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<concept xml:lang="en" id="GUID-BD9CBBE8-9389-50F9-98B1-0A07F7E2891C"><title>How to Wait for the Write Buffer to Empty: Tutorial</title><prolog><metadata><keywords/></metadata></prolog><conbody><p>This tutorial shows how to wait for the device driver to transmit data when a write request has previously been terminated early. </p> <p>The tutorial <xref href="GUID-294EF1C3-E7EC-5B93-B4F4-ECA50DD6993F.dita">How to Terminate Write Requests Early</xref> shows how the <xref href="GUID-3B4E8ED5-72F7-3E51-B188-3C1045526DDF.dita#GUID-3B4E8ED5-72F7-3E51-B188-3C1045526DDF/GUID-8FB1FC0F-EF29-3EE9-BD4B-359CE42F3796"><apiname>RComm::Write</apiname></xref> API can return early. </p> <p>To wait for the buffer to be empty, call <xref href="GUID-3B4E8ED5-72F7-3E51-B188-3C1045526DDF.dita#GUID-3B4E8ED5-72F7-3E51-B188-3C1045526DDF/GUID-27B1F841-8478-33E0-A168-11DC468183C0"><apiname>RComm::Write()</apiname></xref> in one of two ways: </p> <ul><li id="GUID-92DCE453-6E78-57DA-BAC3-CC62645B359F"><p>sending an empty descriptor: </p> <codeblock id="GUID-9A469B13-EEEF-5465-92E4-B271801408C5" xml:space="preserve">outputBuffer.Zero();

commPort.Write (requeststatus,outputBuffer);</codeblock> </li> <li id="GUID-982A2F50-B25B-55F2-BEB2-FEB3ABE13080"><p>sending a descriptor with an optional length parameter of zero: </p> <codeblock id="GUID-013C9C10-2F2E-5574-BA1B-F27219B99226" xml:space="preserve">commPort.Write (requeststatus,outputBuffer,0);</codeblock> </li> </ul> <p>The state of the <codeph>KConfigWriteBufferedComplete</codeph> bit has no effect when the above methods are used. </p> <p>This is a useful feature that enables something like a file transfer of a series of blocks to be sent efficiently making use of early completion, while still being able to guarantee through the method above that all the data has actually cleared the transmitter at end of the transfer. </p> </conbody></concept>