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Overview
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. However, since the current FSM API does not provide a way to view the current state outside of string comparisons, a wrapper struct will be used to hold both the FSMs as well as their current states. In addition, the code defining each FSM has been split up, which will make it easier to add new FSMs in the future if needed. As of now, the driver input system is controlled by four FSMs.
Power State Machine:
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- Receiver POWER signal while in brake and neutral.
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- 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.
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Off
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- Receiver POWER_OFF signal while in brake and neutral.
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Brake
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- Receive POWER_ON signal while in the off state
- Receive GAS_BRAKE signal while in coast, drive, or cruise control
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Coast
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- Receive GAS_COAST signal while in the brake or drive state
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- Receive GAS_DRIVE while in the coast state or brake state (Direction state must be in either forward or reverse)
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- 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.
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- Receive DIRECTION_SELECTOR_NEUTRAL signal while the Pedal FSM is in the brake state
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- Receive DIRECTION_SELECTOR_FORWARD signal while the Pedal FSM is in the brake state
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- Receive DIRECTION_SELECTOR_REVERSE signal while the Pedal FSM is in the brake state
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Turn Signal State Machine
This state machine governs the states of the turn signals made by the driver. Independent from the other FSMs.
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- Receive TURN_SIGNAL_NONE signal while either signal is active
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- Receive TURN_SIGNAL_LEFT signal while the left signal is inactive
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- Receive TURN_SIGNAL_RIGHT signal while the right signal is inactive
Hazard Light State Machine
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Hazard lights are currently active
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- Receive HAZARD_LIGHT_ON signal while hazard lights are off
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- Receive HAZARD_LIGHT_OFF signal while hazard lights are on
Possible State Transition Solutions
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Combine pedal state and direction state into one FSM
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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.
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Use boolean array to record active states
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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
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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.
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SMT32F0 Interrupts
Interrupts on the SMT32 are managed by the extended interrupts and events controller (EXTI), which allows for the management of up to 32 different interrupt lines (23 external and 9 internal). Each line can have both its active edge and interrupt priority programmed independently.
In order to generate an interrupt for an external line, the line must be configured. To do this, the bit in the interrupt mask register (EXTI_IMR) corresponding to the interrupt line must be set to '1', along with the corresponding bits in the desired edge trigger registers (Should an interrupt be triggered on a high-to-low or low-to-high change?), which are EXTI_RTSR and EXTI_FTSR for rising and falling edges respectively. Once this is done, an interrupt request will be generated once the selected edge appears on the external interrupt line and the pending bit corresponding to said interrupt line will be set. The STM32 will clear this bit automatically once the ISR concludes.
The STM32 has the first 16 external interrupt lines set aside for the GPIOs, meaning that there are only 16 digital interrupts available for use on the STM32. The GPIOs are mapped to the external interrupt lines as follows:
This means that only one port can have have an interrupt enabled for a given pin number at a time. For instance, enabling interrupt on PA0 will preclude the enabling of interrupts for pin 0 of any other port.
Pin Assignments
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Handling Inputs
The driver control inputs will be connected to onboard GPIOs. As we are only concerned with handling each input as they are triggered, most of the inputs will be set to be handled through the use of a common ISR. The ISR will then look at the debounced state of the triggering input device and raise the proper event in the event queue. The event queue will then be used to send the necessary messages over CAN and I2C.objective for the driver controls firmware is to create a robust system capable of both properly keeping track of the state of the vehicle when responding to user inputs, as well as being able to send out the correct messages to other subsystems of the car.
The driver controls system works by waiting for the user to take an action such as a button press, which will then be used to construct an event to push to a global queue. When the event is ready to be raised from this queue, the system observes the current state of the car to determine whether the event is safe to be processed at the current time. If an event is raised at an unsafe time (i.e. flooring it while in neutral), then the event will be discarded.
To monitor the current state of the car, a series of Finite State Machines is used to monitor each input device. The different states of each FSM have a corresponding check function, which can be used to approve or decline an event according to it's current state. An event arbiter module is then used to run the check functions of all active FSMs, and the event is only processed if they all determine the event to be safe to run.
Once a given event is processed, the FSMs change state to reflect the event. A CAN message is then sent to the relevant subsystem based on the data held in the event.
Sequence Diagram
