FreeRTOS+TCP Configuration
The FreeRTOSIPConfig.h header file
FreeRTOS+TCP applications must provide a FreeRTOSIPConfig.h header file –
in which the parameters described on this page can be defined.
The Configuration Examples
page demonstrates how to set key configuration parameters for systems
that need to minimise RAM consumption and systems that need to maximise
throughput.
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Constants Affecting the TCP/IP Stack Task Execution Behaviour
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Debug, Trace and Logging Settings
See also TCP/IP Trace Macros.
-
Hardware and Driver Specific Settings
-
TCP Specific Constants
-
UDP Specific Constants
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Other Constants Effecting Socket Behaviour
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Constants Affecting the ARP Behaviour
-
Constants Affecting DHCP and Name Service Behaviour
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Constants Affecting IP and ICMP Behaviour
-
Constants Providing Target Support
the TCP/IP stack executes it its own RTOS task (although
any application RTOS task can
make use of its services through the published sockets API). ipconfigIP_TASK_PRIORITY
sets the priority of the RTOS task that executes the TCP/IP stack.
The priority is a
standard FreeRTOS task priority
so can take any value from 0 (the lowest priority)
to (configMAX_PRIORITIES – 1) (the highest priority). configMAX_PRIORITIES is
a standard FreeRTOS configuration parameter defined in FreeRTOSConfig.h, not
FreeRTOSIPConfig.h.
Consideration needs to be given as to the priority assigned to the RTOS task
executing the TCP/IP stack relative to the priority assigned to tasks that use the TCP/IP stack.
The size, in words (not bytes), of the stack allocated to the FreeRTOS+TCP
RTOS task. FreeRTOS includes
optional stack overflow detection.
If ipconfigUSE_NETWORK_EVENT_HOOK is set to 1 then FreeRTOS+TCP will call the
network event hook at the appropriate times. If ipconfigUSE_NETWORK_EVENT_HOOK
is not set to 1 then the network event hook will never be called.
A FreeRTOS queue is used to send events from application tasks to the IP
stack. ipconfigEVENT_QUEUE_LENGTH sets the maximum number of events that can
be queued for processing at any one time. The event queue must be a minimum of
5 greater than the total number of network buffers.
Trace Macros
Information on the available TCP/IP stack trace macros is provided on a
separate page.
The TCP/IP stack outputs debugging messages by calling the FreeRTOS_debug_printf
macro. To obtain debugging messages set ipconfigHAS_DEBUG_PRINTF to 1, then
define FreeRTOS_debug_printf() to a function that takes a printf() style format
string and variable number of inputs, and sends the formatted messages to an
output of your choice.
Do not define FreeRTOS_debug_printf if ipconfigHAS_DEBUG_PRINTF is set to 0.
The following code is taken from the
FreeRTOS+TCP example for the RTOS’s Win32 simulator,
which has the ability to output debugging messages to a UDP port, standard out,
and to a disk file:
extern void vLoggingPrintf( const char *pcFormatString, … );
#define ipconfigHAS_DEBUG_PRINTF 0
#if( ipconfigHAS_DEBUG_PRINTF == 1 )
#define FreeRTOS_debug_printf(X) vLoggingPrintf X
#endif
Defining ipconfigHAS_DEBUG_PRINTF and FreeRTOS_debug_printf in FreeRTOSIPConfig.h
The function that performs the output (vLoggingPrintf() in the code above)
must be reentrant.
Some of the TCP/IP stack demo applications generate output messages. The TCP/IP stack
outputs these messages by calling the FreeRTOS_printf
macro. To obtain the demo application messages set ipconfigHAS_PRINTF to 1, then
define FreeRTOS_printf() to a function that takes a printf() style format
string and variable number of inputs, and sends the formatted messages to an
output of your choice.
Do not define FreeRTOS_printf if ipconfigHAS_PRINTF is set to 0.
The following code is taken from the
FreeRTOS+TCP example for the RTOS’s Win32 simulator,
which has the ability to output application messages to a UDP port, standard out,
and to a disk file:
extern void vLoggingPrintf( const char *pcFormatString, … );
#define ipconfigHAS_PRINTF 0
#if( ipconfigHAS_PRINTF == 1 )
#define FreeRTOS_printf(X) vLoggingPrintf X
#endif
Defining ipconfigHAS_PRINTF and FreeRTOS_printf in FreeRTOSIPConfig.h
The function that performs the output (vLoggingPrintf() in the code above)
must be reentrant.
ipconfigTCP_MAY_LOG_PORT( x ) can be defined to specify which port numbers should or
should not be logged by FreeRTOS_lprintf(). For example, the following definition
will not generate log messages for ports 23 or 2402:
#define ipconfigTCP_MAY_LOG_PORT(xPort) ( ( ( xPort ) != 23 ) && ( ( xPort ) != 2402 ) )
Filtering Log Messages
A FreeRTOS queue is used to send events from application tasks to the IP stack.
ipconfigEVENT_QUEUE_LENGTH sets the
maximum number of events that can be queued for processing at any one time. If
ipconfigCHECK_IP_QUEUE_SPACE is set to 1 then the uxGetMinimumIPQueueSpace()
function can be
used to query the minimum amount of free space that has existed in the queue
since the system booted.
UBaseType_t uxGetMinimumIPQueueSpace( void );
uxGetMinimumIPQueueSpace() function prototype
ipconfigWATCHDOG_TIMER() is a macro that is called on each iteration of the
IP task and may be useful if the application included watchdog type functionality
that needs to know the IP task is still cycling (although the fact that the IP
task is cycling does not necessarily indicate it is functioning correctly).
ipconfigWATCHDOG_TIMER() can be defined to perform any action desired by the
application writer. If ipconfigWATCHDOG_TIMER() is left undefined then it will be removed
completely by the pre-processor (it will default to an empty macro).
If the microcontroller on which FreeRTOS+TCP is running is big endian then
ipconfigBYTE_ORDER must be set to pdFREERTOS_BIG_ENDIAN. If the microcontroller
is little endian then ipconfigBYTE_ORDER must be set to pdFREERTOS_LITTLE_ENDIAN.
The
Byte Order and Endian
section of the Embedded Networking Basics and Glossary page provides an
explanation of byte order considerations in IP networks.
If the network driver or network hardware is calculating the IP, TCP and UDP
checksums of outgoing packets then set ipconfigDRIVER_INCLUDED_TX_IP_CHECKSUM to
1, otherwise set ipconfigDRIVER_INCLUDED_TX_IP_CHECKSUM to 0.
Throughput and processor load are greatly improved by implementing drivers that
make use of hardware checksum calculations.
If the network driver or network hardware is calculating the IP, TCP and UDP
checksums of incoming packets, and discarding packets that are found to contain
invalid checksums, then set ipconfigDRIVER_INCLUDED_RX_IP_CHECKSUM to
1, otherwise set ipconfigDRIVER_INCLUDED_RX_IP_CHECKSUM to 0.
Throughput and processor load are greatly improved by implementing drivers that
make use of hardware checksum calculations.
Note: From FreeRTOS+TCP V2.3.0, the length is checked in software even
when it has already been checked in hardware.
Ethernet/hardware MAC addresses
are used to address Ethernet frames. If the network driver or hardware is
discarding packets that do not contain a MAC address of interest then set
ipconfigETHERNET_DRIVER_FILTERS_FRAME_TYPES to 1. Otherwise set
ipconfigETHERNET_DRIVER_FILTERS_FRAME_TYPES to 0.
Throughput and processor load are greatly improved by implementing network address
filtering in hardware. Most network interfaces allow multiple MAC addresses to
be defined so filtering can allow through the unique hardware address of the node,
the broadcast address, and various multicast addresses.
For expert users only.
Whereas ipconfigETHERNET_DRIVER_FILTERS_FRAME_TYPES is used to specify whether
or not the network driver or hardware filters Ethernet frames,
ipconfigETHERNET_DRIVER_FILTERS_PACKETS is used to specify whether or not the
network driver filters the IP, UDP or TCP data within the Ethernet frame.
The TCP/IP stack is only interested in receiving data that is either addresses to
a socket (IP address and port number) on the local node, or is a broadcast or
multicast packet. Throughput and process load can be greatly improved by preventing
packets that do not meet these criteria from being sent to the TCP/IP stack.
FreeRTOS provides some features that allow such filtering to take place in the
network driver. For example, xPortHasUDPSocket() can be used as follows:
if( ( xPortHasUdpSocket( xUDPHeader->usDestinationPort ) )
#if( ipconfigUSE_DNS == 1 )
|| ( xUDPHeader->usSourcePort == FreeRTOS_ntohs( ipDNS_PORT ) )
#endif
#if( ipconfigUSE_LLMNR == 1 )
|| ( xUDPHeader->usDestinationPort == FreeRTOS_ntohs( ipLLMNR_PORT ) )
#endif
#if( ipconfigUSE_NBNS == 1 )
|| ( xUDPHeader->usDestinationPort == FreeRTOS_ntohs( ipNBNS_PORT ) )
#endif
)
{
}
else
{
}
Example of filtering UDP packets
The
MTU is the
maximum number of bytes the payload of a network frame can
contain. For normal Ethernet V2 frames the maximum MTU is 1500 (although a lower
number may be required for Internet routing). Setting a
lower value can save RAM, depending on the buffer management scheme used. If
ipconfigCAN_FRAGMENT_OUTGOING_PACKETS is 1 then (ipconfigNETWORK_MTU – 28) must
be divisible by 8.
If ipconfigNETWORK_MTU is not defined then the following defaults will be applied:
#ifndef ipconfigNETWORK_MTU
#ifdef( ipconfigUSE_TCP_WIN == 1 )
#define ipconfigNETWORK_MTU ( 1526 )
#else
#define ipconfigNETWORK_MTU ( 1514 )
#endif
#endif
ipconfigNUM_NETWORK_BUFFER_DESCRIPTORS defines the total number of network buffer that
are available to the TCP/IP stack. The total number of network buffers is limited
to ensure the total amount of RAM that can be consumed by the TCP/IP stack is capped
to a pre-determinable value. How the storage area is actually allocated to the
network buffer structures is not fixed, but part of the portable layer. The simplest
scheme simply allocates the exact amount of storage as it is required.
More information on network buffers and network buffer descriptors is provided on
the pages that describe
porting FreeRTOS+TCP to other hardware and the
pxGetNetworkBufferWithDescriptor()
porting specific API function.
If ipconfigFILTER_OUT_NON_ETHERNET_II_FRAMES is set to 1 then Ethernet frames
that are not in Ethernet II format will be dropped. This option is included for
potential future IP stack developments.
Advanced users only.
When ipconfigUSE_LINKED_RX_MESSAGES is set to 1 it is possible to reduce CPU
load during periods of heavy network traffic by linking multiple received packets
together, then passing all the linked packets to the IP RTOS task in one go.
Advanced users only.
If ipconfigZERO_COPY_TX_DRIVER is set to 1 then the driver function
xNetworkInterfaceOutput()
will always be called with its bReleaseAfterSend parameter set to pdTRUE – meaning
it is always the driver that is responsible for freeing the network buffer and network
buffer descriptor.
This is useful if the driver implements a zero-copy scheme whereby the packet
data is sent directly from within the network buffer (for example by pointing a DMA descriptor
at the data within the network buffer), instead of copying the data out of the
network buffer before the data is sent (for example by copying the data into a
separate pre-allocated DMA descriptor). In such cases the driver needs to take
ownership of the network buffer because the network buffer can only be freed
after the data has actually been transmitted – which might be some time after
the xNetworkInterfaceOutput() function returns. See the examples on the
Porting FreeRTOS to a Different Microcontroller documentation page for
worked examples.
Advanced driver implementation use only.
When the application requests a network buffer, the size of the network buffer
is specified by the application writer, but the size of the network buffer
actually obtained is increased by ipconfigBUFFER_PADDING bytes. The first
ipconfigBUFFER_PADDING bytes of the buffer is then used to hold metadata about
the buffer, and the area that actually stores the data follows the metadata.
This mechanism is transparent to the user as the user only see a pointer to the
area within the buffer actually used to hold network data.
Some network hardware has very specific byte alignment requirements, so
ipconfigBUFFER_PADDING is provided as a configurable parameter to allow the writer
of the network driver to influence the alignment of the start of the data that
follows the metadata.
Set ipconfigUSE_TCP to 1 to enable
TCP.
If ipconfigUSE_TCP is set to 0 then only
UDP is available.
Defines the
Time To Live
TTL) values used in outgoing TCP packets.
Each TCP socket has a buffer for reception and a separate buffer for transmission.
The default buffer size is (4 * ipconfigTCP_MSS).
FreeRTOS_setsockopt() can be used with the FREERTOS_SO_RCVBUF and FREERTOS_SO_SNDBUF
parameters to set the receive and send buffer sizes respectively – but this must
be done between the socket being created and the buffers used by the socket being
created. The receive buffer is not created until data is actually received, and the transmit buffer
is not created until data is actually sent to the socket for transmission.
Once the buffers have been created their size cannot be changed.
If a listening socket
creates a new socket in response to an incoming connect
request then the new socket will inherit the buffers sizes of the listening
socket.
Sliding Windows allows messages to arrive out-of-order.
Set ipconfigUSE_TCP_WIN to 1 to include sliding window behaviour in TCP sockets.
Set ipconfigUSE_TCP_WIN to 0 to exclude sliding window behaviour in TCP sockets.
Sliding windows can increase throughput while minimising network traffic at the
expense of consuming more RAM.
The size of the sliding window can be changed from its default using the
FREERTOS_SO_WIN_PROPERTIES parameter to FreeRTOS_setsockopt(). The sliding window
size is specified in units of MSS (so if the MSS is set to 200 bytes then a
sliding window size of 2 is equal to 400 bytes) and must always be smaller than
or equal to the size of the internal buffers in both directions.
If a listening socket
creates a new socket in response to an incoming connect
request then the new socket will inherit the sliding window sizes of the listening
socket.
If ipconfigUSE_TCP_WIN is set to 1 then each socket will use a sliding window.
Sliding windows allow messages to arrive out-of order, and FreeRTOS+TCP uses
window descriptors to track information about the packets in a window.
A pool of descriptors is allocated when the first TCP connection is made. The
descriptors are shared between all the sockets. ipconfigTCP_WIN_SEG_COUNT set
the number of descriptors in the pool, and each descriptor is approximately
64 bytes.
As an example: If a system will have at most 16 simultaneous TCP connections,
and each connection will have an Rx and Tx window of at most 8 segments, then
the worst case maximum number of descriptors that will be required is 256 ( 16 * 2 * 8 ).
However, the practical worst case is normally much lower than this as most
packets will arrive in order.
TCP time stamp functionality is available, but its usage is quite limited.
Time-stamps can only be used if the initial SYN packet contains the time-stamp
option. In most cases, incoming connection won’t have the time-stamp option set.
Set ipconfigUSE_TCP_TIMESTAMPS to 1 to include TCP time stamp functionality.
Set ipconfigUSE_TCP_TIMESTAMPS to 0 to exclude TCP time stamp functionality.
Sets the
MSS
value (in bytes) for all TCP packets.
Note that FreeRTOS+TCP contains checks that the defined ipconfigNETWORK_MTU and
ipconfigTCP_MSS values are consistent with each other.
Sockets that are connected but do not transmit any data for an extended period
can be disconnected by routers or firewalls that time out. This can be avoided
at the application level by ensuring the application periodically sends a packet.
Alternatively FreeRTOS+TCP can be configured to automatically send keep alive
messages when it detects that a connection is dormant. Note that, while having
FreeRTOS+TCP automatically send keep alive messages is the more convenient method,
it is also the least reliable method because some routers will discard keep alive
messages.
Set ipconfigTCP_KEEP_ALIVE to 1 to have FreeRTOS+TCP periodically send keep
alive messages on connected but dormant sockets. Set ipconfigTCP_KEEP_ALIVE to
0 to prevent the automatic transmission of keep alive messages.
If FreeRTOS+TCP does not receive a reply to a keep alive message then the
connection will be broken and the socket will be marked as closed. Subsequent
FreeRTOS_recv() calls on the socket will return -pdFREERTOS_ERRNO_ENOTCONN.
If ipconfigTCP_KEEP_ALIVE is set to 1 then ipconfigTCP_KEEP_ALIVE_INTERVAL sets
the interval in seconds between successive keep alive messages. Keep alive messages
are not sent at all unless ipconfigTCP_KEEP_ALIVE_INTERVAL seconds have passed
since the last packet was sent or received.
If ipconfigTCP_HANG_PROTECTION is set to 1 then FreeRTOS+TCP will mark a socket
as closed if there is no status change on the socket within the period of time
specified by ipconfigTCP_HANG_PROTECTION_TIME.
If ipconfigTCP_HANG_PROTECTION is set to 1 then ipconfigTCP_HANG_PROTECTION_TIME sets
the interval in seconds between the status of a socket last changing and the
anti-hang mechanism marking the socket as closed.
Normally TCP packets that have a bad or unknown destination will result in a RESET
being sent back to the remote host. If ipconfigIGNORE_UNKNOWN_PACKETS is set to
1 then such resets will be suppressed (not sent).
Defines the
Time To Live
(TTL) values used in outgoing UDP packets.
Sockets have a send block time attribute. If FreeRTOS_sendto() is called but
a network buffer cannot be obtained then the calling RTOS task is held in the Blocked
state (so other tasks can continue to executed) until either a network buffer
becomes available or the send block time expires. If the send block time expires
then the send operation is aborted.
The maximum allowable send block time is
capped to the value set by ipconfigUDP_MAX_SEND_BLOCK_TIME_TICKS. Capping the
maximum allowable send block time prevents prevents a deadlock occurring when
all the network buffers are in use and the tasks that process (and subsequently
free) the network buffers are themselves blocked waiting for a network buffer.
ipconfigUDP_MAX_SEND_BLOCK_TIME_TICKS is specified in RTOS ticks. A time in
milliseconds can be converted to a time in ticks by dividing the time in
milliseconds by portTICK_PERIOD_MS.
ipconfigUDP_MAX_RX_PACKETS defines the maximum number of packets that can exist
in the Rx queue of a UDP socket. For example, if ipconfigUDP_MAX_RX_PACKETS is
set to 5 and there are already 5 packets queued on the UDP socket then subsequent
packets received on that socket will be dropped until the queue length is less
than 5 again.
If ipconfigUDP_PASS_ZERO_CHECKSUM_PACKETS is set to 1 then FreeRTOS+TCP will accept UDP packets
that have their checksum value set to 0, which is in compliance with the UDP specification.
If ipconfigUDP_PASS_ZERO_CHECKSUM_PACKETS is set to 0 then FreeRTOS+TCP will drop UDP packets
that have their checksum value set to 0, which deviates from the UDP specification, but is safer.
Note: This configuration parameter defaults to 0.
Implementing
FreeRTOS_inet_addr()
necessitates the use of string handling
routines, which are relatively large. To save code space the full FreeRTOS_inet_addr()
implementation is made optional, and a smaller and faster alternative called
FreeRTOS_inet_addr_quick() is provided. FreeRTOS_inet_addr() takes an IP in
decimal dot format (for example, “192.168.0.1”) as its parameter.
FreeRTOS_inet_addr_quick() takes an IP address as four separate numerical octets
(for example, 192, 168, 0, 1) as its parameters. If
ipconfigINCLUDE_FULL_INET_ADDR is set to 1 then both FreeRTOS_inet_addr() and
FreeRTOS_indet_addr_quick() are available. If ipconfigINCLUDE_FULL_INET_ADDR is
not set to 1 then only FreeRTOS_indet_addr_quick() is available.
The address of a socket is the combination of its IP address and its port
number.
FreeRTOS_bind()
is used to manually allocate a port number to a socket
(to ‘bind’ the socket to a port), but manual binding is not normally necessary
for client sockets (those sockets that initiate outgoing connections rather than
wait for incoming connections on a known port number). If
ipconfigALLOW_SOCKET_SEND_WITHOUT_BIND is set to 1 then calling
FreeRTOS_sendto() on a socket that has not yet been bound will result in the IP
stack automatically binding the socket to a port number from the range
socketAUTO_PORT_ALLOCATION_START_NUMBER to 0xffff. If
ipconfigALLOW_SOCKET_SEND_WITHOUT_BIND is set to 0 then calling FreeRTOS_sendto()
on a socket that has not yet been bound will result in the send operation being
aborted.
API functions used to read data from a socket can block to wait for data to become
available. ipconfigSOCK_DEFAULT_RECEIVE_BLOCK_TIME sets the default block time
defined in RTOS ticks. If ipconfigSOCK_DEFAULT_RECEIVE_BLOCK_TIME is not defined
then the default block time will be set to portMAX_DELAY – meaning an RTOS task that
is blocked on a socket read will not leave the Blocked state until data is available.
Note tasks in the Blocked state do not consume any CPU time.
ipconfigSOCK_DEFAULT_RECEIVE_BLOCK_TIME is specified in ticks. The macros
pdMS_TO_TICKS() and portTICK_PERIOD_MS can both be used to convert a time
specified in milliseconds to a time specified in ticks.
The time out time can be changed at any time using the FREERTOS_SO_RCVTIMEO parameter
with FreeRTOS_setsockopt(). Note: Infinite block times should be used
with extreme care in order to avoid a situation where all tasks are blocked
indefinitely to wait for another RTOS task (which is also blocked indefinitely) to
free a network buffer.
A socket can be set to non-blocking mode by setting both the send and receive
block time to 0. This might be desirable when an RTOS task is using more than one
socket – in which case blocking can instead by performed on all the sockets at
once using FreeRTOS_select(), or the RTOS task can set ipconfigSOCKET_HAS_USER_SEMAPHORE
to one then block on its own semaphore.
When writing to a socket the write may not be able to proceed immediately. For
example, depending on the configuration, a write might have to wait for a network
buffer to become available. API functions used to write data to a socket can
block to wait for the write to succeed.
ipconfigSOCK_DEFAULT_SEND_BLOCK_TIME sets the default block time
defined in RTOS ticks. If ipconfigSOCK_DEFAULT_SEND_BLOCK_TIME is not defined
then the default block time will be set to portMAX_DELAY – meaning an RTOS task that
is blocked on a socket read will not leave the Blocked state until data is available.
Note tasks in the Blocked state do not consume any CPU time.
ipconfigSOCK_DEFAULT_RECEIVE_BLOCK_TIME is specified in ticks. The macros
pdMS_TO_TICKS() and portTICK_PERIOD_MS can both be used to convert a time
specified in milliseconds to a time specified in ticks.
The time out time can be changed at any time using the FREERTOS_SO_SNDTIMEO parameter
with FreeRTOS_setsockopt(). Note: Infinite block times should be used
with extreme care in order to avoid a situation where all tasks are blocked
indefinitely to wait for another RTOS task (which is also blocked indefinitely) to
free a network buffer.
A socket can be set to non-blocking mode by setting both the send and receive
block time to 0. This might be desirable when an RTOS task is using more than one
socket – in which case blocking can instead by performed on all the sockets at
once using FreeRTOS_select(), or the RTOS task can set ipconfigSOCKET_HAS_USER_SEMAPHORE
to one then block on its own semaphore.
A socket can be set to non-blocking mode by setting both the send and receive
block time to 0.
By default sockets will block on a send or receive that cannot complete
immediately. See the description of the ipconfigSOCK_DEFAULT_RECEIVE_BLOCK_TIME
and ipconfigSOCK_DEFAULT_SEND_BLOCK_TIME parameters.
If an RTOS task is using multiple sockets and cannot block on one socket at a time then
the sockets can be set into non-blocking mode, and the RTOS task can block on all the
sockets at once by either using the FreeRTOS_select() function or by setting
ipconfigSOCKET_HAS_USER_SEMAPHORE to 1, using the FREERTOS_SO_SET_SEMAPHORE
parameter with FreeRTOS_setsockopt() to provide a semaphore to the socket, and
then blocking on the semaphore. The semaphore will be given when any of the
sockets are able to proceed – at which time the RTOS task can inspect all the sockets
individually using non blocking API calls to determine which socket caused it to
unblock.
If ipconfigSUPPORT_SIGNALS is set to 1 then the FreeRTOS_SignalSocket() API
function is included in the build.
FreeRTOS_SignalSocket()
can be used to send a signal to a socket, the result of which is that any task
blocked on a read from the socket will leave the Blocked state (abort the
blocking read operation).
Set ipconfigSUPPORT_SELECT_FUNCTION to 1 to include support for the
FreeRTOS_select()
and associated API functions, or 0 to exclude FreeRTOS_select() and associated
API functions from the build.
The ARP cache is a table that maps IP addresses to MAC addresses.
The IP
stack can only send a UDP message to a remove IP address if it knowns the MAC
address associated with the IP address, or the MAC address of the router used to
contact the remote IP address. When a UDP message is received from a remote IP
address the MAC address and IP address are added to the ARP cache. When a UDP
message is sent to a remote IP address that does not already appear in the ARP
cache then the UDP message is replaced by a ARP message that solicits the
required MAC address information.
ipconfigARP_CACHE_ENTRIES defines the maximum
number of entries that can exist in the ARP table at any one time.
ARP requests that do not result in an ARP response will be re-transmitted a
maximum of ipconfigMAX_ARP_RETRANSMISSIONS times before the ARP request is
aborted.
ipconfigMAX_ARP_AGE defines the maximum time between an entry in the ARP
table being created or refreshed and the entry being removed because it is stale.
New ARP requests are sent for ARP cache entries that are nearing their maximum
age.
ipconfigMAX_ARP_AGE is specified in tens of seconds, so a value of 150 is equal
to 1500 seconds (or 25 minutes).
Advanced users only.
If ipconfigARP_REVERSED_LOOKUP is set to 1 then the xGetARPCacheEntryByMac()
function is available for use. xGetARPCacheEntryByMac() performs an IP address
look up from a MAC address.
Advanced users only.
ipconfigARP_STORES_REMOTE_ADDRESSES is provided for the case when a message that
requires a reply arrives from the Internet, but from a computer attached to a
LAN rather than via the defined gateway. Before replying to the message the
TCP/IP stack RTOS task will loop up the message’s IP address in the ARP table – but if
ipconfigARP_STORES_REMOTE_ADDRESSES is set to 0 then ARP
will return the MAC address of the defined gateway because the destination address
is outside of the netmask. That might prevent the reply reaching its intended
destination.
If ipconfigARP_STORES_REMOTE_ADDRESSES is set to 1 then remote addresses
will also be stored in the ARP table, along with the MAC address from which the
message was received. This can allow the message in the scenario above to be
routed and delivered correctly.
Advanced users only.
Normally ARP will look up an IP address from a MAC address. If ipconfigUSE_ARP_REVERSED_LOOKUP
is set to 1 then a function that does the reverse is also available.
eARPGetCacheEntryByMac() looks up a MAC address from an IP address.
eARPLookupResult_t eARPGetCacheEntryByMac( MACAddress_t * const pxMACAddress,
uint32_t *pulIPAddress );
eARPGetCacheEntryByMac() function prototype
Advanced users only.
If ipconfigUSE_ARP_REMOVE_ENTRY is set to 1 then ulARPRemoveCacheEntryByMac()
is included in the build. ulARPRemoveCacheEntryByMac() uses a MAC address to
look up, and then remove, an entry from the ARP cache. If the MAC address is
found in the ARP cache then the IP address associated with the MAC address is
returned. If the MAC address is not found in the ARP cache then 0 is returned.
uint32_t ulARPRemoveCacheEntryByMac( const MACAddress_t * pxMACAddress );
ulARPRemoveCacheEntryByMac() function prototype
Set ipconfigUSE_DNS to 1 to include a basic DNS client/resolver. DNS is used
through the
FreeRTOS_gethostbyname() API function.
ipconfigDNS_REQUEST_ATTEMPTS sets the number of times ARP will attempt to obtain
an ARP response before giving up.
If ipconfigUSE_DNS_CACHE is set to 1 then the DNS cache will be enabled. If
ipconfigUSE_DNS_CACHE is set to 0 then the DNS cache will be disabled.
If ipconfigUSE_DNS_CACHE is set to 1 then ipconfigDNS_CACHE_ENTRIES defines the
number of entries in the DNS cache.
The maximum number of characters a DNS host name can take, including the NULL
terminator.
Set ipconfigUSE_LLMNR to 1 to include
LLMNR.
Set ipconfigUSE_NBNS to 1 to include
NBNS.
If ipconfigUSE_DHCP is 1 then FreeRTOS+TCP will attempt to retrieve an IP
address, netmask, DNS server address and gateway address from a DHCP server – and
revert to using the defined static address if an IP address cannot be obtained.
If ipconfigUSE_DHCP is 0 then FreeRTOS+TCP will not attempt to obtain its address
information from a DHCP server, and instead immediately use the defined static address
information.
When ipconfigUSE_DHCP is set to 1, DHCP requests will be sent out at
increasing time intervals until either a reply is received from a DHCP server
and accepted, or the interval between transmissions reaches
ipconfigMAXIMUM_DISCOVER_TX_PERIOD. The TCP/IP stack will revert to using the
static IP address passed as a parameter to
FreeRTOS_IPInit() if the
re-transmission time interval reaches ipconfigMAXIMUM_DISCOVER_TX_PERIOD without
a DHCP reply being received.
A normal
DHCP transaction
involves the following sequence:
-
The client sends a DHCP discovery packet to request an IP address from
the DHCP server.
-
The DHCP server responds with an offer packet that contains the offered
IP address.
-
The client sends a DHCP request packet in order to claim the offered
IP address
-
The DHCP server sends an acknowledgement packet to grant the client use
of the offered IP address, and to send additional configuration
information to the client. Additional configuration information typically
includes the IP address of the
gateway, the
IP address of the DNS
server, and the IP address lease length.
If ipconfigUSE_DHCP_HOOK is set to 1 then FreeRTOS+TCP will call an
application provided hook (or ‘callback’) function called xApplicationDHCPUserHook()
both before the initial discovery packet is sent, and after a DHCP offer has
been received – the hook function can be used to terminate the DHCP process at
either one of these two phases in the DHCP sequence. For example, the application
writer can effectively disable DHCP, even when ipconfigUSE_DHCP
is set to 1, by terminating the DHCP process before the initial discovery packet
is sent. As another example, the application writer can check a static IP address
is compatible with the network to which the device is connected by receiving an
IP address offer from a DHCP server, but then terminating the DHCP process without
sending a request packet to claim the offered IP address.
If ipconfigUSE_DHCP_HOOK is set to 1 then the application writer must
provide a hook (callback) function with the following name and prototype:
eDHCPCallbackAnswer_t xApplicationDHCPHook( eDHCPCallbackPhase_t eDHCPPhase,
uint32_t ulIPAddress );
The name and prototype of the DHCP application hook function
Where eDHCPCallbackQuestion_t and eDHCPCallbackAnswer_t are defined as follows
typedef enum eDHCP_QUESTIONS
{
eDHCPPhasePreDiscover,
eDHCPPhasePreRequest,
} eDHCPCallbackQuestion_t;
typedef enum eDHCP_ANSWERS
{
eDHCPContinue,
eDHCPUseDefaults,
eDHCPStopNoChanges,
} eDHCPCallbackAnswer_t;
The eDHCPCallbackQuestion_t and eDHCPCallbackAnswer_t definitions
For example purposes only, below is a reference xApplicationDHCPHook implementation
that allows the DHCP sequence to proceed up to the point where an IP address is
offered, at which point the offered IP address is compared to the statically
configured IP address. If the offered and statically configured IP addresses are
on the same subnet then the statically configured IP address is used. If the
offered and statically configured IP addresses are not on the same subnet then
the IP address offered by the DHCP server is used.
eDHCPCallbackAnswer_t xApplicationDHCPHook( eDHCPCallbackPhase_t eDHCPPhase,
uint32_t ulIPAddress )
{
eDHCPCallbackAnswer_t eReturn;
uint32_t ulStaticIPAddress, ulStaticNetMask;
switch( eDHCPPhase )
{
case eDHCPPhasePreDiscover :
eReturn = eDHCPContinue;
break;
case eDHCPPhasePreRequest :
ulStaticIPAddress = FreeRTOS_inet_addr_quick( configIP_ADDR0,
configIP_ADDR1,
configIP_ADDR2,
configIP_ADDR3 );
ulStaticNetMask = FreeRTOS_inet_addr_quick( configNET_MASK0,
configNET_MASK1,
configNET_MASK2,
configNET_MASK3 );
ulStaticIPAddress &= ulStaticNetMask;
ulIPAddress &= ulStaticNetMask;
if( ulStaticIPAddress == ulIPAddress )
{
eReturn = eDHCPUseDefaults;
}
else
{
eReturn = eDHCPContinue;
}
break;
default :
eReturn = eDHCPContinue;
break;
}
return eReturn;
}
A reference xApplicationDHCPHook() implementation
When the eDHCPPhase parameter is set to eDHCPPhasePreDiscover the ulIPAddress
parameter is set to the IP address already in use. When the
eDHCPPhase parameter is set to eDHCPPhasePreRequest the ulIPAddress parameter is set to
the IP address offered by the DHCP server.
Often DHCP servers can show the names of devices that have leased IP addresses.
When ipconfigDHCP_REGISTER_HOSTNAME is set to 1 the device running FreeRTOS+TCP
can identify itself to a DHCP server with a human readable name by returning
the name from an application provided hook (or ‘callback’) function called
pcApplicationHostnameHook().
When ipconfigDHCP_REGISTER_HOSTNAME is set to 1 the application must provide a
hook (callback) function with the following name and prototype:
const char *pcApplicationHostnameHook( void );
The name and prototype of the application provided hook function that returns the devices name
If ipconfigCAN_FRAGMENT_OUTGOING_PACKETS is set to 1 then UDP packets that
contain more data than will fit in a single network frame will be fragmented
across multiple IP packets. Also see the ipconfigNETWORK_MTU setting. If
ipconfigCAN_FRAGMENT_OUTGOING_PACKETS is 1 then (ipconfigNETWORK_MTU – 28) must
be divisible by 8. Setting ipconfigCAN_FRAGMENT_OUTGOING_PACKETS to 1 will
increase both the code size and execution time.
If ipconfigREPLY_TO_INCOMING_PINGS is set to 1 then the TCP/IP stack will
generate replies to incoming ICMP echo (ping) requests.
If ipconfigSUPPORT_OUTGOING_PINGS is set to 1 then the FreeRTOS_SendPingRequest()
API function is available.
If ipconfigIP_PASS_PACKETS_WITH_IP_OPTIONS is set to 1 then FreeRTOS+TCP accepts IP packets
that contain IP options, but does not process the options (IP options are not supported).
If ipconfigIP_PASS_PACKETS_WITH_IP_OPTIONS is set to 0 then FreeRTOS+TCP will drop IP
packets that contain IP options.
ipconfigRAND32() is called by the TCP/IP stack to generate a random number that
is then used as a DHCP transaction number. Random number generation is performed
via this macro to allow applications to use their own random number generation
method. For example, it might be possible to generate a random number by
sampling noise on an analogue input.
Note:
The random number generator must be seeded before the TCP/IP stack is started,
so before
FreeRTOS_IPInit() is called.
If the compiler in use supports inline functions, and portINLINE is defined to
the correct inline keyword for the compiler, then set ipconfigHAS_INLINE_FUNCTIONS
to 1. Otherwise set ipconfigHAS_INLINE_FUNCTIONS to 0 which will result in
some inline functions using an alternative macro implementation.
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