FreeRTOS_FD_ISSET()

[FreeRTOS+TCP API Reference]

FreeRTOS_sockets.h 
BaseType_t FreeRTOS_FD_ISSET( Socket_t xSocket, SocketSet_t xSocketSet );

Check if a socket in a socket set has an event bit set. ipconfigSUPPORT_SELECT_FUNCTION must be set to 1 in FreeRTOSIPConfig.h for FreeRTOS_FD_ISSET() to be available.


Socket Sets allow an application RTOS task to block on multiple sockets simultaneously.

To use a socket set:

  1. Create a socket set by calling FreeRTOS_CreateSocketSet(). A socket set is equivalent to the Berkeley sockets fd_set type.

  2. Add one or more sockets to the set using calls to FreeRTOS_FD_SET(). FreeRTOS_FD_SET() is equivalent to the Berkeley sockets FD_SET() macro.

  3. Call FreeRTOS_Select() to test the sockets in the set to see if any of the sockets have an event pending.

  4. If FreeRTOS_select() returns a non-zero value then check all sockets in the set using a call to FreeRTOS_FD_ISSET() to determine which events are pending.

The event bits of interest are a bitwise OR combination of one or more of the following values:

eSELECT_READ For a socket that is reading data, the eSELECT_READ event will be pending in a socket as long as the socket contains unread data.

For a socket that is listening for new connections, the eSELECT_READ event will be pended each time a new connection is received.

eSELECT_WRITE The eSELECT_WRITE event will remain pending as long as the socket has space for writing.

If a TCP socket is actively connecting to a pear the eSELECT_WRITE event will be triggered as soon as the connection is established.

One the eSELECT_WRITE event has been pended it should either be disabled, or the caller should write enough data to the socket so as to completely fill up the transmit buffer - otherwise the pending eSELECT_WRITE event will not be cleared.

eSELECT_EXCEPT The eSELECT_EXCEPT event will become pending if the socket gets disconnected.

The FreeRTOS_FD_CLR() API functions clears event bits of interest and removes a socket from a set.

Parameters:

xSocket   The socket within the socket set being tested to see if it has any event bits set.

xSocketSet   The socket set to which the socket is being added.

Returns:

The function returns a bit-mask of the values eSELECT_READ (1), eSELECT_WRITE (2) and eSELECT_EXCEPT (4). Only the bits of interest specified using calls to FreeRTOS_FD_SET() will be returned.

Example usage:

See the example on the FreeRTOS_select() documentation page.