Pseudocode for FARMERTXmitSM.c

Transmits data packets from the controller (FARMER) to the hovercraft (DOG)
	 via UART.



InitFARMERTXmitSM
	Save the priority of this service
	Initialize into the first state, WaitingToSendFirstByte
 	Post the initial transiti	on event
end of InitFARMERTXmitSM


RunFARMERTXmitSM

	switch on the CurrentState
		case WaitingToSendFirstByte state       
			if the event type is ES_BEGIN_TXMIT
				Save the event param that describes the packet type
       		    If constructing the packet of specified type is successful
					Reset the index of number of bytes sent
					Set CurrentState to SendingAPacket
					call helper function to begin transmitting
				else
					constructing packet failed, do nothing
				end if
			end if
      		break
				 
    	case SendingAPacket state
			if the event type is ES_ALL_BYTES_SENT
				Set CurrentState to WaitingToSendFirstByte
			else if event type is ES_LOST_CONNECTION
				Set CurrentState to WaitingToSendFirstByte
			end if
			break
	end switch on Current State
  return ReturnEvent
end RunFARMERTXmitSM


FARMERTXmitISR

	(Only respond to the interrupt that we care about: TXMIS)
	If transmit interrupts are unmasked and it fired
		Clear UART TXmit interrupt by setting TXIC in UARTICR (interrupt clear register)
		
		if we have sent all of the bytes
			Disable UART TXmit interrupt by clearing interrupt mask bit in UART mask reg
			Post ES_ALL_BYTES_SENT to TXmitSM
		else (we are not done sending bytes yet)
			Write the new data to data register UARTDR
			Increment BytesSentIndex
		end if
	else
		(TXMIS is not set, meaning it's not a transmit interrupt, so take no action)
	end if 
end FARMERTXmitISR




ConstructPacket
	Constructs the packet that will be sent by filling out the
	TxPacket array with appropriate data
 
 	If PacketType is REQ_2_PAIR
		Set PacketSize accordingly
		Set FrameDataSize accordingly
		Set destination address to 'Broadcast', because it's a request to pair
		Create XBee header
		Fill out RF data of TxPacket, not encrypted.
		Get number of DOG to pair with from the FARMER's pair selector (DOG selector) mechanism
		SetXBeeChecksum
		Return true because packet was created successfully
	else if PacketType is ENCR_KEY
		Set PacketSize accordingly
		Set FrameDataSize accordingly
		Get destination address from RX service 
		Create XBee header
		Create the encryption key so that you have something to send
		Using the encryption key generated, fill out the RF data of this packet
		Create an index variable to track RF data byte that's being set to an encr byte
		start the 'for' loop at RF data start +1 because of the PacketType bit that's first
		looping over the encryption key that was sent in the RF Data, save each to TxPacket
		SetXBeeChecksum
		Reset the encryption index because it's a new pairing
		Return true because packet was created successfully
	else if PacketType is CTRL
		Set PacketSize accordingly
		Set FrameDataSize accordingly
		Get destination address from RX service
		Create XBee header
		Get Fwd/Back data from TiltService
		Get Left/Right data from TiltService
		Get Peripheral status and Brake status
		Fill out RF data of TxPacket, WITH ENCRYPTION
		TxPacket @ header location equals PacketType XOR'ed with EncryptKey @ encryption index
		Increment encryption index
		TxPacket @ header location+1 equals FwdRevCtrl XOR'ed with EncryptKey @ encryption index
		Increment encryption index
		TxPacket @ header location+2 equals LeftRightCtrl XOR'ed with EncryptKey @ encryption index
		Increment encryption index
		TxPacket @ header location+3 equals DigitalCtrl XOR'ed with EncryptKey @ encryption index
		Increment encryption index
	
		SetXBeeChecksum
		Return true because packet was created successfully
	else 
		bad packet type, packet was not created. return false
	end if
end ConstructPacket


CreateXBeeHeader
	Creates the header, which is all the bytes before the RF data
	
	TxPacket[0] equals 0x7E 
	TxPacket[1] equals length of MSB which is 0x00
	TxPacket[2] equals length of LSB
	TxPacket[3] equals API_ID for a transmit request
	TxPacket[4] equals FRAME_ID which is arbitrary, not specified in comm protocol
	TxPacket[5] equals Destination Address MSB
	TxPacket[6] equals Destination Address LSB
	TxPacket[7] equals OPTIONS, which in our case is 0x00
end CreateXBeeHeader



SetXBeeChecksum

	Calculates checksum and puts that value in last byte of TxPacket[]
	
	for each byte in the framing data
		Add current TxPacket to the sum
	end for loop
	Calculate XBeeChecksum by subtracting sum from 0xff

	Set the last byte in the TxPacket array to be the XBeeCheckSum that was just calculated
end SetXBeeChecksum



StartFARMERTXmit
Kicks off transmission of a packet and will cause a UART Tx interrupt, 
	which will be handled in FARMERTXmitISR

	if there is room to transfer a byte (Txmit Fifo Empty = TXFE is set)
		Write the new data to data register UARTDR
		Enable UART TXmit interrupt by setting interrupt mask bit in UART mask reg
		so that when the byte is done sending, it fires an interrupt
		Increment BytesSentIndex (goes from 0 to 1 here)
		Return true because first byte was successfully transmitted
	else (there is not room to transmit a byte because the transmit fifo is full)
		return false
	end if
end StartFARMERTXmit



CreateEncryptionKey
	Creates the 32-byte encryption key by generating 32 bytes randomly

 	initialize a for loop to go from 0 to 31
		Generate a random number between 0 - 255 for each byte in the encryption key
	end for loop
end CreateEncryptionKey