{"id":3304,"date":"2025-04-18T04:29:13","date_gmt":"2025-04-18T04:29:13","guid":{"rendered":"https:\/\/webprojects.cloud\/wordpress\/splatco\/?post_type=spl_knowledgebase&p=3304"},"modified":"2025-06-10T09:22:08","modified_gmt":"2025-06-10T09:22:08","slug":"multitrack-basic-the-yieldtask-instruction","status":"publish","type":"spl_knowledgebase","link":"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/tutorials-application-notes-and-white-papers\/tutorial-multitrack\/multitrack-basic-the-yieldtask-instruction\/","title":{"rendered":"MultiTrack (Basic): The YieldTask instruction"},"content":{"rendered":"\n

In the previous lesson I showed you how potentially\u00a0blocking<\/em>\u00a0instructions like\u00a0WaitOn<\/a><\/code>\u00a0and\u00a0Pause<\/a><\/code>\u00a0will automatically cause a task switch, i.e. cause the task to\u00a0yield<\/em>\u00a0so another task can run. But what if there are no such instructions being executed?<\/p>\n\n\n\n

The YieldTask<\/code> instruction lets you force a task switch anywhere you like in your program. This is something you have to think about, for two reasons:<\/p>\n\n\n\n

    \n
  1. If a task never yields, no other task will get a chance to run.<\/li>\n\n\n\n
  2. If a MultiTrack task executes more than 255 instructions without yielding, the controller will suffer a fatal runtime error (we made it that way to force you to do the right thing!)<\/li>\n<\/ol>\n\n\n\n

    To illustrate this, copy the following into SPLat\/PC and run it:
    (Click here<\/a>\u00a0for some tips for working around problems with copy and paste out of Internet Explorer and HTML-help\u00a0(.chm)<\/code>\u00a0files)<\/p>\n\n\n\n

                    LaunchTask  TaskA\n                LaunchTask  TaskB\n                RunTasksForever\n\nTaskA:          On          0\n                Pause       1\n                Off         0\n                Pause       1\n                GoTo        TaskA\n\nTaskB:          IncM        0\n                GoTo        TaskB\n<\/pre>\n\n\n\n
    The program will “bomb out” after a short while. A YieldTask<\/code> placed after the IncM<\/code> instruction will allow it to run properly. Try it!<\/p>\n\n\n\n
    Here’s an example of a task that uses\u00a0YieldTask<\/code>. This task will monitor inputs 2 and 3 simultaneously. If input 2 comes on it increments\u00a0RAM<\/a>\u00a0location\u00a0Count<\/code>. If input 3 comes on it decrements\u00a0Count<\/code>. Having counted up or down it waits for both inputs to be off, then repeats.<\/p>\n\n\n\n
    CountFunc:       GoIfInOn    2,CountUp\n                 GoIfInOn    3,CountDn\n                 YieldTask               ;Give someone else a go\n                 GoTo        CountFunc   ;Loop and repeat\n\nCountUp:         IncM        Count\n                 GoTo        WaitForBothOff\n\nCountDn:         DecM        Count\nWaitForBothOff:  YieldTask\n                 GoIfInOn    2,WaitForBothOff\n                 GoIfInOn    3,WaitForBothOff\n                 GoTo        CountFunc\nCount:           mEQU        10            ;Declare the RAM variable\n\t\t\t<\/pre>\n\n\n\n
    Exercise 1:<\/h6>\n\n\n\n
    Combine the above task with the dual flasher example in the\u00a0earlier example<\/a>\u00a0and get it running. Take time to study what the\u00a0YieldTask<\/code>\u00a0is doing.<\/p>\n\n\n\n
    Hint: You can monitor\u00a0Count<\/code>\u00a0at location 10 in the\u00a0Data Memory<\/a>\u00a0window in SPLat\/PC (explore the Window menu if this is unfamiliar ground).<\/p>\n\n\n\n
    Exercise 2:<\/h6>\n\n\n\n
    The first loop of CountFunc <\/code>(the first 4 instructions) uses one instruction more than necessary. Rearrange it so it only use 3 instructions. Hint: Move the YieldTask <\/code>to the start of the loop, eliminate the unconditional GoTo <\/code>and modify the remaining two conditional GoTo<\/code>‘s so it works. Note: In general you should not stress over minor inefficiencies like this one in your code. In fact, unless you are pushing the limits of available memory, some inefficiencies are a good investment if they make the code easier to read.<\/p>\n\n\n\n
    Exercise 3:<\/h6>\n\n\n\n
    Consider the following rewritten snippet of code:<\/p>\n\n\n\n
    WaitForBothOff:  WaitOff     2\n                 WaitOff     3\n                 GoTo        CountFunc<\/pre>\n\n\n\n
    This would seem to achieve the same result with a saving of 2 lines of code. However, the original will only “trip” when both inputs are off simultaneously. Work out why the the above snippet could “trip” with input 2 on and input 3 off.<\/p>\n","protected":false},"excerpt":{"rendered":"
    In the previous lesson I showed you how potentially\u00a0blocking\u00a0instructions like\u00a0WaitOn\u00a0and\u00a0Pause\u00a0will automatically cause a task switch, i.e. cause the task to\u00a0yield\u00a0so another task can run. But…<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":3299,"menu_order":1,"template":"","class_list":["post-3304","spl_knowledgebase","type-spl_knowledgebase","status-publish","hentry"],"acf":[],"yoast_head":"\nMultiTrack (Basic): The YieldTask instruction - SPLat Controls<\/title>\n<meta name=\"robots\" content=\"noindex, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"MultiTrack (Basic): The YieldTask instruction - SPLat Controls\" \/>\n<meta property=\"og:description\" content=\"In the previous lesson I showed you how potentially\u00a0blocking\u00a0instructions like\u00a0WaitOn\u00a0and\u00a0Pause\u00a0will automatically cause a task switch, i.e. cause the task to\u00a0yield\u00a0so another task can run. 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