FreeRTOS ported to the PSoC 4

Correction: The CapSense component does not use SysTick; the issue was an unrelated interrupt issue.

Nice job Nick. I downloaded that and it ran like a charm. Did you run into the problem where you have to enable interrupts before you start CapSense? It's caught me a few times.

I added CapSense to your design and use it to vary the blink rate. I had to adjust the RAM allocation settings a bit though. In the CYDWR file I changed the stack to 0x80 (only used by main() anyway) and made the heap 0 (the task memory is allocated from a heap controlled by FreeRTOS). I also reduced the default task stack to 50 short ints. The CapSense needs a little more, so I doubled that value.

-- Mark.

I did indeed run into that issue. Why did you need to shift the stack?

Well, your code worked fine - I did not have to change a thing.

I then added a CapSense component and a task to monitor it periodically. That caused PSoC Creator to complain that I was out of RAM. I just made a few changes to make it fit. The main cause of the problem was that Creator assumes you want it to pick your stack and heap size. FreeRTOS does that for you and so I had a large amount of RAM allocated that was never going to be used. In the FreeRTOSDemo.cydwr file I changed the stack size to about 80 bytes, which is plenty to run main() and kick off the RTOS. I set the heap size to 0 bytes because it is not used by FreeRTOS at all.

That freed up a lot of room for the task stacks and FreeRTOS heap. I believe that FreeRTOS allocates task control blocks and stacks out on array of size configTOTAL_HEAP_SIZE (ucHeap). I have not had a chance to really dig into RAM usage memory with FreeRTOS though - I just wanted to play with your "port", ran into a problem and solved it. I hope to take a closer look in the new year.

-- Mark.

Ah, good catch. I had wondered why so much RAM was unavailable for the FreeRTOS stack.

Hello,

Im very new to RTOS. I purchased a PSOC4 pioneer kit. i have gotten really familier with how to use it vie the example projects.  what would be the best way to get started using FreeRTOS. Where does my main() go? I would like to run the sample projects with FreeRTOS to learn. How can this be done?

Steve,

Start by trying out the demo project, and modifying the thread functions. main() is still your main, but it just sets up tasks and starts the RTOS; most of your code should go in the task functions. The FreeRTOS docs have a lot of detail, including tutorials.

I took Nicholas' project and it worked out of the box. I think that is good place to start for you, Steve. I'd never used Free RTOS before and I was learning about it in minutes.

-- Mark.

Thanks guy

I figured it out got it working. now i am trying to figure what benefits this gives me? watched a couple rtos video and they said the task scheduling techniques and queues between task.

Yes, I like to use an RTOS with CapSense. I put the CapSense scanning code in one task and push the results into a queue or a mailbox. Then I can write "application code" that just uses the queue for instructions - it does not have to worry about all the scanning and reading and interpreting finger activity.

One nice feature of FreeRTOS is the idea of co-routines - these can save you a lot of SRAM because, unlike tasks, they share a stack.

-- Mark.