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.
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Parameters:
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xStreamBuffer
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The handle of the stream buffer to which a stream is
being sent.
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pvTxData
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A pointer to the buffer that holds the bytes to be copied
into the stream buffer.
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xDataLengthBytes
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The maximum number of bytes to copy from pvTxData
into the stream buffer.
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xTicksToWait
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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.
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Returns:
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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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