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December 2021 Releases:
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FreeRTOS 202111.00 Release:
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[RTOS Stream Buffer API]


BaseType_t xStreamBufferSetTriggerLevel( StreamBufferHandle_t xStreamBuffer,
                                         size_t xTriggerLevel );

A stream buffer's trigger level is 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.

A trigger level is set when the stream buffer is created, and can be modified using xStreamBufferSetTriggerLevel().

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

xStreamBuffer   The handle of the stream buffer being updated.
xTriggerLevel   The new trigger level for the stream buffer.
If xTriggerLevel was less than or equal to the stream buffer's length then the trigger level will be updated and pdTRUE is returned. Otherwise pdFALSE is returned.




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