text: #!/usr/bin/env python3
  from cereal import car
  from math import fabs
  
  from common.conversions import Conversions as CV
  from selfdrive.car import STD_CARGO_KG, scale_rot_inertia, scale_tire_stiffness, gen_empty_fingerprint, get_safety_config
  from selfdrive.car.gm.values import CAR, CruiseButtons, \
                                      AccState, CarControllerParams
  from selfdrive.car.interfaces import CarInterfaceBase
  
  ButtonType = car.CarState.ButtonEvent.Type
  EventName = car.CarEvent.EventName
  
  class CarInterface(CarInterfaceBase):
    @staticmethod
    def get_pid_accel_limits(CP, current_speed, cruise_speed):
      params = CarControllerParams()
      return params.ACCEL_MIN, params.ACCEL_MAX
  
    # Determined by iteratively plotting and minimizing error for f(angle, speed) = steer.
    @staticmethod
    def get_steer_feedforward_volt(desired_angle, v_ego):
      desired_angle *= 0.02904609
      sigmoid = desired_angle / (1 + fabs(desired_angle))
      return 0.10006696 * sigmoid * (v_ego + 3.12485927)
  
    @staticmethod
    def get_steer_feedforward_acadia(desired_angle, v_ego):
      desired_angle *= 0.09760208
      sigmoid = desired_angle / (1 + fabs(desired_angle))
      return 0.04689655 * sigmoid * (v_ego + 10.028217)
  
    def get_steer_feedforward_function(self):
      if self.CP.carFingerprint == CAR.VOLT:
        return self.get_steer_feedforward_volt
      elif self.CP.carFingerprint == CAR.ACADIA:
        return self.get_steer_feedforward_acadia
      else:
        return CarInterfaceBase.get_steer_feedforward_default
  
    @staticmethod
    def get_params(candidate, fingerprint=gen_empty_fingerprint(), car_fw=None, disable_radar=False):
      ret = CarInterfaceBase.get_std_params(candidate, fingerprint)
      ret.carName = "gm"
      ret.safetyConfigs = [get_safety_config(car.CarParams.SafetyModel.gm)]
      ret.pcmCruise = False  # stock cruise control is kept off
  
      # These cars have been put into dashcam only due to both a lack of users and test coverage.
      # These cars likely still work fine. Once a user confirms each car works and a test route is
      # added to selfdrive/car/tests/routes.py, we can remove it from this list.
      ret.dashcamOnly = candidate in {CAR.CADILLAC_ATS, CAR.HOLDEN_ASTRA, CAR.MALIBU, CAR.BUICK_REGAL}
  
      # Presence of a camera on the object bus is ok.
      # Have to go to read_only if ASCM is online (ACC-enabled cars),
      # or camera is on powertrain bus (LKA cars without ACC).
      ret.openpilotLongitudinalControl = True
      tire_stiffness_factor = 0.444  # not optimized yet
  
      # Start with a baseline lateral tuning for all GM vehicles. Override tuning as needed in each model section below.
      ret.minSteerSpeed = 7 * CV.MPH_TO_MS
      ret.lateralTuning.pid.kiBP, ret.lateralTuning.pid.kpBP = [[0.], [0.]]
      ret.lateralTuning.pid.kpV, ret.lateralTuning.pid.kiV = [[0.2], [0.00]]
      ret.lateralTuning.pid.kf = 0.00004   # full torque for 20 deg at 80mph means 0.00007818594
      ret.steerRateCost = 1.0
      ret.steerActuatorDelay = 0.1  # Default delay, not measured yet
  
      if candidate == CAR.VOLT:
        # supports stop and go, but initial engage must be above 18mph (which include conservatism)
        ret.minEnableSpeed = 18 * CV.MPH_TO_MS
        ret.mass = 1607. + STD_CARGO_KG
        ret.wheelbase = 2.69
        ret.steerRatio = 17.7  # Stock 15.7, LiveParameters
        tire_stiffness_factor = 0.469 # Stock Michelin Energy Saver A/S, LiveParameters
        ret.steerRatioRear = 0.
        ret.centerToFront = ret.wheelbase * 0.45 # Volt Gen 1, TODO corner weigh
  
        ret.lateralTuning.pid.kpBP = [0., 40.]
        ret.lateralTuning.pid.kpV = [0., 0.17]
        ret.lateralTuning.pid.kiBP = [0.]
        ret.lateralTuning.pid.kiV = [0.]
        ret.lateralTuning.pid.kf = 1. # get_steer_feedforward_volt()
        ret.steerActuatorDelay = 0.2
  
      elif candidate == CAR.MALIBU:
        # supports stop and go, but initial engage must be above 18mph (which include conservatism)
        ret.minEnableSpeed = 18 * CV.MPH_TO_MS
        ret.mass = 1496. + STD_CARGO_KG
        ret.wheelbase = 2.83
        ret.steerRatio = 15.8
        ret.steerRatioRear = 0.
        ret.centerToFront = ret.wheelbase * 0.4  # wild guess
  
      elif candidate == CAR.HOLDEN_ASTRA:
        ret.mass = 1363. + STD_CARGO_KG
        ret.wheelbase = 2.662
        # Remaining parameters copied from Volt for now
        ret.centerToFront = ret.wheelbase * 0.4
        ret.minEnableSpeed = 18 * CV.MPH_TO_MS
        ret.steerRatio = 15.7
        ret.steerRatioRear = 0.
  
      elif candidate == CAR.ACADIA:
        ret.minEnableSpeed = -1.  # engage speed is decided by pcm
        ret.mass = 4353. * CV.LB_TO_KG + STD_CARGO_KG
        ret.wheelbase = 2.86
        ret.steerRatio = 14.4  # end to end is 13.46
        ret.steerRatioRear = 0.
        ret.centerToFront = ret.wheelbase * 0.4
        ret.lateralTuning.pid.kf = 1. # get_steer_feedforward_acadia()
  
      elif candidate == CAR.BUICK_REGAL:
        ret.minEnableSpeed = 18 * CV.MPH_TO_MS
        ret.mass = 3779. * CV.LB_TO_KG + STD_CARGO_KG  # (3849+3708)/2
        ret.wheelbase = 2.83  # 111.4 inches in meters
        ret.steerRatio = 14.4  # guess for tourx
        ret.steerRatioRear = 0.
        ret.centerToFront = ret.wheelbase * 0.4  # guess for tourx
  
      elif candidate == CAR.CADILLAC_ATS:
        ret.minEnableSpeed = 18 * CV.MPH_TO_MS
        ret.mass = 1601. + STD_CARGO_KG
        ret.wheelbase = 2.78
        ret.steerRatio = 15.3
        ret.steerRatioRear = 0.
        ret.centerToFront = ret.wheelbase * 0.49
  
      elif candidate == CAR.ESCALADE_ESV:
        ret.minEnableSpeed = -1.  # engage speed is decided by pcm
        ret.mass = 2739. + STD_CARGO_KG
        ret.wheelbase = 3.302
        ret.steerRatio = 17.3
        ret.centerToFront = ret.wheelbase * 0.49
        ret.lateralTuning.pid.kiBP, ret.lateralTuning.pid.kpBP = [[10., 41.0], [10., 41.0]]
        ret.lateralTuning.pid.kpV, ret.lateralTuning.pid.kiV = [[0.13, 0.24], [0.01, 0.02]]
        ret.lateralTuning.pid.kf = 0.000045
        tire_stiffness_factor = 1.0
  
      # TODO: get actual value, for now starting with reasonable value for
      # civic and scaling by mass and wheelbase
      ret.rotationalInertia = scale_rot_inertia(ret.mass, ret.wheelbase)
  
      # TODO: start from empirically derived lateral slip stiffness for the civic and scale by
      # mass and CG position, so all cars will have approximately similar dyn behaviors
      ret.tireStiffnessFront, ret.tireStiffnessRear = scale_tire_stiffness(ret.mass, ret.wheelbase, ret.centerToFront,
                                                                           tire_stiffness_factor=tire_stiffness_factor)
  
      ret.longitudinalTuning.kpBP = [5., 35.]
      ret.longitudinalTuning.kpV = [2.4, 1.5]
      ret.longitudinalTuning.kiBP = [0.]
      ret.longitudinalTuning.kiV = [0.36]
  
      ret.steerLimitTimer = 0.4
      ret.radarTimeStep = 0.0667  # GM radar runs at 15Hz instead of standard 20Hz
  
      return ret
  
    # returns a car.CarState
    def update(self, c, can_strings):
      self.cp.update_strings(can_strings)
      self.cp_loopback.update_strings(can_strings)
  
      ret = self.CS.update(self.cp, self.cp_loopback)
  
      ret.canValid = self.cp.can_valid and self.cp_loopback.can_valid
      ret.steeringRateLimited = self.CC.steer_rate_limited if self.CC is not None else False
  
      buttonEvents = []
  
      if self.CS.cruise_buttons != self.CS.prev_cruise_buttons and self.CS.prev_cruise_buttons != CruiseButtons.INIT:
        be = car.CarState.ButtonEvent.new_message()
        be.type = ButtonType.unknown
        if self.CS.cruise_buttons != CruiseButtons.UNPRESS:
          be.pressed = True
          but = self.CS.cruise_buttons
        else:
          be.pressed = False
          but = self.CS.prev_cruise_buttons
        if but == CruiseButtons.RES_ACCEL:
          if not (ret.cruiseState.enabled and ret.standstill):
            be.type = ButtonType.accelCruise  # Suppress resume button if we're resuming from stop so we don't adjust speed.
        elif but == CruiseButtons.DECEL_SET:
          be.type = ButtonType.decelCruise
        elif but == CruiseButtons.CANCEL:
          be.type = ButtonType.cancel
        elif but == CruiseButtons.MAIN:
          be.type = ButtonType.altButton3
        buttonEvents.append(be)
  
      ret.buttonEvents = buttonEvents
  
      events = self.create_common_events(ret, pcm_enable=False)
  
      if ret.vEgo < self.CP.minEnableSpeed:
        events.add(EventName.belowEngageSpeed)
      if ret.cruiseState.standstill:
        events.add(EventName.resumeRequired)
      if self.CS.pcm_acc_status == AccState.FAULTED:
        events.add(EventName.accFaulted)
      if ret.vEgo < self.CP.minSteerSpeed:
        events.add(car.CarEvent.EventName.belowSteerSpeed)
  
      # handle button presses
      for b in ret.buttonEvents:
        # do enable on both accel and decel buttons
        if b.type in (ButtonType.accelCruise, ButtonType.decelCruise) and not b.pressed:
          events.add(EventName.buttonEnable)
        # do disable on button down
        if b.type == ButtonType.cancel and b.pressed:
          events.add(EventName.buttonCancel)
  
      ret.events = events.to_msg()
  
      # copy back carState packet to CS
      self.CS.out = ret.as_reader()
  
      return self.CS.out
  
    def apply(self, c):
      ret = self.CC.update(c, self.CS)
      return ret
  