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 <span id="projectnumber">Version 2.1.3</span>
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<a href="#nested-classes">Data Structures</a> |
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<div class="title">Message Queue<div class="ingroups"><a class="el" href="group__CMSIS__RTOS.html">CMSIS-RTOS API v2</a></div></div> </div>
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<p>Exchange messages between threads in a FIFO-like operation.
<a href="#details">More...</a></p>
<table class="memberdecls">
<tr class="heading"><td colspan="2"><h2 class="groupheader"><a name="nested-classes"></a>
Data Structures</h2></td></tr>
<tr class="memitem:structosMessageQueueAttr__t"><td class="memItemLeft" align="right" valign="top">struct  </td><td class="memItemRight" valign="bottom"><a class="el" href="group__CMSIS__RTOS__Message.html#structosMessageQueueAttr__t">osMessageQueueAttr_t</a></td></tr>
<tr class="memdesc:structosMessageQueueAttr__t"><td class="mdescLeft"> </td><td class="mdescRight">Attributes structure for message queue. <a href="group__CMSIS__RTOS__Message.html#structosMessageQueueAttr__t">More...</a><br/></td></tr>
<tr class="separator:structosMessageQueueAttr__t"><td class="memSeparator" colspan="2"> </td></tr>
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<tr class="heading"><td colspan="2"><h2 class="groupheader"><a name="func-members"></a>
Functions</h2></td></tr>
<tr class="memitem:ga24e895a00f9d484db33aaf784c57bfed"><td class="memItemLeft" align="right" valign="top"><a class="el" href="cmsis__os2_8h.html#a206dbc05367e03c39fc6d4d1ebcff317">osMessageQueueId_t</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="group__CMSIS__RTOS__Message.html#ga24e895a00f9d484db33aaf784c57bfed">osMessageQueueNew</a> (uint32_t msg_count, uint32_t msg_size, const <a class="el" href="group__CMSIS__RTOS__Message.html#structosMessageQueueAttr__t">osMessageQueueAttr_t</a> *attr)</td></tr>
<tr class="memdesc:ga24e895a00f9d484db33aaf784c57bfed"><td class="mdescLeft"> </td><td class="mdescRight">Create and Initialize a Message Queue object. <a href="#ga24e895a00f9d484db33aaf784c57bfed">More...</a><br/></td></tr>
<tr class="separator:ga24e895a00f9d484db33aaf784c57bfed"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:gae7cf7bf2b97a5ae481fb60fcce99247a"><td class="memItemLeft" align="right" valign="top">const char * </td><td class="memItemRight" valign="bottom"><a class="el" href="group__CMSIS__RTOS__Message.html#gae7cf7bf2b97a5ae481fb60fcce99247a">osMessageQueueGetName</a> (<a class="el" href="cmsis__os2_8h.html#a206dbc05367e03c39fc6d4d1ebcff317">osMessageQueueId_t</a> mq_id)</td></tr>
<tr class="memdesc:gae7cf7bf2b97a5ae481fb60fcce99247a"><td class="mdescLeft"> </td><td class="mdescRight">Get name of a Message Queue object. <a href="#gae7cf7bf2b97a5ae481fb60fcce99247a">More...</a><br/></td></tr>
<tr class="separator:gae7cf7bf2b97a5ae481fb60fcce99247a"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:gaa515fc8b956f721a8f72b2c505813bfc"><td class="memItemLeft" align="right" valign="top"><a class="el" href="group__CMSIS__RTOS__Definitions.html#ga6c0dbe6069e4e7f47bb4cd32ae2b813e">osStatus_t</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="group__CMSIS__RTOS__Message.html#gaa515fc8b956f721a8f72b2c505813bfc">osMessageQueuePut</a> (<a class="el" href="cmsis__os2_8h.html#a206dbc05367e03c39fc6d4d1ebcff317">osMessageQueueId_t</a> mq_id, const void *msg_ptr, uint8_t msg_prio, uint32_t timeout)</td></tr>
<tr class="memdesc:gaa515fc8b956f721a8f72b2c505813bfc"><td class="mdescLeft"> </td><td class="mdescRight">Put a Message into a Queue or timeout if Queue is full. <a href="#gaa515fc8b956f721a8f72b2c505813bfc">More...</a><br/></td></tr>
<tr class="separator:gaa515fc8b956f721a8f72b2c505813bfc"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:gad90d4959466a7a65105061da8256ab9e"><td class="memItemLeft" align="right" valign="top"><a class="el" href="group__CMSIS__RTOS__Definitions.html#ga6c0dbe6069e4e7f47bb4cd32ae2b813e">osStatus_t</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="group__CMSIS__RTOS__Message.html#gad90d4959466a7a65105061da8256ab9e">osMessageQueueGet</a> (<a class="el" href="cmsis__os2_8h.html#a206dbc05367e03c39fc6d4d1ebcff317">osMessageQueueId_t</a> mq_id, void *msg_ptr, uint8_t *msg_prio, uint32_t timeout)</td></tr>
<tr class="memdesc:gad90d4959466a7a65105061da8256ab9e"><td class="mdescLeft"> </td><td class="mdescRight">Get a Message from a Queue or timeout if Queue is empty. <a href="#gad90d4959466a7a65105061da8256ab9e">More...</a><br/></td></tr>
<tr class="separator:gad90d4959466a7a65105061da8256ab9e"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:gac24f87d4f395e9e9c900c320e45ade8a"><td class="memItemLeft" align="right" valign="top">uint32_t </td><td class="memItemRight" valign="bottom"><a class="el" href="group__CMSIS__RTOS__Message.html#gac24f87d4f395e9e9c900c320e45ade8a">osMessageQueueGetCapacity</a> (<a class="el" href="cmsis__os2_8h.html#a206dbc05367e03c39fc6d4d1ebcff317">osMessageQueueId_t</a> mq_id)</td></tr>
<tr class="memdesc:gac24f87d4f395e9e9c900c320e45ade8a"><td class="mdescLeft"> </td><td class="mdescRight">Get maximum number of messages in a Message Queue. <a href="#gac24f87d4f395e9e9c900c320e45ade8a">More...</a><br/></td></tr>
<tr class="separator:gac24f87d4f395e9e9c900c320e45ade8a"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:ga96d3d84069b20359de48109e28a1a89e"><td class="memItemLeft" align="right" valign="top">uint32_t </td><td class="memItemRight" valign="bottom"><a class="el" href="group__CMSIS__RTOS__Message.html#ga96d3d84069b20359de48109e28a1a89e">osMessageQueueGetMsgSize</a> (<a class="el" href="cmsis__os2_8h.html#a206dbc05367e03c39fc6d4d1ebcff317">osMessageQueueId_t</a> mq_id)</td></tr>
<tr class="memdesc:ga96d3d84069b20359de48109e28a1a89e"><td class="mdescLeft"> </td><td class="mdescRight">Get maximum message size in a Memory Pool. <a href="#ga96d3d84069b20359de48109e28a1a89e">More...</a><br/></td></tr>
<tr class="separator:ga96d3d84069b20359de48109e28a1a89e"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:ga6a32ac394fcff568b251c160cc3014b2"><td class="memItemLeft" align="right" valign="top">uint32_t </td><td class="memItemRight" valign="bottom"><a class="el" href="group__CMSIS__RTOS__Message.html#ga6a32ac394fcff568b251c160cc3014b2">osMessageQueueGetCount</a> (<a class="el" href="cmsis__os2_8h.html#a206dbc05367e03c39fc6d4d1ebcff317">osMessageQueueId_t</a> mq_id)</td></tr>
<tr class="memdesc:ga6a32ac394fcff568b251c160cc3014b2"><td class="mdescLeft"> </td><td class="mdescRight">Get number of queued messages in a Message Queue. <a href="#ga6a32ac394fcff568b251c160cc3014b2">More...</a><br/></td></tr>
<tr class="separator:ga6a32ac394fcff568b251c160cc3014b2"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:gaddf0904427436dd3880d46263c2dc9fa"><td class="memItemLeft" align="right" valign="top">uint32_t </td><td class="memItemRight" valign="bottom"><a class="el" href="group__CMSIS__RTOS__Message.html#gaddf0904427436dd3880d46263c2dc9fa">osMessageQueueGetSpace</a> (<a class="el" href="cmsis__os2_8h.html#a206dbc05367e03c39fc6d4d1ebcff317">osMessageQueueId_t</a> mq_id)</td></tr>
<tr class="memdesc:gaddf0904427436dd3880d46263c2dc9fa"><td class="mdescLeft"> </td><td class="mdescRight">Get number of available slots for messages in a Message Queue. <a href="#gaddf0904427436dd3880d46263c2dc9fa">More...</a><br/></td></tr>
<tr class="separator:gaddf0904427436dd3880d46263c2dc9fa"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:gac6dce7f9ad132d266292c2e979d861b4"><td class="memItemLeft" align="right" valign="top"><a class="el" href="group__CMSIS__RTOS__Definitions.html#ga6c0dbe6069e4e7f47bb4cd32ae2b813e">osStatus_t</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="group__CMSIS__RTOS__Message.html#gac6dce7f9ad132d266292c2e979d861b4">osMessageQueueReset</a> (<a class="el" href="cmsis__os2_8h.html#a206dbc05367e03c39fc6d4d1ebcff317">osMessageQueueId_t</a> mq_id)</td></tr>
<tr class="memdesc:gac6dce7f9ad132d266292c2e979d861b4"><td class="mdescLeft"> </td><td class="mdescRight">Reset a Message Queue to initial empty state. <a href="#gac6dce7f9ad132d266292c2e979d861b4">More...</a><br/></td></tr>
<tr class="separator:gac6dce7f9ad132d266292c2e979d861b4"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:gaba987f665444e0d83fa6a3a68bc72abe"><td class="memItemLeft" align="right" valign="top"><a class="el" href="group__CMSIS__RTOS__Definitions.html#ga6c0dbe6069e4e7f47bb4cd32ae2b813e">osStatus_t</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="group__CMSIS__RTOS__Message.html#gaba987f665444e0d83fa6a3a68bc72abe">osMessageQueueDelete</a> (<a class="el" href="cmsis__os2_8h.html#a206dbc05367e03c39fc6d4d1ebcff317">osMessageQueueId_t</a> mq_id)</td></tr>
<tr class="memdesc:gaba987f665444e0d83fa6a3a68bc72abe"><td class="mdescLeft"> </td><td class="mdescRight">Delete a Message Queue object. <a href="#gaba987f665444e0d83fa6a3a68bc72abe">More...</a><br/></td></tr>
<tr class="separator:gaba987f665444e0d83fa6a3a68bc72abe"><td class="memSeparator" colspan="2"> </td></tr>
</table>
<a name="details" id="details"></a><h2 class="groupheader">Description</h2>
<p><b>Message</b> <b>passing</b> is another basic communication model between threads. In the message passing model, one thread sends data explicitly, while another thread receives it. The operation is more like some kind of I/O rather than a direct access to information to be shared. In CMSIS-RTOS, this mechanism is called s <b>message</b> <b>queue</b>. The data is passed from one thread to another in a FIFO-like operation. Using message queue functions, you can control, send, receive, or wait for messages. The data to be passed can be of integer or pointer type:</p>
<div class="image">
<img src="MessageQueue.png" alt="MessageQueue.png"/>
<div class="caption">
CMSIS-RTOS Message Queue</div></div>
<p> Compared to a <a class="el" href="group__CMSIS__RTOS__PoolMgmt.html">Memory Pool</a>, message queues are less efficient in general, but solve a broader range of problems. Sometimes, threads do not have a common address space or the use of shared memory raises problems, such as mutual exclusion.</p>
<dl class="section note"><dt>Note</dt><dd>The functions <a class="el" href="group__CMSIS__RTOS__Message.html#gaa515fc8b956f721a8f72b2c505813bfc">osMessageQueuePut</a>, <a class="el" href="group__CMSIS__RTOS__Message.html#gad90d4959466a7a65105061da8256ab9e">osMessageQueueGet</a>, <a class="el" href="group__CMSIS__RTOS__Message.html#gac24f87d4f395e9e9c900c320e45ade8a">osMessageQueueGetCapacity</a>, <a class="el" href="group__CMSIS__RTOS__Message.html#ga96d3d84069b20359de48109e28a1a89e">osMessageQueueGetMsgSize</a>, <a class="el" href="group__CMSIS__RTOS__Message.html#ga6a32ac394fcff568b251c160cc3014b2">osMessageQueueGetCount</a>, <a class="el" href="group__CMSIS__RTOS__Message.html#gaddf0904427436dd3880d46263c2dc9fa">osMessageQueueGetSpace</a> can be called from <a class="el" href="theory_of_operation.html#CMSIS_RTOS_ISR_Calls">Interrupt Service Routines</a>. </dd>
<dd>
Refer to <a class="el" href="config_rtx5.html#msgQueueConfig">Message Queue Configuration</a> for RTX5 configuration options. </dd></dl>
<hr/><h2 class="groupheader">Data Structure Documentation</h2>
<a name="structosMessageQueueAttr__t" id="structosMessageQueueAttr__t"></a>
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<td class="memname">struct osMessageQueueAttr_t</td>
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<div class="textblock"><p>Specifies the following attributes for the <a class="el" href="group__CMSIS__RTOS__Message.html#ga24e895a00f9d484db33aaf784c57bfed">osMessageQueueNew</a> function. </p>
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<tr><th colspan="3">Data Fields</th></tr>
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<a class="anchor" id="ab74e6bf80237ddc4109968cedc58c151"></a>const char *</td>
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name</td>
<td class="fielddoc">
name of the message queue <p>Pointer to a constant string with a human readable name (displayed during debugging) of the message queue object.</p>
<p>Default: <span class="XML-Token">NULL</span> no name specified. </p>
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<a class="anchor" id="a6e93b49cb79c12f768d72580c7731f30"></a>uint32_t</td>
<td class="fieldname">
attr_bits</td>
<td class="fielddoc">
attribute bits <p>Reserved for future use (must be set to '0' for future compatibility). </p>
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<a class="anchor" id="a1e100dc33d403841ed3c344e3397868e"></a>void *</td>
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cb_mem</td>
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memory for control block <p>Pointer to a memory for the message queue control block object. Refer to <a class="el" href="theory_of_operation.html#StaticObjectMemory">Static Object Memory</a> for more information.</p>
<p>Default: <span class="XML-Token">NULL</span> to use <a class="el" href="group__CMSIS__RTOS__MemoryMgmt.html#CMSIS_RTOS_MemoryMgmt_Automatic">Automatic Dynamic Allocation</a> for the message queue control block. </p>
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<a class="anchor" id="aa55a4335d12dc2785dc00fdc292d1159"></a>uint32_t</td>
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cb_size</td>
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size of provided memory for control block <p>The size (in bytes) of memory block passed with <a class="el" href="group__CMSIS__RTOS__Message.html#a1e100dc33d403841ed3c344e3397868e">cb_mem</a>. For RTX, the minimum value is defined with <a class="el" href="group__rtx5__specific__defines.html#gaa8d067c476faa6bfc8e5e21f3b3c844e">osRtxMessageQueueCbSize</a> (higher values are permitted).</p>
<p>Default: <span class="XML-Token">0</span> as the default is no memory provided with <a class="el" href="group__CMSIS__RTOS__Message.html#a1e100dc33d403841ed3c344e3397868e">cb_mem</a>. </p>
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<a class="anchor" id="a4e208dc0fb049b42c4b90cbd2791c5ad"></a>void *</td>
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mq_mem</td>
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memory for data storage <p>Pointer to a memory for the message queue data. Refer to <a class="el" href="theory_of_operation.html#StaticObjectMemory">Static Object Memory</a> for more information.</p>
<p>Default: <span class="XML-Token">NULL</span> to use <a class="el" href="group__CMSIS__RTOS__MemoryMgmt.html#CMSIS_RTOS_MemoryMgmt_Automatic">Automatic Dynamic Allocation</a> for the memory pool data. </p>
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<a class="anchor" id="ac1cc09f875e20c926920b57bb83c70ee"></a>uint32_t</td>
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mq_size</td>
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size of provided memory for data storage <p>The size (in bytes) of memory block passed with <a class="el" href="group__CMSIS__RTOS__Message.html#a4e208dc0fb049b42c4b90cbd2791c5ad">mq_mem</a>. The minimum memory block size is <code>msg_count * msg_size</code> (parameters of the <a class="el" href="group__CMSIS__RTOS__Message.html#ga24e895a00f9d484db33aaf784c57bfed">osMessageQueueNew</a> function). The <em>msg_size</em> is rounded up to a double even number to ensure 32-bit alignment of the memory blocks.</p>
<p>Default: 0 as the default is no memory provided with <a class="el" href="group__CMSIS__RTOS__Message.html#a4e208dc0fb049b42c4b90cbd2791c5ad">mq_mem</a>. </p>
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<h2 class="groupheader">Function Documentation</h2>
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<td class="memname"><a class="el" href="cmsis__os2_8h.html#a206dbc05367e03c39fc6d4d1ebcff317">osMessageQueueId_t</a> osMessageQueueNew </td>
<td>(</td>
<td class="paramtype">uint32_t </td>
<td class="paramname"><em>msg_count</em>, </td>
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<td class="paramtype">uint32_t </td>
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<td class="paramtype">const <a class="el" href="group__CMSIS__RTOS__Message.html#structosMessageQueueAttr__t">osMessageQueueAttr_t</a> * </td>
<td class="paramname"><em>attr</em> </td>
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<td>)</td>
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<dl class="params"><dt>Parameters</dt><dd>
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<tr><td class="paramdir">[in]</td><td class="paramname">msg_count</td><td>maximum number of messages in queue. </td></tr>
<tr><td class="paramdir">[in]</td><td class="paramname">msg_size</td><td>maximum message size in bytes. </td></tr>
<tr><td class="paramdir">[in]</td><td class="paramname">attr</td><td>message queue attributes; NULL: default values. </td></tr>
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<dl class="section return"><dt>Returns</dt><dd>message queue ID for reference by other functions or NULL in case of error.</dd></dl>
<p>The function <a class="el" href="group__CMSIS__RTOS__Message.html#ga24e895a00f9d484db33aaf784c57bfed">osMessageQueueNew</a> creates and initializes a message queue object. The function returns a message queue object identifier or <span class="XML-Token">NULL</span> in case of an error.</p>
<p>The function can be called after kernel initialization with <a class="el" href="group__CMSIS__RTOS__KernelCtrl.html#gae818f6611d25ba3140bede410a52d659">osKernelInitialize</a>. It is possible to create message queue objects before the RTOS kernel is started with <a class="el" href="group__CMSIS__RTOS__KernelCtrl.html#ga9ae2cc00f0d89d7b6a307bba942b5221">osKernelStart</a>.</p>
<p>The total amount of memory required for the message queue data is at least <code>msg_count * msg_size</code>. The <em>msg_size</em> is rounded up to a double even number to ensure 32-bit alignment of the memory blocks.</p>
<p>The memory blocks allocated from the message queue have a fixed size defined with the parameter <code>msg_size</code>.</p>
<dl class="section note"><dt>Note</dt><dd>This function <b>cannot</b> be called from <a class="el" href="theory_of_operation.html#CMSIS_RTOS_ISR_Calls">Interrupt Service Routines</a>.</dd></dl>
<p><b>Code Example</b></p>
<p>Refer to <a class="el" href="group__CMSIS__RTOS__Message.html#gaa515fc8b956f721a8f72b2c505813bfc">osMessageQueuePut</a> </p>
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<td class="memname">const char * osMessageQueueGetName </td>
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<td class="paramtype"><a class="el" href="cmsis__os2_8h.html#a206dbc05367e03c39fc6d4d1ebcff317">osMessageQueueId_t</a> </td>
<td class="paramname"><em>mq_id</em></td><td>)</td>
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<dl class="params"><dt>Parameters</dt><dd>
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<tr><td class="paramdir">[in]</td><td class="paramname">mq_id</td><td>message queue ID obtained by <a class="el" href="group__CMSIS__RTOS__Message.html#ga24e895a00f9d484db33aaf784c57bfed">osMessageQueueNew</a>. </td></tr>
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<dl class="section return"><dt>Returns</dt><dd>name as null-terminated string.</dd></dl>
<p>The function <b>osMessageQueueGetName</b> returns the pointer to the name string of the message queue identified by parameter <em>mq_id</em> or <span class="XML-Token">NULL</span> in case of an error.</p>
<dl class="section note"><dt>Note</dt><dd>This function <b>cannot</b> be called from <a class="el" href="theory_of_operation.html#CMSIS_RTOS_ISR_Calls">Interrupt Service Routines</a>. </dd></dl>
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<td class="memname"><a class="el" href="group__CMSIS__RTOS__Definitions.html#ga6c0dbe6069e4e7f47bb4cd32ae2b813e">osStatus_t</a> osMessageQueuePut </td>
<td>(</td>
<td class="paramtype"><a class="el" href="cmsis__os2_8h.html#a206dbc05367e03c39fc6d4d1ebcff317">osMessageQueueId_t</a> </td>
<td class="paramname"><em>mq_id</em>, </td>
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<td class="paramkey"></td>
<td></td>
<td class="paramtype">const void * </td>
<td class="paramname"><em>msg_ptr</em>, </td>
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<td class="paramkey"></td>
<td></td>
<td class="paramtype">uint8_t </td>
<td class="paramname"><em>msg_prio</em>, </td>
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<td class="paramkey"></td>
<td></td>
<td class="paramtype">uint32_t </td>
<td class="paramname"><em>timeout</em> </td>
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<dl class="params"><dt>Parameters</dt><dd>
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<tr><td class="paramdir">[in]</td><td class="paramname">mq_id</td><td>message queue ID obtained by <a class="el" href="group__CMSIS__RTOS__Message.html#ga24e895a00f9d484db33aaf784c57bfed">osMessageQueueNew</a>. </td></tr>
<tr><td class="paramdir">[in]</td><td class="paramname">msg_ptr</td><td>pointer to buffer with message to put into a queue. </td></tr>
<tr><td class="paramdir">[in]</td><td class="paramname">msg_prio</td><td>message priority. </td></tr>
<tr><td class="paramdir">[in]</td><td class="paramname">timeout</td><td><a class="el" href="theory_of_operation.html#CMSIS_RTOS_TimeOutValue">Timeout Value</a> or 0 in case of no time-out. </td></tr>
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<dl class="section return"><dt>Returns</dt><dd>status code that indicates the execution status of the function.</dd></dl>
<p>The blocking function <b>osMessageQueuePut</b> puts the message pointed to by <em>msg_ptr</em> into the the message queue specified by parameter <em>mq_id</em>. The parameter <em>msg_prio</em> is used to sort message according their priority (higher numbers indicate a higher priority) on insertion.</p>
<p>The parameter <em>timeout</em> specifies how long the system waits to put the message into the queue. While the system waits, the thread that is calling this function is put into the <a class="el" href="group__CMSIS__RTOS__ThreadMgmt.html#ThreadStates">BLOCKED</a> state. The parameter <a class="el" href="theory_of_operation.html#CMSIS_RTOS_TimeOutValue">timeout</a> can have the following values:</p>
<ul>
<li>when <em>timeout</em> is <span class="XML-Token">0</span>, the function returns instantly (i.e. try semantics).</li>
<li>when <em>timeout</em> is set to <b>osWaitForever</b> the function will wait for an infinite time until the message is delivered (i.e. wait semantics).</li>
<li>all other values specify a time in kernel ticks for a timeout (i.e. timed-wait semantics).</li>
</ul>
<p>Possible <a class="el" href="group__CMSIS__RTOS__Definitions.html#ga6c0dbe6069e4e7f47bb4cd32ae2b813e">osStatus_t</a> return values:</p>
<ul>
<li><em>osOK:</em> the message has been put into the queue.</li>
<li><em>osErrorTimeout:</em> the message could not be put into the queue in the given time (wait-timed semantics).</li>
<li><em>osErrorResource:</em> not enough space in the queue (try semantics).</li>
<li><em>osErrorParameter:</em> parameter <em>mq_id</em> is <span class="XML-Token">NULL</span> or invalid, non-zero timeout specified in an ISR.</li>
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<dl class="section note"><dt>Note</dt><dd>May be called from <a class="el" href="theory_of_operation.html#CMSIS_RTOS_ISR_Calls">Interrupt Service Routines</a> if the parameter <em>timeout</em> is set to <span class="XML-Token">0</span>.</dd></dl>
<p><b>Code Example:</b> </p>
<div class="fragment"><div class="line"><span class="preprocessor">#include "<a class="code" href="cmsis__os2_8h.html">cmsis_os2.h</a>"</span> <span class="comment">// CMSIS RTOS header file</span></div>
<div class="line"> </div>
<div class="line"><span class="comment">/*----------------------------------------------------------------------------</span></div>
<div class="line"><span class="comment"> * Message Queue creation & usage</span></div>
<div class="line"><span class="comment"> *---------------------------------------------------------------------------*/</span></div>
<div class="line"> </div>
<div class="line"><span class="preprocessor">#define MSGQUEUE_OBJECTS 16 // number of Message Queue Objects</span></div>
<div class="line"><span class="preprocessor"></span> </div>
<div class="line"><span class="keyword">typedef</span> <span class="keyword">struct </span>{ <span class="comment">// object data type</span></div>
<div class="line"> uint8_t Buf[32];</div>
<div class="line"> uint8_t Idx;</div>
<div class="line">} MSGQUEUE_OBJ_t;</div>
<div class="line"> </div>
<div class="line"><a class="code" href="cmsis__os2_8h.html#a206dbc05367e03c39fc6d4d1ebcff317">osMessageQueueId_t</a> mid_MsgQueue; <span class="comment">// message queue id</span></div>
<div class="line"> </div>
<div class="line"><a class="code" href="group__CMSIS__RTOS__ThreadMgmt.html#gaa6c32fe2a3e0a2e01f212d55b02e51c7">osThreadId_t</a> tid_Thread_MsgQueue1; <span class="comment">// thread id 1</span></div>
<div class="line"><a class="code" href="group__CMSIS__RTOS__ThreadMgmt.html#gaa6c32fe2a3e0a2e01f212d55b02e51c7">osThreadId_t</a> tid_Thread_MsgQueue2; <span class="comment">// thread id 2</span></div>
<div class="line"> </div>
<div class="line"><span class="keywordtype">void</span> Thread_MsgQueue1 (<span class="keywordtype">void</span> *argument); <span class="comment">// thread function 1</span></div>
<div class="line"><span class="keywordtype">void</span> Thread_MsgQueue2 (<span class="keywordtype">void</span> *argument); <span class="comment">// thread function 2</span></div>
<div class="line"> </div>
<div class="line"><span class="keywordtype">int</span> Init_MsgQueue (<span class="keywordtype">void</span>) {</div>
<div class="line"> </div>
<div class="line"> mid_MsgQueue = <a class="code" href="group__CMSIS__RTOS__Message.html#ga24e895a00f9d484db33aaf784c57bfed">osMessageQueueNew</a>(MSGQUEUE_OBJECTS, <span class="keyword">sizeof</span>(MSGQUEUE_OBJ_t), NULL);</div>
<div class="line"> <span class="keywordflow">if</span> (mid_MsgQueue == NULL) {</div>
<div class="line"> ; <span class="comment">// Message Queue object not created, handle failure</span></div>
<div class="line"> }</div>
<div class="line"> </div>
<div class="line"> tid_Thread_MsgQueue1 = <a class="code" href="group__CMSIS__RTOS__ThreadMgmt.html#ga48d68b8666d99d28fa646ee1d2182b8f">osThreadNew</a>(Thread_MsgQueue1, NULL, NULL);</div>
<div class="line"> <span class="keywordflow">if</span> (tid_Thread_MsgQueue1 == NULL) {</div>
<div class="line"> <span class="keywordflow">return</span>(-1);</div>
<div class="line"> }</div>
<div class="line"> tid_Thread_MsgQueue2 = <a class="code" href="group__CMSIS__RTOS__ThreadMgmt.html#ga48d68b8666d99d28fa646ee1d2182b8f">osThreadNew</a>(Thread_MsgQueue2, NULL, NULL);</div>
<div class="line"> <span class="keywordflow">if</span> (tid_Thread_MsgQueue2 == NULL) {</div>
<div class="line"> <span class="keywordflow">return</span>(-1);</div>
<div class="line"> }</div>
<div class="line"> </div>
<div class="line"> <span class="keywordflow">return</span>(0);</div>
<div class="line">}</div>
<div class="line"> </div>
<div class="line"><span class="keywordtype">void</span> Thread_MsgQueue1 (<span class="keywordtype">void</span> *argument) {</div>
<div class="line"> MSGQUEUE_OBJ_t msg;</div>
<div class="line"> </div>
<div class="line"> <span class="keywordflow">while</span> (1) {</div>
<div class="line"> ; <span class="comment">// Insert thread code here...</span></div>
<div class="line"> msg.Buf[0] = 0x55U; <span class="comment">// do some work...</span></div>
<div class="line"> msg.Idx = 0U;</div>
<div class="line"> <a class="code" href="group__CMSIS__RTOS__Message.html#gaa515fc8b956f721a8f72b2c505813bfc">osMessageQueuePut</a>(mid_MsgQueue, &msg, 0U, 0U);</div>
<div class="line"> <a class="code" href="group__CMSIS__RTOS__ThreadMgmt.html#gad01c7ec26535b1de6b018bb9466720e2">osThreadYield</a>(); <span class="comment">// suspend thread</span></div>
<div class="line"> }</div>
<div class="line">}</div>
<div class="line"> </div>
<div class="line"><span class="keywordtype">void</span> Thread_MsgQueue2 (<span class="keywordtype">void</span> *argument) {</div>
<div class="line"> MSGQUEUE_OBJ_t msg;</div>
<div class="line"> osStatus_t status;</div>
<div class="line"> </div>
<div class="line"> <span class="keywordflow">while</span> (1) {</div>
<div class="line"> ; <span class="comment">// Insert thread code here...</span></div>
<div class="line"> status = <a class="code" href="group__CMSIS__RTOS__Message.html#gad90d4959466a7a65105061da8256ab9e">osMessageQueueGet</a>(mid_MsgQueue, &msg, NULL, 0U); <span class="comment">// wait for message</span></div>
<div class="line"> <span class="keywordflow">if</span> (status == <a class="code" href="cmsis__os2_8h.html#ga6c0dbe6069e4e7f47bb4cd32ae2b813ea9e1c9e2550bb4de8969a935acffc968f">osOK</a>) {</div>
<div class="line"> ; <span class="comment">// process data</span></div>
<div class="line"> }</div>
<div class="line"> }</div>
<div class="line">}</div>
</div><!-- fragment -->
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<td class="memname"><a class="el" href="group__CMSIS__RTOS__Definitions.html#ga6c0dbe6069e4e7f47bb4cd32ae2b813e">osStatus_t</a> osMessageQueueGet </td>
<td>(</td>
<td class="paramtype"><a class="el" href="cmsis__os2_8h.html#a206dbc05367e03c39fc6d4d1ebcff317">osMessageQueueId_t</a> </td>
<td class="paramname"><em>mq_id</em>, </td>
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<td class="paramtype">void * </td>
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<dl class="params"><dt>Parameters</dt><dd>
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<tr><td class="paramdir">[in]</td><td class="paramname">mq_id</td><td>message queue ID obtained by <a class="el" href="group__CMSIS__RTOS__Message.html#ga24e895a00f9d484db33aaf784c57bfed">osMessageQueueNew</a>. </td></tr>
<tr><td class="paramdir">[out]</td><td class="paramname">msg_ptr</td><td>pointer to buffer for message to get from a queue. </td></tr>
<tr><td class="paramdir">[out]</td><td class="paramname">msg_prio</td><td>pointer to buffer for message priority or NULL. </td></tr>
<tr><td class="paramdir">[in]</td><td class="paramname">timeout</td><td><a class="el" href="theory_of_operation.html#CMSIS_RTOS_TimeOutValue">Timeout Value</a> or 0 in case of no time-out. </td></tr>
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<dl class="section return"><dt>Returns</dt><dd>status code that indicates the execution status of the function.</dd></dl>
<p>The function <b>osMessageQueueGet</b> retrieves a message from the message queue specified by the parameter <em>mq_id</em> and saves it to the buffer pointed to by the parameter <em>msg_ptr</em>. The message priority is stored to parameter <em>msg_prio</em> if not token{NULL}.</p>
<p>The parameter <em>timeout</em> specifies how long the system waits to retrieve the message from the queue. While the system waits, the thread that is calling this function is put into the <a class="el" href="group__CMSIS__RTOS__ThreadMgmt.html#ThreadStates">BLOCKED</a> state. The parameter <a class="el" href="theory_of_operation.html#CMSIS_RTOS_TimeOutValue">timeout</a> can have the following values:</p>
<ul>
<li>when <em>timeout</em> is <span class="XML-Token">0</span>, the function returns instantly (i.e. try semantics).</li>
<li>when <em>timeout</em> is set to <b>osWaitForever</b> the function will wait for an infinite time until the message is retrieved (i.e. wait semantics).</li>
<li>all other values specify a time in kernel ticks for a timeout (i.e. timed-wait semantics).</li>
</ul>
<p>Possible <a class="el" href="group__CMSIS__RTOS__Definitions.html#ga6c0dbe6069e4e7f47bb4cd32ae2b813e">osStatus_t</a> return values:</p>
<ul>
<li><em>osOK:</em> the message has been retrieved from the queue.</li>
<li><em>osErrorTimeout:</em> the message could not be retrieved from the queue in the given time (timed-wait semantics).</li>
<li><em>osErrorResource:</em> nothing to get from the queue (try semantics).</li>
<li><em>osErrorParameter:</em> parameter <em>mq_id</em> is <span class="XML-Token">NULL</span> or invalid, non-zero timeout specified in an ISR.</li>
</ul>
<dl class="section note"><dt>Note</dt><dd>May be called from <a class="el" href="theory_of_operation.html#CMSIS_RTOS_ISR_Calls">Interrupt Service Routines</a> if the parameter <em>timeout</em> is set to <span class="XML-Token">0</span>.</dd></dl>
<p><b>Code Example</b></p>
<p>Refer to <a class="el" href="group__CMSIS__RTOS__Message.html#gaa515fc8b956f721a8f72b2c505813bfc">osMessageQueuePut</a> </p>
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<td class="memname">uint32_t osMessageQueueGetCapacity </td>
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<td class="paramtype"><a class="el" href="cmsis__os2_8h.html#a206dbc05367e03c39fc6d4d1ebcff317">osMessageQueueId_t</a> </td>
<td class="paramname"><em>mq_id</em></td><td>)</td>
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<dl class="params"><dt>Parameters</dt><dd>
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<tr><td class="paramdir">[in]</td><td class="paramname">mq_id</td><td>message queue ID obtained by <a class="el" href="group__CMSIS__RTOS__Message.html#ga24e895a00f9d484db33aaf784c57bfed">osMessageQueueNew</a>. </td></tr>
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<dl class="section return"><dt>Returns</dt><dd>maximum number of messages.</dd></dl>
<p>The function <b>osMessageQueueGetCapacity</b> returns the maximum number of messages in the message queue object specified by parameter <em>mq_id</em> or <span class="XML-Token">0</span> in case of an error.</p>
<dl class="section note"><dt>Note</dt><dd>This function may be called from <a class="el" href="theory_of_operation.html#CMSIS_RTOS_ISR_Calls">Interrupt Service Routines</a>. </dd></dl>
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<td class="memname">uint32_t osMessageQueueGetMsgSize </td>
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<td class="paramtype"><a class="el" href="cmsis__os2_8h.html#a206dbc05367e03c39fc6d4d1ebcff317">osMessageQueueId_t</a> </td>
<td class="paramname"><em>mq_id</em></td><td>)</td>
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<dl class="params"><dt>Parameters</dt><dd>
<table class="params">
<tr><td class="paramdir">[in]</td><td class="paramname">mq_id</td><td>message queue ID obtained by <a class="el" href="group__CMSIS__RTOS__Message.html#ga24e895a00f9d484db33aaf784c57bfed">osMessageQueueNew</a>. </td></tr>
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<dl class="section return"><dt>Returns</dt><dd>maximum message size in bytes.</dd></dl>
<p>The function <b>osMessageQueueGetMsgSize</b> returns the maximum message size in bytes for the message queue object specified by parameter <em>mq_id</em> or <span class="XML-Token">0</span> in case of an error.</p>
<dl class="section note"><dt>Note</dt><dd>This function may be called from <a class="el" href="theory_of_operation.html#CMSIS_RTOS_ISR_Calls">Interrupt Service Routines</a>. </dd></dl>
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<td class="memname">uint32_t osMessageQueueGetCount </td>
<td>(</td>
<td class="paramtype"><a class="el" href="cmsis__os2_8h.html#a206dbc05367e03c39fc6d4d1ebcff317">osMessageQueueId_t</a> </td>
<td class="paramname"><em>mq_id</em></td><td>)</td>
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<dl class="params"><dt>Parameters</dt><dd>
<table class="params">
<tr><td class="paramdir">[in]</td><td class="paramname">mq_id</td><td>message queue ID obtained by <a class="el" href="group__CMSIS__RTOS__Message.html#ga24e895a00f9d484db33aaf784c57bfed">osMessageQueueNew</a>. </td></tr>
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<dl class="section return"><dt>Returns</dt><dd>number of queued messages.</dd></dl>
<p>The function <b>osMessageQueueGetCount</b> returns the number of queued messages in the message queue object specified by parameter <em>mq_id</em> or <span class="XML-Token">0</span> in case of an error.</p>
<dl class="section note"><dt>Note</dt><dd>This function may be called from <a class="el" href="theory_of_operation.html#CMSIS_RTOS_ISR_Calls">Interrupt Service Routines</a>. </dd></dl>
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<td class="memname">uint32_t osMessageQueueGetSpace </td>
<td>(</td>
<td class="paramtype"><a class="el" href="cmsis__os2_8h.html#a206dbc05367e03c39fc6d4d1ebcff317">osMessageQueueId_t</a> </td>
<td class="paramname"><em>mq_id</em></td><td>)</td>
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<dl class="params"><dt>Parameters</dt><dd>
<table class="params">
<tr><td class="paramdir">[in]</td><td class="paramname">mq_id</td><td>message queue ID obtained by <a class="el" href="group__CMSIS__RTOS__Message.html#ga24e895a00f9d484db33aaf784c57bfed">osMessageQueueNew</a>. </td></tr>
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<dl class="section return"><dt>Returns</dt><dd>number of available slots for messages.</dd></dl>
<p>The function <b>osMessageQueueGetSpace</b> returns the number available slots for messages in the message queue object specified by parameter <em>mq_id</em> or <span class="XML-Token">0</span> in case of an error.</p>
<dl class="section note"><dt>Note</dt><dd>This function may be called from <a class="el" href="theory_of_operation.html#CMSIS_RTOS_ISR_Calls">Interrupt Service Routines</a>. </dd></dl>
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<td class="memname"><a class="el" href="group__CMSIS__RTOS__Definitions.html#ga6c0dbe6069e4e7f47bb4cd32ae2b813e">osStatus_t</a> osMessageQueueReset </td>
<td>(</td>
<td class="paramtype"><a class="el" href="cmsis__os2_8h.html#a206dbc05367e03c39fc6d4d1ebcff317">osMessageQueueId_t</a> </td>
<td class="paramname"><em>mq_id</em></td><td>)</td>
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<dl class="params"><dt>Parameters</dt><dd>
<table class="params">
<tr><td class="paramdir">[in]</td><td class="paramname">mq_id</td><td>message queue ID obtained by <a class="el" href="group__CMSIS__RTOS__Message.html#ga24e895a00f9d484db33aaf784c57bfed">osMessageQueueNew</a>. </td></tr>
</table>
</dd>
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<dl class="section return"><dt>Returns</dt><dd>status code that indicates the execution status of the function.</dd></dl>
<p>The function <b>osMessageQueueReset</b> resets the message queue specified by the parameter <em>mq_id</em>.</p>
<p>Possible <a class="el" href="group__CMSIS__RTOS__Definitions.html#ga6c0dbe6069e4e7f47bb4cd32ae2b813e">osStatus_t</a> return values:</p>
<ul>
<li><em>osOK:</em> the message queue has been rest.</li>
<li><em>osErrorParameter:</em> parameter <em>mq_id</em> is <span class="XML-Token">NULL</span> or invalid.</li>
<li><em>osErrorResource:</em> the message queue is in an invalid state.</li>
<li><em>osErrorISR:</em> <b>osMessageQueueReset</b> cannot be called from interrupt service routines.</li>
</ul>
<dl class="section note"><dt>Note</dt><dd>This function <b>cannot</b> be called from <a class="el" href="theory_of_operation.html#CMSIS_RTOS_ISR_Calls">Interrupt Service Routines</a>. </dd></dl>
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<td class="memname"><a class="el" href="group__CMSIS__RTOS__Definitions.html#ga6c0dbe6069e4e7f47bb4cd32ae2b813e">osStatus_t</a> osMessageQueueDelete </td>
<td>(</td>
<td class="paramtype"><a class="el" href="cmsis__os2_8h.html#a206dbc05367e03c39fc6d4d1ebcff317">osMessageQueueId_t</a> </td>
<td class="paramname"><em>mq_id</em></td><td>)</td>
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<dl class="params"><dt>Parameters</dt><dd>
<table class="params">
<tr><td class="paramdir">[in]</td><td class="paramname">mq_id</td><td>message queue ID obtained by <a class="el" href="group__CMSIS__RTOS__Message.html#ga24e895a00f9d484db33aaf784c57bfed">osMessageQueueNew</a>. </td></tr>
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<dl class="section return"><dt>Returns</dt><dd>status code that indicates the execution status of the function.</dd></dl>
<p>The function <b>osMessageQueueDelete</b> deletes a message queue object specified by parameter <em>mq_id</em>. It releases internal memory obtained for message queue handling. After this call, the <em>mq_id</em> is no longer valid and cannot be used. The message queue may be created again using the function <a class="el" href="group__CMSIS__RTOS__Message.html#ga24e895a00f9d484db33aaf784c57bfed">osMessageQueueNew</a>.</p>
<p>Possible <a class="el" href="group__CMSIS__RTOS__Definitions.html#ga6c0dbe6069e4e7f47bb4cd32ae2b813e">osStatus_t</a> return values:</p>
<ul>
<li><em>osOK:</em> the message queue object has been deleted.</li>
<li><em>osErrorParameter:</em> parameter <em>mq_id</em> is <span class="XML-Token">NULL</span> or invalid.</li>
<li><em>osErrorResource:</em> the message queue is in an invalid state.</li>
<li><em>osErrorISR:</em> <b>osMessageQueueDelete</b> cannot be called from interrupt service routines.</li>
</ul>
<dl class="section note"><dt>Note</dt><dd>This function <b>cannot</b> be called from <a class="el" href="theory_of_operation.html#CMSIS_RTOS_ISR_Calls">Interrupt Service Routines</a>. </dd></dl>
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