xMessageBufferCreateStatic

Collaboration diagram for xMessageBufferCreateStatic:

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.

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

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 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.
pxSendCompletedCallback	Callback invoked when a new message is sent to the message buffer. If the parameter is NULL or xMessageBufferCreate() is called without the parameter, then it will use the default implementation provided by sbSEND_COMPLETED macro. To enable the callback, configUSE_SB_COMPLETED_CALLBACK must be set to 1 in FreeRTOSConfig.h.
pxReceiveCompletedCallback	Callback invoked when a message is read from a message buffer. If the parameter is NULL or xMessageBufferCreate() is called without the parameter, it will use the default implementation provided by sbRECEIVE_COMPLETED macro. To enable the callback, configUSE_SB_COMPLETED_CALLBACK must be set to 1 in FreeRTOSConfig.h.

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 use:

  // 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.
  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( ucStorageBuffer ),
                                                ucStorageBuffer,
                                                &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.
  }