Software

This page details the design choices and implementation of all the software used in the completion of this project. In particular, the boatFramework consists of four main services.

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.

Pseudo-code:

XBee Communications:

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

Receiving pairing message from mallard modules and pair:

0x7E - 0x00 - 0x09 (Length LSB) - 0x81 - 0x21 (MyAddress) - (SourceMSB & LSB) - (RSSI Byte) - (OptByte) - 0x02 (Status) - (SourceMSB) - (SourceLSB) - 0x00 - CheckSum

Responding with fuel status (ChargeVal is 0xFF before pairing and the calculated charge value after):

0x7E - 0x00 - 0x06 (Length LSB) - 0x01 - 0x00 - (DestinationMSB & LSB) - 0x01 (OptByte) - ChargeVal - CheckSum

CommunicationService (Boat)

Handles wireless communication between the Quackraft and the Mallard controller module over UART. It receives and validates command packets, manages controller pairing and connection timeouts, forwards driving and cannon-control commands to the appropriate services, and tracks the boat’s charge/fuel state. It also sends status updates, including the current charge level, back to the controller.

Module-level variables: MyPriority, pairedStatus, pairedAddressLSB, ChargeVal, InitializeFuel, rxBuf[], txBuf[], receivedByte, CheckSumVal, newMessageStarted

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

Function InitCommunicationServiceService(Priority)

Set MyPriority to Priority

Print initialization messages

Post ES_INIT event to this queue

Return true if successful, false otherwise

Function PostCommunicationServiceService(ThisEvent)

Post event to this queue

Function RunCommunicationServiceService(ThisEvent)

Initialize ReturnEvent as ES_NO_EVENT

switch (ThisEvent.EventType)

case ES_INIT:

Initialize UART hardware

Enable UART receive interrupts

break

case ES_TIMEOUT:

if(EventParam is UNPAIRING_TIMER)

Set pairedStatus to false

Post ES_UNPAIRED to PairedServoService

Post ES_UNPAIRED to DrivingService

break

case ES_RX_BYTE:

if(received byte is START_BYTE)

Clear receive buffer

Begin assembling a new message

Store START_BYTE

else if(new message is being assembled)

Shift receive buffer

Add newest byte

if(receive buffer contains complete message)

Validate checksum and packet fields

if(message is valid)

Interpret message contents

Send response packet containing current ChargeVal

Stop assembling current message

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

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 ValidReceivedMessage()

Compute expected checksum

If checksum does not match

Return false

Verify:

Start byte

Length bytes

API identifier

Destination address

Return true if all fields are valid

Function InterpretMessage()

// Pairing request

If not paired and received pairing message

Save controller address

Set pairedStatus true

Start UNPAIRING_TIMER

Reset ChargeVal

Enable fuel initialization

Post ES_PAIRED to PairedServoService

// Messages from paired controller

Else if paired and source address matches

If charging message

Restart UNPAIRING_TIMER

Increase ChargeVal by 8

Limit ChargeVal to maximum value

Post ES_CHARGING

Else if driving message

If first drive message after pairing

Initialize ChargeVal to full

Clear initialization flag

Restart UNPAIRING_TIMER

Extract:

Throttle joystick value

Steering joystick value

Digital shoot command

If ChargeVal is zero

Force throttle to neutral

Force steering to neutral

Post ES_CANNON_STOP

Else

If boat is moving

Decrease ChargeVal

If shoot button pressed

Decrease ChargeVal

Post ES_CANNON_START

Else

Post ES_CANNON_STOP

Combine steering and throttle values

Post ES_DRIVE to DrivingService

Function SendMsgToMallardModule(Charge)

Construct transmit packet:

Start byte

Length bytes

API fields

Paired controller address

Current Charge value

Compute checksum

Append checksum

Transmit packet byte-by-byte through UART

DrivingService (Boat)

This service uses Timer 2 with Output Compares 2 and 3 for the left and right DC motors on the drive train, respectively.

Module-level variables: MyPriority

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

Function InitDCMotorService(Priority)

set MyPriority to Priority

Initialize OCs 2 and 3 on timer 2 using our PIC32_PWM_Lib calls:

configure timer, set channel, assign channel to timer, map channeltoOutputPin,

Initialize analog, digital, output for all the motor pins

Set the dutyCycle in both motors to 0, to ensure they start off

Post ES_INIT event to this queue

Return true if the event posted successfully, false otherwise

Function PostDCMotorService(ThisEvent)

Post event to this queue

Function RunDCMotorService(ThisEvent)

Initialize ReturnEvent as ES_NO_EVENT

switch (ThisEvent.EventType)

case ES_INIT:

// Do nothing, announce

break;

case ES_MOTORS_OFF:

// Stop the robot, set duty cycle to 0.

break;

case ES_MOTOR_PRIMITIVE:

Execute primitive according to ThisEvent.EventParam

(Function that maps forwards, backwards, rotateCW, etc. with corresponding duty cycles)

For primitives that use line following or encoder counts, post corresponding events to DriveCorrectionService to start that functionality

break;

return ReturnEvent

BoatActionService (Boat)

This service uses Timer 2 with Output Compares 2 and 3 for the left and right DC motors on the drive train, respectively.

Module-level variables: MyPriority

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

Function InitDCMotorService(Priority)

set MyPriority to Priority

Initialize OCs 2 and 3 on timer 2 using our PIC32_PWM_Lib calls:

configure timer, set channel, assign channel to timer, map channeltoOutputPin,

Initialize analog, digital, output for all the motor pins

Set the dutyCycle in both motors to 0, to ensure they start off

Post ES_INIT event to this queue

Return true if the event posted successfully, false otherwise

Function PostDCMotorService(ThisEvent)

Post event to this queue

Function RunDCMotorService(ThisEvent)

Initialize ReturnEvent as ES_NO_EVENT

switch (ThisEvent.EventType)

case ES_INIT:

// Do nothing, announce

break;

case ES_MOTORS_OFF:

// Stop the robot, set duty cycle to 0.

break;

case ES_MOTOR_PRIMITIVE:

Execute primitive according to ThisEvent.EventParam

(Function that maps forwards, backwards, rotateCW, etc. with corresponding duty cycles)

For primitives that use line following or encoder counts, post corresponding events to DriveCorrectionService to start that functionality

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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