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Handling FreeRTOS interrupts with some delay

Posted by kand123 on July 29, 2015

Hello everybody,

I am working on a project which consists of an embedded system with an Atmel AVR32 microcontroller and FreeRTOS. The system has 8 fans connected to different GPIO pins and it produces separate interrupt for every fan (if it is faulty or not installed and if it is OK). I have implemented this specification with a FreeRTOS ISR and a queue (using xQueueSendFromISR when the status change) by sending the status to a task which wait for queue reception. The task then informs the user. My problem is that I want to delay for some time after an interrupt arise in order to be sure of the fan status avoiding rapid on/off situations. How can I do this in FreeRTOS apart from implemented 8 tasks and checking the status of every fan with some delay?

Thanks in advance.

Handling FreeRTOS interrupts with some delay

Posted by heinbali01 on July 29, 2015

Hi Kostas,

Atmel AVR32, is that a UC3 ?

If you need debouncing of 8 signals, is it still useful to use hardware interrupts?

You might also create a task that wakes up at regular intervals and let it poll for changes. Only after N confirmations of a new status the task will produce an event.

And of course, you can still use the hw interrupts for urgent signals like an over-voltage, or an electric motor control.


Handling FreeRTOS interrupts with some delay

Posted by kand123 on July 29, 2015

Hi Hein,

Yes I use Atmel AVR32 UC3C.

I use hardware interrupts to get every one of the 8 signals which is not urgent signals. My problem is that I need to debounce every one of them.

How can I do this using interrupts or it is better to use one task and poll every one of them at regular interval which is not safe as these are asynchronous events.


Handling FreeRTOS interrupts with some delay

Posted by richard_damon on July 30, 2015

One way to use interrupts to catch the leading edge of a bouncing signal, but not get overloaded with the bounces is to disable the interrupt on the leading edge, and kick off a timer function to fire after the bounce time to re-enable the interrupt.

But, since you make the comment that you want to wait a bit before reporting (which could be done in that timer function I just mentioned), it likely means that just polling periodically may also be sufficient. This is basically a requirements trade off. The use of interrupts and a timer may give you slightly faster response, and possibly lower cpu usage (since it really does nothing in the case of no change), while periodic polling is likely simpler code.

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