{"id":7842,"date":"2016-05-23T10:02:57","date_gmt":"2016-05-23T09:02:57","guid":{"rendered":"https:\/\/blogs.mentor.com\/colinwalls\/?p=7842"},"modified":"2026-03-26T16:48:56","modified_gmt":"2026-03-26T20:48:56","slug":"simple-task-scheduling-a-question-and-an-answer","status":"publish","type":"post","link":"https:\/\/blogs.sw.siemens.com\/embedded-software\/2016\/05\/23\/simple-task-scheduling-a-question-and-an-answer\/","title":{"rendered":"Simple real-time task scheduling – a question and an answer"},"content":{"rendered":"

I recently received an email, from somebody with whom I was not acquainted, with the subject line “Probably a silly question\u201d. This got my attention, as I think the only silly thing about a question is not asking it. It certainly was not a silly question. The emailer was asking about implementation of a real time system and I gave him some advice, which I hope was helpful.<\/p>\n

With his permission, I will share the question and my answer …<\/p>\n

As the question was about implementing a real time system, my default response would be advice about using an RTOS. Although, in this case, it might have been a valid response, it is probably not the best answer. Here is what he asked:<\/p>\n

I am using a bare metal app with a super loop. Using polling inside for 3 tasks at different time periods. So am I better off using a simple for loop or using the timer module present in the Atmel SAM D20 Arm M0+ microcontroller ?<\/em><\/p>\n

100usec – action A<\/em>
\n1msec – action B<\/em>
\n10msec – action C<\/em><\/p>\n

Obviously, a for loop\/delay is the easiest way but it keeps the processor working and it may not be easy to put the microcontroller to sleep to conserve power. So I am taking a look at implementing it using timers. Please let me know if I am doing it wrong ?!<\/em><\/p>\n

The nature of the three actions is unimportant. Suffice it to say that they are small amounts of processing that needs to be performed at regular intervals.<\/p>\n

It would be quite possible to use an RTOS. Each action would be coded as a task something like this:<\/p>\n

void task_A()\n{\n action_A();\n RTOS_delay(100);\n}\n\n<\/pre>\n
void task_B()\n{\n action_B();\n RTOS_delay(1000);\n}\n\n<\/pre>\n
void task_C()\n{\n action_C();\n RTOS_delay(10000);\n}\n\n<\/pre>\n
If the application was the starting point for something bigger – i.e. much more functionality\/complexity might be added later – utilizing an RTOS may be an excellent idea. This is because an RTOS supports a multi-threaded structure which is very scaleable, so adding new functionality is less likely to adversely affect existing code. Of course, I feel honor bound to recommend our own Nucleus RTOS<\/a>, which is ideal for such an application.<\/p>\n
However, in this case, I had the impression that the project was bounded and I suggested setting up a 100usec timer interrupt and coding the ISR thus:<\/p>\n
interrupt void timer_ISR()\n{\n static int timer_B = 0;\n static int timer_C = 0;\n\n<\/pre>\n
 action_A();\n\n<\/pre>\n
 if (timer_B-- == 0)\n {\n  action_B();\n  timer_B = 10;\n }\n\n<\/pre>\n
 if (timer_C-- == 0)\n {\n  action_C();\n  timer_C = 100;\n }\n}\n\n<\/pre>\n
Any other suggestions on how to address this problem? Please comment, email or contact me via social media.<\/p>\n
I am also very open to queries such as this, so please feel free to ask.<\/p>\n
\"\"<\/a>\"\"<\/a>\"\"<\/a>\"\"<\/a>\"\"<\/a>\"\"<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"
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