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 <span id="projectnumber">Version 2.1.0</span>
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<div id="projectbrief">Real-Time Operating System: API and RTX Reference Implementation</div>
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<a href="#nested-classes">Data Structures</a> |
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<div class="title">Semaphores<div class="ingroups"><a class="el" href="group__CMSIS__RTOS.html">CMSIS-RTOS2 API</a></div></div> </div>
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<p>Access shared resources simultaneously from different threads.
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<a href="#details">More...</a></p>
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<table class="memberdecls">
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<tr class="heading"><td colspan="2"><h2 class="groupheader"><a name="nested-classes"></a>
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Data Structures</h2></td></tr>
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<tr class="memitem:structosSemaphoreAttr__t"><td class="memItemLeft" align="right" valign="top">struct  </td><td class="memItemRight" valign="bottom"><a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#structosSemaphoreAttr__t">osSemaphoreAttr_t</a></td></tr>
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<tr class="memdesc:structosSemaphoreAttr__t"><td class="mdescLeft"> </td><td class="mdescRight">Attributes structure for semaphore. <a href="group__CMSIS__RTOS__SemaphoreMgmt.html#structosSemaphoreAttr__t">More...</a><br/></td></tr>
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<tr class="separator:structosSemaphoreAttr__t"><td class="memSeparator" colspan="2"> </td></tr>
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</table><table class="memberdecls">
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Typedefs</h2></td></tr>
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<tr class="memitem:ga6e1c1c4b04175bb92b013c8f37249f40"><td class="memItemLeft" align="right" valign="top">typedef void * </td><td class="memItemRight" valign="bottom"><a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga6e1c1c4b04175bb92b013c8f37249f40">osSemaphoreId_t</a></td></tr>
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<tr class="separator:ga6e1c1c4b04175bb92b013c8f37249f40"><td class="memSeparator" colspan="2"> </td></tr>
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</table><table class="memberdecls">
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<tr class="heading"><td colspan="2"><h2 class="groupheader"><a name="func-members"></a>
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Functions</h2></td></tr>
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<tr class="memitem:ga2a39806ace781a0008a4374ca701b14a"><td class="memItemLeft" align="right" valign="top"><a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga6e1c1c4b04175bb92b013c8f37249f40">osSemaphoreId_t</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga2a39806ace781a0008a4374ca701b14a">osSemaphoreNew</a> (uint32_t max_count, uint32_t initial_count, const <a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#structosSemaphoreAttr__t">osSemaphoreAttr_t</a> *attr)</td></tr>
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<tr class="memdesc:ga2a39806ace781a0008a4374ca701b14a"><td class="mdescLeft"> </td><td class="mdescRight">Create and Initialize a Semaphore object. <a href="#ga2a39806ace781a0008a4374ca701b14a">More...</a><br/></td></tr>
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<tr class="separator:ga2a39806ace781a0008a4374ca701b14a"><td class="memSeparator" colspan="2"> </td></tr>
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<tr class="memitem:ga9586952051f00285f1482dbe6695bbc4"><td class="memItemLeft" align="right" valign="top">const char * </td><td class="memItemRight" valign="bottom"><a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga9586952051f00285f1482dbe6695bbc4">osSemaphoreGetName</a> (<a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga6e1c1c4b04175bb92b013c8f37249f40">osSemaphoreId_t</a> semaphore_id)</td></tr>
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<tr class="memdesc:ga9586952051f00285f1482dbe6695bbc4"><td class="mdescLeft"> </td><td class="mdescRight">Get name of a Semaphore object. <a href="#ga9586952051f00285f1482dbe6695bbc4">More...</a><br/></td></tr>
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<tr class="separator:ga9586952051f00285f1482dbe6695bbc4"><td class="memSeparator" colspan="2"> </td></tr>
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<tr class="memitem:ga7e94c8b242a0c81f2cc79ec22895c87b"><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__SemaphoreMgmt.html#ga7e94c8b242a0c81f2cc79ec22895c87b">osSemaphoreAcquire</a> (<a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga6e1c1c4b04175bb92b013c8f37249f40">osSemaphoreId_t</a> semaphore_id, uint32_t timeout)</td></tr>
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<tr class="memdesc:ga7e94c8b242a0c81f2cc79ec22895c87b"><td class="mdescLeft"> </td><td class="mdescRight">Acquire a Semaphore token or timeout if no tokens are available. <a href="#ga7e94c8b242a0c81f2cc79ec22895c87b">More...</a><br/></td></tr>
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<tr class="separator:ga7e94c8b242a0c81f2cc79ec22895c87b"><td class="memSeparator" colspan="2"> </td></tr>
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<tr class="memitem:ga0abcee1b5449d7a6928fb9248c690bb6"><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__SemaphoreMgmt.html#ga0abcee1b5449d7a6928fb9248c690bb6">osSemaphoreRelease</a> (<a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga6e1c1c4b04175bb92b013c8f37249f40">osSemaphoreId_t</a> semaphore_id)</td></tr>
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<tr class="memdesc:ga0abcee1b5449d7a6928fb9248c690bb6"><td class="mdescLeft"> </td><td class="mdescRight">Release a Semaphore token that was acquired by <a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga7e94c8b242a0c81f2cc79ec22895c87b">osSemaphoreAcquire</a>. <a href="#ga0abcee1b5449d7a6928fb9248c690bb6">More...</a><br/></td></tr>
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<tr class="separator:ga0abcee1b5449d7a6928fb9248c690bb6"><td class="memSeparator" colspan="2"> </td></tr>
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<tr class="memitem:ga7559d4dff3cda9992fc5ab5de3e74c70"><td class="memItemLeft" align="right" valign="top">uint32_t </td><td class="memItemRight" valign="bottom"><a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga7559d4dff3cda9992fc5ab5de3e74c70">osSemaphoreGetCount</a> (<a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga6e1c1c4b04175bb92b013c8f37249f40">osSemaphoreId_t</a> semaphore_id)</td></tr>
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<tr class="memdesc:ga7559d4dff3cda9992fc5ab5de3e74c70"><td class="mdescLeft"> </td><td class="mdescRight">Get current Semaphore token count. <a href="#ga7559d4dff3cda9992fc5ab5de3e74c70">More...</a><br/></td></tr>
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<tr class="separator:ga7559d4dff3cda9992fc5ab5de3e74c70"><td class="memSeparator" colspan="2"> </td></tr>
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<tr class="memitem:ga81258ce9c67fa89f07cc49d2e136cd88"><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__SemaphoreMgmt.html#ga81258ce9c67fa89f07cc49d2e136cd88">osSemaphoreDelete</a> (<a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga6e1c1c4b04175bb92b013c8f37249f40">osSemaphoreId_t</a> semaphore_id)</td></tr>
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<tr class="memdesc:ga81258ce9c67fa89f07cc49d2e136cd88"><td class="mdescLeft"> </td><td class="mdescRight">Delete a Semaphore object. <a href="#ga81258ce9c67fa89f07cc49d2e136cd88">More...</a><br/></td></tr>
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<tr class="separator:ga81258ce9c67fa89f07cc49d2e136cd88"><td class="memSeparator" colspan="2"> </td></tr>
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</table>
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<a name="details" id="details"></a><h2 class="groupheader">Description</h2>
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<p>Semaphores are used to manage and protect access to shared resources. Semaphores are very similar to <a class="el" href="group__CMSIS__RTOS__MutexMgmt.html">Mutexes</a>. Whereas a Mutex permits just one thread to access a shared resource at a time, a semaphore can be used to permit a fixed number of threads/ISRs to access a pool of shared resources. Using semaphores, access to a group of identical peripherals can be managed (for example multiple DMA channels).</p>
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<div class="image">
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<img src="Semaphore.png" alt="Semaphore.png"/>
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<div class="caption">
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CMSIS-RTOS Semaphore</div></div>
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<p> A semaphore object should be initialized to the maximum number of available tokens. This number of available resources is specified as parameter of the <a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga2a39806ace781a0008a4374ca701b14a">osSemaphoreNew</a> function. Each time a semaphore token is obtained with <a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga7e94c8b242a0c81f2cc79ec22895c87b">osSemaphoreAcquire</a>, the semaphore count is decremented. When the semaphore count is 0, no semaphore token can be obtained. The thread/ISR that tries to obtain the semaphore token needs to wait until the next token is free. Semaphores are released with <a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga0abcee1b5449d7a6928fb9248c690bb6">osSemaphoreRelease</a> incrementing the semaphore count.</p>
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<dl class="section note"><dt>Note</dt><dd>The functions <a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga7e94c8b242a0c81f2cc79ec22895c87b">osSemaphoreAcquire</a>, <a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga7559d4dff3cda9992fc5ab5de3e74c70">osSemaphoreGetCount</a>, and <a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga0abcee1b5449d7a6928fb9248c690bb6">osSemaphoreRelease</a> can be called from <a class="el" href="theory_of_operation.html#CMSIS_RTOS_ISR_Calls">Interrupt Service Routines</a>.</dd>
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<dd>
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Refer to <a class="el" href="config_rtx5.html#semaphoreConfig">Semaphore Configuration</a> for RTX5 configuration options.</dd></dl>
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<h2>Semaphore Use Cases </h2>
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<p>Due to their flexibility, semaphores cover a wide range of synchronizing applications. At the same time, they are perhaps the most challenging RTOS object to understand. The following explains a use case for semaphores, taken from the book <a href="http://www.greenteapress.com/semaphores/" target="_blank">The Little Book Of Semaphores</a> by Allen B. Downey which is available for free download.</p>
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<p><b>Non-binary Semaphore (Multiplex)</b></p>
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<p>A multiplex limits the number of threads that can access a critical section of code. For example, this could be a function accessing DMA resources which can only support a limited number of calls.</p>
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<p>To allow multiple threads to run the function, initialize a semaphore to the maximum number of threads that can be allowed. The number of tokens in the semaphore represents the number of additional threads that may enter. If this number is zero, then the next thread trying to access the function will have to wait until one of the other threads exits and releases its token. When all threads have exited the token number is back to n. The following example shows the code for one of the threads that might access the resource:</p>
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<div class="fragment"><div class="line"><a class="code" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga6e1c1c4b04175bb92b013c8f37249f40">osSemaphoreId_t</a> multiplex_id;</div>
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<div class="line"> </div>
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<div class="line"><span class="keywordtype">void</span> thread_n (<span class="keywordtype">void</span>)</div>
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<div class="line"> {</div>
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<div class="line"> multiplex_id = <a class="code" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga2a39806ace781a0008a4374ca701b14a">osSemaphoreNew</a>(3, 3, NULL);</div>
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<div class="line"> <span class="keywordflow">while</span>(1)</div>
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<div class="line"> {</div>
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<div class="line"> <a class="code" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga7e94c8b242a0c81f2cc79ec22895c87b">osSemaphoreAcquire</a>(multiplex_id, <a class="code" href="group__CMSIS__RTOS__Definitions.html#ga9eb9a7a797a42e4b55eb171ecc609ddb">osWaitForever</a>);</div>
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<div class="line"> <span class="comment">// do something</span></div>
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<div class="line"> <a class="code" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga0abcee1b5449d7a6928fb9248c690bb6">osSemaphoreRelease</a>(multiplex_id);</div>
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<div class="line"> }</div>
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<div class="line"> }</div>
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</div><!-- fragment --> <hr/><h2 class="groupheader">Data Structure Documentation</h2>
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<a name="structosSemaphoreAttr__t" id="structosSemaphoreAttr__t"></a>
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<div class="memitem">
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<div class="memproto">
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<table class="memname">
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<tr>
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<td class="memname">struct osSemaphoreAttr_t</td>
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</tr>
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</table>
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</div><div class="memdoc">
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<div class="textblock"></div><table class="fieldtable">
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<tr><th colspan="3">Data Fields</th></tr>
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<tr><td class="fieldtype">
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<a class="anchor" id="a8f8f80d37794cde9472343e4487ba3eb"></a>const char *</td>
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<td class="fieldname">
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name</td>
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<td class="fielddoc">
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name of the semaphore </td></tr>
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<tr><td class="fieldtype">
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<a class="anchor" id="a712a8f140170e6798f561e783265a279"></a>uint32_t</td>
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<td class="fieldname">
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attr_bits</td>
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<td class="fielddoc">
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attribute bits </td></tr>
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<tr><td class="fieldtype">
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<a class="anchor" id="a8c66c30fe3b487298af0e70eb93a197a"></a>void *</td>
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<td class="fieldname">
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cb_mem</td>
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<td class="fielddoc">
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memory for control block </td></tr>
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<tr><td class="fieldtype">
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<a class="anchor" id="a5c542fd75887b7be589b39a2062910de"></a>uint32_t</td>
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<td class="fieldname">
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cb_size</td>
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<td class="fielddoc">
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size of provided memory for control block </td></tr>
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</table>
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</div>
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</div>
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<h2 class="groupheader">Typedef Documentation</h2>
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<td class="memname"><a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga6e1c1c4b04175bb92b013c8f37249f40">osSemaphoreId_t</a></td>
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<p>Semaphore ID identifies the semaphore. </p>
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</div>
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</div>
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<h2 class="groupheader">Function Documentation</h2>
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<td class="memname"><a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga6e1c1c4b04175bb92b013c8f37249f40">osSemaphoreId_t</a> osSemaphoreNew </td>
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<td>(</td>
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<td class="paramtype">uint32_t </td>
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<td class="paramname"><em>max_count</em>, </td>
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<td class="paramkey"></td>
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<td></td>
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<td class="paramtype">uint32_t </td>
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<td class="paramname"><em>initial_count</em>, </td>
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<td class="paramkey"></td>
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<td></td>
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<td class="paramtype">const <a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#structosSemaphoreAttr__t">osSemaphoreAttr_t</a> * </td>
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<td class="paramname"><em>attr</em> </td>
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</tr>
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<tr>
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<td></td>
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<td>)</td>
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<td></td><td></td>
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</div><div class="memdoc">
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<dl class="params"><dt>Parameters</dt><dd>
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<table class="params">
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<tr><td class="paramdir">[in]</td><td class="paramname">max_count</td><td>maximum number of available tokens. </td></tr>
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<tr><td class="paramdir">[in]</td><td class="paramname">initial_count</td><td>initial number of available tokens. </td></tr>
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<tr><td class="paramdir">[in]</td><td class="paramname">attr</td><td>semaphore attributes; NULL: default values. </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>semaphore ID for reference by other functions or NULL in case of error.</dd></dl>
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<p>The function <b>osSemaphoreNew</b> creates and initializes a semaphore object that is used to manage access to shared resources and returns the pointer to the semaphore object identifier or <span class="XML-Token">NULL</span> in case of an error.</p>
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<p>The parameter <em>max_count</em> specifies the maximum number of available tokens. A <em>max_count</em> value of 1 creates a binary semaphore.</p>
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<p>The parameter <em>initial_count</em> sets the initial number of available tokens.</p>
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<p>The parameter <em>attr</em> specifies additional semaphore attributes. Default attributes will be used if set to <span class="XML-Token">NULL</span>.</p>
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<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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<p><b>Code Example</b> </p>
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<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>
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<div class="line"> </div>
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<div class="line"><span class="keywordtype">void</span> Thread_Semaphore (<span class="keywordtype">void</span> *argument); <span class="comment">// thread function</span></div>
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<div class="line"><a class="code" href="group__CMSIS__RTOS__ThreadMgmt.html#gaa6c32fe2a3e0a2e01f212d55b02e51c7">osThreadId_t</a> tid_Thread_Semaphore; <span class="comment">// thread id</span></div>
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<div class="line"> </div>
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<div class="line"><a class="code" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga6e1c1c4b04175bb92b013c8f37249f40">osSemaphoreId_t</a> sid_Thread_Semaphore; <span class="comment">// semaphore id</span></div>
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<div class="line"> </div>
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<div class="line"><span class="keywordtype">int</span> Init_Semaphore (<span class="keywordtype">void</span>)</div>
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<div class="line">{</div>
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<div class="line"> </div>
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<div class="line"> sid_Thread_Semaphore = <a class="code" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga2a39806ace781a0008a4374ca701b14a">osSemaphoreNew</a>(2, 2, NULL);</div>
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<div class="line"> <span class="keywordflow">if</span> (!sid_Thread_Semaphore) {</div>
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<div class="line"> ; <span class="comment">// Semaphore object not created, handle failure</span></div>
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<div class="line"> }</div>
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<div class="line"> </div>
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<div class="line"> tid_Thread_Semaphore = <a class="code" href="group__CMSIS__RTOS__ThreadMgmt.html#ga48d68b8666d99d28fa646ee1d2182b8f">osThreadNew</a> (Thread_Semaphore, NULL, NULL);</div>
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<div class="line"> <span class="keywordflow">if</span> (!tid_Thread_Semaphore) {</div>
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<div class="line"> <span class="keywordflow">return</span>(-1);</div>
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<div class="line"> }</div>
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<div class="line"> </div>
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<div class="line"> <span class="keywordflow">return</span>(0);</div>
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<div class="line">}</div>
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<div class="line"> </div>
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<div class="line"><span class="keywordtype">void</span> Thread_Semaphore (<span class="keywordtype">void</span> *argument)</div>
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<div class="line">{</div>
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<div class="line"> <a class="code" href="group__CMSIS__RTOS__Definitions.html#ga6c0dbe6069e4e7f47bb4cd32ae2b813e">osStatus_t</a> val;</div>
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<div class="line"> </div>
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<div class="line"> <span class="keywordflow">while</span> (1) {</div>
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<div class="line"> ; <span class="comment">// Insert thread code here...</span></div>
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<div class="line"> </div>
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<div class="line"> val = <a class="code" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga7e94c8b242a0c81f2cc79ec22895c87b">osSemaphoreAcquire</a> (sid_Thread_Semaphore, 10); <span class="comment">// wait 10 mSec</span></div>
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<div class="line"> <span class="keywordflow">switch</span> (val) {</div>
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<div class="line"> <span class="keywordflow">case</span> <a class="code" href="cmsis__os2_8h.html#ga6c0dbe6069e4e7f47bb4cd32ae2b813ea9e1c9e2550bb4de8969a935acffc968f">osOK</a>:</div>
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<div class="line"> ; <span class="comment">// Use protected code here...</span></div>
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<div class="line"> <a class="code" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga0abcee1b5449d7a6928fb9248c690bb6">osSemaphoreRelease</a> (sid_Thread_Semaphore); <span class="comment">// Return a token back to a semaphore</span></div>
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<div class="line"> <span class="keywordflow">break</span>;</div>
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<div class="line"> <span class="keywordflow">case</span> <a class="code" href="cmsis__os2_8h.html#ga6c0dbe6069e4e7f47bb4cd32ae2b813ea8fc5801e8b0482bdf22ad63a77f0155d">osErrorResource</a>:</div>
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<div class="line"> <span class="keywordflow">break</span>;</div>
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<div class="line"> <span class="keywordflow">case</span> <a class="code" href="cmsis__os2_8h.html#ga6c0dbe6069e4e7f47bb4cd32ae2b813eac24adca6a5d072c9f01c32178ba0d109">osErrorParameter</a>:</div>
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<div class="line"> <span class="keywordflow">break</span>;</div>
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<div class="line"> <span class="keywordflow">default</span>:</div>
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<div class="line"> <span class="keywordflow">break</span>;</div>
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<div class="line"> }</div>
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<div class="line"> </div>
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<div class="line"> <a class="code" href="group__CMSIS__RTOS__ThreadMgmt.html#gad01c7ec26535b1de6b018bb9466720e2">osThreadYield</a> (); <span class="comment">// suspend thread</span></div>
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<div class="line"> }</div>
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<div class="line">}</div>
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</div><!-- fragment -->
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</div>
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<td class="memname">const char * osSemaphoreGetName </td>
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<td>(</td>
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<td class="paramtype"><a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga6e1c1c4b04175bb92b013c8f37249f40">osSemaphoreId_t</a> </td>
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<td class="paramname"><em>semaphore_id</em></td><td>)</td>
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<td></td>
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<dl class="params"><dt>Parameters</dt><dd>
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<table class="params">
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<tr><td class="paramdir">[in]</td><td class="paramname">semaphore_id</td><td>semaphore ID obtained by <a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga2a39806ace781a0008a4374ca701b14a">osSemaphoreNew</a>. </td></tr>
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</table>
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<dl class="section return"><dt>Returns</dt><dd>name as NULL terminated string.</dd></dl>
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<p>The function <b>osSemaphoreGetName</b> returns the pointer to the name string of the semaphore identified by parameter <em>semaphore_id</em> or <span class="XML-Token">NULL</span> in case of an error.</p>
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<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> osSemaphoreAcquire </td>
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<td>(</td>
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<td class="paramtype"><a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga6e1c1c4b04175bb92b013c8f37249f40">osSemaphoreId_t</a> </td>
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<td class="paramname"><em>semaphore_id</em>, </td>
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<td class="paramkey"></td>
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<td></td>
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<td class="paramtype">uint32_t </td>
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<td class="paramname"><em>timeout</em> </td>
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<td></td>
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<td>)</td>
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</div><div class="memdoc">
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<dl class="params"><dt>Parameters</dt><dd>
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<table class="params">
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<tr><td class="paramdir">[in]</td><td class="paramname">semaphore_id</td><td>semaphore ID obtained by <a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga2a39806ace781a0008a4374ca701b14a">osSemaphoreNew</a>. </td></tr>
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<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>
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<dl class="section return"><dt>Returns</dt><dd>status code that indicates the execution status of the function.</dd></dl>
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<p>The blocking function <b>osSemaphoreAcquire</b> waits until a token of the semaphore object specified by parameter <em>semaphore_id</em> becomes available. If a token is available, the function instantly returns and decrements the token count.</p>
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<p>The parameter <em>timeout</em> specifies how long the system waits to acquire the token. While the system waits, the thread/ISR that is calling this function is put into the <b>BLOCKED</b> state. The parameter <a class="el" href="theory_of_operation.html#CMSIS_RTOS_TimeOutValue">timeout</a> can have the following values:</p>
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<ul>
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<li>when <em>timeout</em> is <span class="XML-Token">0</span>, the function returns instantly.</li>
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<li>when <em>timeout</em> is set to <b>osWaitForever</b> the function will wait for an infinite time until the semaphore becomes available.</li>
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<li>all other values specify a time in kernel ticks for a timeout.</li>
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</ul>
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<p>Possible <a class="el" href="group__CMSIS__RTOS__Definitions.html#ga6c0dbe6069e4e7f47bb4cd32ae2b813e">osStatus_t</a> return values:</p>
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<ul>
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<li><em>osOK:</em> the token has been obtained.</li>
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<li><em>osErrorTimeout:</em> the token could not be obtained in the given time.</li>
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<li><em>osErrorResource:</em> the token could not be obtained when no <em>timeout</em> was specified.</li>
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<li><em>osErrorParameter:</em> the parameter <em>semaphore_id</em> is incorrect.</li>
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</ul>
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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>
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<p><b>Code Example</b></p>
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<p>Refer to <a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga2a39806ace781a0008a4374ca701b14a">osSemaphoreNew</a>. </p>
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<td class="memname"><a class="el" href="group__CMSIS__RTOS__Definitions.html#ga6c0dbe6069e4e7f47bb4cd32ae2b813e">osStatus_t</a> osSemaphoreRelease </td>
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<td>(</td>
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<td class="paramtype"><a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga6e1c1c4b04175bb92b013c8f37249f40">osSemaphoreId_t</a> </td>
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<td class="paramname"><em>semaphore_id</em></td><td>)</td>
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<td></td>
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<dl class="params"><dt>Parameters</dt><dd>
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<table class="params">
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<tr><td class="paramdir">[in]</td><td class="paramname">semaphore_id</td><td>semaphore ID obtained by <a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga2a39806ace781a0008a4374ca701b14a">osSemaphoreNew</a>. </td></tr>
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</table>
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<dl class="section return"><dt>Returns</dt><dd>status code that indicates the execution status of the function.</dd></dl>
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<p>The function <b>osSemaphoreRelease</b> releases a token of the semaphore object specified by parameter <em>semaphore_id</em>. Other threads/ISRs that currently wait for a token of this semaphore object will be put into the <b>READY</b> state.</p>
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<p>Possible <a class="el" href="group__CMSIS__RTOS__Definitions.html#ga6c0dbe6069e4e7f47bb4cd32ae2b813e">osStatus_t</a> return values:</p>
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<ul>
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<li><em>osOK:</em> the token has been correctly released and the count increased.</li>
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<li><em>osErrorResource:</em> the maximum token count has been reached.</li>
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<li><em>osErrorParameter:</em> the parameter <em>semaphore_id</em> is incorrect.</li>
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</ul>
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<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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<p><b>Code Example</b></p>
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<p>Refer to <a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga2a39806ace781a0008a4374ca701b14a">osSemaphoreNew</a>. </p>
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<td class="memname">uint32_t osSemaphoreGetCount </td>
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<td>(</td>
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<td class="paramtype"><a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga6e1c1c4b04175bb92b013c8f37249f40">osSemaphoreId_t</a> </td>
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<td class="paramname"><em>semaphore_id</em></td><td>)</td>
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<td></td>
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<dl class="params"><dt>Parameters</dt><dd>
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<table class="params">
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<tr><td class="paramdir">[in]</td><td class="paramname">semaphore_id</td><td>semaphore ID obtained by <a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga2a39806ace781a0008a4374ca701b14a">osSemaphoreNew</a>. </td></tr>
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<dl class="section return"><dt>Returns</dt><dd>number of tokens available.</dd></dl>
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<p>The function <b>osSemaphoreGetCount</b> returns the count of available semaphores of the semaphore object specified by parameter <em>semaphore_id</em>. In case of an error, it returns <span class="XML-Token">0</span>.</p>
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<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> osSemaphoreDelete </td>
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<td>(</td>
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<td class="paramtype"><a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga6e1c1c4b04175bb92b013c8f37249f40">osSemaphoreId_t</a> </td>
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<td class="paramname"><em>semaphore_id</em></td><td>)</td>
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<dl class="params"><dt>Parameters</dt><dd>
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<table class="params">
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<tr><td class="paramdir">[in]</td><td class="paramname">semaphore_id</td><td>semaphore ID obtained by <a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga2a39806ace781a0008a4374ca701b14a">osSemaphoreNew</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>
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<p>The function <b>osSemaphoreDelete</b> deletes a semaphore object specified by parameter <em>semaphore_id</em>. It releases internal memory obtained for semaphore handling. After this call, the <em>semaphore_id</em> is no longer valid and cannot be used. The semaphore may be created again using the function <a class="el" href="group__CMSIS__RTOS__SemaphoreMgmt.html#ga2a39806ace781a0008a4374ca701b14a">osSemaphoreNew</a>.</p>
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<p>Possible <a class="el" href="group__CMSIS__RTOS__Definitions.html#ga6c0dbe6069e4e7f47bb4cd32ae2b813e">osStatus_t</a> return values:</p>
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<ul>
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<li><em>osOK:</em> the semaphore object has been deleted.</li>
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<li><em>osErrorParameter:</em> the parameter <em>semaphore_id</em> is <span class="XML-Token">NULL</span> or invalid.</li>
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<li><em>osErrorResource:</em> the semaphore specified by parameter <em>semaphore_id</em> is in an invalid semaphore state.</li>
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<li><em>osErrorISR:</em> <b>osSemaphoreDelete</b> cannot be called from interrupt service routines.</li>
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</ul>
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<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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