Quality RTOS & Embedded Software

  Real time embedded FreeRTOS RSS feed  

xStreamBufferCreateStatic()
[RTOS Stream Buffer API]


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.

Stream buffer functionality is enabled by including the FreeRTOS/source/stream_buffer.c source file in the build.

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 + 1 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.
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 usage:

/* 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 ucBufferStorage[ 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( ucBufferStorage ),
                                               xTriggerLevel,
                                               ucBufferStorage,
                                               &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. */
}





Copyright (C) Amazon Web Services, Inc. or its affiliates. All rights reserved.