📄 void ossempend.htm
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<h1><span lang=EN-US style='font-size:14.0pt;mso-bidi-font-size:9.0pt'>void
OSSemPend(OS_EVENT *pevent, INT16U timeout, INT8U *err);<o:p></o:p></span></h1>
<p class=Descript><span class=CodeInText><span lang=EN-US style='font-size:
12.0pt;font-family:"Courier New"'>OSSemPend()</span></span><span lang=EN-US> is
used when a task desires to get exclusive access to a resource, synchronize its
activities with an ISR, a task or until an event occurs.<span
style="mso-spacerun: yes"> </span>If a task calls </span><b><span
lang=EN-US style='font-family:"Courier New"'>OSSemPend()</span></b><span
lang=EN-US> and the value of the semaphore is greater than 0, then </span><b><span
lang=EN-US style='font-family:"Courier New"'>OSSemPend()</span></b><span
lang=EN-US> will decrement the semaphore and return to its caller.<span
style="mso-spacerun: yes"> </span>However, if the value of the semaphore
is equal to zero, </span><b><span lang=EN-US style='font-family:"Courier New"'>OSSemPend()
</span></b><span lang=EN-US>places the calling task in the waiting list for the
semaphore.<span style="mso-spacerun: yes"> </span>The task will thus wait
until a task or an ISR signals the semaphore or, the specified timeout expires.
If the semaphore is signaled before the timeout expires, µC/OS-II will resume
the highest priority task that is waiting for the semaphore.<span
style="mso-spacerun: yes"> </span>A pended task that has been suspended
with </span><span class=CodeInText><span lang=EN-US style='font-size:12.0pt;
font-family:"Courier New"'>OSTaskSuspend()</span></span><span lang=EN-US> can
obtain the semaphore.<span style="mso-spacerun: yes"> </span>The task
will, however, remain suspended until the task is resumed by calling </span><span
class=CodeInText><span lang=EN-US style='font-size:12.0pt;font-family:"Courier New"'>OSTaskResume()</span></span><span
lang=EN-US>.<span style="mso-spacerun: yes"> </span></span></p>
<p class=NewSectionPara><span lang=EN-US><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></p>
<p class=NewSectionPara><b><span lang=EN-US>Arguments<o:p></o:p></span></b></p>
<p class=Descript><b><span lang=EN-US style='font-family:"Courier New"'>pevent</span></b><span
lang=EN-US> is a pointer to the semaphore.<span style="mso-spacerun:
yes"> </span>This pointer is returned to your application when the
semaphore is created (see </span><b><span lang=EN-US style='font-family:"Courier New"'>OSSemCreate()</span></b><span
lang=EN-US>).</span></p>
<p class=Descript><b><span lang=EN-US style='font-family:"Courier New"'>timeout</span></b><span
lang=EN-US> is used to allow the task to resume execution if a message is not
received from the mailbox within the specified number of clock ticks.<span
style="mso-spacerun: yes"> </span>A </span><b><span lang=EN-US
style='font-family:"Courier New"'>timeout</span></b><span lang=EN-US> value of 0
indicates that the task desires to wait forever for the message.<span
style="mso-spacerun: yes"> </span>The maximum </span><b><span lang=EN-US
style='font-family:"Courier New"'>timeout</span></b><span lang=EN-US> is 65535
clock ticks.<span style="mso-spacerun: yes"> </span>The timeout value is
not synchronized with the clock tick.<span style="mso-spacerun: yes">
</span>The timeout count starts being decremented on the next clock tick which
could potentially occur immediately.</span></p>
<p class=Descript><b><span lang=EN-US style='font-family:"Courier New"'>err</span></b><span
lang=EN-US> is a pointer to a variable which will be used to hold an error
code.<span style="mso-spacerun: yes"> </span></span><b><span lang=EN-US
style='font-family:"Courier New"'>OSSemPend()</span></b><span lang=EN-US> sets </span><b><span
lang=EN-US style='font-family:"Courier New"'>*err</span></b><span lang=EN-US>
to either:</span></p>
<p class=Descript style='margin-left:54.0pt;text-indent:-18.0pt'><span
lang=EN-US>1) <span style='mso-tab-count:1'> </span></span><b><span
lang=EN-US style='font-family:"Courier New"'>OS_NO_ERR</span></b><span
lang=EN-US>, the semaphore is available</span></p>
<p class=Descript style='margin-left:54.0pt;text-indent:-18.0pt'><span
lang=EN-US>2) <span style='mso-tab-count:1'> </span></span><b><span
lang=EN-US style='font-family:"Courier New"'>OS_TIMEOUT</span></b><span
lang=EN-US>, the semaphore was not signaled within the specified timeout</span></p>
<p class=Descript style='margin-left:54.0pt;text-indent:-18.0pt'><span
lang=EN-US>3) <span style='mso-tab-count:1'> </span></span><b><span
lang=EN-US style='font-family:"Courier New"'>OS_ERR_PEND_ISR</span></b><span
lang=EN-US>, you called this function from an ISR and µC/OS-II would have to
suspend the ISR.<span style="mso-spacerun: yes"> </span>In general, you
should not call </span><b><span lang=EN-US style='font-family:"Courier New"'>OSMboxPend()</span></b><span
lang=EN-US>.<span style="mso-spacerun: yes"> </span>µC/OS-II checks for
this situation in case you do anyway. </span></p>
<p class=NewSectionPara><span lang=EN-US><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></p>
<p class=NewSectionPara><b><span lang=EN-US>Notes/Warnings<o:p></o:p></span></b></p>
<p class=Descript><span lang=EN-US>Semaphores must be created before they are
used. </span></p>
<p class=Descript><span lang=EN-US><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></p>
<p class=NewSectionPara><b><span lang=EN-US>Example<o:p></o:p></span></b></p>
<div style='border:solid #999999 1.5pt;padding:1.0pt 1.0pt 15.0pt 1.0pt;
background:#F2F2F2;mso-shading:windowtext;mso-pattern:gray-5 auto'>
<p class=CodeSeg style='border:none;mso-border-alt:solid #999999 1.5pt;
padding:0cm;mso-padding-alt:1.0pt 1.0pt 15.0pt 1.0pt'><span lang=EN-US><span
style='mso-tab-count:1'> </span>OS_EVENT *DispSem;</span></p>
<p class=CodeSeg style='border:none;mso-border-alt:solid #999999 1.5pt;
padding:0cm;mso-padding-alt:1.0pt 1.0pt 15.0pt 1.0pt'><span lang=EN-US><span
style='mso-tab-count:1'> </span>void DispTask(void *pdata)</span></p>
<p class=CodeSeg style='border:none;mso-border-alt:solid #999999 1.5pt;
padding:0cm;mso-padding-alt:1.0pt 1.0pt 15.0pt 1.0pt'><span lang=EN-US><span
style='mso-tab-count:1'> </span>{</span></p>
<p class=CodeSeg style='border:none;mso-border-alt:solid #999999 1.5pt;
padding:0cm;mso-padding-alt:1.0pt 1.0pt 15.0pt 1.0pt'><span lang=EN-US><span
style="mso-spacerun: yes"> </span>INT8U<span
style="mso-spacerun: yes"> </span>err;</span></p>
<p class=CodeSeg style='border:none;mso-border-alt:solid #999999 1.5pt;
padding:0cm;mso-padding-alt:1.0pt 1.0pt 15.0pt 1.0pt'><span lang=EN-US><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></p>
<p class=CodeSeg style='border:none;mso-border-alt:solid #999999 1.5pt;
padding:0cm;mso-padding-alt:1.0pt 1.0pt 15.0pt 1.0pt'><span lang=EN-US><span
style="mso-spacerun: yes"> </span>pdata = pdata;</span></p>
<p class=CodeSeg style='border:none;mso-border-alt:solid #999999 1.5pt;
padding:0cm;mso-padding-alt:1.0pt 1.0pt 15.0pt 1.0pt'><span lang=EN-US><span
style="mso-spacerun: yes"> </span>for (;;) {</span></p>
<p class=CodeSeg style='border:none;mso-border-alt:solid #999999 1.5pt;
padding:0cm;mso-padding-alt:1.0pt 1.0pt 15.0pt 1.0pt'><span lang=EN-US><span
style="mso-spacerun: yes"> </span><span style='mso-tab-count:3'> </span>.
<span style='mso-tab-count:9'> </span></span></p>
<p class=CodeSeg style='border:none;mso-border-alt:solid #999999 1.5pt;
padding:0cm;mso-padding-alt:1.0pt 1.0pt 15.0pt 1.0pt'><span lang=EN-US><span
style='mso-tab-count:3'> </span>.</span></p>
<p class=CodeSeg style='border:none;mso-border-alt:solid #999999 1.5pt;
padding:0cm;mso-padding-alt:1.0pt 1.0pt 15.0pt 1.0pt'><span lang=EN-US><span
style='mso-tab-count:3'> </span>OSSemPend(DispSem,
0, &err); </span></p>
<p class=CodeSeg style='border:none;mso-border-alt:solid #999999 1.5pt;
padding:0cm;mso-padding-alt:1.0pt 1.0pt 15.0pt 1.0pt'><span lang=EN-US><span
style="mso-spacerun: yes"> </span><span style='mso-tab-count:3'> </span>.
<span style='mso-tab-count:2'> </span>/*
The only way this task continues is if … */<span style='mso-tab-count:1'> </span></span></p>
<p class=CodeSeg style='border:none;mso-border-alt:solid #999999 1.5pt;
padding:0cm;mso-padding-alt:1.0pt 1.0pt 15.0pt 1.0pt'><span lang=EN-US><span
style='mso-tab-count:3'> </span>.<span
style="mso-spacerun:
yes"> </span>/* …
the semaphore is signaled!<span style="mso-spacerun:
yes">
</span>*/</span></p>
<p class=CodeSeg style='border:none;mso-border-alt:solid #999999 1.5pt;
padding:0cm;mso-padding-alt:1.0pt 1.0pt 15.0pt 1.0pt'><span lang=EN-US><span
style="mso-spacerun: yes"> </span>}</span></p>
<p class=CodeSeg style='border:none;mso-border-alt:solid #999999 1.5pt;
padding:0cm;mso-padding-alt:1.0pt 1.0pt 15.0pt 1.0pt'><span lang=EN-US><span
style='mso-tab-count:1'> </span>}</span></p>
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EN-US;mso-fareast-language:ZH-CN;mso-bidi-language:AR-SA'><br clear=all
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<p class=MsoNormal><span lang=EN-US><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></p>
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