Task interrupt by higher priority task

[ujur007]

I have a question about tasks with different priorities and interrupts.

So for example I am using I2C and UART with different tasks and suppose I2C is in the midst of transaction and UART task interrupt is triggered. How this will be handled in nRF SDK API?

For example, I2C byte is transmitting and first 4 bits have already transmitted, what will happen if task is switched to UART at this point? How to avoid this behaviour? I know that DMA can help to overcome such situations but what if there is no DMA? Can this create a soft/hard fault?

I know there is Zephyr working as backend for this feature but not sure exactly how this is done. 

[Priyanka]

Hi Ujjval,

Essentially the driver for these peripherals have the same interrupt priority. For example, please take a look at this: https://github.com/nrfconnect/sdk-zephyr/blob/2a88dad0458cf2fd4f9f62ffe3c464fbd6db9919/dts/arm/nordic/nrf52840.dtsi#L102 

Here, you can see that the priority level for all is NRF_DEFAULT_IRQ_PRIORITY (which is 1)

So first the I2C irq handler will complete, and then the UART irq handler will be served. You can find the various interrupt priorities in the dts files. 

Regards,

Priyanka

[ujur007]

Hi Priyanka, 

I am specifically also interested to know about tasks with different priorities. Let's say a task with I2C functions have less priority than a task with UART functions.

[Priyanka]

Hi ujjval,

Sorry for missing the query. Usually tasks which are being processed are completed before any other tasks are taken again. Otherwise you will specifically need to send a command to pause the current task and first process another incoming task.

-Priyanka

[ujur007]

Hi Priyanka,

Thanks that you reply.

BTW I was looking for same answer online as well but got the 80% satisfactory answer on dev academy. I do not care for 20%, that will be solved with time and experience. !!

I also looked at how ESP32 do this, and found that they are using some inter-locking mechanism so that no other peripheral instant get the access to the same device. And also some critical sections coding mechanism to do this.
So fine for now.! 
Thanks for you support.

academy.nordicsemi.com/.../