If the microcontroller on which FreeRTOS+UDP is running is big endian then
ipconfigBYTE_ORDER must be set to FREERTOS_BIG_ENDIAN. If the microcontroller
is little endian then ipconfigBYTE_ORDER must be set to FREERTOS_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.
The IP stack executes it its own task (although any application task can
make use of its services through the published sockets API). ipconfigUDP_TASK_PRIORITY
sets the priority of the task that executes the 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
Consideration needs to be given as to the priority assigned to the task
executing the IP stack relative to the priority assigned to tasks that use the IP stack.
If ipconfigUSE_NETWORK_EVENT_HOOK is set to 1 then FreeRTOS+UDP 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.
Sockets have a send block time attribute. If FreeRTOS_sendto() is called but
a network buffer cannot be obtained then the calling 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 ipconfigMAX_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.
ipconfigMAX_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.
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
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
The ARP cache is a table that maps IP addresses to MAC addresses.
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
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
ipconfigMAX_ARP_AGE is specified in tens of seconds, so a value of 150 is equal
to 1500 seconds (or 25 minutes). */
Set ipconfigUSE_DNS to 1 to include a basic DNS client/resolver. DNS is used
through the FreeRTOS_gethostbyname() API function.
If ipconfigUSE_DHCP is 1 then FreeRTOS+UDP 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+UDP will not attempt to obtain its address
information from a DHCP server, and instead immediately use the defined static address
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 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.
ipconfigRAND32() is called by the 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.
Defines the Time To Live (TTL) values used in outgoing UDP packets.
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.
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. 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 ipconfigREPLY_TO_INCOMING_PINGS is set to 1 then the 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.
ipconfigNUM_NETWORK_BUFFERS defines the total number of network buffer that
are available to the IP stack. The total number of network buffers is limited
to ensure the total amount of RAM that can be consumed by the 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.
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.
If ipconfigETHERNET_DRIVER_FILTERS_FRAME_TYPES is set to 1 then it is the
responsibility of the Ethernet interface to filter out packets that are of no
interest. If the Ethernet interface does not implement this functionality, then
set ipconfigETHERNET_DRIVER_FILTERS_FRAME_TYPES to 0 to have the IP stack
perform the filtering instead (it is much less efficient for the stack to do it
because the packet will already have been passed into the stack). If the
Ethernet driver does all the necessary filtering in hardware then software
filtering can be removed by using a value other than 1 or 0.
Set ipconfigFREERTOS_PLUS_NABTO to 1 to support the Nabto protocol, or 0 to
exclude support for the Nabto protocol. If ipconfigFREERTOS_PLUS_NABTO is set
to one then the project must include the FreeRTOS+Nabto source code (or reference a
pre-build FreeRTOS+Nabto library).