LibrariesinsideAPI reference

Updated Jun 2025

ulApplicationGetNextSequenceNumber()

[FreeRTOS-Plus-TCP API Reference]

FreeRTOS_sockets.h

1uint32_t ulApplicationGetNextSequenceNumber( uint32_t ulSourceAddress,
2                                             uint16_t usSourcePort,
3                                             uint32_t ulDestinationAddress,
4                                             uint16_t usDestinationPort );

ulApplicationGetNextSequenceNumber is an application defined hook (or callback) function that is called by the FreeRTOS-Plus-TCP stack to get a difficult to predict sequence number for the 4-value address tuple for a TCP connection.

Callback functions are implemented by the application writer, but called by the TCP/IP stack. The prototype of the callback function must exactly match the prototype above (including the function name).

Parameters:

  • ulSourceAddress

    The IPv4 address of the device.

  • usSourcePort

    The port number of the device to which the TCP socket is bound.

  • ulDestinationAddress

    The IPv4 address of the peer.

  • usDestinationPort

    The port of the peer to which the TCP connection is being made.

Return value:

A 32-bit hard to predict number should be returned by this hook to be used as the initial sequence number for the TCP connection.