web/docs/group__sem.html

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 103
 104 <div class="header">
 105   <div class="summary">
 106 <a href="#func-members">Functions</a>  </div>
 107   <div class="headertitle"><div class="title">sem<div class="ingroups"><a class="el" href="group__high__level.html">High Level APIs</a> &raquo; <a class="el" href="group__pico__sync.html">pico_sync</a></div></div></div>
 108 </div><!--header-->
 109 <div class="contents">
 110
 111 <p>Semaphore API for restricting access to a resource.
 112 <a href="#details">More...</a></p>
 113 <table class="memberdecls">
 114 <tr class="heading"><td colspan="2"><h2 class="groupheader"><a id="func-members" name="func-members"></a>
 115 Functions</h2></td></tr>
 116 <tr class="memitem:gab4e56b5ccfacafd2fb17765e702a21ba"><td class="memItemLeft" align="right" valign="top">void&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="group__sem.html#gab4e56b5ccfacafd2fb17765e702a21ba">sem_init</a> (<a class="el" href="structsemaphore.html">semaphore_t</a> *sem, int16_t initial_permits, int16_t max_permits)</td></tr>
 117 <tr class="memdesc:gab4e56b5ccfacafd2fb17765e702a21ba"><td class="mdescLeft">&#160;</td><td class="mdescRight">Initialise a semaphore structure.  <a href="group__sem.html#gab4e56b5ccfacafd2fb17765e702a21ba">More...</a><br /></td></tr>
 118 <tr class="separator:gab4e56b5ccfacafd2fb17765e702a21ba"><td class="memSeparator" colspan="2">&#160;</td></tr>
 119 <tr class="memitem:gad9e065ef0c0e59309f9bdb5fb74bb7c1"><td class="memItemLeft" align="right" valign="top">int&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="group__sem.html#gad9e065ef0c0e59309f9bdb5fb74bb7c1">sem_available</a> (<a class="el" href="structsemaphore.html">semaphore_t</a> *sem)</td></tr>
 120 <tr class="memdesc:gad9e065ef0c0e59309f9bdb5fb74bb7c1"><td class="mdescLeft">&#160;</td><td class="mdescRight">Return number of available permits on the semaphore.  <a href="group__sem.html#gad9e065ef0c0e59309f9bdb5fb74bb7c1">More...</a><br /></td></tr>
 121 <tr class="separator:gad9e065ef0c0e59309f9bdb5fb74bb7c1"><td class="memSeparator" colspan="2">&#160;</td></tr>
 122 <tr class="memitem:gaeac89066f5fdbde0c7db2718464dcbde"><td class="memItemLeft" align="right" valign="top">bool&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="group__sem.html#gaeac89066f5fdbde0c7db2718464dcbde">sem_release</a> (<a class="el" href="structsemaphore.html">semaphore_t</a> *sem)</td></tr>
 123 <tr class="memdesc:gaeac89066f5fdbde0c7db2718464dcbde"><td class="mdescLeft">&#160;</td><td class="mdescRight">Release a permit on a semaphore.  <a href="group__sem.html#gaeac89066f5fdbde0c7db2718464dcbde">More...</a><br /></td></tr>
 124 <tr class="separator:gaeac89066f5fdbde0c7db2718464dcbde"><td class="memSeparator" colspan="2">&#160;</td></tr>
 125 <tr class="memitem:gab6c128952e4981a95ce2e2d093a8a3ba"><td class="memItemLeft" align="right" valign="top">void&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="group__sem.html#gab6c128952e4981a95ce2e2d093a8a3ba">sem_reset</a> (<a class="el" href="structsemaphore.html">semaphore_t</a> *sem, int16_t permits)</td></tr>
 126 <tr class="memdesc:gab6c128952e4981a95ce2e2d093a8a3ba"><td class="mdescLeft">&#160;</td><td class="mdescRight">Reset semaphore to a specific number of available permits.  <a href="group__sem.html#gab6c128952e4981a95ce2e2d093a8a3ba">More...</a><br /></td></tr>
 127 <tr class="separator:gab6c128952e4981a95ce2e2d093a8a3ba"><td class="memSeparator" colspan="2">&#160;</td></tr>
 128 <tr class="memitem:gaefa22667355703497ae883f68a87aacf"><td class="memItemLeft" align="right" valign="top">void&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="group__sem.html#gaefa22667355703497ae883f68a87aacf">sem_acquire_blocking</a> (<a class="el" href="structsemaphore.html">semaphore_t</a> *sem)</td></tr>
 129 <tr class="memdesc:gaefa22667355703497ae883f68a87aacf"><td class="mdescLeft">&#160;</td><td class="mdescRight">Acquire a permit from the semaphore.  <a href="group__sem.html#gaefa22667355703497ae883f68a87aacf">More...</a><br /></td></tr>
 130 <tr class="separator:gaefa22667355703497ae883f68a87aacf"><td class="memSeparator" colspan="2">&#160;</td></tr>
 131 <tr class="memitem:ga38275bfc4c00e5039028f58860709610"><td class="memItemLeft" align="right" valign="top">bool&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="group__sem.html#ga38275bfc4c00e5039028f58860709610">sem_acquire_timeout_ms</a> (<a class="el" href="structsemaphore.html">semaphore_t</a> *sem, uint32_t timeout_ms)</td></tr>
 132 <tr class="memdesc:ga38275bfc4c00e5039028f58860709610"><td class="mdescLeft">&#160;</td><td class="mdescRight">Acquire a permit from a semaphore, with timeout.  <a href="group__sem.html#ga38275bfc4c00e5039028f58860709610">More...</a><br /></td></tr>
 133 <tr class="separator:ga38275bfc4c00e5039028f58860709610"><td class="memSeparator" colspan="2">&#160;</td></tr>
 134 <tr class="memitem:ga0f5a509fb132e8e764795a66773500ad"><td class="memItemLeft" align="right" valign="top">bool&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="group__sem.html#ga0f5a509fb132e8e764795a66773500ad">sem_acquire_timeout_us</a> (<a class="el" href="structsemaphore.html">semaphore_t</a> *sem, uint32_t timeout_us)</td></tr>
 135 <tr class="memdesc:ga0f5a509fb132e8e764795a66773500ad"><td class="mdescLeft">&#160;</td><td class="mdescRight">Acquire a permit from a semaphore, with timeout.  <a href="group__sem.html#ga0f5a509fb132e8e764795a66773500ad">More...</a><br /></td></tr>
 136 <tr class="separator:ga0f5a509fb132e8e764795a66773500ad"><td class="memSeparator" colspan="2">&#160;</td></tr>
 137 <tr class="memitem:ga4410f17fc2f35b91e5bcfaf18bcf26ae"><td class="memItemLeft" align="right" valign="top">bool&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="group__sem.html#ga4410f17fc2f35b91e5bcfaf18bcf26ae">sem_acquire_block_until</a> (<a class="el" href="structsemaphore.html">semaphore_t</a> *sem, <a class="el" href="group__timestamp.html#ga8b7f3d602cc053f05bacceeacc257ed8">absolute_time_t</a> until)</td></tr>
 138 <tr class="memdesc:ga4410f17fc2f35b91e5bcfaf18bcf26ae"><td class="mdescLeft">&#160;</td><td class="mdescRight">Wait to acquire a permit from a semaphore until a specific time.  <a href="group__sem.html#ga4410f17fc2f35b91e5bcfaf18bcf26ae">More...</a><br /></td></tr>
 139 <tr class="separator:ga4410f17fc2f35b91e5bcfaf18bcf26ae"><td class="memSeparator" colspan="2">&#160;</td></tr>
 140 <tr class="memitem:ga25b473ab6f287e4a6a0c9d0288a0a497"><td class="memItemLeft" align="right" valign="top">bool&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="group__sem.html#ga25b473ab6f287e4a6a0c9d0288a0a497">sem_try_acquire</a> (<a class="el" href="structsemaphore.html">semaphore_t</a> *sem)</td></tr>
 141 <tr class="memdesc:ga25b473ab6f287e4a6a0c9d0288a0a497"><td class="mdescLeft">&#160;</td><td class="mdescRight">Attempt to acquire a permit from a semaphore without blocking.  <a href="group__sem.html#ga25b473ab6f287e4a6a0c9d0288a0a497">More...</a><br /></td></tr>
 142 <tr class="separator:ga25b473ab6f287e4a6a0c9d0288a0a497"><td class="memSeparator" colspan="2">&#160;</td></tr>
 143 </table>
 144 <a name="details" id="details"></a><h2 class="groupheader">Detailed Description</h2>
 145 <p >Semaphore API for restricting access to a resource. </p>
 146 <p >A semaphore holds a number of available permits. <code>sem_acquire</code> methods will acquire a permit if available (reducing the available count by 1) or block if the number of available permits is 0. <a class="el" href="group__sem.html#gaeac89066f5fdbde0c7db2718464dcbde">sem_release()</a> increases the number of available permits by one potentially unblocking a <code>sem_acquire</code> method.</p>
 147 <p >Note that <a class="el" href="group__sem.html#gaeac89066f5fdbde0c7db2718464dcbde">sem_release()</a> may be called an arbitrary number of times, however the number of available permits is capped to the max_permit value specified during semaphore initialization.</p>
 148 <p >Although these semaphore related functions can be used from IRQ handlers, it is obviously preferable to only release semaphores from within an IRQ handler (i.e. avoid blocking) </p>
 149 <h2 class="groupheader">Function Documentation</h2>
 150 <a id="ga4410f17fc2f35b91e5bcfaf18bcf26ae" name="ga4410f17fc2f35b91e5bcfaf18bcf26ae"></a>
 151 <h2 class="memtitle"><span class="permalink"><a href="#ga4410f17fc2f35b91e5bcfaf18bcf26ae">&#9670;&nbsp;</a></span>sem_acquire_block_until()</h2>
 152
 153 <div class="memitem">
 154 <div class="memproto">
 155       <table class="memname">
 156         <tr>
 157           <td class="memname">bool sem_acquire_block_until </td>
 158           <td>(</td>
 159           <td class="paramtype"><a class="el" href="structsemaphore.html">semaphore_t</a> *&#160;</td>
 160           <td class="paramname"><em>sem</em>, </td>
 161         </tr>
 162         <tr>
 163           <td class="paramkey"></td>
 164           <td></td>
 165           <td class="paramtype"><a class="el" href="group__timestamp.html#ga8b7f3d602cc053f05bacceeacc257ed8">absolute_time_t</a>&#160;</td>
 166           <td class="paramname"><em>until</em>&#160;</td>
 167         </tr>
 168         <tr>
 169           <td></td>
 170           <td>)</td>
 171           <td></td><td></td>
 172         </tr>
 173       </table>
 174 </div><div class="memdoc">
 175
 176 <p>Wait to acquire a permit from a semaphore until a specific time. </p>
 177 <p >This function will block and wait if no permits are available, until the specified timeout time. If the timeout is reached the function will return false, otherwise it will return true.</p>
 178 <dl class="params"><dt>Parameters</dt><dd>
 179   <table class="params">
 180     <tr><td class="paramname">sem</td><td>Pointer to semaphore structure </td></tr>
 181     <tr><td class="paramname">until</td><td>The time after which to return if the sem is not available. </td></tr>
 182   </table>
 183   </dd>
 184 </dl>
 185 <dl class="section return"><dt>Returns</dt><dd>true if permit was acquired, false if the until time was reached before acquiring. </dd></dl>
 186
 187 </div>
 188 </div>
 189 <a id="gaefa22667355703497ae883f68a87aacf" name="gaefa22667355703497ae883f68a87aacf"></a>
 190 <h2 class="memtitle"><span class="permalink"><a href="#gaefa22667355703497ae883f68a87aacf">&#9670;&nbsp;</a></span>sem_acquire_blocking()</h2>
 191
 192 <div class="memitem">
 193 <div class="memproto">
 194       <table class="memname">
 195         <tr>
 196           <td class="memname">void sem_acquire_blocking </td>
 197           <td>(</td>
 198           <td class="paramtype"><a class="el" href="structsemaphore.html">semaphore_t</a> *&#160;</td>
 199           <td class="paramname"><em>sem</em></td><td>)</td>
 200           <td></td>
 201         </tr>
 202       </table>
 203 </div><div class="memdoc">
 204
 205 <p>Acquire a permit from the semaphore. </p>
 206 <p >This function will block and wait if no permits are available.</p>
 207 <dl class="params"><dt>Parameters</dt><dd>
 208   <table class="params">
 209     <tr><td class="paramname">sem</td><td>Pointer to semaphore structure </td></tr>
 210   </table>
 211   </dd>
 212 </dl>
 213
 214 </div>
 215 </div>
 216 <a id="ga38275bfc4c00e5039028f58860709610" name="ga38275bfc4c00e5039028f58860709610"></a>
 217 <h2 class="memtitle"><span class="permalink"><a href="#ga38275bfc4c00e5039028f58860709610">&#9670;&nbsp;</a></span>sem_acquire_timeout_ms()</h2>
 218
 219 <div class="memitem">
 220 <div class="memproto">
 221       <table class="memname">
 222         <tr>
 223           <td class="memname">bool sem_acquire_timeout_ms </td>
 224           <td>(</td>
 225           <td class="paramtype"><a class="el" href="structsemaphore.html">semaphore_t</a> *&#160;</td>
 226           <td class="paramname"><em>sem</em>, </td>
 227         </tr>
 228         <tr>
 229           <td class="paramkey"></td>
 230           <td></td>
 231           <td class="paramtype">uint32_t&#160;</td>
 232           <td class="paramname"><em>timeout_ms</em>&#160;</td>
 233         </tr>
 234         <tr>
 235           <td></td>
 236           <td>)</td>
 237           <td></td><td></td>
 238         </tr>
 239       </table>
 240 </div><div class="memdoc">
 241
 242 <p>Acquire a permit from a semaphore, with timeout. </p>
 243 <p >This function will block and wait if no permits are available, until the defined timeout has been reached. If the timeout is reached the function will return false, otherwise it will return true.</p>
 244 <dl class="params"><dt>Parameters</dt><dd>
 245   <table class="params">
 246     <tr><td class="paramname">sem</td><td>Pointer to semaphore structure </td></tr>
 247     <tr><td class="paramname">timeout_ms</td><td>Time to wait to acquire the semaphore, in milliseconds. </td></tr>
 248   </table>
 249   </dd>
 250 </dl>
 251 <dl class="section return"><dt>Returns</dt><dd>false if timeout reached, true if permit was acquired. </dd></dl>
 252
 253 </div>
 254 </div>
 255 <a id="ga0f5a509fb132e8e764795a66773500ad" name="ga0f5a509fb132e8e764795a66773500ad"></a>
 256 <h2 class="memtitle"><span class="permalink"><a href="#ga0f5a509fb132e8e764795a66773500ad">&#9670;&nbsp;</a></span>sem_acquire_timeout_us()</h2>
 257
 258 <div class="memitem">
 259 <div class="memproto">
 260       <table class="memname">
 261         <tr>
 262           <td class="memname">bool sem_acquire_timeout_us </td>
 263           <td>(</td>
 264           <td class="paramtype"><a class="el" href="structsemaphore.html">semaphore_t</a> *&#160;</td>
 265           <td class="paramname"><em>sem</em>, </td>
 266         </tr>
 267         <tr>
 268           <td class="paramkey"></td>
 269           <td></td>
 270           <td class="paramtype">uint32_t&#160;</td>
 271           <td class="paramname"><em>timeout_us</em>&#160;</td>
 272         </tr>
 273         <tr>
 274           <td></td>
 275           <td>)</td>
 276           <td></td><td></td>
 277         </tr>
 278       </table>
 279 </div><div class="memdoc">
 280
 281 <p>Acquire a permit from a semaphore, with timeout. </p>
 282 <p >This function will block and wait if no permits are available, until the defined timeout has been reached. If the timeout is reached the function will return false, otherwise it will return true.</p>
 283 <dl class="params"><dt>Parameters</dt><dd>
 284   <table class="params">
 285     <tr><td class="paramname">sem</td><td>Pointer to semaphore structure </td></tr>
 286     <tr><td class="paramname">timeout_us</td><td>Time to wait to acquire the semaphore, in microseconds. </td></tr>
 287   </table>
 288   </dd>
 289 </dl>
 290 <dl class="section return"><dt>Returns</dt><dd>false if timeout reached, true if permit was acquired. </dd></dl>
 291
 292 </div>
 293 </div>
 294 <a id="gad9e065ef0c0e59309f9bdb5fb74bb7c1" name="gad9e065ef0c0e59309f9bdb5fb74bb7c1"></a>
 295 <h2 class="memtitle"><span class="permalink"><a href="#gad9e065ef0c0e59309f9bdb5fb74bb7c1">&#9670;&nbsp;</a></span>sem_available()</h2>
 296
 297 <div class="memitem">
 298 <div class="memproto">
 299       <table class="memname">
 300         <tr>
 301           <td class="memname">int sem_available </td>
 302           <td>(</td>
 303           <td class="paramtype"><a class="el" href="structsemaphore.html">semaphore_t</a> *&#160;</td>
 304           <td class="paramname"><em>sem</em></td><td>)</td>
 305           <td></td>
 306         </tr>
 307       </table>
 308 </div><div class="memdoc">
 309
 310 <p>Return number of available permits on the semaphore. </p>
 311 <dl class="params"><dt>Parameters</dt><dd>
 312   <table class="params">
 313     <tr><td class="paramname">sem</td><td>Pointer to semaphore structure </td></tr>
 314   </table>
 315   </dd>
 316 </dl>
 317 <dl class="section return"><dt>Returns</dt><dd>The number of permits available on the semaphore. </dd></dl>
 318
 319 </div>
 320 </div>
 321 <a id="gab4e56b5ccfacafd2fb17765e702a21ba" name="gab4e56b5ccfacafd2fb17765e702a21ba"></a>
 322 <h2 class="memtitle"><span class="permalink"><a href="#gab4e56b5ccfacafd2fb17765e702a21ba">&#9670;&nbsp;</a></span>sem_init()</h2>
 323
 324 <div class="memitem">
 325 <div class="memproto">
 326       <table class="memname">
 327         <tr>
 328           <td class="memname">void sem_init </td>
 329           <td>(</td>
 330           <td class="paramtype"><a class="el" href="structsemaphore.html">semaphore_t</a> *&#160;</td>
 331           <td class="paramname"><em>sem</em>, </td>
 332         </tr>
 333         <tr>
 334           <td class="paramkey"></td>
 335           <td></td>
 336           <td class="paramtype">int16_t&#160;</td>
 337           <td class="paramname"><em>initial_permits</em>, </td>
 338         </tr>
 339         <tr>
 340           <td class="paramkey"></td>
 341           <td></td>
 342           <td class="paramtype">int16_t&#160;</td>
 343           <td class="paramname"><em>max_permits</em>&#160;</td>
 344         </tr>
 345         <tr>
 346           <td></td>
 347           <td>)</td>
 348           <td></td><td></td>
 349         </tr>
 350       </table>
 351 </div><div class="memdoc">
 352
 353 <p>Initialise a semaphore structure. </p>
 354 <dl class="params"><dt>Parameters</dt><dd>
 355   <table class="params">
 356     <tr><td class="paramname">sem</td><td>Pointer to semaphore structure </td></tr>
 357     <tr><td class="paramname">initial_permits</td><td>How many permits are initially acquired </td></tr>
 358     <tr><td class="paramname">max_permits</td><td>Total number of permits allowed for this semaphore </td></tr>
 359   </table>
 360   </dd>
 361 </dl>
 362
 363 </div>
 364 </div>
 365 <a id="gaeac89066f5fdbde0c7db2718464dcbde" name="gaeac89066f5fdbde0c7db2718464dcbde"></a>
 366 <h2 class="memtitle"><span class="permalink"><a href="#gaeac89066f5fdbde0c7db2718464dcbde">&#9670;&nbsp;</a></span>sem_release()</h2>
 367
 368 <div class="memitem">
 369 <div class="memproto">
 370       <table class="memname">
 371         <tr>
 372           <td class="memname">bool sem_release </td>
 373           <td>(</td>
 374           <td class="paramtype"><a class="el" href="structsemaphore.html">semaphore_t</a> *&#160;</td>
 375           <td class="paramname"><em>sem</em></td><td>)</td>
 376           <td></td>
 377         </tr>
 378       </table>
 379 </div><div class="memdoc">
 380
 381 <p>Release a permit on a semaphore. </p>
 382 <p >Increases the number of permits by one (unless the number of permits is already at the maximum). A blocked <code>sem_acquire</code> will be released if the number of permits is increased.</p>
 383 <dl class="params"><dt>Parameters</dt><dd>
 384   <table class="params">
 385     <tr><td class="paramname">sem</td><td>Pointer to semaphore structure </td></tr>
 386   </table>
 387   </dd>
 388 </dl>
 389 <dl class="section return"><dt>Returns</dt><dd>true if the number of permits available was increased. </dd></dl>
 390
 391 </div>
 392 </div>
 393 <a id="gab6c128952e4981a95ce2e2d093a8a3ba" name="gab6c128952e4981a95ce2e2d093a8a3ba"></a>
 394 <h2 class="memtitle"><span class="permalink"><a href="#gab6c128952e4981a95ce2e2d093a8a3ba">&#9670;&nbsp;</a></span>sem_reset()</h2>
 395
 396 <div class="memitem">
 397 <div class="memproto">
 398       <table class="memname">
 399         <tr>
 400           <td class="memname">void sem_reset </td>
 401           <td>(</td>
 402           <td class="paramtype"><a class="el" href="structsemaphore.html">semaphore_t</a> *&#160;</td>
 403           <td class="paramname"><em>sem</em>, </td>
 404         </tr>
 405         <tr>
 406           <td class="paramkey"></td>
 407           <td></td>
 408           <td class="paramtype">int16_t&#160;</td>
 409           <td class="paramname"><em>permits</em>&#160;</td>
 410         </tr>
 411         <tr>
 412           <td></td>
 413           <td>)</td>
 414           <td></td><td></td>
 415         </tr>
 416       </table>
 417 </div><div class="memdoc">
 418
 419 <p>Reset semaphore to a specific number of available permits. </p>
 420 <p >Reset value should be from 0 to the max_permits specified in the init function</p>
 421 <dl class="params"><dt>Parameters</dt><dd>
 422   <table class="params">
 423     <tr><td class="paramname">sem</td><td>Pointer to semaphore structure </td></tr>
 424     <tr><td class="paramname">permits</td><td>the new number of available permits </td></tr>
 425   </table>
 426   </dd>
 427 </dl>
 428
 429 </div>
 430 </div>
 431 <a id="ga25b473ab6f287e4a6a0c9d0288a0a497" name="ga25b473ab6f287e4a6a0c9d0288a0a497"></a>
 432 <h2 class="memtitle"><span class="permalink"><a href="#ga25b473ab6f287e4a6a0c9d0288a0a497">&#9670;&nbsp;</a></span>sem_try_acquire()</h2>
 433
 434 <div class="memitem">
 435 <div class="memproto">
 436       <table class="memname">
 437         <tr>
 438           <td class="memname">bool sem_try_acquire </td>
 439           <td>(</td>
 440           <td class="paramtype"><a class="el" href="structsemaphore.html">semaphore_t</a> *&#160;</td>
 441           <td class="paramname"><em>sem</em></td><td>)</td>
 442           <td></td>
 443         </tr>
 444       </table>
 445 </div><div class="memdoc">
 446
 447 <p>Attempt to acquire a permit from a semaphore without blocking. </p>
 448 <p >This function will return false without blocking if no permits are available, otherwise it will acquire a permit and return true.</p>
 449 <dl class="params"><dt>Parameters</dt><dd>
 450   <table class="params">
 451     <tr><td class="paramname">sem</td><td>Pointer to semaphore structure </td></tr>
 452   </table>
 453   </dd>
 454 </dl>
 455 <dl class="section return"><dt>Returns</dt><dd>true if permit was acquired. </dd></dl>
 456
 457 </div>
 458 </div>
 459 </div><!-- contents -->
 460 </div><!-- doc-content -->
 461
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 464 </html>