xStreamBufferCreateStatic

Collaboration diagram for xStreamBufferCreateStatic:

stream_buffer.h

StreamBufferHandle_t xStreamBufferCreateStatic( size_t xBufferSizeBytes,
                                                size_t xTriggerLevelBytes,
                                                uint8_t *pucStreamBufferStorageArea,
                                                StaticStreamBuffer_t *pxStaticStreamBuffer );

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

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

Parameters

xBufferSizeBytes	The size, in bytes, of the buffer pointed to by the pucStreamBufferStorageArea parameter.
xTriggerLevelBytes	The number of bytes that must be in the stream buffer before a task that is blocked on the stream buffer to wait for data is moved out of the blocked state. For example, if a task is blocked on a read of an empty stream buffer that has a trigger level of 1 then the task will be unblocked when a single byte is written to the buffer or the task's block time expires. As another example, if a task is blocked on a read of an empty stream buffer that has a trigger level of 10 then the task will not be unblocked until the stream buffer contains at least 10 bytes or the task's block time expires. If a reading task's block time expires before the trigger level is reached then the task will still receive however many bytes are actually available. Setting a trigger level of 0 will result in a trigger level of 1 being used. It is not valid to specify a trigger level that is greater than the buffer size.
pucStreamBufferStorageArea	Must point to a uint8_t array that is at least xBufferSizeBytes big. This is the array to which streams are copied when they are written to the stream buffer.
pxStaticStreamBuffer	Must point to a variable of type StaticStreamBuffer_t, which will be used to hold the stream buffer's data structure.
pxSendCompletedCallback	Callback invoked when number of bytes at least equal to trigger level is sent to the stream buffer. If the parameter is NULL, 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 more than zero bytes are read from a stream buffer. If the parameter is NULL, 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 stream buffer is created successfully then a handle to the created stream buffer is returned. If either pucStreamBufferStorageArea or pxStaticstreamBuffer are NULL then NULL is returned.

Example use:

  // Used to dimension the array used to hold the streams.  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 streams within the stream
  // buffer.
  static uint8_t ucStorageBuffer[ STORAGE_SIZE_BYTES ];
 
  // The variable used to hold the stream buffer structure.
  StaticStreamBuffer_t xStreamBufferStruct;
 
  void MyFunction( void )
  {
  StreamBufferHandle_t xStreamBuffer;
  const size_t xTriggerLevel = 1;
 
   xStreamBuffer = xStreamBufferCreateStatic( sizeof( ucStorageBuffer ),
                                              xTriggerLevel,
                                              ucStorageBuffer,
                                              &xStreamBufferStruct );
 
   // As neither the pucStreamBufferStorageArea or pxStaticStreamBuffer
   // parameters were NULL, xStreamBuffer will not be NULL, and can be used to
   // reference the created stream buffer in other stream buffer API calls.
 
   // Other code that uses the stream buffer can go here.
  }