Overview
The objective of the driver input system is to wait on the actions taken by the user and use those events to broadcast the relevant message to the correct device.
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 |
|
| On | The vehicle is on |
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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 |
|
Coast | The gas pedal is pressed just enough to allow the car to coast. |
|
| Drive | The brakes are engaged and the car is not moving |
|
| Cruise Control | The car is currently in cruise control mode |
|
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 |
|
| Forward | The vehicle is in forward gear |
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| Reverse | The vehicle is in reverse |
|
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 |
|
| Left signal | The car has the left signal active |
|
| Right signal | The car has the left signal active |
|
Hazard Light State Machine
| State | Description | Transition |
|---|---|---|
| Hazard Light On | Hazard lights are currently active |
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| Hazard Light Off | Hazard lights are currently inactive |
|
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.
Driver Inputs
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
| Input Device | Pin |
|---|---|
| Power | PC0 |
| Gas Pedal | PC1 |
| Direction Selector | PC2 - PC3 |
| Cruise Control | PC4 |
| Cruise Control Increase | PC5 |
| Cruise Control Decrease | PC6 |
| Turn Signal | PC7 - PC8 |
| Hazard Light Switch | PC9 |
| Hazard Light | PC10 |
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.
The prototype of the system used a switch statement to determine the correct event to raise. However, given the amount of inputs that the system will need to serve in the future, using individual callbacks may