Driver Control Software

Overview

The objective of the driver input system is to wait on the events generated by the attached input devices and use those events to broadcast the relevant message to the correct subsystem. Since the events will, for the most part, be user-initiated, using interrupts is the ideal way to handle incoming events. A series of finite state machines will be used to monitor the current state of the vehicle based on the actions generated by each event.

Driver Inputs

IO Initialization

To simplify device setup, two separate modules have been created to take care of IO initialization for both digital and analog inputs. A configuration file has also been set up to define the addresses used for each device.

In addition, since the type of ISR needed to handle an input event will depend on whether the input is digital or analog, the responsibility for handling the events for particular device will fall onto either the digital or analog module, depending on the device.

Input Handling

Since input commands are to be made by the user, the events will be handled through the ISRs.

CAN Data Scheme

Until a sufficient protocol can be defined for sending driver input data over CAN, we will be using the following dummy scheme for the event data field:

Bits	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15
Contents	Device identifier				Device

the

Pin Assignments

Input Device	Pin	Type
Power	PC0	Digital
Gas Pedal	PA1	Analog
Mechanical Brake	PA2	Analog
Direction Selector Forward	PB2	Digital
Direction Selector Reverse	PB3	Digital
Cruise Control	PC4	Digital
Cruise Control Increase	PC5	Digital
Cruise Control Decrease	PC6	Digital
Turn Signal Right	PC7	Digital
Turn Signal Left	PC8	Digital
Hazard Light Switch	PC9	Digital

Finite State Machine

The program will be controlled through the use of multiple Finite State Machines to ensure that inputs are only serviced at the appropriate periods.

Within the state machines used in this system, there exist transitions that depend on the current states of other state machines. As a result, an event must be ok'd by all active FSMs before a transition can be made. This way, dependencies between different FSMs can be supported while keeping separate the implementations of each state machine.

Power State Machine:

Keeps track of the car's functional state.

State	Description	Transition
Off	The vehicle is off	Receiver POWER signal while in brake and neutral.
On	The vehicle is on	Receiver POWER signal while in the off state.

Pedal State Machine:

This state machine governs the running state of the car and defines the conditions under which the driver can turn on and move the vehicle. Transitions for this FSM depend on the state of the directional state machine.

State	Description	Transition
Brake	The car is on, but braking is active	Receive POWER signal while in the off state Receive GAS_BRAKE signal while in coast, drive, or cruise control
Coast	The gas pedal is pressed just enough to allow the car to coast.	Receive GAS_COAST signal while in the brake or drive state
Drive	The brakes are engaged and the car is not moving	Receive GAS_DRIVE while in the coast state or brake state (Direction state must be in either forward or reverse)
Cruise Control	The car is currently in cruise control mode	Receive CRUISE_CONTROL_ON while in coast or drive

Directional State Machine

This state machine governs the possible gear shifts made by the user. Transitions in the pedal state machine depend on the current state of this FSM.

State	Description	Transition
Neutral	The vehicle is in neutral gear	Receive DIRECTION_SELECTOR_NEUTRAL signal while the Pedal FSM is in the brake state
Forward	The vehicle is in forward gear	Receive DIRECTION_SELECTOR_FORWARD signal while the Pedal FSM is in the brake state
Reverse	The vehicle is in reverse	Receive DIRECTION_SELECTOR_REVERSE signal while the Pedal FSM is in the brake state

Turn Signal State Machine

This state machine governs the states of the turn signals made by the driver. Independent from the other FSMs.

State	Description	Transition
No signal	The car is currently not signalling	Receive TURN_SIGNAL_NONE signal while either signal is active
Left signal	The car has the left signal active	Receive TURN_SIGNAL_LEFT signal while the left signal is inactive
Right signal	The car has the left signal active	Receive TURN_SIGNAL_RIGHT signal while the right signal is inactive

Hazard Light State Machine

State	Description	Transition
Hazard Light On	Hazard lights are currently active	Receive HAZARD_LIGHT_ON signal while hazard lights are off
Hazard Light Off	Hazard lights are currently inactive	Receive HAZARD_LIGHT_OFF signal while hazard lights are on

Possible State Transition Solutions

Combine pedal state and direction state into one FSM

This option will eliminate the FSM interdependence as well as allow for the elimination of the state IDs. However, the resulting FSMs would become much more complex, and there may exist better solutions.

Use boolean array to record active states

Would eliminate FSM dependencies and state IDs and allow us to refer to the array to observe the needed states. However, it would make changes could become difficult to make. Also, the boolean would need to be globally exposed for modification by the FSMs

Give each state a list of forbidden events

Each state's output function will take an event ID as an input and return true if the event ID does not appear in a given list of forbidden IDs. Once an event has been popped from the event queue, all FSMs will run this function. All results must be true for the event to be processed.

This solution would eliminate the dependencies between FSMs, as well as the need for state IDs. Additionally, this list of forbidden id would be private to each state, meaning that changing this list would be very easy to do without alterations to any other part of the program.

Additionally, it may be useful to have the FSMs stored in an array rather than in the fsm_group struct. This will allow us to iterate through the active fsms and make it easier to do operations on multiple ones at once.