[pypiezo.git] / pypiezo / base.py

# Copyright (C) 2011-2012 W. Trevor King <wking@drexel.edu>
#
# This file is part of pypiezo.
#
# pypiezo is free software: you can redistribute it and/or modify it under the
# terms of the GNU General Public License as published by the Free Software
# Foundation, either version 3 of the License, or (at your option) any later
# version.
#
# pypiezo is distributed in the hope that it will be useful, but WITHOUT ANY
# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
# A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along with
# pypiezo.  If not, see <http://www.gnu.org/licenses/>.

"Basic piezo control."

import math as _math
from time import sleep as _sleep

import numpy as _numpy
from scipy.stats import linregress as _linregress

try:
    import matplotlib as _matplotlib
    import matplotlib.pyplot as _matplotlib_pyplot
    import time as _time  # for timestamping lines on plots
except (ImportError, RuntimeError), e:
    _matplotlib = None
    _matplotlib_import_error = e

from pycomedi.constant import AREF, TRIG_SRC, SDF
from pycomedi.utility import inttrig_insn, Reader, Writer

from . import LOG as _LOG
from . import config as _config
from . import package_config as _package_config


def convert_bits_to_volts(config, data):
    """Convert bit-valued data to volts.

    >>> config = _config.ChannelConfig()
    >>> config['conversion-coefficients'] = [1, 2, 3]
    >>> config['conversion-origin'] = -1
    >>> convert_bits_to_volts(config, -1)
    1
    >>> convert_bits_to_volts(
    ...     config, _numpy.array([-1, 0, 1, 2], dtype=_numpy.float))
    array([  1.,   6.,  17.,  34.])
    """
    coefficients = config['conversion-coefficients']
    origin = config['conversion-origin']
    return _numpy.polyval(list(reversed(coefficients)), data-origin)

def convert_volts_to_bits(config, data):
    """Convert bit-valued data to volts.

    >>> config = _config.ChannelConfig()
    >>> config['inverse-conversion-coefficients'] = [1, 2, 3]
    >>> config['inverse-conversion-origin'] = -1
    >>> convert_volts_to_bits(config, -1)
    1
    >>> convert_volts_to_bits(
    ...     config, _numpy.array([-1, 0, 1, 2], dtype=_numpy.float))
    array([  1.,   6.,  17.,  34.])

    Note that the inverse coeffiecient and offset are difficult to
    derive from the forward coefficient and offset.  The current
    Comedilib conversion functions, `comedi_to_physical()` and
    `comedi_from_physical()` take `comedi_polynomial_t` conversion
    arguments.  `comedi_polynomial_t` is defined in `comedilib.h`_,
    and holds a polynomial of length
    `COMEDI_MAX_NUM_POLYNOMIAL_COEFFICIENTS`, currently set to 4.  The
    inverse of this cubic polynomial might be another polynomial, but
    it might also have a more complicated form.  A general inversion
    solution is considered too complicated, so when you're setting up
    your configuration, you should use Comedilib to save both the
    forward and inverse coefficients and offsets.

    .. _comedilib.h: http://www.comedi.org/git?p=comedi/comedilib.git;a=blob;f=include/comedilib.h;hb=HEAD
    """
    origin = config['inverse-conversion-origin']
    inverse_coefficients = config['inverse-conversion-coefficients']
    if len(inverse_coefficients) == 0:
        raise NotImplementedError('cubic polynomial inversion')
    return _numpy.polyval(list(reversed(inverse_coefficients)), data-origin)

def convert_volts_to_meters(config, data):
    """Convert volt-valued data to meters.

    >>> config = _config.AxisConfig()
    >>> config['gain'] = 20.0
    >>> config['sensitivity'] = 8e-9
    >>> convert_volts_to_meters(config, 1)
    1.6e-07
    >>> convert_volts_to_meters(
    ...     config, _numpy.array([1, 6, 17, 34], dtype=_numpy.float))
    ... # doctest: +ELLIPSIS
    array([  1.6...e-07,   9.6...e-07,   2.7...e-06,
             5.4...e-06])
    """
    return data * config['gain'] * config['sensitivity']

def convert_meters_to_volts(config, data):
    """Convert bit-valued data to volts.

    >>> config = _config.AxisConfig()
    >>> config['gain'] = 20.0
    >>> config['sensitivity'] = 8e-9
    >>> convert_meters_to_volts(config, 1.6e-7)
    1.0
    >>> convert_meters_to_volts(
    ...     config, _numpy.array([1.6e-7, 9.6e-7, 2.72e-6, 5.44e-6],
    ...                          dtype=_numpy.float))
    array([  1.,   6.,  17.,  34.])
    """
    return data / (config['gain'] * config['sensitivity'])

def convert_bits_to_meters(axis_config, data):
    """Convert bit-valued data to meters.

    >>> channel_config = _config.ChannelConfig()
    >>> channel_config['conversion-coefficients'] = [1, 2, 3]
    >>> channel_config['conversion-origin'] = -1
    >>> axis_config = _config.AxisConfig()
    >>> axis_config['gain'] = 20.0
    >>> axis_config['sensitivity'] = 8e-9
    >>> axis_config['channel'] = channel_config
    >>> convert_bits_to_meters(axis_config, 1)
    ... # doctest: +ELLIPSIS
    2.7...e-06
    >>> convert_bits_to_meters(
    ...     axis_config, _numpy.array([-1, 0, 1, 2], dtype=_numpy.float))
    ... # doctest: +ELLIPSIS
    array([  1.6...e-07,   9.6...e-07,   2.7...e-06,
             5.4...e-06])
    """
    data = convert_bits_to_volts(axis_config['channel'], data)
    return convert_volts_to_meters(axis_config, data)

def convert_meters_to_bits(axis_config, data):
    """Convert meter-valued data to volts.

    >>> channel_config = _config.ChannelConfig()
    >>> channel_config['inverse-conversion-coefficients'] = [1, 2, 3]
    >>> channel_config['inverse-conversion-origin'] = -1
    >>> axis_config = _config.AxisConfig()
    >>> axis_config['gain'] = 20.0
    >>> axis_config['sensitivity'] = 8e-9
    >>> axis_config['channel'] = channel_config
    >>> convert_meters_to_bits(axis_config, 1.6e-7)
    17.0
    >>> convert_meters_to_bits(
    ...     axis_config,
    ...     _numpy.array([1.6e-7, 9.6e-7, 2.72e-6, 5.44e-6],
    ...                  dtype=_numpy.float))
    array([   17.,   162.,  1009.,  3746.])
    """
    data = convert_meters_to_volts(axis_config, data)
    return convert_volts_to_bits(axis_config['channel'], data)

def get_axis_name(axis_config):
    """Return the name of an axis from the `AxisConfig`

    This is useful, for example, with
    `Config.select_config(get_attribute=get_axis_name)`.
    """
    channel_config = axis_config['channel']
    return channel_config['name']

def _setup_channel_config(config, channel):
    """Initialize the `ChannelConfig` `config` using the
    `AnalogChannel` `channel`.
    """
    config['device'] = channel.subdevice.device.filename
    config['subdevice'] = channel.subdevice.index
    config['channel'] = channel.index
    config['maxdata'] = channel.get_maxdata()
    config['range'] = channel.range.value
    config['analog-reference'] = AREF.index_by_value(channel.aref.value)
    converter = channel.get_converter()
    config['conversion-origin'
           ] = converter.get_to_physical_expansion_origin()
    config['conversion-coefficients'
           ] = converter.get_to_physical_coefficients()
    config['inverse-conversion-origin'
           ] = converter.get_from_physical_expansion_origin()
    config['inverse-conversion-coefficients'
           ] = converter.get_from_physical_coefficients()


class PiezoAxis (object):
    """A one-dimensional piezoelectric actuator.

    If used, the montoring channel must (as of now) be on the same
    device as the controlling channel.

    >>> from pycomedi.device import Device
    >>> from pycomedi.subdevice import StreamingSubdevice
    >>> from pycomedi.channel import AnalogChannel
    >>> from pycomedi.constant import (AREF, SUBDEVICE_TYPE, UNIT)

    >>> d = Device('/dev/comedi0')
    >>> d.open()

    >>> s_in = d.find_subdevice_by_type(SUBDEVICE_TYPE.ai,
    ...     factory=StreamingSubdevice)
    >>> s_out = d.find_subdevice_by_type(SUBDEVICE_TYPE.ao,
    ...     factory=StreamingSubdevice)

    >>> axis_channel = s_out.channel(
    ...     0, factory=AnalogChannel, aref=AREF.ground)
    >>> monitor_channel = s_in.channel(
    ...     0, factory=AnalogChannel, aref=AREF.diff)
    >>> for chan in [axis_channel, monitor_channel]:
    ...     chan.range = chan.find_range(unit=UNIT.volt, min=-10, max=10)

    >>> config = _config.AxisConfig()
    >>> config.update({'gain':20, 'sensitivity':8e-9})
    >>> config['channel'] = _config.OutputChannelConfig()
    >>> config['monitor'] = _config.InputChannelConfig()
    >>> config['monitor']['device'] = '/dev/comediX'

    >>> p = PiezoAxis(config=config)
    ... # doctest: +NORMALIZE_WHITESPACE
    Traceback (most recent call last):
      ...
    NotImplementedError: piezo axis control and monitor on different devices
     (/dev/comedi0 and /dev/comediX)

    >>> config['monitor']['device'] = config['channel']['device']
    >>> p = PiezoAxis(config=config,
    ...     axis_channel=axis_channel, monitor_channel=monitor_channel)

    >>> p.setup_config()
    >>> print(config['channel'].dump())
    name: 
    device: /dev/comedi0
    subdevice: 1
    channel: 0
    maxdata: 65535
    range: 0
    analog-reference: ground
    conversion-coefficients: -10.0, 0.000305180437934
    conversion-origin: 0.0
    inverse-conversion-coefficients: 0.0, 3276.75
    inverse-conversion-origin: -10.0
    >>> print(config['monitor'].dump())
    name: 
    device: /dev/comedi0
    subdevice: 0
    channel: 0
    maxdata: 65535
    range: 0
    analog-reference: diff
    conversion-coefficients: -10.0, 0.000305180437934
    conversion-origin: 0.0
    inverse-conversion-coefficients: 0.0, 3276.75
    inverse-conversion-origin: -10.0

    >>> convert_bits_to_meters(p.config, 0)
    ... # doctest: +ELLIPSIS
    -1.6...e-06

    >>> d.close()
    """
    def __init__(self, config, axis_channel=None, monitor_channel=None):
        self.config = config
        if (config['monitor'] and
            config['channel']['device'] != config['monitor']['device']):
            raise NotImplementedError(
                ('piezo axis control and monitor on different devices '
                 '(%s and %s)') % (
                    config['channel']['device'],
                    config['monitor']['device']))
        if not axis_channel:
            raise NotImplementedError(
                'pypiezo not yet capable of opening its own axis channel')
            #axis_channel = pycomedi...
        self.axis_channel = axis_channel
        if config['monitor'] and not monitor_channel:
            raise NotImplementedError(
                'pypiezo not yet capable of opening its own monitor channel')
            #monitor_channel = pycomedi...
        self.monitor_channel = monitor_channel
        self.name = config['channel']['name']

    def setup_config(self):
        "Initialize the axis (and monitor) configs."
        _setup_channel_config(self.config['channel'], self.axis_channel)
        if self.monitor_channel:
            _setup_channel_config(
                self.config['monitor'], self.monitor_channel)
        if self.config['minimum'] is None:
            self.config['minimum'] = convert_bits_to_volts(
                self.config['channel'], 0)
        if self.config['maximum'] is None:
            self.config['maximum'] = convert_bits_to_volts(
                self.config['channel'], self.axis_channel.get_maxdata())


class InputChannel(object):
    """An input channel monitoring some interesting parameter.

    >>> from pycomedi.device import Device
    >>> from pycomedi.subdevice import StreamingSubdevice
    >>> from pycomedi.channel import AnalogChannel
    >>> from pycomedi.constant import AREF, SUBDEVICE_TYPE, UNIT

    >>> d = Device('/dev/comedi0')
    >>> d.open()

    >>> s = d.find_subdevice_by_type(SUBDEVICE_TYPE.ai,
    ...     factory=StreamingSubdevice)

    >>> channel = s.channel(0, factory=AnalogChannel, aref=AREF.diff)
    >>> channel.range = channel.find_range(unit=UNIT.volt, min=-10, max=10)

    >>> channel_config = _config.InputChannelConfig()

    >>> c = InputChannel(config=channel_config, channel=channel)
    >>> c.setup_config()
    >>> print(channel_config.dump())
    name: 
    device: /dev/comedi0
    subdevice: 0
    channel: 0
    maxdata: 65535
    range: 0
    analog-reference: diff
    conversion-coefficients: -10.0, 0.000305180437934
    conversion-origin: 0.0
    inverse-conversion-coefficients: 0.0, 3276.75
    inverse-conversion-origin: -10.0

    >>> convert_bits_to_volts(c.config, 0)
    -10.0

    >>> d.close()
    """
    def __init__(self, config, channel=None):
        self.config = config
        if not channel:
            raise NotImplementedError(
                'pypiezo not yet capable of opening its own channel')
            #channel = pycomedi...
        self.channel = channel
        self.name = config['name']

    def setup_config(self):
        _setup_channel_config(self.config, self.channel)


class Piezo (object):
    """A piezo actuator-controlled experiment.

    >>> from pprint import pprint
    >>> from pycomedi.device import Device
    >>> from pycomedi.subdevice import StreamingSubdevice
    >>> from pycomedi.channel import AnalogChannel
    >>> from pycomedi.constant import AREF, SUBDEVICE_TYPE, UNIT

    >>> d = Device('/dev/comedi0')
    >>> d.open()

    >>> s_in = d.find_subdevice_by_type(SUBDEVICE_TYPE.ai,
    ...     factory=StreamingSubdevice)
    >>> s_out = d.find_subdevice_by_type(SUBDEVICE_TYPE.ao,
    ...     factory=StreamingSubdevice)

    >>> axis_channel = s_out.channel(
    ...     0, factory=AnalogChannel, aref=AREF.ground)
    >>> monitor_channel = s_in.channel(
    ...     0, factory=AnalogChannel, aref=AREF.diff)
    >>> input_channel = s_in.channel(1, factory=AnalogChannel, aref=AREF.diff)
    >>> for chan in [axis_channel, monitor_channel, input_channel]:
    ...     chan.range = chan.find_range(unit=UNIT.volt, min=-10, max=10)

    >>> axis_config = _config.AxisConfig()
    >>> axis_config.update({'gain':20, 'sensitivity':8e-9})
    >>> axis_config['channel'] = _config.OutputChannelConfig()
    >>> axis_config['channel']['name'] = 'z'
    >>> axis_config['monitor'] = _config.InputChannelConfig()
    >>> input_config = _config.InputChannelConfig()
    >>> input_config['name'] = 'some-input'

    >>> a = PiezoAxis(config=axis_config, axis_channel=axis_channel,
    ...     monitor_channel=monitor_channel)
    >>> a.setup_config()

    >>> c = InputChannel(config=input_config, channel=input_channel)
    >>> c.setup_config()

    >>> p = Piezo(axes=[a], inputs=[c], name='Charlie')
    >>> inputs = p.read_inputs()
    >>> pprint(inputs)  # doctest: +SKIP
    {'some-input': 34494L, 'z-monitor': 32669L}

    >>> pos = convert_volts_to_bits(p.config['axes'][0]['channel'], 0)
    >>> pos
    32767.5
    >>> p.jump('z', pos)
    >>> p.last_output == {'z': int(pos)}
    True

    :meth:`ramp` raises an error if passed an invalid `data` `dtype`.

    >>> output_data = _numpy.arange(0, int(pos), step=int(pos/10),
    ...     dtype=_numpy.float)
    >>> output_data = output_data.reshape((len(output_data), 1))
    >>> input_data = p.ramp(data=output_data, frequency=10,
    ...     output_names=['z'], input_names=['z-monitor', 'some-input'])
    Traceback (most recent call last):
      ...
    ValueError: output dtype float64 does not match expected <type 'numpy.uint16'>
    >>> output_data = _numpy.arange(0, int(pos), step=int(pos/10),
    ...     dtype=p.channel_dtype('z', direction='output'))
    >>> output_data = output_data.reshape((len(output_data), 1))
    >>> input_data = p.ramp(data=output_data, frequency=10,
    ...     output_names=['z'], input_names=['z-monitor', 'some-input'])
    >>> input_data  # doctest: +SKIP
    array([[    0, 25219],
           [ 3101, 23553],
           [ 6384, 22341],
           [ 9664, 21465],
           [12949, 20896],
           [16232, 20614],
           [19516, 20588],
           [22799, 20801],
           [26081, 21233],
           [29366, 21870],
           [32646, 22686]], dtype=uint16)

    >>> p.last_output == {'z': output_data[-1]}
    True

    >>> data = p.named_ramp(data=output_data, frequency=10,
    ...     output_names=['z'], input_names=['z-monitor', 'some-input'])
    >>> pprint(data)  # doctest: +ELLIPSIS, +SKIP
    {'some-input': array([21666, 20566, ..., 22395], dtype=uint16),
     'z': array([    0,  3276,  ..., 32760], dtype=uint16),
     'z-monitor': array([ 3102,  6384,  ..., 32647], dtype=uint16)}

    >>> d.close()
    """
    def __init__(self, axes, inputs, name=None):
        self.axes = axes
        self.inputs = inputs
        self.config = _config.PiezoConfig()
        self.name = name
        self.config['name'] = name
        self.config['axes'] = [x.config for x in axes]
        self.config['inputs'] = [x.config for x in inputs]
        self.last_output = {}

    def axis_by_name(self, name):
        "Get an axis by its name."
        for axis in self.axes:
            if axis.name == name:
                return axis
        raise ValueError(name)

    def input_channel_by_name(self, name):
        "Get an input channel by its name."
        for input_channel in self.inputs:
            if input_channel.name == name:
                return input_channel
        raise ValueError(name)

    def channels(self, direction=None):
        """Iterate through all `(name, channel)` tuples.

        ===========  ===================
        `direction`  Returned channels
        ===========  ===================
        'input'      all input channels
        'output'     all output channels
        None         all channels
        ===========  ===================
        """
        if direction not in ('input', 'output', None):
            raise ValueError(direction)
        for a in self.axes:
            if direction != 'input':
                yield (a.name, a.axis_channel)
            if a.monitor_channel and direction != 'output':
                yield ('%s-monitor' % a.name, a.monitor_channel)
        if direction != 'output':
            for c in self.inputs:
                yield (c.name, c.channel)

    def channel_by_name(self, name, direction=None):
        """Get a channel by its name.

        Setting `direction` (see :meth:`channels`) may allow a more
        efficient search.
        """
        for n,channel in self.channels(direction=direction):
            if n == name:
                return channel
        raise ValueError(name)

    def channel_dtype(self, channel_name, direction=None):
        """Get a channel's data type by name.

        Setting `direction` (see :meth:`channels`) may allow a more
        efficient search.
        """
        channel = self.channel_by_name(name=channel_name, direction=direction)
        return channel.subdevice.get_dtype()

    def read_inputs(self):
        "Read all inputs and return a `name`->`value` dictionary."
        # There is no multi-channel read instruction, so preform reads
        # sequentially.
        ret = dict([(n, c.data_read())
                    for n,c in self.channels(direction='input')])
        _LOG.debug('current position: %s' % ret)
        return ret

    def jump(self, axis_name, position, steps=1, sleep=None):
        "Move the output named `axis_name` to `position`."
        _LOG.debug('jump %s to %s in %d steps' % (axis_name, position, steps))
        if steps > 1:
            try:
                orig_pos = self.last_output[axis_name]
            except KeyError, e:
                _LOG.warn(
                    ("cannot make a soft jump to {} because we don't have a "
                     'last-output position for {}').format(
                        position, axis_name))
                steps = 1
            else:
                for pos in _numpy.linspace(orig_pos, position, steps+1)[1:]:
                    self.jump(axis_name=axis_name, position=pos)
                    if sleep:
                        _sleep(sleep)
                return
        position = int(position)
        channel = self.channel_by_name(name=axis_name)
        channel.data_write(position)
        self.last_output[axis_name] = position

    def ramp(self, data, frequency, output_names, input_names=()):
        """Synchronized IO ramp writing `data` and reading `in_names`.

        Parameters
        ----------
        data : numpy array-like
            Row for each cycle, column for each output channel.
        frequency : float
            Target cycle frequency in Hz.
        output_names : list of strings
            Names of output channels in the same order as the columns
            of `data`.
        input_names : list of strings
            Names of input channels to monitor in the same order as
            the columns of the returned array.
        """
        if len(data.shape) != 2:
            raise ValueError(
                'ramp data must be two dimensional, not %d' % len(data.shape))
        if data.shape[1] != len(output_names):
            raise ValueError(
                'ramp data should have on column for each input, '
                'but has %d columns for %d inputs'
                % (data.shape[1], len(output_names)))
        n_samps = data.shape[0]
        log_string = 'ramp %d samples at %g Hz.  out: %s, in: %s' % (
            n_samps, frequency, output_names, input_names)
        _LOG.debug(log_string)  # _LOG on one line for easy commenting-out
        # TODO: check range?
        output_channels = [self.channel_by_name(name=n, direction='output')
                           for n in output_names]
        inputs = [self.channel_by_name(name=n, direction='input')
                          for n in input_names]

        ao_subdevice = output_channels[0].subdevice
        ai_subdevice = inputs[0].subdevice
        device = ao_subdevice.device

        output_dtype = ao_subdevice.get_dtype()
        if data.dtype != output_dtype:
            raise ValueError('output dtype %s does not match expected %s'
                             % (data.dtype, output_dtype))
        input_data = _numpy.ndarray(
            (n_samps, len(inputs)), dtype=ai_subdevice.get_dtype())

        _LOG.debug('setup ramp commands')
        scan_period_ns = int(1e9 / frequency)
        ai_cmd = ai_subdevice.get_cmd_generic_timed(
            len(inputs), scan_period_ns)
        ao_cmd = ao_subdevice.get_cmd_generic_timed(
            len(output_channels), scan_period_ns)

        ai_cmd.start_src = TRIG_SRC.int
        ai_cmd.start_arg = 0
        ai_cmd.stop_src = TRIG_SRC.count
        ai_cmd.stop_arg = n_samps
        ai_cmd.chanlist = inputs
        #ao_cmd.start_src = TRIG_SRC.ext
        #ao_cmd.start_arg = 18  # NI card AI_START1 internal AI start signal
        ao_cmd.start_src = TRIG_SRC.int
        ao_cmd.start_arg = 0
        ao_cmd.stop_src = TRIG_SRC.count
        ao_cmd.stop_arg = n_samps-1
        ao_cmd.chanlist = output_channels

        ai_subdevice.cmd = ai_cmd
        ao_subdevice.cmd = ao_cmd
        for i in range(3):
            rc = ai_subdevice.command_test()
            if rc is None: break
            _LOG.debug('analog input test %d: %s' % (i, rc))
        for i in range(3):
            rc = ao_subdevice.command_test()
            if rc is None: break
            _LOG.debug('analog output test %d: %s' % (i, rc))

        _LOG.debug('lock subdevices for ramp')
        ao_subdevice.lock()
        try:
            ai_subdevice.lock()
            try:
                _LOG.debug('load ramp commands')
                ao_subdevice.command()
                ai_subdevice.command()

                writer = Writer(ao_subdevice, data)
                writer.start()
                reader = Reader(ai_subdevice, input_data)
                reader.start()

                _LOG.debug('arm analog output')
                device.do_insn(inttrig_insn(ao_subdevice))
                _LOG.debug('trigger ramp (via analog input)')
                device.do_insn(inttrig_insn(ai_subdevice))
                _LOG.debug('ramp running')

                writer.join()
                reader.join()
                _LOG.debug('ramp complete')
            finally:
                #_LOG.debug('AI flags: %s' % ai_subdevice.get_flags())
                ai_subdevice.cancel()
                ai_subdevice.unlock()
        finally:
            # release busy flag, which seems to not be cleared
            # automatically.  See
            #   http://groups.google.com/group/comedi_list/browse_thread/thread/4c7040989197abad/
            #_LOG.debug('AO flags: %s' % ao_subdevice.get_flags())
            ao_subdevice.cancel()
            ao_subdevice.unlock()
            _LOG.debug('unlocked subdevices after ramp')

        for i,name in enumerate(output_names):
            self.last_output[name] = data[-1,i]

        if _package_config['matplotlib']:
            if not _matplotlib:
                raise _matplotlib_import_error
            figure = _matplotlib_pyplot.figure()
            axes = figure.add_subplot(1, 1, 1)
            axes.hold(True)
            timestamp = _time.strftime('%H%M%S')
            axes.set_title('piezo ramp %s' % timestamp)
            for d,names in [(data, output_names),
                            (input_data, input_names)]:
                for i,name in enumerate(names):
                    axes.plot(d[:,i], label=name)
            figure.show()
        return input_data

    def named_ramp(self, data, frequency, output_names, input_names=()):
        input_data = self.ramp(
            data=data, frequency=frequency, output_names=output_names,
            input_names=input_names)
        ret = {}
        for i,name in enumerate(output_names):
            ret[name] = data[:,i]
        for i,name in enumerate(input_names):
            ret[name] = input_data[:,i]
        return ret