devlib/utils/serial_port.py

#    Copyright 2013-2015 ARM Limited
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#


import time
from contextlib import contextmanager
from logging import Logger

import serial

import pexpect
from distutils.version import StrictVersion as V
if V(pexpect.__version__) < V('4.0.0'):
    import fdpexpect
else:
    from pexpect import fdpexpect
# Adding pexpect exceptions into this module's namespace
from pexpect import EOF, TIMEOUT  # NOQA pylint: disable=W0611

from devlib.exception import HostError


def pulse_dtr(conn, state=True, duration=0.1):
    """Set the DTR line of the specified serial connection to the specified state
    for the specified duration (note: the initial state of the line is *not* checked."""
    conn.setDTR(state)
    time.sleep(duration)
    conn.setDTR(not state)


def get_connection(timeout, init_dtr=None, logcls=Logger,
                   *args, **kwargs):
    if init_dtr is not None:
        kwargs['dsrdtr'] = True
    try:
        conn = serial.Serial(*args, **kwargs)
    except serial.SerialException as e:
        raise HostError(e.message)
    if init_dtr is not None:
        conn.setDTR(init_dtr)
    conn.nonblocking()
    conn.flushOutput()
    target = fdpexpect.fdspawn(conn.fileno(), timeout=timeout)
    target.logfile_read = logcls('read')
    target.logfile_send = logcls('send')

    # Monkey-patching sendline to introduce a short delay after
    # chacters are sent to the serial. If two sendline s are issued
    # one after another the second one might start putting characters
    # into the serial device before the first one has finished, causing
    # corruption. The delay prevents that.
    tsln = target.sendline

    def sendline(x):
        tsln(x)
        time.sleep(0.1)

    target.sendline = sendline
    return target, conn


def write_characters(conn, line, delay=0.05):
    """Write a single line out to serial charcter-by-character. This will ensure that nothing will
    be dropped for longer lines."""
    line = line.rstrip('\r\n')
    for c in line:
        conn.send(c)
        time.sleep(delay)
    conn.sendline('')


@contextmanager
def open_serial_connection(timeout, get_conn=False, init_dtr=None,
                           logcls=Logger, *args, **kwargs):
    """
    Opens a serial connection to a device.

    :param timeout: timeout for the fdpexpect spawn object.
    :param conn: ``bool`` that specfies whether the underlying connection
                 object should be yielded as well.
    :param init_dtr: specifies the initial DTR state stat should be set.

    All arguments are passed into the __init__ of serial.Serial. See
    pyserial documentation for details:

        http://pyserial.sourceforge.net/pyserial_api.html#serial.Serial

    :returns: a pexpect spawn object connected to the device.
              See: http://pexpect.sourceforge.net/pexpect.html

    """
    target, conn = get_connection(timeout, init_dtr=init_dtr,
                                  logcls=logcls, *args, **kwargs)
    if get_conn:
        yield target, conn
    else:
        yield target

    target.close()  # Closes the file descriptor used by the conn.
    del conn