FreeRTOS-Labs/Source/FreeRTOS-Plus-TCP/FreeRTOS_IP.c

/*
 * FreeRTOS+TCP 191100 experimental
 * Copyright (C) 2018 Amazon.com, Inc. or its affiliates.  All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of
 * this software and associated documentation files (the "Software"), to deal in
 * the Software without restriction, including without limitation the rights to
 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
 * the Software, and to permit persons to whom the Software is furnished to do so,
 * subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
 * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
 * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
 * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 * http://aws.amazon.com/freertos
 * http://www.FreeRTOS.org
 */

/* Standard includes. */
#include <stdint.h>
#include <stdio.h>
#include <string.h>

/* FreeRTOS includes. */
#include "FreeRTOS.h"
#include "task.h"
#include "queue.h"
#include "semphr.h"

/* FreeRTOS+TCP includes. */
#include "FreeRTOS_IP.h"
#include "FreeRTOS_Sockets.h"
#include "FreeRTOS_IP_Private.h"
#include "FreeRTOS_ARP.h"
#include "FreeRTOS_UDP_IP.h"
#include "FreeRTOS_TCP_IP.h"
#include "FreeRTOS_DHCP.h"
#include "NetworkInterface.h"
#include "NetworkBufferManagement.h"
#include "FreeRTOS_DNS.h"


/* Used to ensure the structure packing is having the desired effect.  The
'volatile' is used to prevent compiler warnings about comparing a constant with
a constant. */
#define ipEXPECTED_EthernetHeader_t_SIZE	( ( size_t ) 14 )
#define ipEXPECTED_ARPHeader_t_SIZE			( ( size_t ) 28 )
#define ipEXPECTED_IPHeader_t_SIZE			( ( size_t ) 20 )
#define ipEXPECTED_IGMPHeader__SIZE			( ( size_t ) 8 )
#define ipEXPECTED_ICMPHeader_t_SIZE		( ( size_t ) 8 )
#define ipEXPECTED_UDPHeader_t_SIZE			( ( size_t ) 8 )
#define ipEXPECTED_TCPHeader_t_SIZE			( ( size_t ) 20 )


/* ICMP protocol definitions. */
#define ipICMP_ECHO_REQUEST				( ( uint8_t ) 8 )
#define ipICMP_ECHO_REPLY				( ( uint8_t ) 0 )


/* Time delay between repeated attempts to initialise the network hardware. */
#define ipINITIALISATION_RETRY_DELAY	( pdMS_TO_TICKS( 3000 ) )

/* Defines how often the ARP timer callback function is executed.  The time is
shorted in the Windows simulator as simulated time is not real time. */
#ifndef	ipARP_TIMER_PERIOD_MS
	#ifdef _WINDOWS_
		#define ipARP_TIMER_PERIOD_MS	( 500 ) /* For windows simulator builds. */
	#else
		#define ipARP_TIMER_PERIOD_MS	( 10000 )
	#endif
#endif

#ifndef iptraceIP_TASK_STARTING
	#define	iptraceIP_TASK_STARTING()	do {} while( 0 )
#endif

#if( ( ipconfigUSE_TCP == 1 ) && !defined( ipTCP_TIMER_PERIOD_MS ) )
	/* When initialising the TCP timer,
	give it an initial time-out of 1 second. */
	#define ipTCP_TIMER_PERIOD_MS	( 1000 )
#endif

/* If ipconfigETHERNET_DRIVER_FILTERS_FRAME_TYPES is set to 1, then the Ethernet
driver will filter incoming packets and only pass the stack those packets it
considers need processing.  In this case ipCONSIDER_FRAME_FOR_PROCESSING() can
be #defined away.  If ipconfigETHERNET_DRIVER_FILTERS_FRAME_TYPES is set to 0
then the Ethernet driver will pass all received packets to the stack, and the
stack must do the filtering itself.  In this case ipCONSIDER_FRAME_FOR_PROCESSING
needs to call eConsiderFrameForProcessing. */
#if ipconfigETHERNET_DRIVER_FILTERS_FRAME_TYPES == 0
	#define ipCONSIDER_FRAME_FOR_PROCESSING( pucEthernetBuffer ) eConsiderFrameForProcessing( ( pucEthernetBuffer ) )
#else
	#define ipCONSIDER_FRAME_FOR_PROCESSING( pucEthernetBuffer ) eProcessBuffer
#endif

/* The character used to fill ICMP echo requests, and therefore also the
character expected to fill ICMP echo replies. */
#define ipECHO_DATA_FILL_BYTE						'x'

#if( ipconfigBYTE_ORDER == pdFREERTOS_LITTLE_ENDIAN )
	/* The bits in the two byte IP header field that make up the fragment offset value. */
	#define ipFRAGMENT_OFFSET_BIT_MASK				( ( uint16_t ) 0xff0f )
#else
	/* The bits in the two byte IP header field that make up the fragment offset value. */
	#define ipFRAGMENT_OFFSET_BIT_MASK				( ( uint16_t ) 0x0fff )
#endif /* ipconfigBYTE_ORDER */

/* The maximum time the IP task is allowed to remain in the Blocked state if no
events are posted to the network event queue. */
#ifndef	ipconfigMAX_IP_TASK_SLEEP_TIME
	#define ipconfigMAX_IP_TASK_SLEEP_TIME ( pdMS_TO_TICKS( 10000UL ) )
#endif

/* When a new TCP connection is established, the value of
'ulNextInitialSequenceNumber' will be used as the initial sequence number.  It
is very important that at start-up, 'ulNextInitialSequenceNumber' contains a
random value.  Also its value must be increased continuously in time, to prevent
a third party guessing the next sequence number and take-over a TCP connection.
It is advised to increment it by 1 ever 4us, which makes about 256 times
per ms: */
#define ipINITIAL_SEQUENCE_NUMBER_FACTOR	256UL

/* Returned as the (invalid) checksum when the protocol being checked is not
handled.  The value is chosen simply to be easy to spot when debugging. */
#define ipUNHANDLED_PROTOCOL		0x4321u

/* Returned to indicate a valid checksum when the checksum does not need to be
calculated. */
#define ipCORRECT_CRC				0xffffu

/* Returned as the (invalid) checksum when the length of the data being checked
had an invalid length. */
#define ipINVALID_LENGTH			0x1234u

/*-----------------------------------------------------------*/

typedef struct xIP_TIMER
{
	uint32_t
		bActive : 1,	/* This timer is running and must be processed. */
		bExpired : 1;	/* Timer has expired and a task must be processed. */
	TimeOut_t xTimeOut;
	TickType_t ulRemainingTime;
	TickType_t ulReloadTime;
} IPTimer_t;

/* Used in checksum calculation. */
typedef union _xUnion32
{
	uint32_t u32;
	uint16_t u16[ 2 ];
	uint8_t u8[ 4 ];
} xUnion32;

/* Used in checksum calculation. */
typedef union _xUnionPtr
{
	uint32_t *u32ptr;
	uint16_t *u16ptr;
	uint8_t *u8ptr;
} xUnionPtr;

/*-----------------------------------------------------------*/

/*
 * The main TCP/IP stack processing task.  This task receives commands/events
 * from the network hardware drivers and tasks that are using sockets.  It also
 * maintains a set of protocol timers.
 */
static void prvIPTask( void *pvParameters );

/*
 * Called when new data is available from the network interface.
 */
static void prvProcessEthernetPacket( NetworkBufferDescriptor_t * const pxNetworkBuffer );

/*
 * Process incoming IP packets.
 */
static eFrameProcessingResult_t prvProcessIPPacket( IPPacket_t * const pxIPPacket, NetworkBufferDescriptor_t * const pxNetworkBuffer );

#if ( ipconfigREPLY_TO_INCOMING_PINGS == 1 ) || ( ipconfigSUPPORT_OUTGOING_PINGS == 1 )
	/*
	 * Process incoming ICMP packets.
	 */
	static eFrameProcessingResult_t prvProcessICMPPacket( ICMPPacket_t * const pxICMPPacket );
#endif /* ( ipconfigREPLY_TO_INCOMING_PINGS == 1 ) || ( ipconfigSUPPORT_OUTGOING_PINGS == 1 ) */

/*
 * Turns around an incoming ping request to convert it into a ping reply.
 */
#if ( ipconfigREPLY_TO_INCOMING_PINGS == 1 )
	static eFrameProcessingResult_t prvProcessICMPEchoRequest( ICMPPacket_t * const pxICMPPacket );
#endif /* ipconfigREPLY_TO_INCOMING_PINGS */

/*
 * Processes incoming ping replies.  The application callback function
 * vApplicationPingReplyHook() is called with the results.
 */
#if ( ipconfigSUPPORT_OUTGOING_PINGS == 1 )
	static void prvProcessICMPEchoReply( ICMPPacket_t * const pxICMPPacket );
#endif /* ipconfigSUPPORT_OUTGOING_PINGS */

/*
 * Called to create a network connection when the stack is first started, or
 * when the network connection is lost.
 */
static void prvProcessNetworkDownEvent( void );

/*
 * Checks the ARP, DHCP and TCP timers to see if any periodic or timeout
 * processing is required.
 */
static void prvCheckNetworkTimers( void );

/*
 * Determine how long the IP task can sleep for, which depends on when the next
 * periodic or timeout processing must be performed.
 */
static TickType_t prvCalculateSleepTime( void );

/*
 * The network card driver has received a packet.  In the case that it is part
 * of a linked packet chain, walk through it to handle every message.
 */
static void prvHandleEthernetPacket( NetworkBufferDescriptor_t *pxBuffer );

/*
 * Utility functions for the light weight IP timers.
 */
static void prvIPTimerStart( IPTimer_t *pxTimer, TickType_t xTime );
static BaseType_t prvIPTimerCheck( IPTimer_t *pxTimer );
static void prvIPTimerReload( IPTimer_t *pxTimer, TickType_t xTime );

static eFrameProcessingResult_t prvAllowIPPacket( const IPPacket_t * const pxIPPacket,
	NetworkBufferDescriptor_t * const pxNetworkBuffer, UBaseType_t uxHeaderLength );

/*-----------------------------------------------------------*/

/* The queue used to pass events into the IP-task for processing. */
QueueHandle_t xNetworkEventQueue = NULL;

/*_RB_ Requires comment. */
uint16_t usPacketIdentifier = 0U;

/* For convenience, a MAC address of all 0xffs is defined const for quick
reference. */
const MACAddress_t xBroadcastMACAddress = { { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff } };

/* Structure that stores the netmask, gateway address and DNS server addresses. */
NetworkAddressingParameters_t xNetworkAddressing = { 0, 0, 0, 0, 0 };

/* Default values for the above struct in case DHCP
does not lead to a confirmed request. */
NetworkAddressingParameters_t xDefaultAddressing = { 0, 0, 0, 0, 0 };

/* Used to ensure network down events cannot be missed when they cannot be
posted to the network event queue because the network event queue is already
full. */
static BaseType_t xNetworkDownEventPending = pdFALSE;

/* Stores the handle of the task that handles the stack.  The handle is used
(indirectly) by some utility function to determine if the utility function is
being called by a task (in which case it is ok to block) or by the IP task
itself (in which case it is not ok to block). */
static TaskHandle_t xIPTaskHandle = NULL;

#if( ipconfigUSE_TCP != 0 )
	/* Set to a non-zero value if one or more TCP message have been processed
	within the last round. */
	static BaseType_t xProcessedTCPMessage;
#endif

/* Simple set to pdTRUE or pdFALSE depending on whether the network is up or
down (connected, not connected) respectively. */
static BaseType_t xNetworkUp = pdFALSE;

/*
A timer for each of the following processes, all of which need attention on a
regular basis:
	1. ARP, to check its table entries
	2. DPHC, to send requests and to renew a reservation
	3. TCP, to check for timeouts, resends
	4. DNS, to check for timeouts when looking-up a domain.
 */
static IPTimer_t xARPTimer;
#if( ipconfigUSE_DHCP != 0 )
	static IPTimer_t xDHCPTimer;
#endif
#if( ipconfigUSE_TCP != 0 )
	static IPTimer_t xTCPTimer;
#endif
#if( ipconfigDNS_USE_CALLBACKS != 0 )
	static IPTimer_t xDNSTimer;
#endif

/* Set to pdTRUE when the IP task is ready to start processing packets. */
static BaseType_t xIPTaskInitialised = pdFALSE;

#if( ipconfigCHECK_IP_QUEUE_SPACE != 0 )
	/* Keep track of the lowest amount of space in 'xNetworkEventQueue'. */
	static UBaseType_t uxQueueMinimumSpace = ipconfigEVENT_QUEUE_LENGTH;
#endif

/*-----------------------------------------------------------*/

static void prvIPTask( void *pvParameters )
{
IPStackEvent_t xReceivedEvent;
TickType_t xNextIPSleep;
FreeRTOS_Socket_t *pxSocket;
struct freertos_sockaddr xAddress;

	/* Just to prevent compiler warnings about unused parameters. */
	( void ) pvParameters;

	/* A possibility to set some additional task properties. */
	iptraceIP_TASK_STARTING();

	/* Generate a dummy message to say that the network connection has gone
	down.  This will cause this task to initialise the network interface.  After
	this it is the responsibility of the network interface hardware driver to
	send this message if a previously connected network is disconnected. */
	FreeRTOS_NetworkDown();

	#if( ipconfigUSE_TCP == 1 )
	{
		/* Initialise the TCP timer. */
		prvIPTimerReload( &xTCPTimer, pdMS_TO_TICKS( ipTCP_TIMER_PERIOD_MS ) );
	}
	#endif

	/* Initialisation is complete and events can now be processed. */
	xIPTaskInitialised = pdTRUE;

	FreeRTOS_debug_printf( ( "prvIPTask started\n" ) );

	/* Loop, processing IP events. */
	for( ;; )
	{
		ipconfigWATCHDOG_TIMER();

		/* Check the ARP, DHCP and TCP timers to see if there is any periodic
		or timeout processing to perform. */
		prvCheckNetworkTimers();

		/* Calculate the acceptable maximum sleep time. */
		xNextIPSleep = prvCalculateSleepTime();

		/* Wait until there is something to do. If the following call exits
		 * due to a time out rather than a message being received, set a
		 * 'NoEvent' value. */
		if ( xQueueReceive( xNetworkEventQueue, ( void * ) &xReceivedEvent, xNextIPSleep ) == pdFALSE ) 
		{
			xReceivedEvent.eEventType = eNoEvent;
		}

		#if( ipconfigCHECK_IP_QUEUE_SPACE != 0 )
		{
			if( xReceivedEvent.eEventType != eNoEvent )
			{
			UBaseType_t uxCount;

				uxCount = uxQueueSpacesAvailable( xNetworkEventQueue );
				if( uxQueueMinimumSpace > uxCount )
				{
					uxQueueMinimumSpace = uxCount;
				}
			}
		}
		#endif /* ipconfigCHECK_IP_QUEUE_SPACE */

		iptraceNETWORK_EVENT_RECEIVED( xReceivedEvent.eEventType );

		switch( xReceivedEvent.eEventType )
		{
			case eNetworkDownEvent :
				/* Attempt to establish a connection. */
				xNetworkUp = pdFALSE;
				prvProcessNetworkDownEvent();
				break;

			case eNetworkRxEvent:
				/* The network hardware driver has received a new packet.  A
				pointer to the received buffer is located in the pvData member
				of the received event structure. */
				prvHandleEthernetPacket( ( NetworkBufferDescriptor_t * ) ( xReceivedEvent.pvData ) );
				break;

			case eARPTimerEvent :
				/* The ARP timer has expired, process the ARP cache. */
				vARPAgeCache();
				break;

			case eSocketBindEvent:
				/* FreeRTOS_bind (a user API) wants the IP-task to bind a socket
				to a port. The port number is communicated in the socket field
				usLocalPort. vSocketBind() will actually bind the socket and the
				API will unblock as soon as the eSOCKET_BOUND event is
				triggered. */
				pxSocket = ( FreeRTOS_Socket_t * ) ( xReceivedEvent.pvData );
				xAddress.sin_addr = 0u;	/* For the moment. */
				xAddress.sin_port = FreeRTOS_ntohs( pxSocket->usLocalPort );
				pxSocket->usLocalPort = 0u;
				vSocketBind( pxSocket, &xAddress, sizeof( xAddress ), pdFALSE );

				/* Before 'eSocketBindEvent' was sent it was tested that
				( xEventGroup != NULL ) so it can be used now to wake up the
				user. */
				pxSocket->xEventBits |= eSOCKET_BOUND;
				vSocketWakeUpUser( pxSocket );
				break;

			case eSocketCloseEvent :
				/* The user API FreeRTOS_closesocket() has sent a message to the
				IP-task to actually close a socket. This is handled in
				vSocketClose().  As the socket gets closed, there is no way to
				report back to the API, so the API won't wait for the result */
				vSocketClose( ( FreeRTOS_Socket_t * ) ( xReceivedEvent.pvData ) );
				break;

			case eStackTxEvent :
				/* The network stack has generated a packet to send.  A
				pointer to the generated buffer is located in the pvData
				member of the received event structure. */
				vProcessGeneratedUDPPacket( ( NetworkBufferDescriptor_t * ) ( xReceivedEvent.pvData ) );
				break;

			case eDHCPEvent:
				/* The DHCP state machine needs processing. */
				#if( ipconfigUSE_DHCP == 1 )
				{
					vDHCPProcess( pdFALSE );
				}
				#endif /* ipconfigUSE_DHCP */
				break;

			case eSocketSelectEvent :
				/* FreeRTOS_select() has got unblocked by a socket event,
				vSocketSelect() will check which sockets actually have an event
				and update the socket field xSocketBits. */
				#if( ipconfigSUPPORT_SELECT_FUNCTION == 1 )
				{
					vSocketSelect( ( SocketSelect_t * ) ( xReceivedEvent.pvData ) );
				}
				#endif /* ipconfigSUPPORT_SELECT_FUNCTION == 1 */
				break;

			case eSocketSignalEvent :
				#if( ipconfigSUPPORT_SIGNALS != 0 )
				{
					/* Some task wants to signal the user of this socket in
					order to interrupt a call to recv() or a call to select(). */
					FreeRTOS_SignalSocket( ( Socket_t ) xReceivedEvent.pvData );
				}
				#endif /* ipconfigSUPPORT_SIGNALS */
				break;

			case eTCPTimerEvent :
				#if( ipconfigUSE_TCP == 1 )
				{
					/* Simply mark the TCP timer as expired so it gets processed
					the next time prvCheckNetworkTimers() is called. */
					xTCPTimer.bExpired = pdTRUE_UNSIGNED;
				}
				#endif /* ipconfigUSE_TCP */
				break;

			case eTCPAcceptEvent:
				/* The API FreeRTOS_accept() was called, the IP-task will now
				check if the listening socket (communicated in pvData) actually
				received a new connection. */
				#if( ipconfigUSE_TCP == 1 )
				{
					pxSocket = ( FreeRTOS_Socket_t * ) ( xReceivedEvent.pvData );

					if( xTCPCheckNewClient( pxSocket ) != pdFALSE )
					{
						pxSocket->xEventBits |= eSOCKET_ACCEPT;
						vSocketWakeUpUser( pxSocket );
					}
				}
				#endif /* ipconfigUSE_TCP */
				break;

			case eTCPNetStat:
				/* FreeRTOS_netstat() was called to have the IP-task print an
				overview of all sockets and their connections */
				#if( ( ipconfigUSE_TCP == 1 ) && ( ipconfigHAS_PRINTF == 1 ) )
				{
					vTCPNetStat();
				}
				#endif /* ipconfigUSE_TCP */
				break;

			default :
				/* Should not get here. */
				break;
		}

		if( xNetworkDownEventPending != pdFALSE )
		{
			/* A network down event could not be posted to the network event
			queue because the queue was full.  Try posting again. */
			FreeRTOS_NetworkDown();
		}
	}
}
/*-----------------------------------------------------------*/

BaseType_t xIsCallingFromIPTask( void )
{
BaseType_t xReturn;

	if( xTaskGetCurrentTaskHandle() == xIPTaskHandle )
	{
		xReturn = pdTRUE;
	}
	else
	{
		xReturn = pdFALSE;
	}

	return xReturn;
}
/*-----------------------------------------------------------*/

static void prvHandleEthernetPacket( NetworkBufferDescriptor_t *pxBuffer )
{
	#if( ipconfigUSE_LINKED_RX_MESSAGES == 0 )
	{
		/* When ipconfigUSE_LINKED_RX_MESSAGES is not set to 0 then only one
		buffer will be sent at a time.  This is the default way for +TCP to pass
		messages from the MAC to the TCP/IP stack. */
		prvProcessEthernetPacket( pxBuffer );
	}
	#else /* ipconfigUSE_LINKED_RX_MESSAGES */
	{
	NetworkBufferDescriptor_t *pxNextBuffer;

		/* An optimisation that is useful when there is high network traffic.
		Instead of passing received packets into the IP task one at a time the
		network interface can chain received packets together and pass them into
		the IP task in one go.  The packets are chained using the pxNextBuffer
		member.  The loop below walks through the chain processing each packet
		in the chain in turn. */
		do
		{
			/* Store a pointer to the buffer after pxBuffer for use later on. */
			pxNextBuffer = pxBuffer->pxNextBuffer;

			/* Make it NULL to avoid using it later on. */
			pxBuffer->pxNextBuffer = NULL;

			prvProcessEthernetPacket( pxBuffer );
			pxBuffer = pxNextBuffer;

		/* While there is another packet in the chain. */
		} while( pxBuffer != NULL );
	}
	#endif /* ipconfigUSE_LINKED_RX_MESSAGES */
}
/*-----------------------------------------------------------*/

static TickType_t prvCalculateSleepTime( void )
{
TickType_t xMaximumSleepTime;

	/* Start with the maximum sleep time, then check this against the remaining
	time in any other timers that are active. */
	xMaximumSleepTime = ipconfigMAX_IP_TASK_SLEEP_TIME;

	if( xARPTimer.bActive != pdFALSE_UNSIGNED )
	{
		if( xARPTimer.ulRemainingTime < xMaximumSleepTime )
		{
			xMaximumSleepTime = xARPTimer.ulReloadTime;
		}
	}

	#if( ipconfigUSE_DHCP == 1 )
	{
		if( xDHCPTimer.bActive != pdFALSE_UNSIGNED )
		{
			if( xDHCPTimer.ulRemainingTime < xMaximumSleepTime )
			{
				xMaximumSleepTime = xDHCPTimer.ulRemainingTime;
			}
		}
	}
	#endif /* ipconfigUSE_DHCP */

	#if( ipconfigUSE_TCP == 1 )
	{
		if( xTCPTimer.ulRemainingTime < xMaximumSleepTime )
		{
			xMaximumSleepTime = xTCPTimer.ulRemainingTime;
		}
	}
	#endif

	#if( ipconfigDNS_USE_CALLBACKS != 0 )
	{
		if( xDNSTimer.bActive != pdFALSE )
		{
			if( xDNSTimer.ulRemainingTime < xMaximumSleepTime )
			{
				xMaximumSleepTime = xDNSTimer.ulRemainingTime;
			}
		}
	}
	#endif

	return xMaximumSleepTime;
}
/*-----------------------------------------------------------*/

static void prvCheckNetworkTimers( void )
{
	/* Is it time for ARP processing? */
	if( prvIPTimerCheck( &xARPTimer ) != pdFALSE )
	{
		xSendEventToIPTask( eARPTimerEvent );
	}

	#if( ipconfigUSE_DHCP == 1 )
	{
		/* Is it time for DHCP processing? */
		if( prvIPTimerCheck( &xDHCPTimer ) != pdFALSE )
		{
			xSendEventToIPTask( eDHCPEvent );
		}
	}
	#endif /* ipconfigUSE_DHCP */

	#if( ipconfigDNS_USE_CALLBACKS != 0 )
	{
	extern void vDNSCheckCallBack( void *pvSearchID );

		/* Is it time for DNS processing? */
		if( prvIPTimerCheck( &xDNSTimer ) != pdFALSE )
		{
			vDNSCheckCallBack( NULL );
		}
	}
	#endif /* ipconfigDNS_USE_CALLBACKS */

	#if( ipconfigUSE_TCP == 1 )
	{
	BaseType_t xWillSleep;
	TickType_t xNextTime;
	BaseType_t xCheckTCPSockets;

		if( uxQueueMessagesWaiting( xNetworkEventQueue ) == 0u )
		{
			xWillSleep = pdTRUE;
		}
		else
		{
			xWillSleep = pdFALSE;
		}

		/* Sockets need to be checked if the TCP timer has expired. */
		xCheckTCPSockets = prvIPTimerCheck( &xTCPTimer );

		/* Sockets will also be checked if there are TCP messages but the
		message queue is empty (indicated by xWillSleep being true). */
		if( ( xProcessedTCPMessage != pdFALSE ) && ( xWillSleep != pdFALSE ) )
		{
			xCheckTCPSockets = pdTRUE;
		}

		if( xCheckTCPSockets != pdFALSE )
		{
			/* Attend to the sockets, returning the period after which the
			check must be repeated. */
			xNextTime = xTCPTimerCheck( xWillSleep );
			prvIPTimerStart( &xTCPTimer, xNextTime );
			xProcessedTCPMessage = 0;
		}
	}
	#endif /* ipconfigUSE_TCP == 1 */
}
/*-----------------------------------------------------------*/

static void prvIPTimerStart( IPTimer_t *pxTimer, TickType_t xTime )
{
	vTaskSetTimeOutState( &pxTimer->xTimeOut );
	pxTimer->ulRemainingTime = xTime;

	if( xTime == ( TickType_t ) 0 )
	{
		pxTimer->bExpired = pdTRUE_UNSIGNED;
	}
	else
	{
		pxTimer->bExpired = pdFALSE_UNSIGNED;
	}

	pxTimer->bActive = pdTRUE_UNSIGNED;
}
/*-----------------------------------------------------------*/

static void prvIPTimerReload( IPTimer_t *pxTimer, TickType_t xTime )
{
	pxTimer->ulReloadTime = xTime;
	prvIPTimerStart( pxTimer, xTime );
}
/*-----------------------------------------------------------*/

static BaseType_t prvIPTimerCheck( IPTimer_t *pxTimer )
{
BaseType_t xReturn;

	if( pxTimer->bActive == pdFALSE_UNSIGNED )
	{
		/* The timer is not enabled. */
		xReturn = pdFALSE;
	}
	else
	{
		/* The timer might have set the bExpired flag already, if not, check the
		value of xTimeOut against ulRemainingTime. */
		if( ( pxTimer->bExpired != pdFALSE_UNSIGNED ) ||
			( xTaskCheckForTimeOut( &( pxTimer->xTimeOut ), &( pxTimer->ulRemainingTime ) ) != pdFALSE ) )
		{
			prvIPTimerStart( pxTimer, pxTimer->ulReloadTime );
			xReturn = pdTRUE;
		}
		else
		{
			xReturn = pdFALSE;
		}
	}

	return xReturn;
}
/*-----------------------------------------------------------*/

void FreeRTOS_NetworkDown( void )
{
static const IPStackEvent_t xNetworkDownEvent = { eNetworkDownEvent, NULL };
const TickType_t xDontBlock = ( TickType_t ) 0;

	/* Simply send the network task the appropriate event. */
	if( xSendEventStructToIPTask( &xNetworkDownEvent, xDontBlock ) != pdPASS )
	{
		/* Could not send the message, so it is still pending. */
		xNetworkDownEventPending = pdTRUE;
	}
	else
	{
		/* Message was sent so it is not pending. */
		xNetworkDownEventPending = pdFALSE;
	}

	iptraceNETWORK_DOWN();
}
/*-----------------------------------------------------------*/

BaseType_t FreeRTOS_NetworkDownFromISR( void )
{
static const IPStackEvent_t xNetworkDownEvent = { eNetworkDownEvent, NULL };
BaseType_t xHigherPriorityTaskWoken = pdFALSE;

	/* Simply send the network task the appropriate event. */
	if( xQueueSendToBackFromISR( xNetworkEventQueue, &xNetworkDownEvent, &xHigherPriorityTaskWoken ) != pdPASS )
	{
		xNetworkDownEventPending = pdTRUE;
	}
	else
	{
		xNetworkDownEventPending = pdFALSE;
	}

	iptraceNETWORK_DOWN();

	return xHigherPriorityTaskWoken;
}
/*-----------------------------------------------------------*/

void *FreeRTOS_GetUDPPayloadBuffer( size_t xRequestedSizeBytes, TickType_t xBlockTimeTicks )
{
NetworkBufferDescriptor_t *pxNetworkBuffer;
void *pvReturn;

	/* Cap the block time.  The reason for this is explained where
	ipconfigUDP_MAX_SEND_BLOCK_TIME_TICKS is defined (assuming an official
	FreeRTOSIPConfig.h header file is being used). */
	if( xBlockTimeTicks > ipconfigUDP_MAX_SEND_BLOCK_TIME_TICKS )
	{
		xBlockTimeTicks = ipconfigUDP_MAX_SEND_BLOCK_TIME_TICKS;
	}

	/* Obtain a network buffer with the required amount of storage. */
	pxNetworkBuffer = pxGetNetworkBufferWithDescriptor( sizeof( UDPPacket_t ) + xRequestedSizeBytes, xBlockTimeTicks );

	if( pxNetworkBuffer != NULL )
	{
		/* Set the actual packet size in case a bigger buffer was returned. */
		pxNetworkBuffer->xDataLength = sizeof( UDPPacket_t ) + xRequestedSizeBytes;

		/* Leave space for the UPD header. */
		pvReturn = ( void * ) &( pxNetworkBuffer->pucEthernetBuffer[ ipUDP_PAYLOAD_OFFSET_IPv4 ] );
	}
	else
	{
		pvReturn = NULL;
	}

	return ( void * ) pvReturn;
}
/*-----------------------------------------------------------*/

NetworkBufferDescriptor_t *pxDuplicateNetworkBufferWithDescriptor( NetworkBufferDescriptor_t * const pxNetworkBuffer,
	BaseType_t xNewLength )
{
NetworkBufferDescriptor_t * pxNewBuffer;

	/* This function is only used when 'ipconfigZERO_COPY_TX_DRIVER' is set to 1.
	The transmit routine wants to have ownership of the network buffer
	descriptor, because it will pass the buffer straight to DMA. */
	pxNewBuffer = pxGetNetworkBufferWithDescriptor( ( size_t ) xNewLength, ( TickType_t ) 0 );

	if( pxNewBuffer != NULL )
	{
		/* Set the actual packet size in case a bigger buffer than requested
		was returned. */
		pxNewBuffer->xDataLength = xNewLength;

		/* Copy the original packet information. */
		pxNewBuffer->ulIPAddress = pxNetworkBuffer->ulIPAddress;
		pxNewBuffer->usPort = pxNetworkBuffer->usPort;
		pxNewBuffer->usBoundPort = pxNetworkBuffer->usBoundPort;
		memcpy( pxNewBuffer->pucEthernetBuffer, pxNetworkBuffer->pucEthernetBuffer, pxNetworkBuffer->xDataLength );
	}

	return pxNewBuffer;
}
/*-----------------------------------------------------------*/

#if( ipconfigZERO_COPY_TX_DRIVER != 0 ) || ( ipconfigZERO_COPY_RX_DRIVER != 0 )

	NetworkBufferDescriptor_t *pxPacketBuffer_to_NetworkBuffer( const void *pvBuffer )
	{
	uint8_t *pucBuffer;
	NetworkBufferDescriptor_t *pxResult;

		if( pvBuffer == NULL )
		{
			pxResult = NULL;
		}
		else
		{
			/* Obtain the network buffer from the zero copy pointer. */
			pucBuffer = ( uint8_t * ) pvBuffer;

			/* The input here is a pointer to a payload buffer.  Subtract the
			size of the header in the network buffer, usually 8 + 2 bytes. */
			pucBuffer -= ipBUFFER_PADDING;

			/* Here a pointer was placed to the network descriptor.  As a
			pointer is dereferenced, make sure it is well aligned. */
			if( ( ( ( uint32_t ) pucBuffer ) & ( sizeof( pucBuffer ) - ( size_t ) 1 ) ) == ( uint32_t ) 0 )
			{
				pxResult = * ( ( NetworkBufferDescriptor_t ** ) pucBuffer );
			}
			else
			{
				pxResult = NULL;
			}
		}

		return pxResult;
	}

#endif /* ipconfigZERO_COPY_TX_DRIVER != 0 */
/*-----------------------------------------------------------*/

NetworkBufferDescriptor_t *pxUDPPayloadBuffer_to_NetworkBuffer( void *pvBuffer )
{
uint8_t *pucBuffer;
NetworkBufferDescriptor_t *pxResult;

	if( pvBuffer == NULL )
	{
		pxResult = NULL;
	}
	else
	{
		/* Obtain the network buffer from the zero copy pointer. */
		pucBuffer = ( uint8_t * ) pvBuffer;

		/* The input here is a pointer to a payload buffer.  Subtract
		the total size of a UDP/IP header plus the size of the header in
		the network buffer, usually 8 + 2 bytes. */
		pucBuffer -= ( sizeof( UDPPacket_t ) + ipBUFFER_PADDING );

		/* Here a pointer was placed to the network descriptor,
		As a pointer is dereferenced, make sure it is well aligned */
		if( ( ( ( uint32_t ) pucBuffer ) & ( sizeof( pucBuffer ) - 1 ) ) == 0 )
		{
			/* The following statement may trigger a:
			warning: cast increases required alignment of target type [-Wcast-align].
			It has been confirmed though that the alignment is suitable. */
			pxResult = * ( ( NetworkBufferDescriptor_t ** ) pucBuffer );
		}
		else
		{
			pxResult = NULL;
		}
	}

	return pxResult;
}
/*-----------------------------------------------------------*/

void FreeRTOS_ReleaseUDPPayloadBuffer( void *pvBuffer )
{
	vReleaseNetworkBufferAndDescriptor( pxUDPPayloadBuffer_to_NetworkBuffer( pvBuffer ) );
}
/*-----------------------------------------------------------*/

/*_RB_ Should we add an error or assert if the task priorities are set such that the servers won't function as expected? */
/*_HT_ There was a bug in FreeRTOS_TCP_IP.c that only occurred when the applications' priority was too high.
 As that bug has been repaired, there is not an urgent reason to warn.
 It is better though to use the advised priority scheme. */
BaseType_t FreeRTOS_IPInit( const uint8_t ucIPAddress[ ipIP_ADDRESS_LENGTH_BYTES ], const uint8_t ucNetMask[ ipIP_ADDRESS_LENGTH_BYTES ], const uint8_t ucGatewayAddress[ ipIP_ADDRESS_LENGTH_BYTES ], const uint8_t ucDNSServerAddress[ ipIP_ADDRESS_LENGTH_BYTES ], const uint8_t ucMACAddress[ ipMAC_ADDRESS_LENGTH_BYTES ] )
{
BaseType_t xReturn = pdFALSE;

	/* This function should only be called once. */
	configASSERT( xIPIsNetworkTaskReady() == pdFALSE );
	configASSERT( xNetworkEventQueue == NULL );
	configASSERT( xIPTaskHandle == NULL );

	/* Check structure packing is correct. */
	configASSERT( sizeof( EthernetHeader_t ) == ipEXPECTED_EthernetHeader_t_SIZE );
	configASSERT( sizeof( ARPHeader_t ) == ipEXPECTED_ARPHeader_t_SIZE );
	configASSERT( sizeof( IPHeader_t ) == ipEXPECTED_IPHeader_t_SIZE );
	configASSERT( sizeof( ICMPHeader_t ) == ipEXPECTED_ICMPHeader_t_SIZE );
	configASSERT( sizeof( UDPHeader_t ) == ipEXPECTED_UDPHeader_t_SIZE );

	/* Attempt to create the queue used to communicate with the IP task. */
	xNetworkEventQueue = xQueueCreate( ( UBaseType_t ) ipconfigEVENT_QUEUE_LENGTH, ( UBaseType_t ) sizeof( IPStackEvent_t ) );
	configASSERT( xNetworkEventQueue );

	if( xNetworkEventQueue != NULL )
	{
		#if ( configQUEUE_REGISTRY_SIZE > 0 )
		{
			/* A queue registry is normally used to assist a kernel aware
			debugger.  If one is in use then it will be helpful for the debugger
			to show information about the network event queue. */
			vQueueAddToRegistry( xNetworkEventQueue, "NetEvnt" );
		}
		#endif /* configQUEUE_REGISTRY_SIZE */

		if( xNetworkBuffersInitialise() == pdPASS )
		{
			/* Store the local IP and MAC address. */
			xNetworkAddressing.ulDefaultIPAddress = FreeRTOS_inet_addr_quick( ucIPAddress[ 0 ], ucIPAddress[ 1 ], ucIPAddress[ 2 ], ucIPAddress[ 3 ] );
			xNetworkAddressing.ulNetMask = FreeRTOS_inet_addr_quick( ucNetMask[ 0 ], ucNetMask[ 1 ], ucNetMask[ 2 ], ucNetMask[ 3 ] );
			xNetworkAddressing.ulGatewayAddress = FreeRTOS_inet_addr_quick( ucGatewayAddress[ 0 ], ucGatewayAddress[ 1 ], ucGatewayAddress[ 2 ], ucGatewayAddress[ 3 ] );
			xNetworkAddressing.ulDNSServerAddress = FreeRTOS_inet_addr_quick( ucDNSServerAddress[ 0 ], ucDNSServerAddress[ 1 ], ucDNSServerAddress[ 2 ], ucDNSServerAddress[ 3 ] );
			xNetworkAddressing.ulBroadcastAddress = ( xNetworkAddressing.ulDefaultIPAddress & xNetworkAddressing.ulNetMask ) |  ~xNetworkAddressing.ulNetMask;

			memcpy( &xDefaultAddressing, &xNetworkAddressing, sizeof( xDefaultAddressing ) );

			#if ipconfigUSE_DHCP == 1
			{
				/* The IP address is not set until DHCP completes. */
				*ipLOCAL_IP_ADDRESS_POINTER = 0x00UL;
			}
			#else
			{
				/* The IP address is set from the value passed in. */
				*ipLOCAL_IP_ADDRESS_POINTER = xNetworkAddressing.ulDefaultIPAddress;

				/* Added to prevent ARP flood to gateway.  Ensure the
				gateway is on the same subnet as the IP	address. */
				configASSERT( ( ( *ipLOCAL_IP_ADDRESS_POINTER ) & xNetworkAddressing.ulNetMask ) == ( xNetworkAddressing.ulGatewayAddress & xNetworkAddressing.ulNetMask ) );
			}
			#endif /* ipconfigUSE_DHCP == 1 */

			/* The MAC address is stored in the start of the default packet
			header fragment, which is used when sending UDP packets. */
			memcpy( ( void * ) ipLOCAL_MAC_ADDRESS, ( void * ) ucMACAddress, ( size_t ) ipMAC_ADDRESS_LENGTH_BYTES );

			/* Prepare the sockets interface. */
			xReturn = vNetworkSocketsInit();

			if( pdTRUE == xReturn )
			{
				/* Create the task that processes Ethernet and stack events. */
				xReturn = xTaskCreate( prvIPTask, "IP-task", ( uint16_t )ipconfigIP_TASK_STACK_SIZE_WORDS, NULL, ( UBaseType_t )ipconfigIP_TASK_PRIORITY, &xIPTaskHandle );
			}
		}
		else
		{
			FreeRTOS_debug_printf( ( "FreeRTOS_IPInit: xNetworkBuffersInitialise() failed\n") );

			/* Clean up. */
			vQueueDelete( xNetworkEventQueue );
			xNetworkEventQueue = NULL;
		}
	}
	else
	{
		FreeRTOS_debug_printf( ( "FreeRTOS_IPInit: Network event queue could not be created\n") );
	}

	return xReturn;
}
/*-----------------------------------------------------------*/

void FreeRTOS_GetAddressConfiguration( uint32_t *pulIPAddress, uint32_t *pulNetMask, uint32_t *pulGatewayAddress, uint32_t *pulDNSServerAddress )
{
	/* Return the address configuration to the caller. */

	if( pulIPAddress != NULL )
	{
		*pulIPAddress = *ipLOCAL_IP_ADDRESS_POINTER;
	}

	if( pulNetMask != NULL )
	{
		*pulNetMask = xNetworkAddressing.ulNetMask;
	}

	if( pulGatewayAddress != NULL )
	{
		*pulGatewayAddress = xNetworkAddressing.ulGatewayAddress;
	}

	if( pulDNSServerAddress != NULL )
	{
		*pulDNSServerAddress = xNetworkAddressing.ulDNSServerAddress;
	}
}
/*-----------------------------------------------------------*/

void FreeRTOS_SetAddressConfiguration( const uint32_t *pulIPAddress, const uint32_t *pulNetMask, const uint32_t *pulGatewayAddress, const uint32_t *pulDNSServerAddress )
{
	/* Update the address configuration. */

	if( pulIPAddress != NULL )
	{
		*ipLOCAL_IP_ADDRESS_POINTER = *pulIPAddress;
	}

	if( pulNetMask != NULL )
	{
		xNetworkAddressing.ulNetMask = *pulNetMask;
	}

	if( pulGatewayAddress != NULL )
	{
		xNetworkAddressing.ulGatewayAddress = *pulGatewayAddress;
	}

	if( pulDNSServerAddress != NULL )
	{
		xNetworkAddressing.ulDNSServerAddress = *pulDNSServerAddress;
	}
}
/*-----------------------------------------------------------*/

#if ( ipconfigSUPPORT_OUTGOING_PINGS == 1 )

	BaseType_t FreeRTOS_SendPingRequest( uint32_t ulIPAddress, size_t xNumberOfBytesToSend, TickType_t xBlockTimeTicks )
	{
	NetworkBufferDescriptor_t *pxNetworkBuffer;
	ICMPHeader_t *pxICMPHeader;
	BaseType_t xReturn = pdFAIL;
	static uint16_t usSequenceNumber = 0;
	uint8_t *pucChar;
	IPStackEvent_t xStackTxEvent = { eStackTxEvent, NULL };

		if( (xNumberOfBytesToSend >= 1 ) && ( xNumberOfBytesToSend < ( ( ipconfigNETWORK_MTU - sizeof( IPHeader_t ) ) - sizeof( ICMPHeader_t ) ) ) && ( uxGetNumberOfFreeNetworkBuffers() >= 3 ) )
		{
			pxNetworkBuffer = pxGetNetworkBufferWithDescriptor( xNumberOfBytesToSend + sizeof( ICMPPacket_t ), xBlockTimeTicks );

			if( pxNetworkBuffer != NULL )
			{
				pxICMPHeader = ( ICMPHeader_t * ) &( pxNetworkBuffer->pucEthernetBuffer[ ipIP_PAYLOAD_OFFSET ] );
				usSequenceNumber++;

				/* Fill in the basic header information. */
				pxICMPHeader->ucTypeOfMessage = ipICMP_ECHO_REQUEST;
				pxICMPHeader->ucTypeOfService = 0;
				pxICMPHeader->usIdentifier = usSequenceNumber;
				pxICMPHeader->usSequenceNumber = usSequenceNumber;

				/* Find the start of the data. */
				pucChar = ( uint8_t * ) pxICMPHeader;
				pucChar += sizeof( ICMPHeader_t );

				/* Just memset the data to a fixed value. */
				memset( ( void * ) pucChar, ( int ) ipECHO_DATA_FILL_BYTE, xNumberOfBytesToSend );

				/* The message is complete, IP and checksum's are handled by
				vProcessGeneratedUDPPacket */
				pxNetworkBuffer->pucEthernetBuffer[ ipSOCKET_OPTIONS_OFFSET ] = FREERTOS_SO_UDPCKSUM_OUT;
				pxNetworkBuffer->ulIPAddress = ulIPAddress;
				pxNetworkBuffer->usPort = ipPACKET_CONTAINS_ICMP_DATA;
				pxNetworkBuffer->xDataLength = xNumberOfBytesToSend + sizeof( ICMPHeader_t );

				/* Send to the stack. */
				xStackTxEvent.pvData = pxNetworkBuffer;

				if( xSendEventStructToIPTask( &xStackTxEvent, xBlockTimeTicks) != pdPASS )
				{
					vReleaseNetworkBufferAndDescriptor( pxNetworkBuffer );
					iptraceSTACK_TX_EVENT_LOST( ipSTACK_TX_EVENT );
				}
				else
				{
					xReturn = usSequenceNumber;
				}
			}
		}
		else
		{
			/* The requested number of bytes will not fit in the available space
			in the network buffer. */
		}

		return xReturn;
	}

#endif /* ipconfigSUPPORT_OUTGOING_PINGS == 1 */
/*-----------------------------------------------------------*/

BaseType_t xSendEventToIPTask( eIPEvent_t eEvent )
{
IPStackEvent_t xEventMessage;
const TickType_t xDontBlock = ( TickType_t ) 0;

	xEventMessage.eEventType = eEvent;
	xEventMessage.pvData = ( void* )NULL;

	return xSendEventStructToIPTask( &xEventMessage, xDontBlock );
}
/*-----------------------------------------------------------*/

BaseType_t xSendEventStructToIPTask( const IPStackEvent_t *pxEvent, TickType_t xTimeout )
{
BaseType_t xReturn, xSendMessage;

	if( ( xIPIsNetworkTaskReady() == pdFALSE ) && ( pxEvent->eEventType != eNetworkDownEvent ) )
	{
		/* Only allow eNetworkDownEvent events if the IP task is not ready
		yet.  Not going to attempt to send the message so the send failed. */
		xReturn = pdFAIL;
	}
	else
	{
		xSendMessage = pdTRUE;

		#if( ipconfigUSE_TCP == 1 )
		{
			if( pxEvent->eEventType == eTCPTimerEvent )
			{
				/* TCP timer events are sent to wake the timer task when
				xTCPTimer has expired, but there is no point sending them if the
				IP task is already awake processing other message. */
				xTCPTimer.bExpired = pdTRUE_UNSIGNED;

				if( uxQueueMessagesWaiting( xNetworkEventQueue ) != 0u )
				{
					/* Not actually going to send the message but this is not a
					failure as the message didn't need to be sent. */
					xSendMessage = pdFALSE;
				}
			}
		}
		#endif /* ipconfigUSE_TCP */

		if( xSendMessage != pdFALSE )
		{
			/* The IP task cannot block itself while waiting for itself to
			respond. */
			if( ( xIsCallingFromIPTask() == pdTRUE ) && ( xTimeout > ( TickType_t ) 0 ) )
			{
				xTimeout = ( TickType_t ) 0;
			}

			xReturn = xQueueSendToBack( xNetworkEventQueue, pxEvent, xTimeout );

			if( xReturn == pdFAIL )
			{
				/* A message should have been sent to the IP task, but wasn't. */
				FreeRTOS_debug_printf( ( "xSendEventStructToIPTask: CAN NOT ADD %d\n", pxEvent->eEventType ) );
				iptraceSTACK_TX_EVENT_LOST( pxEvent->eEventType );
			}
		}
		else
		{
			/* It was not necessary to send the message to process the event so
			even though the message was not sent the call was successful. */
			xReturn = pdPASS;
		}
	}

	return xReturn;
}
/*-----------------------------------------------------------*/

eFrameProcessingResult_t eConsiderFrameForProcessing( const uint8_t * const pucEthernetBuffer )
{
eFrameProcessingResult_t eReturn;
const EthernetHeader_t *pxEthernetHeader;

	pxEthernetHeader = ( const EthernetHeader_t * ) pucEthernetBuffer;

	if( memcmp( ( void * ) ipLOCAL_MAC_ADDRESS, ( void * ) &( pxEthernetHeader->xDestinationAddress ), sizeof( MACAddress_t ) ) == 0 )
	{
		/* The packet was directed to this node directly - process it. */
		eReturn = eProcessBuffer;
	}
	else if( memcmp( ( void * ) xBroadcastMACAddress.ucBytes, ( void * ) pxEthernetHeader->xDestinationAddress.ucBytes, sizeof( MACAddress_t ) ) == 0 )
	{
		/* The packet was a broadcast - process it. */
		eReturn = eProcessBuffer;
	}
	else
#if( ipconfigUSE_LLMNR == 1 )
	if( memcmp( ( void * ) xLLMNR_MacAdress.ucBytes, ( void * ) pxEthernetHeader->xDestinationAddress.ucBytes, sizeof( MACAddress_t ) ) == 0 )
	{
		/* The packet is a request for LLMNR - process it. */
		eReturn = eProcessBuffer;
	}
	else
#endif /* ipconfigUSE_LLMNR */
	{
		/* The packet was not a broadcast, or for this node, just release
		the buffer without taking any other action. */
		eReturn = eReleaseBuffer;
	}

	#if( ipconfigFILTER_OUT_NON_ETHERNET_II_FRAMES == 1 )
	{
	uint16_t usFrameType;

		if( eReturn == eProcessBuffer )
		{
			usFrameType = pxEthernetHeader->usFrameType;
			usFrameType = FreeRTOS_ntohs( usFrameType );

			if( usFrameType <= 0x600U )
			{
				/* Not an Ethernet II frame. */
				eReturn = eReleaseBuffer;
			}
		}
	}
	#endif /* ipconfigFILTER_OUT_NON_ETHERNET_II_FRAMES == 1  */

	return eReturn;
}
/*-----------------------------------------------------------*/

static void prvProcessNetworkDownEvent( void )
{
	/* Stop the ARP timer while there is no network. */
	xARPTimer.bActive = pdFALSE_UNSIGNED;

	#if ipconfigUSE_NETWORK_EVENT_HOOK == 1
	{
		static BaseType_t xCallEventHook = pdFALSE;

		/* The first network down event is generated by the IP stack itself to
		initialise the network hardware, so do not call the network down event
		the first time through. */
		if( xCallEventHook == pdTRUE )
		{
			vApplicationIPNetworkEventHook( eNetworkDown );
		}
		xCallEventHook = pdTRUE;
	}
	#endif

	/* Per the ARP Cache Validation section of https://tools.ietf.org/html/rfc1122, 
	treat network down as a "delivery problem" and flush the ARP cache for this
	interface. */
	FreeRTOS_ClearARP( );

	/* The network has been disconnected (or is being initialised for the first
	time).  Perform whatever hardware processing is necessary to bring it up
	again, or wait for it to be available again.  This is hardware dependent. */
	if( xNetworkInterfaceInitialise() != pdPASS )
	{
		/* Ideally the network interface initialisation function will only
		return when the network is available.  In case this is not the case,
		wait a while before retrying the initialisation. */
		vTaskDelay( ipINITIALISATION_RETRY_DELAY );
		FreeRTOS_NetworkDown();
	}
	else
	{
		/* Set remaining time to 0 so it will become active immediately. */
		#if ipconfigUSE_DHCP == 1
		{
			/* The network is not up until DHCP has completed. */
			vDHCPProcess( pdTRUE );
			xSendEventToIPTask( eDHCPEvent );
		}
		#else
		{
			/* Perform any necessary 'network up' processing. */
			vIPNetworkUpCalls();
		}
		#endif
	}
}
/*-----------------------------------------------------------*/

void vIPNetworkUpCalls( void )
{
	xNetworkUp = pdTRUE;

	#if( ipconfigUSE_NETWORK_EVENT_HOOK == 1 )
	{
		vApplicationIPNetworkEventHook( eNetworkUp );
	}
	#endif /* ipconfigUSE_NETWORK_EVENT_HOOK */

	#if( ipconfigDNS_USE_CALLBACKS != 0 )
	{
		/* The following function is declared in FreeRTOS_DNS.c	and 'private' to
		this library */
		extern void vDNSInitialise( void );
		vDNSInitialise();
	}
	#endif /* ipconfigDNS_USE_CALLBACKS != 0 */

	/* Set remaining time to 0 so it will become active immediately. */
	prvIPTimerReload( &xARPTimer, pdMS_TO_TICKS( ipARP_TIMER_PERIOD_MS ) );
}
/*-----------------------------------------------------------*/

static void prvProcessEthernetPacket( NetworkBufferDescriptor_t * const pxNetworkBuffer )
{
EthernetHeader_t *pxEthernetHeader;
eFrameProcessingResult_t eReturned = eReleaseBuffer;

	configASSERT( pxNetworkBuffer );

	/* Interpret the Ethernet frame. */
	if( pxNetworkBuffer->xDataLength >= sizeof( EthernetHeader_t ) )
	{
		eReturned = ipCONSIDER_FRAME_FOR_PROCESSING( pxNetworkBuffer->pucEthernetBuffer );
		pxEthernetHeader = ( EthernetHeader_t * )( pxNetworkBuffer->pucEthernetBuffer );

		if( eReturned == eProcessBuffer )
		{
			/* Interpret the received Ethernet packet. */
			switch( pxEthernetHeader->usFrameType )
			{
			case ipARP_FRAME_TYPE:
				/* The Ethernet frame contains an ARP packet. */
				if( pxNetworkBuffer->xDataLength >= sizeof( ARPPacket_t ) )
				{
					eReturned = eARPProcessPacket( ( ARPPacket_t * )pxNetworkBuffer->pucEthernetBuffer );
				}
				else
				{
					eReturned = eReleaseBuffer;
				}
				break;

			case ipIPv4_FRAME_TYPE:
				/* The Ethernet frame contains an IP packet. */
				if( pxNetworkBuffer->xDataLength >= sizeof( IPPacket_t ) )
				{
					eReturned = prvProcessIPPacket( ( IPPacket_t * )pxNetworkBuffer->pucEthernetBuffer, pxNetworkBuffer );
				}
				else
				{
					eReturned = eReleaseBuffer;
				}
				break;

			default:
				/* No other packet types are handled.  Nothing to do. */
				eReturned = eReleaseBuffer;
				break;
			}
		}
	}

	/* Perform any actions that resulted from processing the Ethernet frame. */
	switch( eReturned )
	{
		case eReturnEthernetFrame :
			/* The Ethernet frame will have been updated (maybe it was
			an ARP request or a PING request?) and should be sent back to
			its source. */
			vReturnEthernetFrame( pxNetworkBuffer, pdTRUE );
			/* parameter pdTRUE: the buffer must be released once
			the frame has been transmitted */
			break;

		case eFrameConsumed :
			/* The frame is in use somewhere, don't release the buffer
			yet. */
			break;

		default :
			/* The frame is not being used anywhere, and the
			NetworkBufferDescriptor_t structure containing the frame should
			just be	released back to the list of free buffers. */
			vReleaseNetworkBufferAndDescriptor( pxNetworkBuffer );
			break;
	}
}
/*-----------------------------------------------------------*/

static eFrameProcessingResult_t prvAllowIPPacket( const IPPacket_t * const pxIPPacket,
	NetworkBufferDescriptor_t * const pxNetworkBuffer, UBaseType_t uxHeaderLength )
{
eFrameProcessingResult_t eReturn = eProcessBuffer;

#if( ( ipconfigETHERNET_DRIVER_FILTERS_PACKETS == 0 ) || ( ipconfigDRIVER_INCLUDED_RX_IP_CHECKSUM == 0 ) )
	const IPHeader_t * pxIPHeader = &( pxIPPacket->xIPHeader );
#else
	/* or else, the parameter won't be used and the function will be optimised
	away */
	( void ) pxIPPacket;
#endif

	#if( ipconfigETHERNET_DRIVER_FILTERS_PACKETS == 0 )
	{
		/* In systems with a very small amount of RAM, it might be advantageous
		to have incoming messages checked earlier, by the network card driver.
		This method may decrease the usage of sparse network buffers. */
		uint32_t ulDestinationIPAddress = pxIPHeader->ulDestinationIPAddress;

			/* Ensure that the incoming packet is not fragmented (only outgoing
			packets can be fragmented) as these are the only handled IP frames
			currently. */
			if( ( pxIPHeader->usFragmentOffset & ipFRAGMENT_OFFSET_BIT_MASK ) != 0U )
			{
				/* Can not handle, fragmented packet. */
				eReturn = eReleaseBuffer;
			}
			/* 0x45 means: IPv4 with an IP header of 5 x 4 = 20 bytes
			 * 0x47 means: IPv4 with an IP header of 7 x 4 = 28 bytes */
			else if( ( pxIPHeader->ucVersionHeaderLength < 0x45u ) || ( pxIPHeader->ucVersionHeaderLength > 0x4Fu ) )
			{
				/* Can not handle, unknown or invalid header version. */
				eReturn = eReleaseBuffer;
			}
				/* Is the packet for this IP address? */
			else if( ( ulDestinationIPAddress != *ipLOCAL_IP_ADDRESS_POINTER ) &&
				/* Is it the global broadcast address 255.255.255.255 ? */
				( ulDestinationIPAddress != ipBROADCAST_IP_ADDRESS ) &&
				/* Is it a specific broadcast address 192.168.1.255 ? */
				( ulDestinationIPAddress != xNetworkAddressing.ulBroadcastAddress ) &&
			#if( ipconfigUSE_LLMNR == 1 )
				/* Is it the LLMNR multicast address? */
				( ulDestinationIPAddress != ipLLMNR_IP_ADDR ) &&
			#endif
				/* Or (during DHCP negotiation) we have no IP-address yet? */
				( *ipLOCAL_IP_ADDRESS_POINTER != 0UL ) )
			{
				/* Packet is not for this node, release it */
				eReturn = eReleaseBuffer;
			}
	}
	#endif /* ipconfigETHERNET_DRIVER_FILTERS_PACKETS */

	#if( ipconfigDRIVER_INCLUDED_RX_IP_CHECKSUM == 0 )
	{
		/* Some drivers of NIC's with checksum-offloading will enable the above
		define, so that the checksum won't be checked again here */
		if (eReturn == eProcessBuffer )
		{
			/* Is the IP header checksum correct? */
			if( ( pxIPHeader->ucProtocol != ( uint8_t ) ipPROTOCOL_ICMP ) &&
				( usGenerateChecksum( 0UL, ( uint8_t * ) &( pxIPHeader->ucVersionHeaderLength ), ( size_t ) uxHeaderLength ) != ipCORRECT_CRC ) )
			{
				/* Check sum in IP-header not correct. */
				eReturn = eReleaseBuffer;
			}
			/* Is the upper-layer checksum (TCP/UDP/ICMP) correct? */
			else if( usGenerateProtocolChecksum( ( uint8_t * )( pxNetworkBuffer->pucEthernetBuffer ), pxNetworkBuffer->xDataLength, pdFALSE ) != ipCORRECT_CRC )
			{
				/* Protocol checksum not accepted. */
				eReturn = eReleaseBuffer;
			}
		}
	}
	#else
	{
		/* to avoid warning unused parameters */
		( void ) pxNetworkBuffer;
		( void ) uxHeaderLength;
	}
	#endif /* ipconfigDRIVER_INCLUDED_RX_IP_CHECKSUM == 0 */

	return eReturn;
}
/*-----------------------------------------------------------*/

static eFrameProcessingResult_t prvProcessIPPacket( IPPacket_t * const pxIPPacket, NetworkBufferDescriptor_t * const pxNetworkBuffer )
{
eFrameProcessingResult_t eReturn;
IPHeader_t * pxIPHeader = &( pxIPPacket->xIPHeader );
UBaseType_t uxHeaderLength = ( UBaseType_t ) ( ( pxIPHeader->ucVersionHeaderLength & 0x0Fu ) << 2 );
uint8_t ucProtocol;

	/* Bound the calculated header length: take away the Ethernet header size,
	then check if the IP header is claiming to be longer than the remaining
	total packet size. Also check for minimal header field length. */
	if( ( uxHeaderLength > ( pxNetworkBuffer->xDataLength - ipSIZE_OF_ETH_HEADER ) ) ||
		( uxHeaderLength < ipSIZE_OF_IPv4_HEADER ) )
	{
		return eReleaseBuffer;
	}

	ucProtocol = pxIPPacket->xIPHeader.ucProtocol;
	/* Check if the IP headers are acceptable and if it has our destination. */
	eReturn = prvAllowIPPacket( pxIPPacket, pxNetworkBuffer, uxHeaderLength );

	if( eReturn == eProcessBuffer )
	{
		if( uxHeaderLength > ipSIZE_OF_IPv4_HEADER )
		{
			/* All structs of headers expect a IP header size of 20 bytes
			 * IP header options were included, we'll ignore them and cut them out
			 * Note: IP options are mostly use in Multi-cast protocols */
			const size_t optlen = ( ( size_t ) uxHeaderLength ) - ipSIZE_OF_IPv4_HEADER;
			/* From: the previous start of UDP/ICMP/TCP data */
			uint8_t *pucSource = ( uint8_t* )(pxNetworkBuffer->pucEthernetBuffer + sizeof( EthernetHeader_t ) + uxHeaderLength);
			/* To: the usual start of UDP/ICMP/TCP data at offset 20 from IP header */
			uint8_t *pucTarget = ( uint8_t* )(pxNetworkBuffer->pucEthernetBuffer + sizeof( EthernetHeader_t ) + ipSIZE_OF_IPv4_HEADER);
			/* How many: total length minus the options and the lower headers */
			const size_t  xMoveLen = pxNetworkBuffer->xDataLength - optlen - ipSIZE_OF_IPv4_HEADER - ipSIZE_OF_ETH_HEADER;

			memmove( pucTarget, pucSource, xMoveLen );
			pxNetworkBuffer->xDataLength -= optlen;

			/* Fix-up new version/header length field in IP packet. */
			pxIPHeader->ucVersionHeaderLength = ( pxIPHeader->ucVersionHeaderLength & 0xF0 ) | /* High nibble is the version. */
												( ( ipSIZE_OF_IPv4_HEADER >> 2 ) & 0x0F ); /* Low nibble is the header size, in bytes, divided by four. */
		}

		/* Add the IP and MAC addresses to the ARP table if they are not
		already there - otherwise refresh the age of the existing
		entry. */
		if( ucProtocol != ( uint8_t ) ipPROTOCOL_UDP )
		{
			/* Refresh the ARP cache with the IP/MAC-address of the received packet
			 * For UDP packets, this will be done later in xProcessReceivedUDPPacket()
			 * as soon as know that the message will be handled by someone
			 * This will prevent that the ARP cache will get overwritten
			 * with the IP-address of useless broadcast packets
			 */
			vARPRefreshCacheEntry( &( pxIPPacket->xEthernetHeader.xSourceAddress ), pxIPHeader->ulSourceIPAddress );
		}
		switch( ucProtocol )
		{
			case ipPROTOCOL_ICMP :
				/* The IP packet contained an ICMP frame.  Don't bother
				checking the ICMP checksum, as if it is wrong then the
				wrong data will also be returned, and the source of the
				ping will know something went wrong because it will not
				be able to validate what it receives. */
				#if ( ipconfigREPLY_TO_INCOMING_PINGS == 1 ) || ( ipconfigSUPPORT_OUTGOING_PINGS == 1 )
				{
					if( pxNetworkBuffer->xDataLength >= sizeof( ICMPPacket_t ) )
					{
						ICMPPacket_t *pxICMPPacket = ( ICMPPacket_t * )( pxNetworkBuffer->pucEthernetBuffer );
						if( pxIPHeader->ulDestinationIPAddress == *ipLOCAL_IP_ADDRESS_POINTER )
						{
							eReturn = prvProcessICMPPacket( pxICMPPacket );
						}
					}
					else
					{
						eReturn = eReleaseBuffer;
					}
				}
				#endif /* ( ipconfigREPLY_TO_INCOMING_PINGS == 1 ) || ( ipconfigSUPPORT_OUTGOING_PINGS == 1 ) */
				break;

			case ipPROTOCOL_UDP :
				{
					/* The IP packet contained a UDP frame. */
					UDPPacket_t *pxUDPPacket = ( UDPPacket_t * ) ( pxNetworkBuffer->pucEthernetBuffer );

					/* Only proceed if the payload length indicated in the header
					appears to be valid. */
					if ( pxNetworkBuffer->xDataLength >= sizeof( UDPPacket_t ) )
					{
						/* Ensure that downstream UDP packet handling has the lesser
						 * of: the actual network buffer Ethernet frame length, or
						 * the sender's UDP packet header payload length, minus the
						 * size of the UDP header.
						 *
						 * The size of the UDP packet structure in this implementation
						 * includes the size of the Ethernet header, the size of
						 * the IP header, and the size of the UDP header.
						 */

						pxNetworkBuffer->xDataLength -= sizeof( UDPPacket_t );
						if( ( FreeRTOS_ntohs( pxUDPPacket->xUDPHeader.usLength ) - sizeof( UDPHeader_t ) ) <
								pxNetworkBuffer->xDataLength )
						{
							pxNetworkBuffer->xDataLength = FreeRTOS_ntohs( pxUDPPacket->xUDPHeader.usLength ) - sizeof( UDPHeader_t );
						}

						/* Fields in pxNetworkBuffer (usPort, ulIPAddress) are network order. */
						pxNetworkBuffer->usPort = pxUDPPacket->xUDPHeader.usSourcePort;
						pxNetworkBuffer->ulIPAddress = pxUDPPacket->xIPHeader.ulSourceIPAddress;

						/* ipconfigDRIVER_INCLUDED_RX_IP_CHECKSUM:
						 * In some cases, the upper-layer checksum has been calculated
						 * by the NIC driver.
						 *
						 * Pass the packet payload to the UDP sockets implementation. */
						if( xProcessReceivedUDPPacket( pxNetworkBuffer,
													   pxUDPPacket->xUDPHeader.usDestinationPort ) == pdPASS )
						{
							eReturn = eFrameConsumed;
						}
					}
					else
					{
						eReturn = eReleaseBuffer;
					}
				}
				break;

#if ipconfigUSE_TCP == 1
			case ipPROTOCOL_TCP :
				{

					if( xProcessReceivedTCPPacket( pxNetworkBuffer ) == pdPASS )
					{
						eReturn = eFrameConsumed;
					}

					/* Setting this variable will cause xTCPTimerCheck()
					to be called just before the IP-task blocks. */
					xProcessedTCPMessage++;
				}
				break;
#endif
			default	:
				/* Not a supported frame type. */
				break;
		}
	}

	return eReturn;
}
/*-----------------------------------------------------------*/

#if ( ipconfigSUPPORT_OUTGOING_PINGS == 1 )

	static void prvProcessICMPEchoReply( ICMPPacket_t * const pxICMPPacket )
	{
	ePingReplyStatus_t eStatus = eSuccess;
	uint16_t usDataLength, usCount;
	uint8_t *pucByte;

		/* Find the total length of the IP packet. */
		usDataLength = pxICMPPacket->xIPHeader.usLength;
		usDataLength = FreeRTOS_ntohs( usDataLength );

		/* Remove the length of the IP headers to obtain the length of the ICMP
		message itself. */
		usDataLength = ( uint16_t ) ( ( ( uint32_t ) usDataLength ) - ipSIZE_OF_IPv4_HEADER );

		/* Remove the length of the ICMP header, to obtain the length of
		data contained in the ping. */
		usDataLength = ( uint16_t ) ( ( ( uint32_t ) usDataLength ) - ipSIZE_OF_ICMP_HEADER );

		/* Checksum has already been checked before in prvProcessIPPacket */

		/* Find the first byte of the data within the ICMP packet. */
		pucByte = ( uint8_t * ) pxICMPPacket;
		pucByte += sizeof( ICMPPacket_t );

		/* Check each byte. */
		for( usCount = 0; usCount < usDataLength; usCount++ )
		{
			if( *pucByte != ipECHO_DATA_FILL_BYTE )
			{
				eStatus = eInvalidData;
				break;
			}

			pucByte++;
		}

		/* Call back into the application to pass it the result. */
		vApplicationPingReplyHook( eStatus, pxICMPPacket->xICMPHeader.usIdentifier );
	}

#endif
/*-----------------------------------------------------------*/

#if ( ipconfigREPLY_TO_INCOMING_PINGS == 1 )

	static eFrameProcessingResult_t prvProcessICMPEchoRequest( ICMPPacket_t * const pxICMPPacket )
	{
	ICMPHeader_t *pxICMPHeader;
	IPHeader_t *pxIPHeader;
	uint16_t usRequest;

		pxICMPHeader = &( pxICMPPacket->xICMPHeader );
		pxIPHeader = &( pxICMPPacket->xIPHeader );

		/* HT:endian: changed back */
		iptraceSENDING_PING_REPLY( pxIPHeader->ulSourceIPAddress );

		/* The checksum can be checked here - but a ping reply should be
		returned even if the checksum is incorrect so the other end can
		tell that the ping was received - even if the ping reply contains
		invalid data. */
		pxICMPHeader->ucTypeOfMessage = ( uint8_t ) ipICMP_ECHO_REPLY;
		pxIPHeader->ulDestinationIPAddress = pxIPHeader->ulSourceIPAddress;
		pxIPHeader->ulSourceIPAddress = *ipLOCAL_IP_ADDRESS_POINTER;

		/* Update the checksum because the ucTypeOfMessage member in the header
		has been changed to ipICMP_ECHO_REPLY.  This is faster than calling
		usGenerateChecksum(). */

		/* due to compiler warning "integer operation result is out of range" */

		usRequest = ( uint16_t ) ( ( uint16_t )ipICMP_ECHO_REQUEST << 8 );

		if( pxICMPHeader->usChecksum >= FreeRTOS_htons( 0xFFFFu - usRequest ) )
		{
			pxICMPHeader->usChecksum = ( uint16_t )
				( ( ( uint32_t ) pxICMPHeader->usChecksum ) +
					FreeRTOS_htons( usRequest + 1UL ) );
		}
		else
		{
			pxICMPHeader->usChecksum = ( uint16_t )
				( ( ( uint32_t ) pxICMPHeader->usChecksum ) +
					FreeRTOS_htons( usRequest ) );
		}
		return eReturnEthernetFrame;
	}

#endif /* ipconfigREPLY_TO_INCOMING_PINGS == 1 */
/*-----------------------------------------------------------*/

#if ( ipconfigREPLY_TO_INCOMING_PINGS == 1 ) || ( ipconfigSUPPORT_OUTGOING_PINGS == 1 )

	static eFrameProcessingResult_t prvProcessICMPPacket( ICMPPacket_t * const pxICMPPacket )
	{
	eFrameProcessingResult_t eReturn = eReleaseBuffer;

		iptraceICMP_PACKET_RECEIVED();
		switch( pxICMPPacket->xICMPHeader.ucTypeOfMessage )
		{
			case ipICMP_ECHO_REQUEST	:
				#if ( ipconfigREPLY_TO_INCOMING_PINGS == 1 )
				{
					eReturn = prvProcessICMPEchoRequest( pxICMPPacket );
				}
				#endif /* ( ipconfigREPLY_TO_INCOMING_PINGS == 1 ) */
				break;

			case ipICMP_ECHO_REPLY		:
				#if ( ipconfigSUPPORT_OUTGOING_PINGS == 1 )
				{
					prvProcessICMPEchoReply( pxICMPPacket );
				}
				#endif /* ipconfigSUPPORT_OUTGOING_PINGS */
				break;

			default	:
				break;
		}

		return eReturn;
	}

#endif /* ( ipconfigREPLY_TO_INCOMING_PINGS == 1 ) || ( ipconfigSUPPORT_OUTGOING_PINGS == 1 ) */
/*-----------------------------------------------------------*/

uint16_t usGenerateProtocolChecksum( const uint8_t * const pucEthernetBuffer, size_t uxBufferLength, BaseType_t xOutgoingPacket )
{
uint32_t ulLength;
uint16_t usChecksum, *pusChecksum;
const IPPacket_t * pxIPPacket;
UBaseType_t uxIPHeaderLength;
ProtocolPacket_t *pxProtPack;
uint8_t ucProtocol;
#if( ipconfigHAS_DEBUG_PRINTF != 0 )
	const char *pcType;
#endif

	/* Check for minimum packet size. */
	if( uxBufferLength < sizeof( IPPacket_t ) )
	{
		return ipINVALID_LENGTH;
	}

	/* Parse the packet length. */
	pxIPPacket = ( const IPPacket_t * ) pucEthernetBuffer;

	/* Per https://tools.ietf.org/html/rfc791, the four-bit Internet Header
	Length field contains the length of the internet header in 32-bit words. */
	uxIPHeaderLength = ( UBaseType_t ) ( sizeof( uint32_t ) * ( pxIPPacket->xIPHeader.ucVersionHeaderLength & 0x0Fu ) );

	/* Check for minimum packet size. */
	if( uxBufferLength < sizeof( IPPacket_t ) + uxIPHeaderLength - ipSIZE_OF_IPv4_HEADER )
	{
		return ipINVALID_LENGTH;
	}
	if( uxBufferLength < ( size_t ) ( ipSIZE_OF_ETH_HEADER + FreeRTOS_ntohs( pxIPPacket->xIPHeader.usLength ) ) )
	{
		return ipINVALID_LENGTH;
	}

	/* Identify the next protocol. */
	ucProtocol = pxIPPacket->xIPHeader.ucProtocol;

	/* N.B., if this IP packet header includes Options, then the following
	assignment results in a pointer into the protocol packet with the Ethernet
	and IP headers incorrectly aligned. However, either way, the "third"
	protocol (Layer 3 or 4) header will be aligned, which is the convenience
	of this calculation. */
	pxProtPack = ( ProtocolPacket_t * ) ( pucEthernetBuffer + ( uxIPHeaderLength - ipSIZE_OF_IPv4_HEADER ) );

	/* Switch on the Layer 3/4 protocol. */
	if( ucProtocol == ( uint8_t ) ipPROTOCOL_UDP )
	{
		if( uxBufferLength < ( uxIPHeaderLength + ipSIZE_OF_ETH_HEADER + ipSIZE_OF_UDP_HEADER ) )
		{
			return ipINVALID_LENGTH;
		}

		pusChecksum = ( uint16_t * ) ( &( pxProtPack->xUDPPacket.xUDPHeader.usChecksum ) );
		#if( ipconfigHAS_DEBUG_PRINTF != 0 )
		{
			pcType = "UDP";
		}
		#endif	/* ipconfigHAS_DEBUG_PRINTF != 0 */
	}
	else if( ucProtocol == ( uint8_t ) ipPROTOCOL_TCP )
	{
		if( uxBufferLength < ( uxIPHeaderLength + ipSIZE_OF_ETH_HEADER + ipSIZE_OF_TCP_HEADER ) )
		{
			return ipINVALID_LENGTH;
		}

		pusChecksum = ( uint16_t * ) ( &( pxProtPack->xTCPPacket.xTCPHeader.usChecksum ) );
		#if( ipconfigHAS_DEBUG_PRINTF != 0 )
		{
			pcType = "TCP";
		}
		#endif	/* ipconfigHAS_DEBUG_PRINTF != 0 */
	}
	else if( ( ucProtocol == ( uint8_t ) ipPROTOCOL_ICMP ) ||
			( ucProtocol == ( uint8_t ) ipPROTOCOL_IGMP ) )
	{
		if( uxBufferLength < ( uxIPHeaderLength + ipSIZE_OF_ETH_HEADER + ipSIZE_OF_ICMP_HEADER ) )
		{
			return ipINVALID_LENGTH;
		}

		pusChecksum = ( uint16_t * ) ( &( pxProtPack->xICMPPacket.xICMPHeader.usChecksum ) );
		#if( ipconfigHAS_DEBUG_PRINTF != 0 )
		{
			if( ucProtocol == ( uint8_t ) ipPROTOCOL_ICMP )
			{
				pcType = "ICMP";
			}
			else
			{
				pcType = "IGMP";
			}
		}
		#endif	/* ipconfigHAS_DEBUG_PRINTF != 0 */
	}
	else
	{
		/* Unhandled protocol, other than ICMP, IGMP, UDP, or TCP. */
		return ipUNHANDLED_PROTOCOL;
	}

	/* The protocol and checksum field have been identified. Check the direction
	of the packet. */
	if( xOutgoingPacket != pdFALSE )
	{
		/* This is an outgoing packet. Before calculating the checksum, set it
		to zero. */
		*( pusChecksum ) = 0u;
	}
	else if( ( *pusChecksum == 0u ) && ( ucProtocol == ( uint8_t ) ipPROTOCOL_UDP ) )
	{
		/* Sender hasn't set the checksum, no use to calculate it. */
		return ipCORRECT_CRC;
	}

	ulLength = ( uint32_t )
		( FreeRTOS_ntohs( pxIPPacket->xIPHeader.usLength ) - ( ( uint16_t ) uxIPHeaderLength ) ); /* normally minus 20 */

	if( ( ulLength < sizeof( pxProtPack->xUDPPacket.xUDPHeader ) ) ||
		( ulLength > ( uint32_t )( ipconfigNETWORK_MTU - uxIPHeaderLength ) ) )
	{
		#if( ipconfigHAS_DEBUG_PRINTF != 0 )
		{
			FreeRTOS_debug_printf( ( "usGenerateProtocolChecksum[%s]: len invalid: %lu\n", pcType, ulLength ) );
		}
		#endif	/* ipconfigHAS_DEBUG_PRINTF != 0 */

		/* Again, in a 16-bit return value there is no space to indicate an
		error.  For incoming packets, 0x1234 will cause dropping of the packet.
		For outgoing packets, there is a serious problem with the
		format/length */
		return ipINVALID_LENGTH;
	}
	if( ucProtocol <= ( uint8_t ) ipPROTOCOL_IGMP )
	{
		/* ICMP/IGMP do not have a pseudo header for CRC-calculation. */
		usChecksum = ( uint16_t )
			( ~usGenerateChecksum( 0UL,
				( uint8_t * ) &( pxProtPack->xTCPPacket.xTCPHeader ), ( size_t ) ulLength ) );
	}
	else
	{
		/* For UDP and TCP, sum the pseudo header, i.e. IP protocol + length
		fields */
		usChecksum = ( uint16_t ) ( ulLength + ( ( uint16_t ) ucProtocol ) );

		/* And then continue at the IPv4 source and destination addresses. */
		usChecksum = ( uint16_t )
			( ~usGenerateChecksum( ( uint32_t ) usChecksum, ( uint8_t * )&( pxIPPacket->xIPHeader.ulSourceIPAddress ),
				( 2u * sizeof( pxIPPacket->xIPHeader.ulSourceIPAddress ) + ulLength ) ) );

		/* Sum TCP header and data. */
	}

	if( xOutgoingPacket == pdFALSE )
	{
		/* This is in incoming packet. If the CRC is correct, it should be zero. */
		if( usChecksum == 0u )
		{
			usChecksum = ( uint16_t )ipCORRECT_CRC;
		}
	}
	else
	{
		if( ( usChecksum == 0u ) && ( ucProtocol == ( uint8_t ) ipPROTOCOL_UDP ) )
		{
			/* In case of UDP, a calculated checksum of 0x0000 is transmitted
			as 0xffff. A value of zero would mean that the checksum is not used. */
			#if( ipconfigHAS_DEBUG_PRINTF != 0 )
			{
				if( xOutgoingPacket != pdFALSE )
				{
					FreeRTOS_debug_printf( ( "usGenerateProtocolChecksum[%s]: crc swap: %04X\n", pcType, usChecksum ) );
				}
			}
			#endif	/* ipconfigHAS_DEBUG_PRINTF != 0 */

			usChecksum = ( uint16_t )0xffffu;
		}
	}
	usChecksum = FreeRTOS_htons( usChecksum );

	if( xOutgoingPacket != pdFALSE )
	{
		*( pusChecksum ) = usChecksum;
	}
	#if( ipconfigHAS_DEBUG_PRINTF != 0 )
	else if( ( xOutgoingPacket == pdFALSE ) && ( usChecksum != ipCORRECT_CRC ) )
	{
		FreeRTOS_debug_printf( ( "usGenerateProtocolChecksum[%s]: ID %04X: from %lxip to %lxip bad crc: %04X\n",
			pcType,
			FreeRTOS_ntohs( pxIPPacket->xIPHeader.usIdentification ),
			FreeRTOS_ntohl( pxIPPacket->xIPHeader.ulSourceIPAddress ),
			FreeRTOS_ntohl( pxIPPacket->xIPHeader.ulDestinationIPAddress ),
			FreeRTOS_ntohs( *pusChecksum ) ) );
	}
	#endif	/* ipconfigHAS_DEBUG_PRINTF != 0 */

	return usChecksum;
}
/*-----------------------------------------------------------*/

/**
 * This method generates a checksum for a given IPv4 header, per RFC791 (page 14).
 * The checksum algorithm is decribed as:
 *   "[T]he 16 bit one's complement of the one's complement sum of all 16 bit words in the
 *   header.  For purposes of computing the checksum, the value of the checksum field is zero."
 *
 * In a nutshell, that means that each 16-bit 'word' must be summed, after which
 * the number of 'carries' (overflows) is added to the result. If that addition
 * produces an overflow, that 'carry' must also be added to the final result. The final checksum
 * should be the bitwise 'not' (ones-complement) of the result if the packet is
 * meant to be transmitted, but this method simply returns the raw value, probably
 * because when a packet is received, the checksum is verified by checking that
 * ((received & calculated) == 0) without applying a bitwise 'not' to the 'calculated' checksum.
 *
 * This logic is optimized for microcontrollers which have limited resources, so the logic looks odd.
 * It iterates over the full range of 16-bit words, but it does so by processing several 32-bit
 * words at once whenever possible. Its first step is to align the memory pointer to a 32-bit boundary,
 * after which it runs a fast loop to process multiple 32-bit words at once and adding their 'carries'.
 * Finally, it finishes up by processing any remaining 16-bit words, and adding up all of the 'carries'.
 * With 32-bit arithmetic, the number of 16-bit 'carries' produced by sequential additions can be found
 * by looking at the 16 most-significant bits of the 32-bit integer, since a 32-bit int will continue
 * counting up instead of overflowing after 16 bits. That is why the actual checksum calculations look like:
 *   union.u32 = ( uint32_t ) union.u16[ 0 ] + union.u16[ 1 ];
 *
 * Arguments:
 *   ulSum: This argument provides a value to initialize the progressive summation
 *	 of the header's values to. It is often 0, but protocols like TCP or UDP
 *	 can have pseudo-header fields which need to be included in the checksum.
 *   pucNextData: This argument contains the address of the first byte which this
 *	 method should process. The method's memory iterator is initialized to this value.
 *   uxDataLengthBytes: This argument contains the number of bytes that this method
 *	 should process.
 */
uint16_t usGenerateChecksum( uint32_t ulSum, const uint8_t * pucNextData, size_t uxDataLengthBytes )
{
xUnion32 xSum2, xSum, xTerm;
xUnionPtr xSource;		/* Points to first byte */
xUnionPtr xLastSource;	/* Points to last byte plus one */
uint32_t ulAlignBits, ulCarry = 0ul;

	/* Small MCUs often spend up to 30% of the time doing checksum calculations
	This function is optimised for 32-bit CPUs; Each time it will try to fetch
	32-bits, sums it with an accumulator and counts the number of carries. */

	/* Swap the input (little endian platform only). */
	xSum.u32 = FreeRTOS_ntohs( ulSum );
	xTerm.u32 = 0ul;

	xSource.u8ptr = ( uint8_t * ) pucNextData;
	ulAlignBits = ( ( ( uint32_t ) pucNextData ) & 0x03u ); /* gives 0, 1, 2, or 3 */

	/* If byte (8-bit) aligned... */
	if( ( ( ulAlignBits & 1ul ) != 0ul ) && ( uxDataLengthBytes >= ( size_t ) 1 ) )
	{
		xTerm.u8[ 1 ] = *( xSource.u8ptr );
		( xSource.u8ptr )++;
		uxDataLengthBytes--;
		/* Now xSource is word (16-bit) aligned. */
	}

	/* If half-word (16-bit) aligned... */
	if( ( ( ulAlignBits == 1u ) || ( ulAlignBits == 2u ) ) && ( uxDataLengthBytes >= 2u ) )
	{
		xSum.u32 += *(xSource.u16ptr);
		( xSource.u16ptr )++;
		uxDataLengthBytes -= 2u;
		/* Now xSource is word (32-bit) aligned. */
	}

	/* Word (32-bit) aligned, do the most part. */
	xLastSource.u32ptr = ( xSource.u32ptr + ( uxDataLengthBytes / 4u ) ) - 3u;

	/* In this loop, four 32-bit additions will be done, in total 16 bytes.
	Indexing with constants (0,1,2,3) gives faster code than using
	post-increments. */
	while( xSource.u32ptr < xLastSource.u32ptr )
	{
		/* Use a secondary Sum2, just to see if the addition produced an
		overflow. */
		xSum2.u32 = xSum.u32 + xSource.u32ptr[ 0 ];
		if( xSum2.u32 < xSum.u32 )
		{
			ulCarry++;
		}

		/* Now add the secondary sum to the major sum, and remember if there was
		a carry. */
		xSum.u32 = xSum2.u32 + xSource.u32ptr[ 1 ];
		if( xSum2.u32 > xSum.u32 )
		{
			ulCarry++;
		}

		/* And do the same trick once again for indexes 2 and 3 */
		xSum2.u32 = xSum.u32 + xSource.u32ptr[ 2 ];
		if( xSum2.u32 < xSum.u32 )
		{
			ulCarry++;
		}

		xSum.u32 = xSum2.u32 + xSource.u32ptr[ 3 ];

		if( xSum2.u32 > xSum.u32 )
		{
			ulCarry++;
		}

		/* And finally advance the pointer 4 * 4 = 16 bytes. */
		xSource.u32ptr += 4;
	}

	/* Now add all carries. */
	xSum.u32 = ( uint32_t )xSum.u16[ 0 ] + xSum.u16[ 1 ] + ulCarry;

	uxDataLengthBytes %= 16u;
	xLastSource.u8ptr = ( uint8_t * ) ( xSource.u8ptr + ( uxDataLengthBytes & ~( ( size_t ) 1 ) ) );

	/* Half-word aligned. */
	while( xSource.u16ptr < xLastSource.u16ptr )
	{
		/* At least one more short. */
		xSum.u32 += xSource.u16ptr[ 0 ];
		xSource.u16ptr++;
	}

	if( ( uxDataLengthBytes & ( size_t ) 1 ) != 0u )	/* Maybe one more ? */
	{
		xTerm.u8[ 0 ] = xSource.u8ptr[ 0 ];
	}
	xSum.u32 += xTerm.u32;

	/* Now add all carries again. */
	xSum.u32 = ( uint32_t ) xSum.u16[ 0 ] + xSum.u16[ 1 ];

	/* The previous summation might have given a 16-bit carry. */
	xSum.u32 = ( uint32_t ) xSum.u16[ 0 ] + xSum.u16[ 1 ];

	if( ( ulAlignBits & 1u ) != 0u )
	{
		/* Quite unlikely, but pucNextData might be non-aligned, which would
		 mean that a checksum is calculated starting at an odd position. */
		xSum.u32 = ( ( xSum.u32 & 0xffu ) << 8 ) | ( ( xSum.u32 & 0xff00u ) >> 8 );
	}

	/* swap the output (little endian platform only). */
	return FreeRTOS_htons( ( (uint16_t) xSum.u32 ) );
}
/*-----------------------------------------------------------*/

void vReturnEthernetFrame( NetworkBufferDescriptor_t * pxNetworkBuffer, BaseType_t xReleaseAfterSend )
{
EthernetHeader_t *pxEthernetHeader;

#if( ipconfigZERO_COPY_TX_DRIVER != 0 )
	NetworkBufferDescriptor_t *pxNewBuffer;
#endif

	#if defined( ipconfigETHERNET_MINIMUM_PACKET_BYTES )
	{
		if( pxNetworkBuffer->xDataLength < ( size_t ) ipconfigETHERNET_MINIMUM_PACKET_BYTES )
		{
		BaseType_t xIndex;

			FreeRTOS_printf( ( "vReturnEthernetFrame: length %lu\n", ( uint32_t )pxNetworkBuffer->xDataLength ) );
			for( xIndex = ( BaseType_t ) pxNetworkBuffer->xDataLength; xIndex < ( BaseType_t ) ipconfigETHERNET_MINIMUM_PACKET_BYTES; xIndex++ )
			{
				pxNetworkBuffer->pucEthernetBuffer[ xIndex ] = 0u;
			}
			pxNetworkBuffer->xDataLength = ( size_t ) ipconfigETHERNET_MINIMUM_PACKET_BYTES;
		}
	}
	#endif

#if( ipconfigZERO_COPY_TX_DRIVER != 0 )

	if( xReleaseAfterSend == pdFALSE )
	{
		pxNewBuffer = pxDuplicateNetworkBufferWithDescriptor( pxNetworkBuffer, ( BaseType_t ) pxNetworkBuffer->xDataLength );
		xReleaseAfterSend = pdTRUE;
		pxNetworkBuffer = pxNewBuffer;
	}

	if( pxNetworkBuffer != NULL )
#endif
	{
		pxEthernetHeader = ( EthernetHeader_t * ) ( pxNetworkBuffer->pucEthernetBuffer );

		/* Swap source and destination MAC addresses. */
		memcpy( ( void * ) &( pxEthernetHeader->xDestinationAddress ), ( void * ) &( pxEthernetHeader->xSourceAddress ), sizeof( pxEthernetHeader->xDestinationAddress ) );
		memcpy( ( void * ) &( pxEthernetHeader->xSourceAddress) , ( void * ) ipLOCAL_MAC_ADDRESS, ( size_t ) ipMAC_ADDRESS_LENGTH_BYTES );

		/* Send! */
		xNetworkInterfaceOutput( pxNetworkBuffer, xReleaseAfterSend );
	}
}
/*-----------------------------------------------------------*/

uint32_t FreeRTOS_GetIPAddress( void )
{
	/* Returns the IP address of the NIC. */
	return *ipLOCAL_IP_ADDRESS_POINTER;
}
/*-----------------------------------------------------------*/

void FreeRTOS_SetIPAddress( uint32_t ulIPAddress )
{
	/* Sets the IP address of the NIC. */
	*ipLOCAL_IP_ADDRESS_POINTER = ulIPAddress;
}
/*-----------------------------------------------------------*/

uint32_t FreeRTOS_GetGatewayAddress( void )
{
	return xNetworkAddressing.ulGatewayAddress;
}
/*-----------------------------------------------------------*/

uint32_t FreeRTOS_GetDNSServerAddress( void )
{
	return xNetworkAddressing.ulDNSServerAddress;
}
/*-----------------------------------------------------------*/

uint32_t FreeRTOS_GetNetmask( void )
{
	return xNetworkAddressing.ulNetMask;
}
/*-----------------------------------------------------------*/

void FreeRTOS_UpdateMACAddress( const uint8_t ucMACAddress[ipMAC_ADDRESS_LENGTH_BYTES] )
{
	/* Copy the MAC address at the start of the default packet header fragment. */
	memcpy( ( void * )ipLOCAL_MAC_ADDRESS, ( void * )ucMACAddress, ( size_t )ipMAC_ADDRESS_LENGTH_BYTES );
}
/*-----------------------------------------------------------*/

const uint8_t * FreeRTOS_GetMACAddress( void )
{
	return ipLOCAL_MAC_ADDRESS;
}
/*-----------------------------------------------------------*/

void FreeRTOS_SetNetmask ( uint32_t ulNetmask )
{
	xNetworkAddressing.ulNetMask = ulNetmask;
}
/*-----------------------------------------------------------*/

void FreeRTOS_SetGatewayAddress ( uint32_t ulGatewayAddress )
{
	xNetworkAddressing.ulGatewayAddress = ulGatewayAddress;
}
/*-----------------------------------------------------------*/

#if( ipconfigUSE_DHCP == 1 )
	void vIPSetDHCPTimerEnableState( BaseType_t xEnableState )
	{
		if( xEnableState != pdFALSE )
		{
			xDHCPTimer.bActive = pdTRUE_UNSIGNED;
		}
		else
		{
			xDHCPTimer.bActive = pdFALSE_UNSIGNED;
		}
	}
#endif /* ipconfigUSE_DHCP */
/*-----------------------------------------------------------*/

#if( ipconfigUSE_DHCP == 1 )
	void vIPReloadDHCPTimer( uint32_t ulLeaseTime )
	{
		prvIPTimerReload( &xDHCPTimer, ulLeaseTime );
	}
#endif /* ipconfigUSE_DHCP */
/*-----------------------------------------------------------*/

#if( ipconfigDNS_USE_CALLBACKS == 1 )
	void vIPSetDnsTimerEnableState( BaseType_t xEnableState )
	{
		if( xEnableState != 0 )
		{
			xDNSTimer.bActive = pdTRUE;
		}
		else
		{
			xDNSTimer.bActive = pdFALSE;
		}
	}
#endif /* ipconfigUSE_DHCP */
/*-----------------------------------------------------------*/

#if( ipconfigDNS_USE_CALLBACKS != 0 )
	void vIPReloadDNSTimer( uint32_t ulCheckTime )
	{
		prvIPTimerReload( &xDNSTimer, ulCheckTime );
	}
#endif /* ipconfigDNS_USE_CALLBACKS != 0 */
/*-----------------------------------------------------------*/

BaseType_t xIPIsNetworkTaskReady( void )
{
	return xIPTaskInitialised;
}
/*-----------------------------------------------------------*/

BaseType_t FreeRTOS_IsNetworkUp( void )
{
	return xNetworkUp;
}
/*-----------------------------------------------------------*/

#if( ipconfigCHECK_IP_QUEUE_SPACE != 0 )
	UBaseType_t uxGetMinimumIPQueueSpace( void )
	{
		return uxQueueMinimumSpace;
	}
#endif
/*-----------------------------------------------------------*/

/* Provide access to private members for verification. */
#ifdef FREERTOS_TCP_ENABLE_VERIFICATION
	#include "aws_freertos_ip_verification_access_ip_define.h"
#endif