{"id":3579,"date":"2025-04-18T12:14:45","date_gmt":"2025-04-18T12:14:45","guid":{"rendered":"https:\/\/webprojects.cloud\/wordpress\/splatco\/?post_type=spl_knowledgebase&#038;p=3579"},"modified":"2025-06-10T11:56:32","modified_gmt":"2025-06-10T11:56:32","slug":"example-basic-setting-and-testing-semaphores","status":"publish","type":"spl_knowledgebase","link":"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/tutorials-application-notes-and-white-papers\/tutorial-semaphores\/semaphores-programming-examples\/example-basic-setting-and-testing-semaphores\/","title":{"rendered":"Example (Basic): Setting and testing semaphores"},"content":{"rendered":"\n<p>The simplest (and most common) use for semaphores is simply to have your program remember some on\/off or yes\/no item of information for later action. If you are accustomed to relay logic, this is equivalent to using an internal relay to hold onto a bit of information or an intermediate result.<\/p>\n\n\n\n<p>Semaphores use&nbsp;<a href=\"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/glossary-of-terms\/#o414\">RAM<\/a>&nbsp;memory, and memory must be set aside for them. The easiest way to do this is with the&nbsp;<code><a href=\"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/programming-reference\/directives\/defsem-directive\/\">defSEM<\/a><\/code>&nbsp;directive.<\/p>\n\n\n\n<h6 class=\"wp-block-heading\">Example 1:<\/h6>\n\n\n\n<pre class=\"wp-block-preformatted\">sCooling        defSEM\nsFillLow        defSEM\nsFillHigh       defSEM\nsOverTemp       defSEM<\/pre>\n\n\n\n<p>The following&nbsp;<a href=\"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/tutorials-application-notes-and-white-papers\/tutorial-subroutines\/\">subroutine<\/a>&nbsp;<code>CheckLevel<\/code>&nbsp;would return the state of a low, medium or high level probe depending on two of the above semaphores:<\/p>\n\n\n\n<pre class=\"wp-block-preformatted\">CheckLevel:     <a href=\"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/programming-reference\/instructions-arranged-by-function\/goto-gosub-and-related-instructions\/goifst-ssbbllll-d12\/\">GoIfST<\/a>          sFillLow,CheckLow    ;Go to CheckLow if low semaphore set<br>                GoIfST          sFillHigh,CheckHigh  ;Go to Checkhigh if high semaphore set<br>CheckMedium:    Input           iMediumProbe         ;By default must medium<br>                Return<br>CheckLow:       Input           iLowProbe<br>                Return<br>CheckHigh:      Input           iHighProbe<br>                Return<\/pre>\n\n\n\n<h6 class=\"wp-block-heading\">Example 2:<\/h6>\n\n\n\n<p>Semaphores can be set and cleared in several ways. They are directly set and cleared using&nbsp;<code><a href=\"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/programming-reference\/instructions-arranged-by-function\/index-register-instructions\/sets-ssbb-d12\/\">SetS<\/a><\/code>&nbsp;and&nbsp;<code><a href=\"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/programming-reference\/instructions-arranged-by-function\/index-register-instructions\/clrs-ssbb-d12\/\">ClrS<\/a><\/code>&nbsp;instructions. For example, to set or clear the&nbsp;<code>sFillHigh<\/code>&nbsp;semaphore depending on whether the button on input&nbsp;<code>iHighFill<\/code>&nbsp;has been pressed or not:<\/p>\n\n\n\n<pre class=\"wp-block-preformatted\">                SetS            sHighFill          ;Assume switch pressed\n                GoIfInK         iHighFill,HighFill ;Test the switch, skip next inst if pressed\n                ClrS            sHighFill          ;Switch was not pressed ... reset semaphore again\nHighFill:<\/pre>\n\n\n\n<h6 class=\"wp-block-heading\">Example 3:<\/h6>\n\n\n\n<p>You can also change a semaphore by storing the outcome of a previous operation (in the\u00a0<a href=\"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/glossary-of-terms\/#o3808\" target=\"_blank\" rel=\"noreferrer noopener\">X<\/a>\u00a0register) to it. In that case any non-zero result will set the semaphore, and a zero result will clear it. Using the\u00a0<code><a href=\"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/programming-reference\/instructions-arranged-by-function\/index-register-instructions\/stores-ssbb-d12\/\">StoreS<\/a><\/code>\u00a0instruction, the previous example can be simplified:<\/p>\n\n\n\n<pre class=\"wp-block-preformatted\">                InputK          HighFill          ;Read the switch\n                StoreS          sHighFill         ;Save result\n<\/pre>\n\n\n\n<p>If you are using&nbsp;<a href=\"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/tutorials-application-notes-and-white-papers\/tutorial-multitrack\/\">MultiTrack<\/a>, SPLat&#8217;s easy to use multitasking, you should also look at&nbsp;<a href=\"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/programming-reference\/instructions-arranged-by-function\/goto-gosub-and-related-instructions\/goifst-ssbbllll-d12\/\">semaphores for task synchronization<\/a>.<\/p>\n\n\n\n\n","protected":false},"excerpt":{"rendered":"<p>The simplest (and most common) use for semaphores is simply to have your program remember some on\/off or yes\/no item of information for later action&#8230;.<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":3578,"menu_order":0,"template":"","class_list":["post-3579","spl_knowledgebase","type-spl_knowledgebase","status-publish","hentry"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v25.6 - 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