Multitasking on the MSP430F5529 LaunchPad

MSP430 Scheduler

What exactly is multitasking, scheduling, and context switching? This is a great question for those interested in understanding how operating systems work, even small real-time operating systems (RTOS). [Jeffrey] had the same question, so he built a multitasking scheduler for the MSP430F5529 LaunchPad.

These topics are some of the most difficult to wrap your head around in the embedded world. Choosing a project that helps you understand tough topics is a great way to learn, plus it can be very rewarding. In his post, [Jeffrey] goes over the basics of how all of these things work, and how they can be implemented on the MSP430. Overall, it is a great read and very informative. For more information on RTOS, check out a few sections in the FreeRTOS book. Be sure to see his code in action after the break.

[Jeffery] was nice enough to release all of his code as open source, so be sure to check out his repository on GitHub. “Feel free to use it and learn more. I have made the code self explanatory. Enjoy!”

via [43oh.com]

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Putting multitasking on an AVR

[vinod] wanted to familiarize himself with AVR assembly programming, but wanted to do something a little more ambitious than simply blinking an LED. While the completed build does blink a few LEDs, we love that e decided to implement multitasking on his microcontroller.

The program [vinod] came up with uses round robin scheduling to give one of the seven programmed tasks a little bit of compute time every time a timer is triggered. Although it’s extremely simple compared to “real-life” real-time operating systems like VxWorks, it’s still an impressive achievement.

In the video after the break, [vinod] shows off his task-switching with seven LEDs. The white LED is a PWM task, while the six other LEDs are simple toggling tasks  that switch a LED on and off at set intervals independent of each other. This would be hard – if not impossible – to do without some sort of scheduling. Nice work, [vinod].

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C bit field structures for microcontroller multitasking

So you’re getting better at programming microcontrollers and now you want to do several things at once? You know better than that, microcontrollers are only capable of processing one thing at a time. But if you’re clever with your coding you can achieve something that behaves as if several things are going on at once. The most common way to do this is to set a flag using an interrupt, then use the main loop to check for that flag. [S1axter] posted a tutorial on this topic where he uses bit field structures to help simplify time sensitive events.

We think [S1axter] did a fantastic job of explaining this moderately difficult topic clearly and quickly. In the video after the break he begins by explaining what a bit field is and how it is defined. Basically you’re using a C structure to track a flag using just one bit of storage. This way the flag is either set or not. We suggest you pay careful attention to how he declares the structures as volatile, so you don’t have unexpected behavior when you try it yourself.

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