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KERNEL

xMessageBufferCreateStatic()
[RTOS Message Buffer API]


message_buffer.h

MessageBufferHandle_t xMessageBufferCreateStatic(
                                          size_t xBufferSizeBytes,
                                          uint8_t *pucMessageBufferStorageArea,
                                          StaticMessageBuffer_t *pxStaticMessageBuffer );

Creates a new message buffer using statically allocated memory. See xMessageBufferCreate() for a version that uses dynamically allocated memory.

configSUPPORT_STATIC_ALLOCATION must be set to 1 in FreeRTOSConfig.h for xMessageBufferCreateStatic() 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).

Parameters:
xBufferSizeBytes   The size, in bytes, of the buffer pointed to by the pucMessageBufferStorageArea parameter. 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 architecture a 10 byte message will take up 14 bytes of message buffer space. The maximum number of bytes that can be stored in the message buffer is actually (xBufferSizeBytes – 1).
pucMessageBufferStorageArea   Must point to a uint8_t array that is at least xBufferSizeBytes + 1 big. This is the array to which messages are copied when they are written to the message buffer.
pxStaticMessageBuffer   Must point to a variable of type StaticMessageBuffer_t, which will be used to hold the message buffer’s data structure.
Returns:
If the message buffer is created successfully then a handle to the created message buffer is returned. If either pucMessageBufferStorageArea or pxStaticMessageBuffer are NULL then NULL is returned.


Example usage:

/* Used to dimension the array used to hold the messages.  The available space
will actually be one less than this, so 999. */
#define STORAGE_SIZE_BYTES 1000

/* Defines the memory that will actually hold the messages within the message
buffer.  Should be one more than the value passed in the xBufferSizeBytes
parameter. */
static uint8_t ucStorageBuffer[ STORAGE_SIZE_BYTES ];

/* The variable used to hold the message buffer structure. */
StaticMessageBuffer_t xMessageBufferStruct;

void MyFunction( void )
{
MessageBufferHandle_t xMessageBuffer;

    xMessageBuffer = xMessageBufferCreateStatic( sizeof( ucStoragegBuffer ),
                                                 ucBufferStorage,
                                                 &xMessageBufferStruct );

    /* As neither the pucMessageBufferStorageArea or pxStaticMessageBuffer
    parameters were NULL, xMessageBuffer will not be NULL, and can be used to
    reference the created message buffer in other message buffer API calls. */

    /* Other code that uses the message buffer can go here. */
}





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