MotorSafety.h

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// Copyright (c) FIRST and other WPILib contributors.
// Open Source Software; you can modify and/or share it under the terms of
// the WPILib BSD license file in the root directory of this project.
 
#pragma once
 
#include <string>
 
#include <units/time.h>
#include <wpi/mutex.h>
 
#include "frc/Timer.h"
 
namespace frc {
 
/**
 * The Motor Safety feature acts as a watchdog timer for an individual motor. It
 * operates by maintaining a timer that tracks how long it has been since the
 * feed() method has been called for that actuator. Code in the Driver Station
 * class initiates a comparison of these timers to the timeout values for any
 * actuator with safety enabled every 5 received packets (100ms nominal).
 *
 * The subclass should call Feed() whenever the motor value is updated.
 */
class MotorSafety {
 public:
  MotorSafety();
  virtual ~MotorSafety();
 
  MotorSafety(MotorSafety&& rhs);
  MotorSafety& operator=(MotorSafety&& rhs);
 
  /**
   * Feed the motor safety object.
   *
   * Resets the timer on this object that is used to do the timeouts.
   */
  void Feed();
 
  /**
   * Set the expiration time for the corresponding motor safety object.
   *
   * @param expirationTime The timeout value.
   */
  void SetExpiration(units::second_t expirationTime);
 
  /**
   * Retrieve the timeout value for the corresponding motor safety object.
   *
   * @return the timeout value.
   */
  units::second_t GetExpiration() const;
 
  /**
   * Determine if the motor is still operating or has timed out.
   *
   * @return true if the motor is still operating normally and hasn't timed out.
   */
  bool IsAlive() const;
 
  /**
   * 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.
   */
  void SetSafetyEnabled(bool enabled);
 
  /**
   * Return the state of the motor safety enabled flag.
   *
   * Return if the motor safety is currently enabled for this device.
   *
   * @return True if motor safety is enforced for this device.
   */
  bool IsSafetyEnabled() const;
 
  /**
   * 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.
   */
  void Check();
 
  /**
   * 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.
   */
  static void CheckMotors();
 
  virtual void StopMotor() = 0;
 
  /**
   * The return value from this method is printed out when an error occurs
   *
   * This method must not throw!
   */
  virtual std::string GetDescription() const = 0;
 
 private:
  static constexpr auto kDefaultSafetyExpiration = 100_ms;
 
  // The expiration time for this object
  units::second_t m_expiration = kDefaultSafetyExpiration;
 
  // True if motor safety is enabled for this motor
  bool m_enabled = false;
 
  // The FPGA clock value when the motor has expired
  units::second_t m_stopTime = Timer::GetFPGATimestamp();
 
  mutable wpi::mutex m_thisMutex;
};
 
}  // namespace frc