#!/usr/bin/python

import sys
import os
import termios
import struct
import fcntl
import time
import glob

TIOCM_DTR_str = struct.pack('I', termios.TIOCM_DTR)


def set_DTR(fd, level=1):
  """Set terminal status line: Data Terminal Ready"""
  if level:
    fcntl.ioctl(fd, termios.TIOCMBIS, TIOCM_DTR_str)
  else:
    fcntl.ioctl(fd, termios.TIOCMBIC, TIOCM_DTR_str)


def pulse_DTR(dev_file):
  print "opening '%s'" % dev_file
  fd = os.open(dev_file, os.O_RDWR | os.O_NOCTTY)

  ### this shouldn't be needed, as the thing resets on the above open()
  print 'pulsing...'
  set_DTR(fd, 1)
  time.sleep(0.1)
  set_DTR(fd, 0)

  os.close(fd)
  print 'done.'


def usage():
  print 'USAGE: %s /dev/SERIAL-DEVICE' % os.path.basename(__file__)
  sys.exit(1)


if __name__ == '__main__':
  if len(sys.argv) == 1:
    files = glob.glob('/dev/cu.usb*')
    if len(files) != 1:
      usage()
    dev = files[0]
  elif len(sys.argv) == 2:
    dev = sys.argv[1]
  else:
    usage()
  pulse_DTR(dev)