Software

This page details the design choices and implementation of all the software used in the completion of this project. In particular, the controller Framework consists of two main services. MallarCommunicationServices deals with the message handling to the boat, as well as the Drive and Refuel modes logic. Given that our refuel mechanism sends 5 refuel messages per action we implemented the switching between modes via software rather than hardware.

In driving mode the controller sends propulsion and shooting commands from the joysticks, and in refuel mode it sends the corresponding refueling command.

Given that we are using XBee modules to communicate via the Zigbee protocol between two PIC32s we decided to create two copies of the Framework4PIC32. One for the PIC32 on the boat called "boatFramework" and another for the PIC32 on the controller called "controllerFramework". This helped with organization of the events and services that each PIC32 is concerned about. For each framework their will be an overall description of the services used and the pseudo-code for them. All the detailed code can be found in the GitHub repository found in this link.

Controller:

Consists of two main serives. One that handles the main controller logic and actions based on inputs, sensors and information received over the XBee messages (MallardCommunicationService); and another for the fuel logic and display (FuelServoService). The main inputs are a potentiometer for selecting a boat to pair with, a limit switch for indicating refueling, two joystick presses digital inputs for pairing and shooting, and two analog joystick inputs to command throttle and direction.

Pseudo-code:

XBee Communications:

Following the communcations protocol, the main messages used on the boat have the following structure and logic.

Sending pairing message to boats:

0x7E - 0x00 - 0x09 (Length LSB) - 0x01 - 0x00 - (Destination MSB & LSB) - 0x01 (OptByte) - 0x02 (Status) - (MyController MSB & LSB) - 0x00 - CheckSum

Receiving pairing confirmation message from boat:

0x7E - 0x00 - 0x06 (Length LSB) - 0x81 - (Source MSB & LSB) - (RSSI Byte) - (OptByte) - 0xFF (ChargeVal) - CheckSum

Sending driving messages to boat:

0x7E - 0x00 - 0x09 (Length LSB) - 0x01 - 0x00 - (Destination MSB & LSB) - 0x01 (OptByte) - 0x00 (Driving) - (Joy1) - (Joy2) - (Digi)- CheckSum

Note: For our boat the we only use bit 1 of the "Digi" byte to represent shooting (1) or not shooting (0)

Sending charging message to boat:

0x7E - 0x00 - 0x09 (Length LSB) - 0x01 - 0x00 - (Destination MSB & LSB) - 0x01 (OptByte) - 0x01 (Charging) - 0x00 - 0x00 - 0x00 - CheckSum

Receiving charge value update messages from boat:

0x7E - 0x00 - 0x06 (Length LSB) - 0x81 - (Source MSB & LSB) - (RSSI Byte) - (OptByte) - ChargeVal - CheckSum

Event Checkers (Controller)

Event checkers for the pairing button, refuel input, and shooting button. Note that all these inputs are active low and passive floating, so we enable the internal pull-up functionality for all three inputs. I.e. CNPUBbits.CNPUB13 = 1; to enable the pull-up for pin in register RPB13.

/*** EVENT CHECKER: Pair Button RB15***/

Function Check4PairButton

set ReturnValue to false

set static variable Initialized to false

if (is Not Initialized)

// Disable analog, set input, set low

PAIR_BUTTON_ANSEL = 0; // digitial

PAIR_BUTTON_TRIS = 1; // input

PAIR_BUTTON_CNPU = 1; // enable internal pull-up

Initialized = true;

set static variable LastButtonState to 1(assumed not pressed)

read CurrentButtonState from button input pin

compare to static LastButtonState

if (CurrentButtonState is not equal to LastButtonState and CurrentButtonState is 0) // changed from high (passive) to low (active)

set ReturnValue to true

create new event

set event type to ES_START_PAIRING

post event to MallardCommunicationService

set ReturnValue to true

end if

update LastButtonState to CurrentButtonState

return ReturnValue

/*** EVENT CHECKER: Refuel Input RB12***/

Function Check4RefuelInput

set ReturnValue to false

set static variable Initialized to false

if (is Not Initialized)

// Disable analog, set input, set low

REFUEL_INPUT_ANSEL = 0; // digitial

REFUEL_INPUT_TRIS = 1; // input

REFUEL_INPUT_CNPU = 1; // enable internal pull-up

Initialized = true;

set static variable LastButtonState to 1(assumed not pressed)

read CurrentButtonState from button input pin

compare to static LastButtonState

if (CurrentButtonState is not equal to LastButtonState and CurrentButtonState is 0) // changed from high (passive) to low (active)

set ReturnValue to true

create new event

set event type to ES_REFUEL_INPUT

post event to MallardCommunicationService

set ReturnValue to true

end if

update LastButtonState to CurrentButtonState

return ReturnValue

/*** EVENT CHECKER: Shoot Button RB13***/

Function Check4ShootButton

set ReturnValue to false

set static variable Initialized to false

if (is Not Initialized)

// Disable analog, set input, set low

SHOOT_BUTTON_ANSEL = 0; // digitial

SHOOT_BUTTON_TRIS = 1; // input

SHOOT_BUTTON_CNPU = 1; // enable internal pull-up

Initialized = true;

set static variable LastButtonState to 1(assumed not pressed)

read CurrentButtonState from button input pin

compare to static LastButtonState

if (CurrentButtonState is not equal to LastButtonState and CurrentButtonState is 0) // changed from high (passive) to low (active)

set ReturnValue to true

create new event

set event type to ES_SHOOT

post event to MallardCommunicationService

set ReturnValue to true

end if

update LastButtonState to CurrentButtonState

return ReturnValue

MallardCommunicationService(Controller)

Handles wireless communication between the Mallard controller and Quackraft module over UART. It reads joystick, boat-selection potentiometer, and shoot/refuel inputs, handles pairing and connection monitoring, transmits status (pairing/driving/charging) messages to the selected boat, receives Charge Value updates, and forwards fuel information to FuelServoService.

Module-level variables: MyPriority, pairedStatus, desiredAddressLSB, ChargeVal, StatusVal, Joy1Val, Joy2Val, DigiVal, BoatPotVal, rxBuf[], txBuf[], ChargingBytesPending

/*------------------------------ Module Code ------------------------------*/

Function InitMallardCommunicationService(Priority)

set MyPriority to Priority

Print initialization message

Post ES_INIT event to this queue

Return true if the event posted successfully, false otherwise

Function PostMallardCommunicationService(ThisEvent)

Post event to this queue

Function RunMallardCommunicationService(ThisEvent)

Initialize ReturnEvent as ES_NO_EVENT

switch(ThisEvent.EventType)

case ES_INIT:

Initialize UART hardware

Configure ADC channels for:

Joystick 1

Joystick 2

Boat selection potentiometer

Configure pair button input

Configure status LEDs

Initialize variables:

desired boat address

pairing status

joystick midpoint

charge value

pending charge/shoot counters

break

case ES_START_PAIRING:

Read boat selection potentiometer

Determine desired boat address from potentiometer position

Set communication status to PAIRING

Start periodic transmit timer

break

case ES_TIMEOUT:

if SEND_MSG_TIMER expired

Read joystick and potentiometer values

Read shoot button state

Flash pairing LED if not paired

Send communication packet to boat

Restart SEND_MSG_TIMER

if UNPAIRING_TIMER expired

Set pairedStatus false

Turn off paired LED

Return to pairing mode

break

case ES_REFUEL_INPUT:

if paired // Only prepare refuel input commands when paired with a boat

Set communication status to CHARGING

Add charging messages to pending queue

break

case ES_RX_BYTE:

Assemble incoming UART message

When complete message received

Validate message

If valid

Interpret received message

break

default

break

return ReturnEvent

// Helper Functions

Function InitUART()

Configure UART2 for 9600 baud

Configure TX and RX pins

Enable transmitter and receiver

Enable UART RX interrupts

Enable global interrupts

Enable UART

// Using interrupts for receiving messages

Function UART_RX_ISR()

While UART receive buffer contains data

Read received byte

Post ES_RX_BYTE event containing received byte

Clear UART interrupt flag

Function ComputeCheckSum(DataLength)

Sum all bytes in data frame

Compute checksum as 0xFF minus sum

Store checksum in CheckSumVal

Function ReadADCValues()

Read joystick ADC channels

Convert readings to 8-bit values (the ADC values are 10-bits on the PIC32)

Read boat-selection potentiometer

Store values for transmission

Function ValidReceivedMessage()

Verify checksum

Verify:

Start byte

Length bytes

API identifier

Address fields

Return true if message is valid

Function InterpretMessage()

If not paired and valid pairing response received

Set pairedStatus true

Turn on paired LED

Change status to DRIVING

Start unpairing timeout timer

Post ES_PAIRED event

Else if already paired and valid message received

Restart unpairing timeout timer

Update ChargeVal from received packet

Post ES_FUEL_VAL_RECEIVED to FuelServoService

Function SendMsgToQuackraft(Status, Joy1, Joy2, Digi)

Construct communication packet

Insert:

Destination address

Current status

Joystick values

Shoot command

If charging mode

Send charging packet

Decrement pending charging count

Compute checksum

Append checksum

Transmit packet byte-by-byte through UART

FuelServoService (Controller)

Starts in neutral position and moves the corresponding fuel level received from a MallardCommunicationService event. Uses channel 4 with timer 2 on pin RPA2.

Module-level variables: MyPriority, ServoPosition, CurrentFuelVal

/*------------------------------ Module Code ------------------------------*/

Function InitFuelServoService(Priority)

set MyPriority to Priority

Initialize PWM for servo

Setup timer 2 with prescaler 64 and 6250 ticks for the required 50Hz

Setup channel 4 for this servo

Map RPA2 to this output

Set pulse width to neutral position

Initialize CurrentFuelVal to the maximum fuel value

Post ES_INIT event to this queue

Return true if the event posted successfully, false otherwise

Function PostFuelServoService(ThisEvent)

Post event to this queue

Function RunFuelServoService(ThisEvent)

Initialize ReturnEvent as ES_NO_EVENT

switch (ThisEvent.EventType)

case ES_FUEL_VAL_RECEIVED:

Set CurrentFuelVal to the param of this event

Clamp CurrentFuelVal between min and max fuel values in case of an invalid value

Map the CurrentFuelVal to the range of servo positions

Set the mapped value to ServoPosition

Set pulse width on channel 4 to corresponding calculated value

break;

return ReturnEvent

Libraries Used:

PIC32_PWM_Lib: Output compare library to set up timers, channels, modes, and mapping pins. Primary use is servo PWM.

See github for full source code on this link.

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