Ford: parse ACC gap toggle button

Use the ACC gap toggle button signal from the SCCM. There are two other
signals for "increase" and "decrease" gap buttons, but no supported car
has these buttons.

selfdrive/car/ford/carstate.py

@@ -19,6 +19,9 @@ def __init__(self, CP):
 
     self.vehicle_sensors_valid = False
 
+    self.prev_distance_button = 0
+    self.distance_button = 0
+
   def update(self, cp, cp_cam):
     ret = car.CarState.new_message()
 
@@ -83,6 +86,8 @@ def update(self, cp, cp_cam):
     ret.rightBlinker = cp.vl["Steering_Data_FD1"]["TurnLghtSwtch_D_Stat"] == 2
     # TODO: block this going to the camera otherwise it will enable stock TJA
     ret.genericToggle = bool(cp.vl["Steering_Data_FD1"]["TjaButtnOnOffPress"])
+    self.prev_distance_button = self.distance_button
+    self.distance_button = cp.vl["Steering_Data_FD1"]["AccButtnGapTogglePress"]
 
     # lock info
     ret.doorOpen = any([cp.vl["BodyInfo_3_FD1"]["DrStatDrv_B_Actl"], cp.vl["BodyInfo_3_FD1"]["DrStatPsngr_B_Actl"],

selfdrive/car/ford/interface.py

@@ -1,11 +1,12 @@
 from cereal import car
 from panda import Panda
 from openpilot.common.conversions import Conversions as CV
-from openpilot.selfdrive.car import get_safety_config
+from openpilot.selfdrive.car import create_button_events, get_safety_config
 from openpilot.selfdrive.car.ford.fordcan import CanBus
 from openpilot.selfdrive.car.ford.values import Ecu, FordFlags
 from openpilot.selfdrive.car.interfaces import CarInterfaceBase
 
+ButtonType = car.CarState.ButtonEvent.Type
 TransmissionType = car.CarParams.TransmissionType
 GearShifter = car.CarState.GearShifter
 
@@ -61,6 +62,8 @@ def _get_params(ret, candidate, fingerprint, car_fw, experimental_long, docs):
   def _update(self, c):
     ret = self.CS.update(self.cp, self.cp_cam)
 
+    ret.buttonEvents = create_button_events(self.CS.distance_button, self.CS.prev_distance_button, {1: ButtonType.gapAdjustCruise})
+
     events = self.create_common_events(ret, extra_gears=[GearShifter.manumatic])
     if not self.CS.vehicle_sensors_valid:
       events.add(car.CarEvent.EventName.vehicleSensorsInvalid)