tigertail: tigertool command line api

This tool allows an easy commandline interface to set the
USB-C mux position, as well as init and reboot.

BRANCH=None
BUG=b:35849284
TEST=flash, control tigertail successfully

Change-Id: I8d60c215fee04de158c22edca5377c3c6cd48cf0
Reviewed-on: https://chromium-review.googlesource.com/493617
Commit-Ready: Nick Sanders <nsanders@chromium.org>
Tested-by: Nick Sanders <nsanders@chromium.org>
Reviewed-by: Aseda Aboagye <aaboagye@chromium.org>

5 files changed, 784 insertions, 0 deletions

diff --git a/extra/tigertool/ecusb/__init__.py b/extra/tigertool/ecusb/__init__.py
new file mode 100644
index 0000000000..c2af553d57
--- /dev/null
+++ b/extra/tigertool/ecusb/__init__.py
@@ -0,0 +1,5 @@
+# Copyright 2017 The Chromium OS Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+__all__ = ['tiny_servo_common', 'stm32usb', 'stm32uart', 'pty_driver']
diff --git a/extra/tigertool/ecusb/pty_driver.py b/extra/tigertool/ecusb/pty_driver.py
new file mode 100644
index 0000000000..0802675634
--- /dev/null
+++ b/extra/tigertool/ecusb/pty_driver.py
@@ -0,0 +1,291 @@
+# Copyright 2017 The Chromium OS Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""ptyDriver class
+
+This class takes a pty interface and can send commands and expect results
+as regex. This is useful for automating console based interfaces, such as
+the CrOS EC console commands.
+"""
+
+import ast
+import errno
+import fcntl
+import os
+import pexpect
+import fdpexpect
+
+
+# Expecting a result in 3 seconds is plenty even for slow platforms.
+DEFAULT_UART_TIMEOUT = 3
+
+
+class ptyError(Exception):
+  """Exception class for pty errors."""
+
+
+UART_PARAMS = {
+    'uart_cmd': None,
+    'uart_multicmd': None,
+    'uart_regexp': None,
+    'uart_timeout': DEFAULT_UART_TIMEOUT,
+}
+
+
+class ptyDriver(object):
+  """Automate interactive commands on a pty interface."""
+  def __init__(self, interface, params, fast=False):
+    """Init class variables."""
+    self._child = None
+    self._fd = None
+    self._interface = interface
+    self._pty_path = self._interface.get_pty()
+    self._dict = UART_PARAMS.copy()
+    self._fast = fast
+
+  def __del__(self):
+    self.close()
+
+  def close(self):
+    """Close any open files and interfaces."""
+    if self._fd:
+      self._close()
+    self._interface.close()
+
+  def _open(self):
+    """Connect to serial device and create pexpect interface."""
+    assert self._fd is None
+    self._fd = os.open(self._pty_path, os.O_RDWR | os.O_NONBLOCK)
+    # Don't allow forked processes to access.
+    fcntl.fcntl(self._fd, fcntl.F_SETFD,
+                fcntl.fcntl(self._fd, fcntl.F_GETFD) | fcntl.FD_CLOEXEC)
+    self._child = fdpexpect.fdspawn(self._fd)
+    # pexpect defaults to a 100ms delay before sending characters, to
+    # work around race conditions in ssh. We don't need this feature
+    # so we'll change delaybeforesend from 0.1 to 0.001 to speed things up.
+    if self._fast:
+      self._child.delaybeforesend = 0.001
+
+  def _close(self):
+    """Close serial device connection."""
+    os.close(self._fd)
+    self._fd = None
+    self._child = None
+
+  def _flush(self):
+    """Flush device output to prevent previous messages interfering."""
+    if self._child.sendline('') != 1:
+      raise ptyError('Failed to send newline.')
+    while True:
+      try:
+        self._child.expect('.', timeout=0.2)
+      except (pexpect.TIMEOUT, pexpect.EOF):
+        break
+      except OSError as e:
+        # EAGAIN indicates no data available, maybe we didn't wait long enough.
+        if e.errno != errno.EAGAIN:
+          raise
+        break
+
+  def _send(self, cmds):
+    """Send command to EC.
+
+    This function always flushes serial device before sending, and is used as
+    a wrapper function to make sure the channel is always flushed before
+    sending commands.
+
+    Args:
+      cmds: The commands to send to the device, either a list or a string.
+
+    Raises:
+      ptyError: Raised when writing to the device fails.
+    """
+    self._flush()
+    if not isinstance(cmds, list):
+      cmds = [cmds]
+    for cmd in cmds:
+      if self._child.sendline(cmd) != len(cmd) + 1:
+        raise ptyError('Failed to send command.')
+
+  def _issue_cmd(self, cmds):
+    """Send command to the device and do not wait for response.
+
+    Args:
+      cmds: The commands to send to the device, either a list or a string.
+    """
+    self._issue_cmd_get_results(cmds, [])
+
+  def _issue_cmd_get_results(self, cmds,
+                             regex_list, timeout=DEFAULT_UART_TIMEOUT):
+    """Send command to the device and wait for response.
+
+    This function waits for response message matching a regular
+    expressions.
+
+    Args:
+      cmds: The commands issued, either a list or a string.
+      regex_list: List of Regular expressions used to match response message.
+        Note1, list must be ordered.
+        Note2, empty list sends and returns.
+      timeout: time to wait for matching results before failing.
+
+    Returns:
+      List of tuples, each of which contains the entire matched string and
+      all the subgroups of the match. None if not matched.
+      For example:
+        response of the given command:
+          High temp: 37.2
+          Low temp: 36.4
+        regex_list:
+          ['High temp: (\d+)\.(\d+)', 'Low temp: (\d+)\.(\d+)']
+        returns:
+          [('High temp: 37.2', '37', '2'), ('Low temp: 36.4', '36', '4')]
+
+    Raises:
+      ptyError: If timed out waiting for a response
+    """
+    result_list = []
+    self._open()
+    try:
+      self._send(cmds)
+      for regex in regex_list:
+        self._child.expect(regex, timeout)
+        match = self._child.match
+        lastindex = match.lastindex if match and match.lastindex else 0
+        # Create a tuple which contains the entire matched string and all
+        # the subgroups of the match.
+        result = match.group(*range(lastindex + 1)) if match else None
+        result_list.append(result)
+    except pexpect.TIMEOUT:
+      raise ptyError('Timeout waiting for response.')
+    finally:
+      self._close()
+    return result_list
+
+  def _issue_cmd_get_multi_results(self, cmd, regex):
+    """Send command to the device and wait for multiple response.
+
+    This function waits for arbitrary number of response message
+    matching a regular expression.
+
+    Args:
+      cmd: The command issued.
+      regex: Regular expression used to match response message.
+
+    Returns:
+      List of tuples, each of which contains the entire matched string and
+      all the subgroups of the match. None if not matched.
+    """
+    result_list = []
+    self._open()
+    try:
+      self._send(cmd)
+      while True:
+        try:
+          self._child.expect(regex, timeout=0.1)
+          match = self._child.match
+          lastindex = match.lastindex if match and match.lastindex else 0
+          # Create a tuple which contains the entire matched string and all
+          # the subgroups of the match.
+          result = match.group(*range(lastindex + 1)) if match else None
+          result_list.append(result)
+        except pexpect.TIMEOUT:
+          break
+    finally:
+      self._close()
+    return result_list
+
+  def _Set_uart_timeout(self, timeout):
+    """Set timeout value for waiting for the device response.
+
+    Args:
+      timeout: Timeout value in second.
+    """
+    self._dict['uart_timeout'] = timeout
+
+  def _Get_uart_timeout(self):
+    """Get timeout value for waiting for the device response.
+
+    Returns:
+      Timeout value in second.
+    """
+    return self._dict['uart_timeout']
+
+  def _Set_uart_regexp(self, regexp):
+    """Set the list of regular expressions which matches the command response.
+
+    Args:
+      regexp: A string which contains a list of regular expressions.
+    """
+    if not isinstance(regexp, str):
+      raise ptyError('The argument regexp should be a string.')
+    self._dict['uart_regexp'] = ast.literal_eval(regexp)
+
+  def _Get_uart_regexp(self):
+    """Get the list of regular expressions which matches the command response.
+
+    Returns:
+      A string which contains a list of regular expressions.
+    """
+    return str(self._dict['uart_regexp'])
+
+  def _Set_uart_cmd(self, cmd):
+    """Set the UART command and send it to the device.
+
+    If ec_uart_regexp is 'None', the command is just sent and it doesn't care
+    about its response.
+
+    If ec_uart_regexp is not 'None', the command is send and its response,
+    which matches the regular expression of ec_uart_regexp, will be kept.
+    Use its getter to obtain this result. If no match after ec_uart_timeout
+    seconds, a timeout error will be raised.
+
+    Args:
+      cmd: A string of UART command.
+    """
+    if self._dict['uart_regexp']:
+      self._dict['uart_cmd'] = self._issue_cmd_get_results(
+          cmd, self._dict['uart_regexp'], self._dict['uart_timeout'])
+    else:
+      self._dict['uart_cmd'] = None
+      self._issue_cmd(cmd)
+
+  def _Set_uart_multicmd(self, cmds):
+    """Set multiple UART commands and send them to the device.
+
+    Note that ec_uart_regexp is not supported to match the results.
+
+    Args:
+      cmds: A semicolon-separated string of UART commands.
+    """
+    self._issue_cmd(cmds.split(';'))
+
+  def _Get_uart_cmd(self):
+    """Get the result of the latest UART command.
+
+    Returns:
+      A string which contains a list of tuples, each of which contains the
+      entire matched string and all the subgroups of the match. 'None' if
+      the ec_uart_regexp is 'None'.
+    """
+    return str(self._dict['uart_cmd'])
+
+  def _Set_uart_capture(self, cmd):
+    """Set UART capture mode (on or off).
+
+    Once capture is enabled, UART output could be collected periodically by
+    invoking _Get_uart_stream() below.
+
+    Args:
+      cmd: True for on, False for off
+    """
+    self._interface.set_capture_active(cmd)
+
+  def _Get_uart_capture(self):
+    """Get the UART capture mode (on or off)."""
+    return self._interface.get_capture_active()
+
+  def _Get_uart_stream(self):
+    """Get uart stream generated since last time."""
+    return self._interface.get_stream()
diff --git a/extra/tigertool/ecusb/stm32uart.py b/extra/tigertool/ecusb/stm32uart.py
new file mode 100644
index 0000000000..3f39b23faa
--- /dev/null
+++ b/extra/tigertool/ecusb/stm32uart.py
@@ -0,0 +1,235 @@
+# Copyright 2017 The Chromium OS Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""Allow creation of uart/console interface via stm32 usb endpoint."""
+
+import os
+import select
+import sys
+import termios
+import threading
+import time
+import tty
+import usb
+
+import stm32usb
+
+
+class SuartError(Exception):
+  """Class for exceptions of Suart."""
+  def __init__(self, msg, value=0):
+    """SuartError constructor.
+
+    Args:
+      msg: string, message describing error in detail
+      value: integer, value of error when non-zero status returned.  Default=0
+    """
+    super(SuartError, self).__init__(msg, value)
+    self.msg = msg
+    self.value = value
+
+
+class Suart(object):
+  """Provide interface to stm32 serial usb endpoint."""
+  def __init__(self, vendor=0x18d1, product=0x501a, interface=0,
+               serialname=None, ftdi_context=None):
+    """Suart contstructor.
+
+    Initializes stm32 USB stream interface.
+
+    Args:
+      vendor: usb vendor id of stm32 device
+      product: usb product id of stm32 device
+      interface: interface number of stm32 device to use
+      serialname: n/a. Defaults to None.
+      ftdi_context: n/a. Defaults to None.
+
+    Raises:
+      SuartError: If init fails
+    """
+    self._ptym = None
+    self._ptys = None
+    self._ptyname = None
+    self._rx_thread = None
+    self._tx_thread = None
+    self._susb = stm32usb.Susb(vendor=vendor, product=product,
+                               interface=interface, serialname=serialname)
+    self._running = False
+
+  def __del__(self):
+    """Suart destructor."""
+    self.close()
+
+  def close(self):
+    """Stop all running threads."""
+    self._running = False
+    if self._rx_thread:
+      self._rx_thread.join(2)
+      self._rx_thread = None
+    if self._tx_thread:
+      self._tx_thread.join(2)
+      self._tx_thread = None
+
+  def run_rx_thread(self):
+    """Background loop to pass data from USB to pty."""
+    ep = select.epoll()
+    ep.register(self._ptym, select.EPOLLHUP)
+    try:
+      while self._running:
+        events = ep.poll(0)
+        # Check if the pty is connected to anything, or hungup.
+        if not events:
+          try:
+            r = self._susb._read_ep.read(64, self._susb.TIMEOUT_MS)
+            if r:
+              os.write(self._ptym, r)
+
+          # If we miss some characters on pty disconnect, that's fine.
+          # ep.read() also throws USBError on timeout, which we discard.
+          except OSError:
+            pass
+          except usb.core.USBError:
+            pass
+        else:
+          time.sleep(.1)
+    except Exception as e:
+      raise e
+
+  def run_tx_thread(self):
+    """Background loop to pass data from pty to USB."""
+    ep = select.epoll()
+    ep.register(self._ptym, select.EPOLLHUP)
+    try:
+      while self._running:
+        events = ep.poll(0)
+        # Check if the pty is connected to anything, or hungup.
+        if not events:
+          try:
+            r = os.read(self._ptym, 64)
+            if r:
+              self._susb._write_ep.write(r, self._susb.TIMEOUT_MS)
+
+          except OSError:
+            pass
+          except usb.core.USBError:
+            pass
+        else:
+          time.sleep(.1)
+    except Exception as e:
+      raise e
+
+  def run(self):
+    """Creates pthreads to poll stm32 & PTY for data."""
+    m, s = os.openpty()
+    self._ptyname = os.ttyname(s)
+
+    self._ptym = m
+    self._ptys = s
+
+    os.fchmod(s, 0o660)
+
+    # Change the owner and group of the PTY to the user who started servod.
+    try:
+      uid = int(os.environ.get('SUDO_UID', -1))
+    except TypeError:
+      uid = -1
+
+    try:
+      gid = int(os.environ.get('SUDO_GID', -1))
+    except TypeError:
+      gid = -1
+    os.fchown(s, uid, gid)
+
+    tty.setraw(self._ptym, termios.TCSADRAIN)
+
+    # Generate a HUP flag on pty slave fd.
+    os.fdopen(s).close()
+
+    self._running = True
+
+    self._rx_thread = threading.Thread(target=self.run_rx_thread, args=[])
+    self._rx_thread.daemon = True
+    self._rx_thread.start()
+
+    self._tx_thread = threading.Thread(target=self.run_tx_thread, args=[])
+    self._tx_thread.daemon = True
+    self._tx_thread.start()
+
+  def get_uart_props(self):
+    """Get the uart's properties.
+
+    Returns:
+      dict where:
+        baudrate: integer of uarts baudrate
+        bits: integer, number of bits of data Can be 5|6|7|8 inclusive
+        parity: integer, parity of 0-2 inclusive where:
+          0: no parity
+          1: odd parity
+          2: even parity
+        sbits: integer, number of stop bits.  Can be 0|1|2 inclusive where:
+          0: 1 stop bit
+          1: 1.5 stop bits
+          2: 2 stop bits
+    """
+    return {
+        'baudrate': 115200,
+        'bits': 8,
+        'parity': 0,
+        'sbits': 1,
+    }
+
+  def set_uart_props(self, line_props):
+    """Set the uart's properties.
+
+    Note that Suart cannot set properties
+    and will fail if the properties are not the default 115200,8n1.
+
+    Args:
+      line_props: dict where:
+        baudrate: integer of uarts baudrate
+        bits: integer, number of bits of data ( prior to stop bit)
+        parity: integer, parity of 0-2 inclusive where
+          0: no parity
+          1: odd parity
+          2: even parity
+        sbits: integer, number of stop bits.  Can be 0|1|2 inclusive where:
+          0: 1 stop bit
+          1: 1.5 stop bits
+          2: 2 stop bits
+
+    Raises:
+      SuartError: If requested line properties are not the default.
+    """
+    curr_props = self.get_uart_props()
+    for prop in line_props:
+      if line_props[prop] != curr_props[prop]:
+        raise SuartError('Line property %s cannot be set from %s to %s' % (
+            prop, curr_props[prop], line_props[prop]))
+    return True
+
+  def get_pty(self):
+    """Gets path to pty for communication to/from uart.
+
+    Returns:
+      String path to the pty connected to the uart
+    """
+    return self._ptyname
+
+
+def main():
+  """Run a suart test with the default parameters."""
+  try:
+    sobj = Suart()
+    sobj.run()
+
+    # run() is a thread so just busy wait to mimic server.
+    while True:
+      # Ours sleeps to eleven!
+      time.sleep(11)
+  except KeyboardInterrupt:
+    sys.exit(0)
+
+
+if __name__ == '__main__':
+  main()
diff --git a/extra/tigertool/ecusb/stm32usb.py b/extra/tigertool/ecusb/stm32usb.py
new file mode 100644
index 0000000000..4165997e5d
--- /dev/null
+++ b/extra/tigertool/ecusb/stm32usb.py
@@ -0,0 +1,108 @@
+# Copyright 2017 The Chromium OS Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""Allows creation of an interface via stm32 usb."""
+
+import usb
+
+
+class SusbError(Exception):
+  """Class for exceptions of Susb."""
+  def __init__(self, msg, value=0):
+    """SusbError constructor.
+
+    Args:
+      msg: string, message describing error in detail
+      value: integer, value of error when non-zero status returned.  Default=0
+    """
+    super(SusbError, self).__init__(msg, value)
+    self.msg = msg
+    self.value = value
+
+
+class Susb(object):
+  """Provide stm32 USB functionality.
+
+  Instance Variables:
+    _read_ep: pyUSB read endpoint for this interface
+    _write_ep: pyUSB write endpoint for this interface
+  """
+  READ_ENDPOINT = 0x81
+  WRITE_ENDPOINT = 0x1
+  TIMEOUT_MS = 100
+
+  def __init__(self, vendor=0x18d1,
+               product=0x5027, interface=1, serialname=None, logger=None):
+    """Susb constructor.
+
+    Discovers and connects to stm32 USB endpoints.
+
+    Args:
+      vendor: usb vendor id of stm32 device.
+      product: usb product id of stm32 device.
+      interface: interface number ( 1 - 4 ) of stm32 device to use.
+      serialname: string of device serialname.
+      logger: none
+
+    Raises:
+      SusbError: An error accessing Susb object
+    """
+    self._vendor = vendor
+    self._product = product
+    self._interface = interface
+    self._serialname = serialname
+    self._find_device()
+
+  def _find_device(self):
+    """Set up the usb endpoint"""
+    # Find the stm32.
+    dev_list = usb.core.find(idVendor=self._vendor, idProduct=self._product,
+                             find_all=True)
+    if not dev_list:
+      raise SusbError('USB device not found')
+
+    # Check if we have multiple stm32s and we've specified the serial.
+    dev = None
+    if self._serialname:
+      for d in dev_list:
+        dev_serial = usb.util.get_string(d, d.iSerialNumber)
+        if dev_serial == self._serialname:
+          dev = d
+          break
+      if dev is None:
+        raise SusbError('USB device(%s) not found' % self._serialname)
+    else:
+      try:
+        dev = dev_list.next()
+      except StopIteration:
+        raise SusbError('USB device %04x:%04x not found' % (
+            self._vendor, self._product))
+
+    # If we can't set configuration, it's already been set.
+    try:
+      dev.set_configuration()
+    except usb.core.USBError:
+      pass
+
+    # Get an endpoint instance.
+    cfg = dev.get_active_configuration()
+    intf = usb.util.find_descriptor(cfg, bInterfaceNumber=self._interface)
+    self._intf = intf
+    if not intf:
+      raise SusbError('Interface %04x:%04x - 0x%x not found' % (
+          self._vendor, self._product, self._interface))
+
+    # Detach raiden.ko if it is loaded. CCD endpoints support either a kernel
+    # module driver that produces a ttyUSB, or direct endpoint access, but
+    # can't do both at the same time.
+    if dev.is_kernel_driver_active(intf.bInterfaceNumber) is True:
+      dev.detach_kernel_driver(intf.bInterfaceNumber)
+
+    read_ep_number = intf.bInterfaceNumber + self.READ_ENDPOINT
+    read_ep = usb.util.find_descriptor(intf, bEndpointAddress=read_ep_number)
+    self._read_ep = read_ep
+
+    write_ep_number = intf.bInterfaceNumber + self.WRITE_ENDPOINT
+    write_ep = usb.util.find_descriptor(intf, bEndpointAddress=write_ep_number)
+    self._write_ep = write_ep
diff --git a/extra/tigertool/ecusb/tiny_servo_common.py b/extra/tigertool/ecusb/tiny_servo_common.py
new file mode 100644
index 0000000000..a65697b116
--- /dev/null
+++ b/extra/tigertool/ecusb/tiny_servo_common.py
@@ -0,0 +1,145 @@
+# Copyright 2017 The Chromium OS Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""Utilities for using lightweight console functions."""
+
+import datetime
+import errno
+import os
+import re
+import subprocess
+import sys
+import time
+
+import pty_driver
+import stm32uart
+
+
+class TinyServoError(Exception):
+  """Exceptions."""
+
+
+def log(output):
+  """Print output to console, logfiles can be added here.
+
+  Args:
+    output: string to output.
+  """
+  sys.stdout.write(output)
+  sys.stdout.write('\n')
+  sys.stdout.flush()
+
+def check_usb(vidpid):
+  """Check if |vidpid| is present on the system's USB.
+
+  Args:
+    vidpid: string representation of the usb vid:pid, eg. '18d1:2001'
+
+  Returns: True if found, Flase, otherwise.
+  """
+  if subprocess.call(['lsusb', '-d', vidpid], stdout=open('/dev/null', 'w')):
+    return False
+  return True
+
+def check_usb_sn(vidpid):
+  """Return the serial number
+
+  Return the serial number of the first USB device with VID:PID vidpid,
+  or None if no device is found. This will not work well with two of
+  the same device attached.
+
+  Args:
+    vidpid: string representation of the usb vid:pid, eg. '18d1:2001'
+
+  Returns: string serial number if found, None otherwise.
+  """
+  output = subprocess.check_output(['lsusb', '-v', '-d', vidpid])
+  m = re.search(r'^\s*iSerial\s+(.*)$', output, flags=re.M)
+  if m:
+   return m.group(1)
+
+  return None
+
+def wait_for_usb_remove(vidpid, timeout=None):
+  """Wait for USB device with vidpid to be removed.
+
+  Wrapper for wait_for_usb below
+  """
+  wait_for_usb(vidpid, timeout=timeout, desiredpresence=False)
+
+def wait_for_usb(vidpid, timeout=None, desiredpresence=True):
+  """Wait for usb device with vidpid to be present/absent.
+
+  Args:
+    vidpid: string representation of the usb vid:pid, eg. '18d1:2001'
+    timeout: timeout in seconds, None for no timeout.
+    desiredpresence: True for present, False for not present.
+
+  Raises:
+    TinyServoError: on timeout.
+  """
+  if timeout:
+    finish = datetime.datetime.now() + datetime.timedelta(seconds=timeout)
+  while check_usb(vidpid) != desiredpresence:
+    time.sleep(.1)
+    if timeout:
+      if datetime.datetime.now() > finish:
+        raise TinyServoError('Timeout', 'Timeout waiting for USB %s' % vidpid)
+
+def do_serialno(serialno, pty):
+  """Set serialnumber 'serialno' via ec console 'pty'.
+
+  Commands are:
+  # > serialno set 1234
+  # Saving serial number
+  # Serial number: 1234
+
+  Args:
+    serialno: string serial number to set.
+    pty: tinyservo console to send commands.
+
+  Raises:
+    TinyServoError: on failure to set.
+    ptyError: on command interface error.
+  """
+  cmd = 'serialno set %s' % serialno
+  regex = 'Serial number: (.*)$'
+
+  results = pty._issue_cmd_get_results(cmd, [regex])[0]
+  sn = results[1].strip().strip('\n\r')
+
+  if sn == serialno:
+    log('Success !')
+    log('Serial set to %s' % sn)
+  else:
+    log('Serial number set to %s but saved as %s.' % (serialno, sn))
+    raise TinyServoError(
+        'Serial Number',
+        'Serial number set to %s but saved as %s.' % (serialno, sn))
+
+def setup_tinyservod(vidpid, interface, serialno=None):
+  """Set up a pty
+
+  Set up a pty to the ec console in order
+  to send commands. Returns a pty_driver object.
+
+  Args:
+    vidpid: string vidpid of device to access.
+    interface: not used.
+    serialno: string serial no of device requested, optional.
+
+  Returns: pty object
+
+  Raises:
+    UsbError, SusbError: on device not found
+  """
+  vidstr, pidstr = vidpid.split(':')
+  vid = int(vidstr, 16)
+  pid = int(pidstr, 16)
+  suart = stm32uart.Suart(vendor=vid, product=pid,
+                          interface=interface, serialname=serialno)
+  suart.run()
+  pty = pty_driver.ptyDriver(suart, [])
+
+  return pty