:
  type: 0 (unused)


**************************************************************************
Andrew J. Davis,  Manager, ACE Science Center, Caltech, Mail Code 220-47,
Pasadena CA 91125.   Phone: (626)395-1916   Fax: (626)449-8676
Email: ad_at_srl.caltech.edu   Web: http://www.srl.caltech.edu/ACE/ASC

Received on 2003-01-18Z04:08:58