[RTOS Message Buffer API]
MessageBufferHandle_t xMessageBufferCreate( size_t xBufferSizeBytes );
configSUPPORT_DYNAMIC_ALLOCATION must be set to 1 or left undefined in FreeRTOSConfig.h for xMessageBufferCreate() to be available.
Message buffer functionality is enabled by including the FreeRTOS/source/stream_buffer.c source file in the build (as message buffers use stream buffers).
xBufferSizeBytes The total number of bytes (not messages) the message buffer will be able to hold at any one time. When a message is written to the message buffer an additional sizeof( size_t ) bytes are also written to store the message’s length. sizeof( size_t ) is typically 4 bytes on a 32-bit architecture, so on most 32-bit architectures a 10 byte message will take up 14 bytes of message buffer space.
- If NULL is returned, then the message buffer cannot be created because there is insufficient heap memory available for FreeRTOS to allocate the message buffer data structures and storage area. A non-NULL value being returned indicates that the message buffer has been created successfully – the returned value should be stored as the handle to the created message buffer.
void vAFunction( void )
const size_t xMessageBufferSizeBytes = 100;
/* Create a message buffer that can hold 100 bytes. The memory used to hold
both the message buffer structure and the data in the message buffer is
allocated dynamically. */
xMessageBuffer = xMessageBufferCreate( xMessageBufferSizeBytes );
if( xMessageBuffer == NULL )
/* There was not enough heap memory space available to create the
message buffer. */
/* The message buffer was created successfully and can now be used. */