1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
|
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/xhtml;charset=UTF-8"/>
<meta http-equiv="X-UA-Compatible" content="IE=9"/>
<title>Semaphores</title>
<title>CMSIS-RTOS: Semaphores</title>
<link href="tabs.css" rel="stylesheet" type="text/css"/>
<link href="cmsis.css" rel="stylesheet" type="text/css" />
<script type="text/javascript" src="jquery.js"></script>
<script type="text/javascript" src="dynsections.js"></script>
<script type="text/javascript" src="printComponentTabs.js"></script>
<link href="navtree.css" rel="stylesheet" type="text/css"/>
<script type="text/javascript" src="resize.js"></script>
<script type="text/javascript" src="navtree.js"></script>
<script type="text/javascript">
$(document).ready(initResizable);
</script>
<link href="stylsheetf" rel="stylesheet" type="text/css" />
</head>
<body>
<div id="top"><!-- do not remove this div, it is closed by doxygen! -->
<div id="titlearea">
<table cellspacing="0" cellpadding="0">
<tbody>
<tr style="height: 46px;">
<td id="projectlogo"><img alt="Logo" src="CMSIS_Logo_Final.png"/></td>
<td style="padding-left: 0.5em;">
<div id="projectname">CMSIS-RTOS
 <span id="projectnumber">Version 1.02</span>
</div>
<div id="projectbrief">CMSIS-RTOS API: Generic RTOS interface for Cortex-M processor-based devices.</div>
</td>
</tr>
</tbody>
</table>
</div>
<!-- end header part -->
<div id="CMSISnav" class="tabs1">
<ul class="tablist">
<script type="text/javascript">
<!--
writeComponentTabs.call(this);
//-->
</script>
</ul>
</div>
<!-- Generated by Doxygen 1.8.2 -->
<div id="navrow1" class="tabs">
<ul class="tablist">
<li><a href="index.html"><span>Main Page</span></a></li>
<li><a href="pages.html"><span>Usage and Description</span></a></li>
<li><a href="modules.html"><span>Reference</span></a></li>
</ul>
</div>
</div><!-- top -->
<div id="side-nav" class="ui-resizable side-nav-resizable">
<div id="nav-tree">
<div id="nav-tree-contents">
<div id="nav-sync" class="sync"></div>
</div>
</div>
<div id="splitbar" style="-moz-user-select:none;"
class="ui-resizable-handle">
</div>
</div>
<script type="text/javascript">
$(document).ready(function(){initNavTree('group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html','');});
</script>
<div id="doc-content">
<div class="header">
<div class="summary">
<a href="#define-members">Macros</a> |
<a href="#func-members">Functions</a> </div>
<div class="headertitle">
<div class="title">Semaphores</div> </div>
<div class="ingroups"><a class="el" href="group___c_m_s_i_s___r_t_o_s___inter_thread.html">Inter-Thread Communication and Resource Sharing</a></div></div><!--header-->
<div class="contents">
<p>Access shared resources simultaneously from different threads.
<a href="#details">More...</a></p>
<table class="memberdecls">
<tr class="heading"><td colspan="2"><h2 class="groupheader"><a name="define-members"></a>
Macros</h2></td></tr>
<tr class="memitem:ga7da4c7bfb340779c9fc7b321f5ab3e3a"><td class="memItemLeft" align="right" valign="top">#define </td><td class="memItemRight" valign="bottom"><a class="el" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#ga7da4c7bfb340779c9fc7b321f5ab3e3a">osFeature_Semaphore</a>   30</td></tr>
<tr class="memdesc:ga7da4c7bfb340779c9fc7b321f5ab3e3a"><td class="mdescLeft"> </td><td class="mdescRight">maximum count for <a class="el" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#ga97381e8e55cd47cec390bf57c96d6edb">osSemaphoreCreate</a> function <a href="#ga7da4c7bfb340779c9fc7b321f5ab3e3a"></a><br/></td></tr>
<tr class="separator:ga7da4c7bfb340779c9fc7b321f5ab3e3a"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:ga9e66fe361749071e5ab87826c43c2f1b"><td class="memItemLeft" align="right" valign="top">#define </td><td class="memItemRight" valign="bottom"><a class="el" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#ga9e66fe361749071e5ab87826c43c2f1b">osSemaphoreDef</a>(name)   const <a class="el" href="structos_semaphore_def__t.html">osSemaphoreDef_t</a> os_semaphore_def_##name = { 0 }</td></tr>
<tr class="memdesc:ga9e66fe361749071e5ab87826c43c2f1b"><td class="mdescLeft"> </td><td class="mdescRight">Define a Semaphore object. <a href="#ga9e66fe361749071e5ab87826c43c2f1b"></a><br/></td></tr>
<tr class="separator:ga9e66fe361749071e5ab87826c43c2f1b"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:ga03761ee8d2c3cd4544e18364ab301dac"><td class="memItemLeft" align="right" valign="top">#define </td><td class="memItemRight" valign="bottom"><a class="el" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#ga03761ee8d2c3cd4544e18364ab301dac">osSemaphore</a>(name)   &os_semaphore_def_##name</td></tr>
<tr class="memdesc:ga03761ee8d2c3cd4544e18364ab301dac"><td class="mdescLeft"> </td><td class="mdescRight">Access a Semaphore definition. <a href="#ga03761ee8d2c3cd4544e18364ab301dac"></a><br/></td></tr>
<tr class="separator:ga03761ee8d2c3cd4544e18364ab301dac"><td class="memSeparator" colspan="2"> </td></tr>
</table><table class="memberdecls">
<tr class="heading"><td colspan="2"><h2 class="groupheader"><a name="func-members"></a>
Functions</h2></td></tr>
<tr class="memitem:ga97381e8e55cd47cec390bf57c96d6edb"><td class="memItemLeft" align="right" valign="top"><a class="el" href="cmsis__os_8h.html#aa8968896c84094aa973683c84fa06f84">osSemaphoreId</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#ga97381e8e55cd47cec390bf57c96d6edb">osSemaphoreCreate</a> (const <a class="el" href="structos_semaphore_def__t.html">osSemaphoreDef_t</a> *semaphore_def, int32_t count)</td></tr>
<tr class="memdesc:ga97381e8e55cd47cec390bf57c96d6edb"><td class="mdescLeft"> </td><td class="mdescRight">Create and Initialize a Semaphore object used for managing resources. <a href="#ga97381e8e55cd47cec390bf57c96d6edb"></a><br/></td></tr>
<tr class="separator:ga97381e8e55cd47cec390bf57c96d6edb"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:gacc15b0fc8ce1167fe43da33042e62098"><td class="memItemLeft" align="right" valign="top">int32_t </td><td class="memItemRight" valign="bottom"><a class="el" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#gacc15b0fc8ce1167fe43da33042e62098">osSemaphoreWait</a> (<a class="el" href="cmsis__os_8h.html#aa8968896c84094aa973683c84fa06f84">osSemaphoreId</a> semaphore_id, uint32_t millisec)</td></tr>
<tr class="memdesc:gacc15b0fc8ce1167fe43da33042e62098"><td class="mdescLeft"> </td><td class="mdescRight">Wait until a Semaphore token becomes available. <a href="#gacc15b0fc8ce1167fe43da33042e62098"></a><br/></td></tr>
<tr class="separator:gacc15b0fc8ce1167fe43da33042e62098"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:gab108914997c49e14d8ff1ae0d1988ca0"><td class="memItemLeft" align="right" valign="top"><a class="el" href="group___c_m_s_i_s___r_t_o_s___status.html#gae2e091fefc4c767117727bd5aba4d99e">osStatus</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#gab108914997c49e14d8ff1ae0d1988ca0">osSemaphoreRelease</a> (<a class="el" href="cmsis__os_8h.html#aa8968896c84094aa973683c84fa06f84">osSemaphoreId</a> semaphore_id)</td></tr>
<tr class="memdesc:gab108914997c49e14d8ff1ae0d1988ca0"><td class="mdescLeft"> </td><td class="mdescRight">Release a Semaphore token. <a href="#gab108914997c49e14d8ff1ae0d1988ca0"></a><br/></td></tr>
<tr class="separator:gab108914997c49e14d8ff1ae0d1988ca0"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:gabae2801ac2c096f6e8c69a264908f595"><td class="memItemLeft" align="right" valign="top"><a class="el" href="group___c_m_s_i_s___r_t_o_s___status.html#gae2e091fefc4c767117727bd5aba4d99e">osStatus</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#gabae2801ac2c096f6e8c69a264908f595">osSemaphoreDelete</a> (<a class="el" href="cmsis__os_8h.html#aa8968896c84094aa973683c84fa06f84">osSemaphoreId</a> semaphore_id)</td></tr>
<tr class="memdesc:gabae2801ac2c096f6e8c69a264908f595"><td class="mdescLeft"> </td><td class="mdescRight">Delete a Semaphore that was created by <a class="el" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#ga97381e8e55cd47cec390bf57c96d6edb">osSemaphoreCreate</a>. <a href="#gabae2801ac2c096f6e8c69a264908f595"></a><br/></td></tr>
<tr class="separator:gabae2801ac2c096f6e8c69a264908f595"><td class="memSeparator" colspan="2"> </td></tr>
</table>
<a name="details" id="details"></a><h2 class="groupheader">Description</h2>
<p>Semaphores are used to manage and protect access to shared resources. Semaphores are very similar to <a class="el" href="group___c_m_s_i_s___r_t_o_s___mutex_mgmt.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 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>
<div class="image">
<img src="Semaphore.png" alt="Semaphore.png"/>
<div class="caption">
CMSIS-RTOS Semaphore</div></div>
<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___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#ga97381e8e55cd47cec390bf57c96d6edb">osSemaphoreCreate</a> function. Each time a semaphore token is obtained with <a class="el" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#gacc15b0fc8ce1167fe43da33042e62098">osSemaphoreWait</a>, the semaphore count is decremented. When the semaphore count is 0, no semaphore token can be obtained. The thread 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___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#gab108914997c49e14d8ff1ae0d1988ca0">osSemaphoreRelease</a> incrementing the semaphore count.</p>
<dl class="section note"><dt>Note</dt><dd>Semaphore tokens can be acquired from threads and released from threads and ISRs.</dd></dl>
<h2>Working with Semaphores</h2>
<p>Follow these steps to create and use a semaphore:</p>
<ol type="1">
<li>Declare the semaphore container and initialize the semaphore: <div class="fragment"><div class="line"><a class="code" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#ga9e66fe361749071e5ab87826c43c2f1b" title="Define a Semaphore object.">osSemaphoreDef</a> (my_semaphore); <span class="comment">// Declare semaphore</span></div>
<div class="line"><a class="code" href="cmsis__os_8h.html#aa8968896c84094aa973683c84fa06f84" title="Semaphore ID identifies the semaphore (pointer to a semaphore control block).">osSemaphoreId</a> (my_semaphore_id); <span class="comment">// Semaphore ID</span></div>
</div><!-- fragment --></li>
<li>Initialize the semaphore container with a number of tokens within a thread: <div class="fragment"><div class="line">my_semaphore_id = <a class="code" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#ga97381e8e55cd47cec390bf57c96d6edb" title="Create and Initialize a Semaphore object used for managing resources.">osSemaphoreCreate</a>(<a class="code" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#ga03761ee8d2c3cd4544e18364ab301dac" title="Access a Semaphore definition.">osSemaphore</a>(my_semaphore), 4); <span class="comment">// Create semaphore with 4 tokens</span></div>
</div><!-- fragment --> <b>Important:</b> semaphore tokens can be created and destroyed as threads run. This means that can initialize a semaphore with zero tokens and then use one thread to add/create tokens to the semaphore while a second thread removes them. In this way you can distinguish between producer and consumer threads.</li>
<li>Acquire a token from the semaphore container: <div class="fragment"><div class="line"><a class="code" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#gacc15b0fc8ce1167fe43da33042e62098" title="Wait until a Semaphore token becomes available.">osSemaphoreWait</a>(my_semaphore_id, <a class="code" href="cmsis__os_8h.html#a9eb9a7a797a42e4b55eb171ecc609ddb" title="Timeout value.">osWaitForever</a>);</div>
</div><!-- fragment --></li>
<li>When finished using the semaphore resource, send the token back to the semaphore container: <div class="fragment"><div class="line"><a class="code" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#gab108914997c49e14d8ff1ae0d1988ca0" title="Release a Semaphore token.">osSemaphoreRelease</a>(my_semaphore_id);</div>
</div><!-- fragment --></li>
</ol>
<h2>Semaphore Use Cases</h2>
<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>
<p><b>Non-binary Semaphore (Multiplex)</b></p>
<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>
<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. Ths following example shows the code for one of the threads that might access the resource:</p>
<div class="fragment"><div class="line"><a class="code" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#ga9e66fe361749071e5ab87826c43c2f1b" title="Define a Semaphore object.">osSemaphoreDef</a>(multiplex);</div>
<div class="line"><a class="code" href="cmsis__os_8h.html#aa8968896c84094aa973683c84fa06f84" title="Semaphore ID identifies the semaphore (pointer to a semaphore control block).">osSemaphoreId</a> (multiplex_id);</div>
<div class="line"> </div>
<div class="line"><span class="keywordtype">void</span> thread_n (<span class="keywordtype">void</span>)</div>
<div class="line"> {</div>
<div class="line"> multiplex_id = <a class="code" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#ga97381e8e55cd47cec390bf57c96d6edb" title="Create and Initialize a Semaphore object used for managing resources.">osSemaphoreCreate</a>(<a class="code" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#ga03761ee8d2c3cd4544e18364ab301dac" title="Access a Semaphore definition.">osSemaphore</a>(multiplex), 3);</div>
<div class="line"> <span class="keywordflow">while</span>(1)</div>
<div class="line"> {</div>
<div class="line"> <a class="code" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#gacc15b0fc8ce1167fe43da33042e62098" title="Wait until a Semaphore token becomes available.">osSemaphoreWait</a>(multiplex_id, <a class="code" href="cmsis__os_8h.html#a9eb9a7a797a42e4b55eb171ecc609ddb" title="Timeout value.">osWaitForever</a>);</div>
<div class="line"> <span class="comment">// do something</span></div>
<div class="line"> <a class="code" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#gab108914997c49e14d8ff1ae0d1988ca0" title="Release a Semaphore token.">osSemaphoreRelease</a>(multiplex_id);</div>
<div class="line"> }</div>
<div class="line"> }</div>
</div><!-- fragment --> <h2 class="groupheader">Macro Definition Documentation</h2>
<a class="anchor" id="ga7da4c7bfb340779c9fc7b321f5ab3e3a"></a>
<div class="memitem">
<div class="memproto">
<table class="memname">
<tr>
<td class="memname">#define osFeature_Semaphore   30</td>
</tr>
</table>
</div><div class="memdoc">
<p>A CMSIS-RTOS implementation may support semaphores. The value <a class="el" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#ga7da4c7bfb340779c9fc7b321f5ab3e3a">osFeature_Semaphore</a> indicates the maximum index count for a semaphore. </p>
</div>
</div>
<a class="anchor" id="ga03761ee8d2c3cd4544e18364ab301dac"></a>
<div class="memitem">
<div class="memproto">
<table class="memname">
<tr>
<td class="memname">#define osSemaphore</td>
<td>(</td>
<td class="paramtype"> </td>
<td class="paramname">name</td><td>)</td>
<td>   &os_semaphore_def_##name</td>
</tr>
</table>
</div><div class="memdoc">
<p>Access to semaphore object for the functions <a class="el" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#ga97381e8e55cd47cec390bf57c96d6edb">osSemaphoreCreate</a>.</p>
<dl class="params"><dt>Parameters</dt><dd>
<table class="params">
<tr><td class="paramname">name</td><td>name of the semaphore object. </td></tr>
</table>
</dd>
</dl>
<dl class="section note"><dt>Note</dt><dd>CAN BE CHANGED: The parameter to <b>osSemaphore</b> shall be consistent but the macro body is implementation specific in every CMSIS-RTOS. </dd></dl>
</div>
</div>
<a class="anchor" id="ga9e66fe361749071e5ab87826c43c2f1b"></a>
<div class="memitem">
<div class="memproto">
<table class="memname">
<tr>
<td class="memname">#define osSemaphoreDef</td>
<td>(</td>
<td class="paramtype"> </td>
<td class="paramname">name</td><td>)</td>
<td>   const <a class="el" href="structos_semaphore_def__t.html">osSemaphoreDef_t</a> os_semaphore_def_##name = { 0 }</td>
</tr>
</table>
</div><div class="memdoc">
<p>Define a semaphore object that is referenced by <a class="el" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#ga03761ee8d2c3cd4544e18364ab301dac">osSemaphore</a>.</p>
<dl class="params"><dt>Parameters</dt><dd>
<table class="params">
<tr><td class="paramname">name</td><td>name of the semaphore object. </td></tr>
</table>
</dd>
</dl>
<dl class="section note"><dt>Note</dt><dd>CAN BE CHANGED: The parameter to <b>osSemaphoreDef</b> shall be consistent but the macro body is implementation specific in every CMSIS-RTOS. </dd></dl>
</div>
</div>
<h2 class="groupheader">Function Documentation</h2>
<a class="anchor" id="ga97381e8e55cd47cec390bf57c96d6edb"></a>
<div class="memitem">
<div class="memproto">
<table class="memname">
<tr>
<td class="memname"><a class="el" href="cmsis__os_8h.html#aa8968896c84094aa973683c84fa06f84">osSemaphoreId</a> osSemaphoreCreate </td>
<td>(</td>
<td class="paramtype">const <a class="el" href="structos_semaphore_def__t.html">osSemaphoreDef_t</a> * </td>
<td class="paramname"><em>semaphore_def</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">int32_t </td>
<td class="paramname"><em>count</em> </td>
</tr>
<tr>
<td></td>
<td>)</td>
<td></td><td></td>
</tr>
</table>
</div><div class="memdoc">
<dl class="params"><dt>Parameters</dt><dd>
<table class="params">
<tr><td class="paramdir">[in]</td><td class="paramname">semaphore_def</td><td>semaphore definition referenced with <a class="el" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#ga03761ee8d2c3cd4544e18364ab301dac">osSemaphore</a>. </td></tr>
<tr><td class="paramdir">[in]</td><td class="paramname">count</td><td>number of available resources. </td></tr>
</table>
</dd>
</dl>
<dl class="section return"><dt>Returns</dt><dd>semaphore ID for reference by other functions or NULL in case of error. </dd></dl>
<dl class="section note"><dt>Note</dt><dd>MUST REMAIN UNCHANGED: <b>osSemaphoreCreate</b> shall be consistent in every CMSIS-RTOS.</dd></dl>
<p>Create and initialize a Semaphore object that is used to manage access to shared resources. The parameter <em>count</em> specifies the number of available resources. The <em>count</em> value 1 creates a binary semaphore.</p>
<dl class="section note"><dt>Note</dt><dd>Cannot be called from <a class="el" href="_function_overview.html#CMSIS_RTOS_ISR_Calls">Interrupt Service Routines</a>.</dd></dl>
<p><b>Code Example</b> </p>
<div class="fragment"><div class="line"><span class="preprocessor">#include "<a class="code" href="cmsis__os_8h.html">cmsis_os.h</a>"</span></div>
<div class="line"> </div>
<div class="line"><a class="code" href="cmsis__os_8h.html#adfeb153a84a81309e2d958268197617f" title="Thread ID identifies the thread (pointer to a thread control block).">osThreadId</a> tid_thread1; <span class="comment">// ID for thread 1</span></div>
<div class="line"><a class="code" href="cmsis__os_8h.html#adfeb153a84a81309e2d958268197617f" title="Thread ID identifies the thread (pointer to a thread control block).">osThreadId</a> tid_thread2; <span class="comment">// ID for thread 2</span></div>
<div class="line"> </div>
<div class="line"><a class="code" href="cmsis__os_8h.html#aa8968896c84094aa973683c84fa06f84" title="Semaphore ID identifies the semaphore (pointer to a semaphore control block).">osSemaphoreId</a> semaphore; <span class="comment">// Semaphore ID</span></div>
<div class="line"><a class="code" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#ga9e66fe361749071e5ab87826c43c2f1b" title="Define a Semaphore object.">osSemaphoreDef</a>(semaphore); <span class="comment">// Semaphore definition</span></div>
<div class="line"> </div>
<div class="line"><span class="comment">//</span></div>
<div class="line"><span class="comment">// Thread 1 - High Priority - Active every 3ms</span></div>
<div class="line"><span class="comment">//</span></div>
<div class="line"><span class="keywordtype">void</span> thread1 (<span class="keywordtype">void</span> <span class="keyword">const</span> *argument) {</div>
<div class="line"> int32_t value;</div>
<div class="line"></div>
<div class="line"> <span class="keywordflow">while</span> (1) {</div>
<div class="line"> <a class="code" href="group___c_m_s_i_s___r_t_o_s___wait.html#ga02e19d5e723bfb06ba9324d625162255" title="Wait for Timeout (Time Delay).">osDelay</a>(3); <span class="comment">// Pass control to other tasks for 3ms</span></div>
<div class="line"> val = <a class="code" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#gacc15b0fc8ce1167fe43da33042e62098" title="Wait until a Semaphore token becomes available.">osSemaphoreWait</a> (semaphore, 1); <span class="comment">// Wait 1ms for the free semaphore</span></div>
<div class="line"> <span class="keywordflow">if</span> (val > 0) {</div>
<div class="line"> <span class="comment">// If there was no time-out the semaphore was acquired</span></div>
<div class="line"> : <span class="comment">// OK, the interface is free now, use it.</span></div>
<div class="line"> <a class="code" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#gab108914997c49e14d8ff1ae0d1988ca0" title="Release a Semaphore token.">osSemaphoreRelease</a> (semaphore); <span class="comment">// Return a token back to a semaphore</span></div>
<div class="line"> }</div>
<div class="line"> }</div>
<div class="line">}</div>
<div class="line"> </div>
<div class="line"><span class="comment">//</span></div>
<div class="line"><span class="comment">// Thread 2 - Normal Priority - looks for a free semaphore and uses</span></div>
<div class="line"><span class="comment">// the resource whenever it is available</span></div>
<div class="line"><span class="comment">//</span></div>
<div class="line"><span class="keywordtype">void</span> thread2 (<span class="keywordtype">void</span> <span class="keyword">const</span> *argument) {</div>
<div class="line"> <span class="keywordflow">while</span> (1) {</div>
<div class="line"> <a class="code" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#gacc15b0fc8ce1167fe43da33042e62098" title="Wait until a Semaphore token becomes available.">osSemaphoreWait</a> (semaphore, <a class="code" href="cmsis__os_8h.html#a9eb9a7a797a42e4b55eb171ecc609ddb" title="Timeout value.">osWaitForever</a>); <span class="comment">// Wait indefinitely for a free semaphore</span></div>
<div class="line"> <span class="comment">// OK, the interface is free now, use it.</span></div>
<div class="line"> :</div>
<div class="line"> <a class="code" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#gab108914997c49e14d8ff1ae0d1988ca0" title="Release a Semaphore token.">osSemaphoreRelease</a> (semaphore); <span class="comment">// Return a token back to a semaphore.</span></div>
<div class="line"> }</div>
<div class="line">}</div>
<div class="line"> </div>
<div class="line"><span class="comment">// Thread definitions </span></div>
<div class="line"><a class="code" href="group___c_m_s_i_s___r_t_o_s___thread_mgmt.html#gaee93d929beb350f16e5cc7fa602e229f" title="Create a Thread Definition with function, priority, and stack requirements.">osThreadDef</a>(thread1, <a class="code" href="group___c_m_s_i_s___r_t_o_s___thread_mgmt.html#ga7f2b42f1983b9107775ec2a1c69a849aa914433934143a9ba767e59577c56e6c2" title="priority: high">osPriorityHigh</a>, 1, 0);</div>
<div class="line"><a class="code" href="group___c_m_s_i_s___r_t_o_s___thread_mgmt.html#gaee93d929beb350f16e5cc7fa602e229f" title="Create a Thread Definition with function, priority, and stack requirements.">osThreadDef</a>(thread2, <a class="code" href="group___c_m_s_i_s___r_t_o_s___thread_mgmt.html#ga7f2b42f1983b9107775ec2a1c69a849aa45a2895ad30c79fb97de18cac7cc19f1" title="priority: normal (default)">osPriorityNormal</a>, 1, 0);</div>
<div class="line"> </div>
<div class="line"><span class="keywordtype">void</span> StartApplication (<span class="keywordtype">void</span>) {</div>
<div class="line"> semaphore = <a class="code" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#ga97381e8e55cd47cec390bf57c96d6edb" title="Create and Initialize a Semaphore object used for managing resources.">osSemaphoreCreate</a>(<a class="code" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#ga03761ee8d2c3cd4544e18364ab301dac" title="Access a Semaphore definition.">osSemaphore</a>(semaphore), 1);</div>
<div class="line"></div>
<div class="line"> tid_thread1 = <a class="code" href="group___c_m_s_i_s___r_t_o_s___thread_mgmt.html#gac59b5713cb083702dce759c73fd90dff" title="Create a thread and add it to Active Threads and set it to state READY.">osThreadCreate</a>(<a class="code" href="group___c_m_s_i_s___r_t_o_s___thread_mgmt.html#gaf0c7c6b5e09f8be198312144b5c9e453" title="Access a Thread definition.">osThread</a>(thread1), NULL);</div>
<div class="line"> tid_thread2 = <a class="code" href="group___c_m_s_i_s___r_t_o_s___thread_mgmt.html#gac59b5713cb083702dce759c73fd90dff" title="Create a thread and add it to Active Threads and set it to state READY.">osThreadCreate</a>(<a class="code" href="group___c_m_s_i_s___r_t_o_s___thread_mgmt.html#gaf0c7c6b5e09f8be198312144b5c9e453" title="Access a Thread definition.">osThread</a>(thread2), NULL);</div>
<div class="line"> :</div>
<div class="line">}</div>
</div><!-- fragment -->
</div>
</div>
<a class="anchor" id="gabae2801ac2c096f6e8c69a264908f595"></a>
<div class="memitem">
<div class="memproto">
<table class="memname">
<tr>
<td class="memname"><a class="el" href="group___c_m_s_i_s___r_t_o_s___status.html#gae2e091fefc4c767117727bd5aba4d99e">osStatus</a> osSemaphoreDelete </td>
<td>(</td>
<td class="paramtype"><a class="el" href="cmsis__os_8h.html#aa8968896c84094aa973683c84fa06f84">osSemaphoreId</a> </td>
<td class="paramname"><em>semaphore_id</em></td><td>)</td>
<td></td>
</tr>
</table>
</div><div class="memdoc">
<dl class="params"><dt>Parameters</dt><dd>
<table class="params">
<tr><td class="paramdir">[in]</td><td class="paramname">semaphore_id</td><td>semaphore object referenced with <a class="el" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#ga97381e8e55cd47cec390bf57c96d6edb">osSemaphoreCreate</a>. </td></tr>
</table>
</dd>
</dl>
<dl class="section return"><dt>Returns</dt><dd>status code that indicates the execution status of the function. </dd></dl>
<dl class="section note"><dt>Note</dt><dd>MUST REMAIN UNCHANGED: <b>osSemaphoreDelete</b> shall be consistent in every CMSIS-RTOS.</dd></dl>
<p>Delete a Semaphore object. The function 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___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#ga97381e8e55cd47cec390bf57c96d6edb">osSemaphoreCreate</a>.</p>
<p><b><a class="el" href="group___c_m_s_i_s___r_t_o_s___status.html">Status and Error Codes</a></b><br/>
</p>
<ul>
<li><em>osOK:</em> the semaphore object has been deleted.</li>
<li><em>osErrorISR:</em> <a class="el" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#gabae2801ac2c096f6e8c69a264908f595">osSemaphoreDelete</a> cannot be called from interrupt service routines.</li>
<li><em>osErrorResource:</em> the semaphore object could not be deleted.</li>
<li><em>osErrorParameter:</em> the parameter <em>semaphore_id</em> is incorrect.</li>
</ul>
<dl class="section note"><dt>Note</dt><dd>Cannot be called from <a class="el" href="_function_overview.html#CMSIS_RTOS_ISR_Calls">Interrupt Service Routines</a>. </dd></dl>
</div>
</div>
<a class="anchor" id="gab108914997c49e14d8ff1ae0d1988ca0"></a>
<div class="memitem">
<div class="memproto">
<table class="memname">
<tr>
<td class="memname"><a class="el" href="group___c_m_s_i_s___r_t_o_s___status.html#gae2e091fefc4c767117727bd5aba4d99e">osStatus</a> osSemaphoreRelease </td>
<td>(</td>
<td class="paramtype"><a class="el" href="cmsis__os_8h.html#aa8968896c84094aa973683c84fa06f84">osSemaphoreId</a> </td>
<td class="paramname"><em>semaphore_id</em></td><td>)</td>
<td></td>
</tr>
</table>
</div><div class="memdoc">
<dl class="params"><dt>Parameters</dt><dd>
<table class="params">
<tr><td class="paramdir">[in]</td><td class="paramname">semaphore_id</td><td>semaphore object referenced with <a class="el" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#ga97381e8e55cd47cec390bf57c96d6edb">osSemaphoreCreate</a>. </td></tr>
</table>
</dd>
</dl>
<dl class="section return"><dt>Returns</dt><dd>status code that indicates the execution status of the function. </dd></dl>
<dl class="section note"><dt>Note</dt><dd>MUST REMAIN UNCHANGED: <b>osSemaphoreRelease</b> shall be consistent in every CMSIS-RTOS.</dd></dl>
<p>Release a Semaphore token. This increments the count of available semaphore tokens.</p>
<dl class="section note"><dt>Note</dt><dd><a class="el" href="_function_overview.html#CMSIS_RTOS_ISR_Calls">Interrupt Service Routines</a> can call this function.</dd></dl>
<p><b><a class="el" href="group___c_m_s_i_s___r_t_o_s___status.html">Status and Error Codes</a></b><br/>
</p>
<ul>
<li><em>osOK:</em> the semaphore has been released.</li>
<li><em>osErrorResource:</em> all tokens have already been released.</li>
<li><em>osErrorParameter:</em> the parameter <em>semaphore_id</em> is incorrect. </li>
</ul>
</div>
</div>
<a class="anchor" id="gacc15b0fc8ce1167fe43da33042e62098"></a>
<div class="memitem">
<div class="memproto">
<table class="memname">
<tr>
<td class="memname">int32_t osSemaphoreWait </td>
<td>(</td>
<td class="paramtype"><a class="el" href="cmsis__os_8h.html#aa8968896c84094aa973683c84fa06f84">osSemaphoreId</a> </td>
<td class="paramname"><em>semaphore_id</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">uint32_t </td>
<td class="paramname"><em>millisec</em> </td>
</tr>
<tr>
<td></td>
<td>)</td>
<td></td><td></td>
</tr>
</table>
</div><div class="memdoc">
<dl class="params"><dt>Parameters</dt><dd>
<table class="params">
<tr><td class="paramdir">[in]</td><td class="paramname">semaphore_id</td><td>semaphore object referenced with <a class="el" href="group___c_m_s_i_s___r_t_o_s___semaphore_mgmt.html#ga97381e8e55cd47cec390bf57c96d6edb">osSemaphoreCreate</a>. </td></tr>
<tr><td class="paramdir">[in]</td><td class="paramname">millisec</td><td><a class="el" href="_function_overview.html#CMSIS_RTOS_TimeOutValue">Timout Value</a> or 0 in case of no time-out. </td></tr>
</table>
</dd>
</dl>
<dl class="section return"><dt>Returns</dt><dd>number of available tokens, or -1 in case of incorrect parameters. </dd></dl>
<dl class="section note"><dt>Note</dt><dd>MUST REMAIN UNCHANGED: <b>osSemaphoreWait</b> shall be consistent in every CMSIS-RTOS.</dd></dl>
<p>Wait until a Semaphore token becomes available. When no Semaphore token is available, the function waits for the time specified with the parameter <em>millisec</em>.</p>
<p>The argument <em>millisec</em> specifies how long the system waits for a Semaphore token to become available. While the system waits the thread that is calling this function is put into the state <b>WAITING</b>. The <em>millisec</em> timeout can have the following values:</p>
<ul>
<li>when <em>millisec</em> is 0, the function returns instantly.</li>
<li>when <em>millisec</em> is set to <b>osWaitForever</b> the function will wait for an infinite time until the Semaphore token becomes available.</li>
<li>all other values specify a time in millisecond for a timeout.</li>
</ul>
<p>The return value indicates the number of available tokens (the semaphore count value). If 0 is returned, then no semaphore was available.</p>
<dl class="section note"><dt>Note</dt><dd>Cannot be called from <a class="el" href="_function_overview.html#CMSIS_RTOS_ISR_Calls">Interrupt Service Routines</a>. </dd></dl>
</div>
</div>
</div><!-- contents -->
</div><!-- doc-content -->
<!-- start footer part -->
<div id="nav-path" class="navpath"><!-- id is needed for treeview function! -->
<ul>
<li class="footer">Generated on Tue Oct 27 2015 14:35:43 for CMSIS-RTOS by ARM Ltd. All rights reserved.
<!--
<a href="http://www.doxygen.org/index.html">
<img class="footer" src="doxygen.png" alt="doxygen"/></a> 1.8.2
-->
</li>
</ul>
</div>
</body>
</html>
|
