# validated: 2017-12-25 TW d36d72bd4fe9 edu/wpi/first/wpilibj/MotorSafety.java edu/wpi/first/wpilibj/MotorSafetyHelper.java
# ----------------------------------------------------------------------------
# Copyright (c) 2008-2017 FIRST. 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 logging
import threading
import weakref
from .robotstate import RobotState
from .timer import Timer
logger = logging.getLogger(__name__)
__all__ = ["MotorSafety"]
[docs]class MotorSafety:
"""Provides mechanisms to safely shutdown motors if they aren't updated
often enough.
The MotorSafety object is constructed for every object that wants to
implement the Motor Safety protocol. The helper object has the code to
actually do the timing and call the motors stop() method when the timeout
expires. The motor object is expected to call the feed() method whenever
the motors value is updated.
.. robotpy-specific: In the Java implementation this is MotorSafetyHelper
"""
DEFAULT_SAFETY_EXPIRATION = 0.1
helpers = weakref.WeakSet()
helpers_lock = threading.Lock()
@staticmethod
def _reset():
with MotorSafety.helpers_lock:
MotorSafety.helpers.clear()
def __init__(self):
"""The constructor for a MotorSafety object.
The helper object is constructed for every object that wants to
implement the Motor Safety protocol. The helper object has the code
to actually do the timing and call the motors stop() method when the
timeout expires. The motor object is expected to call the feed()
method whenever the motors value is updated.
"""
self.safetyEnabled = False
self.safetyExpiration = MotorSafety.DEFAULT_SAFETY_EXPIRATION
self.safetyStopTime = Timer.getFPGATimestamp()
self.mutex = threading.Lock()
with MotorSafety.helpers_lock:
MotorSafety.helpers.add(self)
[docs] def feed(self):
"""Feed the motor safety object.
Resets the timer on this object that is used to do the timeouts.
"""
with self.mutex:
self.safetyStopTime = Timer.getFPGATimestamp() + self.safetyExpiration
[docs] def setExpiration(self, expirationTime):
"""Set the expiration time for the corresponding motor safety object.
:param expirationTime: The timeout value in seconds.
:type expirationTime: float
"""
with self.mutex:
self.safetyExpiration = expirationTime
[docs] def getExpiration(self):
"""Retrieve the timeout value for the corresponding motor safety
object.
:returns: the timeout value in seconds.
:rtype: float
"""
with self.mutex:
return self.safetyExpiration
[docs] def isAlive(self):
"""Determine of the motor is still operating or has timed out.
:returns: True if the motor is still operating normally and hasn't
timed out.
:rtype: float
"""
with self.mutex:
return not self.safetyEnabled or self.safetyStopTime > Timer.getFPGATimestamp()
[docs] def check(self):
"""Check if this motor has exceeded its timeout.
This method is called periodically to determine if this motor has
exceeded its timeout value. If it has, the stop method is called,
and the motor is shut down until its value is updated again.
"""
with self.mutex:
enabled = self.safetyEnabled
stopTime = self.safetyStopTime
if not enabled or RobotState.isDisabled() or RobotState.isTest():
return
if stopTime < Timer.getFPGATimestamp():
logger.warning("%s... Output not updated often enough." %
self.getDescription())
self.stopMotor()
[docs] def setSafetyEnabled(self, enabled):
"""Enable/disable motor safety for this device.
Turn on and off the motor safety option for this PWM object.
:param enabled: True if motor safety is enforced for this object
:type enabled: bool
"""
with self.mutex:
self.safetyEnabled = bool(enabled)
[docs] def isSafetyEnabled(self):
"""Return the state of the motor safety enabled flag.
Return if the motor safety is currently enabled for this device.
:returns: True if motor safety is enforced for this device
:rtype: bool
"""
with self.mutex:
return self.safetyEnabled
[docs] @staticmethod
def checkMotors():
"""Check the motors to see if any have timed out.
This static method is called periodically to poll all the motors and
stop any that have timed out.
"""
with MotorSafety.helpers_lock:
for msh in MotorSafety.helpers:
msh.check()