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xStreamBufferSend()
[RTOS Stream Buffer API]


stream_buffer.h

size_t xStreamBufferSend( StreamBufferHandle_t xStreamBuffer,
                          const void *pvTxData,
                          size_t xDataLengthBytes,
                          TickType_t xTicksToWait );

Sends bytes to a stream buffer. The bytes are copied into the stream buffer.

NOTE: Uniquely among FreeRTOS objects, the stream buffer implementation (so also the message buffer implementation, as message buffers are built on top of stream buffers) assumes there is only one task or interrupt that will write to the buffer (the writer), and only one task or interrupt that will read from the buffer (the reader). It is safe for the writer and reader to be different tasks or interrupts, but, unlike other FreeRTOS objects, it is not safe to have multiple different writers or multiple different readers. If there are to be multiple different writers then the application writer must place each call to a writing API function (such as xStreamBufferSend()) inside a critical section and use a send block time of 0. Likewise, if there are to be multiple different readers then the application writer must place each call to a reading API function (such as xStreamBufferRead()) inside a critical section and use a receive block time of 0.

Use xStreamBufferSend() to write to a stream buffer from a task. Use xStreamBufferSendFromISR() to write to a stream buffer from an interrupt service routine (ISR).

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

Parameters:
xStreamBuffer   The handle of the stream buffer to which a stream is being sent.
pvTxData   A pointer to the buffer that holds the bytes to be copied into the stream buffer.
xDataLengthBytes   The maximum number of bytes to copy from pvTxData into the stream buffer.
xTicksToWait   The maximum amount of time the task should remain in the Blocked state to wait for enough space to become available in the stream buffer, should the stream buffer contain too little space to hold the another xDataLengthBytes bytes. The block time is specified in tick periods, so the absolute time it represents is dependent on the tick frequency. The macro pdMS_TO_TICKS() can be used to convert a time specified in milliseconds into a time specified in ticks. Setting xTicksToWait to portMAX_DELAY will cause the task to wait indefinitely (without timing out), provided INCLUDE_vTaskSuspend is set to 1 in FreeRTOSConfig.h. If a task times out before it can write all xDataLengthBytes into the buffer it will still write as many bytes as possible. A task does not use any CPU time when it is in the blocked state.
Returns:
The number of bytes written to the stream buffer. If a task times out before it can write all xDataLengthBytes into the buffer it will still write as many bytes as possible.


Example usage:

void vAFunction( StreamBufferHandle_t xStreamBuffer )
{
size_t xBytesSent;
uint8_t ucArrayToSend[] = { 0, 1, 2, 3 };
char *pcStringToSend = "String to send";
const TickType_t x100ms = pdMS_TO_TICKS( 100 );

    /* Send an array to the stream buffer, blocking for a maximum of 100ms to
    wait for enough space to be available in the stream buffer. */
    xBytesSent = xStreamBufferSend( xStreamBuffer,
                                   ( void * ) ucArrayToSend,
                                   sizeof( ucArrayToSend ),
                                   x100ms );

    if( xBytesSent != sizeof( ucArrayToSend ) )
    {
        /* The call to xStreamBufferSend() times out before there was enough
        space in the buffer for the data to be written, but it did
        successfully write xBytesSent bytes. */
    }

    /* Send the string to the stream buffer.  Return immediately if there is not
    enough space in the buffer. */
    xBytesSent = xStreamBufferSend( xStreamBuffer,
                                    ( void * ) pcStringToSend,
                                    strlen( pcStringToSend ), 0 );

    if( xBytesSent != strlen( pcStringToSend ) )
    {
        /* The entire string could not be added to the stream buffer because
        there was not enough free space in the buffer, but xBytesSent bytes
        were sent.  Could try again to send the remaining bytes. */
    }
}






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