FARMERRxSM - XBee Receive Pseudocode

States
WaitFor0x7E, WaitForMSBLen, WaitForLSBLen, ReadDataPacket

/**********************************************************/

InitFARMERRxSM
	Save away priority of service
	(InitUART is called elsewhere in code, cannot double call init)
	Enable UART receive interrupt via the RXIM bit in UARTIM
	ClearRxVars to start
	Set the CurrentState to WaitFor0x7E

/**********************************************************/

PostFARMERRxSM
	Just the usual post to this service

/**********************************************************/

RunFARMERRxSM
	(all receive state machine code is in the ISR)
	If EventType of posted ThisEvent is ES_UART_ERROR_FLAG
		Set CurrentState to WaitFor0x7E
	Switch based on CurrentState
		CurrentState is WaitFor0x7E
		(empty)
		End of case

		CurrentState is WaitForMSBLen
			(empty)
			End of case
					
		CurrentState is WaitForLSBLen
			(empty)
			End of case


		CurrentState is ReadDataPacket
			(empty)
			End of case
	End of switch
Return ReturnEvent
End of RunFARMERRxSM

/**********************************************************/
QueryFARMERRxSM
Take nothing, returns the current state of theFARMERRxSM state machine
Return CurrentState of FARMERRxSM
End of QueryFARMERRxSM

/**********************************************************/

FARMERRxISR
Take nothing, returns nothing

Poll the Rx interrupt
If the RxInterruptBit is set
	Clear the source of the interrupt in UARTICR
	Clear the RxInterruptBit 
	Read the data in UARTDR into NewRxByte
	Read OverRun bit in UARTDR into OverRunBit
	Read BreakError bit in UARTDR into BreakErrorBit
	Read ParityError bit in UARTDR into ParityErrorBit
	Read FramingError bit in UARTDR into FramingErrorBit
	If OverRunFlag OR BreakErrorFlag OR ParityErrorFlag OR FramingError is true 
		Write to UARTECR register to clear error flags 
		Post ES_UART_ERROR_FLAG event to FARMERRxSM
	Else data is good
        Switch based on CurrentState
			CurrentState is WaitFor0x7E
				If EventType of ThisEvent is 0x7E received
					Change CurrentState to WaitForMSBLen
					Call ClearRxVars to clear receive variables
					place RxDataByte into RxDataPacket and increment RxArrayIndex                        
				Endif 
				Break (End of WaitFor0x7E case)

			CurrentState is WaitForMSBLen
				Set MSB of Length to the value event parameter sent from the ISR
				place RxDataByte into RxDataPacket and increment RxArrayIndex
				Change CurrentState to WaitForLSBLen
				Break (End of WaitForMSBLen case) 

			CurrentState is WaitForLSBLen
				Set LSB of Length to the value event parameter sent from the ISR
				Place RxDataByte into RxDataPacket and increment RxArrayIndex
				Combine MSB and LSB into BytesLeft, then calculate a PacketLength         
				Change CurrentState to ReadDataPacket
				Break (End of WaitForLSBLen case)

			CurrentState is ReadDataPacket
				If BytesLeft NOT EQUAL to zero
					place RxDataByte into RxDataPacket 
					increment RxArrayIndex
					Decrement BytesLeft
					Add DataByte to ChkSum
				Else if BytesLeft EQUAL to zero 
					place RxDataByte into RxDataPacket
					Pull XbeeChkSum out of the last index of RxDataPacket
					Subtract running checksum from 0xFF to get the final checksum
					If XbeeChkSum isn’t equal to Rx ChkSum
							Change states to Waitfor0x7E
					Else if ChkSum is good
							Call SaveRFData
							Set CurrentState to WaitFor0x7E
					End if        
				End if
				Break
			End of switch on CurrentState
End of FARMERRxISR

/**********************************************************/

GetDOGAddressMSB
Takes nothing, returns uint8_t DOGAddressMSB
return DOGAddressMSB
End of GetDOGAddressMSB

/**********************************************************/

GetDOGAddressLSB
Takes nothing, returns uint8_t DOGAddressLSB
return DOGAddressLSB
End of GetDOGAddressLSB


/**********************************************************/

GetGyroZStatus
Takes nothing, returns uint16_t gyroStatus

Set uint16_t variable gyroStatus equal to Status message array index GYROZ_MSB left shifted by 8. 
gyroStatus equals gyroStatus OR’d with the Status message array index GYROZ_LSB
return gyroStatus
End of GetGyroZStatus

/**********************************************************/

SaveRFData
Takes nothing, returns nothing
Public function to save message receive as PAIR_ACK, ENCR_RESET, STATUS messages


If the API_ID_INDEX of RxDataPacket array is equal to 0x81 (the Incoming API ID)
	If HEADER_BYTE index of RxDataPacket is PAIR_ACK
		Save the DOGAddressMSB/LSB (source address) to use for checking all future incoming packets
		Create and post ES_PACKET_RX EventType with the Param PAIR_ACK to FARMER_FSM
		End if (PAIR_ACK)
	Else ( the Rx'd packet is not a PAIR_ACK byte)
		If source of RxDataPacket is from our DOG
			Post PacketReceived event to FARMER_FSM with HEADER_BYTE of RxDataPacket as the EventParam
			If length of RxDataPacket is STATUS
				Loop through packet and save RxDataPacket bytes into Status array 
			End if
		End if
	End if
Endif 

End of SaveRFData

/********************************Private Functions ****************************/

printUARTErrors
Takes nothing, returns nothing 
a simple private function to print error messages identifying UART Rx messages

	If OverRun error bit is set
		Print “OverRun Error in UART Rx : Connection Lost”
	Else if break error bit is set
		Print “Break Error in UART Rx : Connection Lost”
	Else if parity error bit is set
		Print “Parity Error in UART Rx : Connection Lost”
	Else if framing error bit is set
		Print “Framing Error in UART Rx : Connection Lost”
	Endif

	clear call error bits
	Return
End of printUARTErrors
        
/**********************************************************/
        
ClearRxDataPacket
Takes nothing, returns nothing
Helper function to clear all data out of RxDataPacket

    For RxDataPacket array position 0 to LONGEST_PACKET_LENGTH
		Set value to zero
	End for
End of ClearRxDataPacket


/**********************************************************/

ClearRxVars
Takes nothing, returns nothing
Helper function to set all Rx vars to zero

Clears FrameLengthMSB, FrameLengthLSB,  PacketLength, ChkSum, XbeeChkSum, RxArryIndex
Calls ClearRxDataPacket
End of ClearRxVars