The focus of the lwIP network stack implementation is to reduce resource usage while still having a full-scale TCP stack. The operating system emulation layer and the network interface allow the network stack to be transplanted into an operating system, as it provides a common interface between lwIP code and the operating system kernel. The network stack of lwIP includes an IP Internet Protocol implementation at the Internet layer that can handle packet forwarding over multiple network interfaces. The Berkeley socket API is optional.

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Berkeley Sockets Wikipedia page. BSD Socket error handling code is very important for robust socket applications. Normally the socket error handling involves the following aspects:. Socket API returns an error.

For more information, see select Errors. Different values indicate different meanings. Socket error when select has exception descriptor. Because select has exception descriptor, the error code will not be given to errno. Its function is to get the current value of the option of any type, any state socket, and store the result in optval. Below is a list of common error codes. The following socket options are supported:.

TCP sockets only. IPv6 sockets only. The fcntl function is a standard API for manipulating options related to a file descriptor. When the file descriptor is a socket, only the following fcntl values are supported:. A TCP socket will return a different mode depending on whether the connection has been closed at either end or is still open at both ends.

When the file descriptor is a socket, only the following ioctl values are supported:. As such, this functionality is enabled but not supported. It is possible to close a socket from a different thread to the one that created it. The close call will block until any function calls currently using that socket from other tasks have returned. The default lwIP implementation is to have these timers enabled all the time, even if no timeout events are active.

This increases CPU usage and power consumption when using automatic light sleep mode. This disables the default lwIP behaviour of keeping TCP connections open if an interface IP changes, in case the interface IP changes back for example, if an interface connection goes down and comes back up. Enable this option to keep TCP connections open in this case, until they time out normally. This may increase the number of sockets in use if a network interface goes down temporarily.

This is a limitation of buffer sizes in the lower layer network interface drivers. If all driver transmit buffers are full then UDP transmission will fail. Suggest applying changes a few at a time and checking the performance each time with a particular application workload. Configure competing tasks to be pinned to a different core, or to run at a lower priority. Except for increasing buffer sizes, most changes which increase throughput will also decrease latency by reducing the amount of CPU time spent in lwIP functions.

The peak heap memory that lwIP consumes is the theoretically-maximum memory that the lwIP driver consumes. Generally, the peak heap memory that lwIP consumes depends on:. However, they may choose to close this TCP connection and create a new one when an error such as a sending failure occurs. Provide feedback about this document. Normally the socket error handling involves the following aspects: Detecting the error.

Geting the error reason code. Handle the error according to the reason code. Important Suggest applying changes a few at a time and checking the performance each time with a particular application workload.


LwIP Application Developers Manual



LWIP reference manual


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