#!/usr/bin/env python
# power on/off an Alcatel Speedtouch 510 modem using some circuitry
# controlled via RTS/DTR

from os import open, O_RDONLY
from sys import argv, stderr, exit
from termios import TIOCMBIS, TIOCMBIC, TIOCM_RTS, TIOCM_DTR
from fcntl import ioctl
from select import select
from struct import pack
from time import sleep

if argv[1:] == ['on']:
	time = 0.02	# >=0.01
elif argv[1:] == ['off']:
	time = 5.0	# >=4.0
else:
	print >>stderr, "Usage: st510 on|off"
	exit(1)

rts = pack('I', TIOCM_RTS)
dtr = pack('I', TIOCM_DTR)
fd = open('/dev/ttyS2', O_RDONLY)
# opening a serial line will assert RTS and DTR but we should not rely on that.
ioctl(fd, TIOCMBIS, rts)

# Charge up the capacitor. This mechanism avoids random resets when
# pulling plugs or powering the system on- and off.
#
#   50 pulses		-
#  250 pulses		10 sec reset possible starting at 3mA
#  500 pulses		15 sec reset possible starting at 4mA
# 1000 pulses - 10.5V	18 sec reset possible starting ar 5mA
#
# 250 pulses will do, 500 works but to stay on the safe side...
for i in range(1000):
	ioctl(fd, TIOCMBIC, dtr)
	select([], [], [], 0.001)
	ioctl(fd, TIOCMBIS, dtr)
	select([], [], [], 0.001)

# Capacitor charged up, DTR is set. fire by clearing RTS
ioctl(fd, TIOCMBIC, rts)
select([], [], [], time)
ioctl(fd, TIOCMBIS, rts)

# if we close fd within 25 seconds then the remaining capacitor charge may generate
# another reset pulse when RTS goes down.
# This could switch the modem back on when we are supposed to switch it off. The other
# way around it gets even worse: when the reset is pressed a number of times while
# the modem has just been switched on it will reload the factory settings (consult the
# manual about the exact reset sequence for this). So, we're anal and wait a full minute.
sleep(60)