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<div class="title">xMessageBufferSend</div> </div>
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<p><a class="el" href="message__buffer_8h.html">message_buffer.h</a></p>
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<pre>
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size_t xMessageBufferSend( MessageBufferHandle_t xMessageBuffer,
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const void *pvTxData,
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size_t xDataLengthBytes,
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TickType_t xTicksToWait );
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<pre></pre></pre><pre><pre> Sends a discrete message to the message buffer. The message can be any
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length that fits within the buffer's free space, and is copied into the
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buffer.</pre></pre><pre><pre> ***NOTE***: Uniquely among FreeRTOS objects, the stream buffer
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implementation (so also the message buffer implementation, as message buffers
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are built on top of stream buffers) assumes there is only one task or
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interrupt that will write to the buffer (the writer), and only one task or
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interrupt that will read from the buffer (the reader). It is safe for the
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writer and reader to be different tasks or interrupts, but, unlike other
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FreeRTOS objects, it is not safe to have multiple different writers or
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multiple different readers. If there are to be multiple different writers
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then the application writer must place each call to a writing API function
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(such as <a class="el" href="message__buffer_8h.html#a858f6da6fe24a226c45caf1634ea1605">xMessageBufferSend()</a>) inside a critical section and set the send
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block time to 0. Likewise, if there are to be multiple different readers
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then the application writer must place each call to a reading API function
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(such as xMessageBufferRead()) inside a critical section and set the receive
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block time to 0.</pre></pre><pre><pre> Use <a class="el" href="message__buffer_8h.html#a858f6da6fe24a226c45caf1634ea1605">xMessageBufferSend()</a> to write to a message buffer from a task. Use
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<a class="el" href="message__buffer_8h.html#aeef5b0c4f8c2db6ca2230a8874813e79">xMessageBufferSendFromISR()</a> to write to a message buffer from an interrupt
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service routine (ISR).</pre></pre><pre><pre><dl class="params"><dt>Parameters</dt><dd>
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<table class="params">
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<tr><td class="paramname">xMessageBuffer</td><td>The handle of the message buffer to which a message is
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being sent.</td></tr>
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<tr><td class="paramname">pvTxData</td><td>A pointer to the message that is to be copied into the
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message buffer.</td></tr>
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<tr><td class="paramname">xDataLengthBytes</td><td>The length of the message. That is, the number of
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bytes to copy from pvTxData into the message buffer. When a message is
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written to the message buffer an additional sizeof( size_t ) bytes are also
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written to store the message's length. sizeof( size_t ) is typically 4 bytes
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on a 32-bit architecture, so on most 32-bit architecture setting
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xDataLengthBytes to 20 will reduce the free space in the message buffer by 24
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bytes (20 bytes of message data and 4 bytes to hold the message length).</td></tr>
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<tr><td class="paramname">xTicksToWait</td><td>The maximum amount of time the calling task should remain
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in the Blocked state to wait for enough space to become available in the
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message buffer, should the message buffer have insufficient space when
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<a class="el" href="message__buffer_8h.html#a858f6da6fe24a226c45caf1634ea1605">xMessageBufferSend()</a> is called. The calling task will never block if
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xTicksToWait is zero. The block time is specified in tick periods, so the
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absolute time it represents is dependent on the tick frequency. The macro
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<a class="el" href="projdefs_8h.html#a353d0f62b82a402cb3db63706c81ec3f">pdMS_TO_TICKS()</a> can be used to convert a time specified in milliseconds into
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a time specified in ticks. Setting xTicksToWait to portMAX_DELAY will cause
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the task to wait indefinitely (without timing out), provided
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INCLUDE_vTaskSuspend is set to 1 in <a class="el" href="_free_r_t_o_s_config_8h.html">FreeRTOSConfig.h</a>. Tasks do not use any
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CPU time when they are in the Blocked state.</td></tr>
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</table>
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</dd>
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</dl>
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<dl class="section return"><dt>Returns</dt><dd>The number of bytes written to the message buffer. If the call to
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<a class="el" href="message__buffer_8h.html#a858f6da6fe24a226c45caf1634ea1605">xMessageBufferSend()</a> times out before there was enough space to write the
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message into the message buffer then zero is returned. If the call did not
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time out then xDataLengthBytes is returned.</dd></dl>
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Example use:
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<pre>
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void vAFunction( MessageBufferHandle_t xMessageBuffer )
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{
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size_t xBytesSent;
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uint8_t ucArrayToSend[] = { 0, 1, 2, 3 };
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char *pcStringToSend = "String to send";
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const TickType_t x100ms = <a class="el" href="projdefs_8h.html#a353d0f62b82a402cb3db63706c81ec3f">pdMS_TO_TICKS( 100 )</a>;</pre></pre></pre><pre><pre><pre> // Send an array to the message buffer, blocking for a maximum of 100ms to
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// wait for enough space to be available in the message buffer.
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xBytesSent = xMessageBufferSend( xMessageBuffer, ( void * ) ucArrayToSend, sizeof( ucArrayToSend ), x100ms );</pre></pre></pre><pre><pre><pre> if( xBytesSent != sizeof( ucArrayToSend ) )
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{
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// The call to <a class="el" href="message__buffer_8h.html#a858f6da6fe24a226c45caf1634ea1605">xMessageBufferSend()</a> times out before there was enough
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// space in the buffer for the data to be written.
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}</pre></pre></pre><pre><pre><pre> // Send the string to the message buffer. Return immediately if there is
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// not enough space in the buffer.
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xBytesSent = xMessageBufferSend( xMessageBuffer, ( void * ) pcStringToSend, strlen( pcStringToSend ), 0 );</pre></pre></pre><pre><pre><pre> if( xBytesSent != strlen( pcStringToSend ) )
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{
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// The string could not be added to the message buffer because there was
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// not enough free space in the buffer.
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}
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}
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</pre> </pre></pre></div><!-- contents -->
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