Source code for wpilib.encoder

# Copyright (c) FIRST 2008-2012. All Rights Reserved.
# Open Source Software - may be modified and shared by FRC teams. The code
# must be accompanied by the FIRST BSD license file in the root directory of
# the project.

import hal
import warnings
import weakref

from .interfaces.counterbase import CounterBase
from .interfaces.pidsource import PIDSource
from .counter import Counter
from .digitalinput import DigitalInput
from .livewindow import LiveWindow
from .resource import Resource
from .sensorbase import SensorBase

from ._impl.utils import match_arglist, HasAttribute

__all__ = ["Encoder"]

def _freeEncoder(encoder):

[docs]class Encoder(SensorBase): """Reads from quadrature encoders. Quadrature encoders are devices that count shaft rotation and can sense direction. The output of the QuadEncoder class is an integer that can count either up or down, and can go negative for reverse direction counting. When creating QuadEncoders, a direction is supplied that changes the sense of the output to make code more readable if the encoder is mounted such that forward movement generates negative values. Quadrature encoders have two digital outputs, an A Channel and a B Channel that are out of phase with each other to allow the FPGA to do direction sensing. All encoders will immediately start counting - reset() them if you need them to be zeroed before use. Instance variables: - aSource: The A phase of the quad encoder - bSource: The B phase of the quad encoder - indexSource: The index source (available on some encoders) .. not_implemented: initEncoder """
[docs] class IndexingType: kResetWhileHigh = 0 kResetWhileLow = 1 kResetOnFallingEdge = 2 kResetOnRisingEdge = 3
EncodingType = CounterBase.EncodingType PIDSourceParameter = PIDSource.PIDSourceParameter def __init__(self, *args, **kwargs): """Encoder constructor. Construct a Encoder given a and b channels and optionally an index channel. The encoder will start counting immediately. The a, b, and optional index channel arguments may be either channel numbers or `DigitalSource` sources. There may also be a boolean reverseDirection, and an encodingType according to the following list. - aSource, bSource - aSource, bSource, reverseDirection - aSource, bSource, reverseDirection, encodingType - aSource, bSource, indexSource, reverseDirection - aSource, bSource, indexSource - aChannel, bChannel - aChannel, bChannel, reverseDirection - aChannel, bChannel, reverseDirection, encodingType - aChannel, bChannel, indexChannel, reverseDirection - aChannel, bChannel, indexChannel For positional arguments, if the passed object has a `getChannelForRouting` function, it is assumed to be a DigitalSource. Alternatively, sources and/or channels may be passed as keyword arguments. The behavior of specifying both a source and a number for the same channel is undefined, as is passing both a positional and a keyword argument for the same channel. In addition, keyword parameters may be provided for reverseDirection and inputType. :param aSource: The source that should be used for the a channel. :param bSource: The source that should be used for the b channel. :param indexSource: The source that should be used for the index channel. :param aChannel: The digital input index that should be used for the a channel. :param bChannel: The digital input index that should be used for the b channel. :param indexChannel: The digital input index that should be used for the index channel. :param reverseDirection: Represents the orientation of the encoder and inverts the output values if necessary so forward represents positive values. Defaults to False if unspecified. :param encodingType: Either k1X, k2X, or k4X to indicate 1X, 2X or 4X decoding. If 4X is selected, then an encoder FPGA object is used and the returned counts will be 4x the encoder spec'd value since all rising and falling edges are counted. If 1X or 2X are selected then a counter object will be used and the returned value will either exactly match the spec'd count or be double (2x) the spec'd count. Defaults to k4X if unspecified. :type encodingType: :class:`Encoder.EncodingType` """ a_source_arg = ("aSource", HasAttribute("getChannelForRouting")) b_source_arg = ("bSource", HasAttribute("getChannelForRouting")) index_source_arg = ("indexSource", HasAttribute("getChannelForRouting")) a_channel_arg = ("aChannel", int) b_channel_arg = ("bChannel", int) index_channel_arg = ("indexChannel", int) argument_templates = [[a_source_arg, b_source_arg], [a_source_arg, b_source_arg, ("reverseDirection", bool)], [a_source_arg, b_source_arg, ("reverseDirection", bool), ("encodingType", int)], [a_source_arg, b_source_arg, index_source_arg], [a_source_arg, b_source_arg, index_source_arg, ("reverseDirection", bool)], [a_channel_arg, b_channel_arg], [a_channel_arg, b_channel_arg, ("reverseDirection", bool)], [a_channel_arg, b_channel_arg, ("reverseDirection", bool), ("encodingType", int)], [a_channel_arg, b_channel_arg, index_channel_arg], [a_channel_arg, b_channel_arg, index_channel_arg, ("reverseDirection", bool)]] _, results = match_arglist('Encoder.__init__', args, kwargs, argument_templates) # keyword arguments aSource = results.pop("aSource", None) bSource = results.pop("bSource", None) indexSource = results.pop("indexSource", None) aChannel = results.pop("aChannel", None) bChannel = results.pop("bChannel", None) indexChannel = results.pop("indexChannel", None) reverseDirection = results.pop("reverseDirection", False) encodingType = results.pop("encodingType", self.EncodingType.k4X) # convert channels into sources self.allocatedA = False self.allocatedB = False self.allocatedIndex = False if aSource is None: if aChannel is None: raise ValueError("didn't specify A channel") aSource = DigitalInput(aChannel) self.allocatedA = True if bSource is None: if bChannel is None: raise ValueError("didn't specify B channel") bSource = DigitalInput(bChannel) self.allocatedB = True if indexSource is None and indexChannel is not None: indexSource = DigitalInput(indexChannel) self.allocatedIndex = True # save to instance variables self.aSource = aSource self.bSource = bSource self.indexSource = indexSource self.encodingType = encodingType self.distancePerPulse = 1.0 # distance of travel for each encoder tick self.pidSource = PIDSource.PIDSourceParameter.kDistance self._encoder = None self.counter = None self.index = 0 if encodingType == self.EncodingType.k4X: self._encoder, self.index = hal.initializeEncoder( aSource.getModuleForRouting(), aSource.getChannelForRouting(), aSource.getAnalogTriggerForRouting(), bSource.getModuleForRouting(), bSource.getChannelForRouting(), bSource.getAnalogTriggerForRouting(), reverseDirection) self._encoder_finalizer = \ weakref.finalize(self, _freeEncoder, self._encoder) self.setMaxPeriod(.5) self.encodingScale = 4 elif encodingType in (self.EncodingType.k2X, self.EncodingType.k1X): # Use Counter object for 1x and 2x encoding self.counter = Counter(encodingType, aSource, bSource, reverseDirection) if encodingType == self.encodingType.k2X: self.encodingScale = 2 else: self.encodingScale = 1 self.index = self.counter.getFPGAIndex() else: raise ValueError("unrecognized encodingType: %s" % encodingType) # Need this to free on unit test wpilib reset Resource._add_global_resource(self) if self.indexSource is not None: self.setIndexSource(self.indexSource) hal.HALReport(hal.HALUsageReporting.kResourceType_Encoder, self.index, encodingType) LiveWindow.addSensorChannel("Encoder", aSource.getChannelForRouting(), self) @property
[docs] def encoder(self): if not self._encoder_finalizer.alive: return None return self._encoder
[docs] def getFPGAIndex(self): """ :returns: The Encoder's FPGA index """ return self.index
[docs] def getEncodingScale(self): """ :returns: The encoding scale factor 1x, 2x, or 4x, per the requested encodingType. Used to divide raw edge counts down to spec'd counts. """ return self.encodingScale
[docs] def free(self): if self.aSource is not None and self.allocatedA: self.allocatedA = False if self.bSource is not None and self.allocatedB: self.allocatedB = False if self.indexSource is not None and self.allocatedIndex: self.allocatedIndex = False self.aSource = None self.bSource = None self.indexSource = None if self.counter is not None: self.counter = None else: self._encoder_finalizer()
[docs] def getRaw(self): """Gets the raw value from the encoder. The raw value is the actual count unscaled by the 1x, 2x, or 4x scale factor. :returns: Current raw count from the encoder """ if self.counter is not None: return self.counter.get() return hal.getEncoder(self.encoder)
[docs] def get(self): """Gets the current count. Returns the current count on the Encoder. This method compensates for the decoding type. :returns: Current count from the Encoder adjusted for the 1x, 2x, or 4x scale factor. """ return int(self.getRaw() * self.decodingScaleFactor())
[docs] def reset(self): """Reset the Encoder distance to zero. Resets the current count to zero on the encoder. """ if self.counter is not None: self.counter.reset() elif self.encoder is not None: hal.resetEncoder(self.encoder) else: raise ValueError("operation on freed port")
[docs] def getPeriod(self): """Returns the period of the most recent pulse. Returns the period of the most recent Encoder pulse in seconds. This method compensates for the decoding type. .. deprecated:: Use :func:`getRate` in favor of this method. This returns unscaled periods and :func:`getRate` scales using value from :func:`getDistancePerPulse`. :returns: Period in seconds of the most recent pulse. """ warnings.warn("use getRate instead", DeprecationWarning) if self.counter is not None: measuredPeriod = self.counter.getPeriod() / self.decodingScaleFactor() elif self.encoder is not None: measuredPeriod = hal.getEncoderPeriod(self.encoder) else: raise ValueError("operation on freed port") return measuredPeriod
[docs] def setMaxPeriod(self, maxPeriod): """Sets the maximum period for stopped detection. Sets the value that represents the maximum period of the Encoder before it will assume that the attached device is stopped. This timeout allows users to determine if the wheels or other shaft has stopped rotating. This method compensates for the decoding type. :param maxPeriod: The maximum time between rising and falling edges before the FPGA will report the device stopped. This is expressed in seconds. """ if self.counter is not None: self.counter.setMaxPeriod(maxPeriod * self.decodingScaleFactor()) elif self.encoder is not None: hal.setEncoderMaxPeriod(self.encoder, maxPeriod) else: raise ValueError("operation on freed port")
[docs] def getStopped(self): """Determine if the encoder is stopped. Using the MaxPeriod value, a boolean is returned that is True if the encoder is considered stopped and False if it is still moving. A stopped encoder is one where the most recent pulse width exceeds the MaxPeriod. :returns: True if the encoder is considered stopped. """ if self.counter is not None: return self.counter.getStopped() elif self.encoder is not None: return hal.getEncoderStopped(self.encoder) else: raise ValueError("operation on freed port")
[docs] def getDirection(self): """The last direction the encoder value changed. :returns: The last direction the encoder value changed. """ if self.counter is not None: return self.counter.getDirection() return hal.getEncoderDirection(self.encoder)
[docs] def decodingScaleFactor(self): """The scale needed to convert a raw counter value into a number of encoder pulses. """ if self.encodingType == self.EncodingType.k1X: return 1.0 elif self.encodingType == self.EncodingType.k2X: return 0.5 elif self.encodingType == self.EncodingType.k4X: return 0.25 else: raise ValueError("unexpected encodingType: %d" % self.encodingType)
[docs] def getDistance(self): """Get the distance the robot has driven since the last reset. :returns: The distance driven since the last reset as scaled by the value from :func:`setDistancePerPulse`. """ return self.getRaw() * self.decodingScaleFactor() * self.distancePerPulse
[docs] def getRate(self): """Get the current rate of the encoder. Units are distance per second as scaled by the value from :func:`setDistancePerPulse`. :returns: The current rate of the encoder. """ return self.distancePerPulse / self.getPeriod()
[docs] def setMinRate(self, minRate): """Set the minimum rate of the device before the hardware reports it stopped. :param minRate: The minimum rate. The units are in distance per second as scaled by the value from :func:`setDistancePerPulse`. """ self.setMaxPeriod(self.distancePerPulse / minRate)
[docs] def setDistancePerPulse(self, distancePerPulse): """Set the distance per pulse for this encoder. This sets the multiplier used to determine the distance driven based on the count value from the encoder. Do not include the decoding type in this scale. The library already compensates for the decoding type. Set this value based on the encoder's rated Pulses per Revolution and factor in gearing reductions following the encoder shaft. This distance can be in any units you like, linear or angular. :param distancePerPulse: The scale factor that will be used to convert pulses to useful units. """ self.distancePerPulse = distancePerPulse
[docs] def setReverseDirection(self, reverseDirection): """Set the direction sensing for this encoder. This sets the direction sensing on the encoder so that it could count in the correct software direction regardless of the mounting. :param reverseDirection: True if the encoder direction should be reversed """ if self.counter is not None: self.counter.setReverseDirection(reverseDirection) else: raise NotImplementedError # FIXME?
[docs] def setSamplesToAverage(self, samplesToAverage): """Set the Samples to Average which specifies the number of samples of the timer to average when calculating the period. Perform averaging to account for mechanical imperfections or as oversampling to increase resolution. TODO: Should this raise an exception, so that the user has to deal with giving an incorrect value? :param samplesToAverage: The number of samples to average from 1 to 127. """ if self.encodingType == self.EncodingType.k4X: hal.setEncoderSamplesToAverage(self.encoder, samplesToAverage) elif self.encodingType in (self.EncodingType.k2X, self.EncodingType.k1X): self.counter.setSamplesToAverage(samplesToAverage)
[docs] def getSamplesToAverage(self): """Get the Samples to Average which specifies the number of samples of the timer to average when calculating the period. Perform averaging to account for mechanical imperfections or as oversampling to increase resolution. :returns: The number of samples being averaged (from 1 to 127) """ if self.encodingType.value == self.EncodingType.k4X: return hal.getEncoderSamplesToAverage(self.encoder) elif self.encodingType in (self.EncodingType.k2X, self.EncodingType.k1X): return self.counter.getSamplesToAverage() else: return 1
[docs] def setPIDSourceParameter(self, pidSource): """Set which parameter of the encoder you are using as a process control variable. The encoder class supports the rate and distance parameters. :param pidSource: An enum to select the parameter. """ if pidSource not in (0, 1): raise ValueError("invalid pidSource: %s" % pidSource) self.pidSource = pidSource
[docs] def pidGet(self): """Implement the PIDSource interface. :returns: The current value of the selected source parameter. """ if self.pidSource == self.PIDSourceParameter.kDistance: return self.getDistance() elif self.pidSource == self.PIDSourceParameter.kRate: return self.getRate() else: return 0.0
[docs] def setIndexSource(self, source, indexing_type=IndexingType.kResetOnRisingEdge): """ Set the index source for the encoder. When this source rises, the encoder count automatically resets. :param source: Either an initialized DigitalSource or a DIO channel number :type: Either a :class:`wpilib.DigitalInput` or number :param indexing_type: The state that will cause the encoder to reset :type: A value from :class:`wpilib.DigitalInput.IndexingType` """ if hasattr(source, "getChannelForRouting"): self.indexSource = source else: self.indexSource = DigitalInput(source) activeHigh = (indexing_type == self.IndexingType.kResetWhileHigh or indexing_type == self.IndexingType.kResetOnRisingEdge) edgeSensitive = (indexing_type == self.IndexingType.kResetOnFallingEdge or indexing_type == self.IndexingType.kResetOnRisingEdge) hal.setEncoderIndexSource(self.encoder, self.indexSource.getChannelForRouting(), self.indexSource.getAnalogTriggerForRouting(), activeHigh, edgeSensitive) # Live Window code, only does anything if live window is activated.
def getSmartDashboardType(self): if self.encodingType == self.EncodingType.k4X: return "Quadrature Encoder" return "Encoder" def updateTable(self): table = self.getTable() if table is not None: table.putNumber("Speed", self.getRate()) table.putNumber("Distance", self.getDistance()) table.putNumber("Distance per Tick", self.distancePerPulse) def startLiveWindowMode(self): pass def stopLiveWindowMode(self): pass