tools/devshell/contrib/set-relay

#!/usr/bin/env python
# Copyright 2019 The Fuchsia Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

#### CATEGORY=Other
### Actuates the state of an external relay by writing a single byte to |tty|.
## usage: fx set-relay [--off|--on] /dev/ttyUSB0
##
## Turn on or off a USB-connected relay on the specified device.

import argparse
import sys

def main():
    parser = argparse.ArgumentParser(
            'Actuates the state of an external relay')
    parser.add_argument('tty',
                        type=argparse.FileType('wb'),
                        help='TTY to which the external relay is connected')
    state_parser = parser.add_mutually_exclusive_group(required=True)
    state_parser.add_argument('--on',  dest='state', action='store_true')
    state_parser.add_argument('--off', dest='state', action='store_false')
    args = parser.parse_args()

    # Different relays require different sequences to turn on/off.  The
    # sequences don't interfere with each other so just do them all.
    if args.state:
      args.tty.write(b'\xa0\x01\x00\xa1')
      args.tty.write(b'\x02')
    else:
      args.tty.write(b'\xa0\x01\x01\xa2')
      args.tty.write(b'\x01')

if __name__ == '__main__':
    sys.exit(main())