Periodic Interrupt Timer

[BALRAM1]

I am Using PIT  which has clock frequency of 40MHz and that PIT i am using for triggering some other function abc() which must get trigger at 400kHz, But when i am trying to set the frequency more than 80kHz the call back of PIT is not receiving the trigger and ultimately the function abc() is not receiving trigger.

My question is this,  that is there limit that we can not go beyond around 80kHz with PIT or I need to activate something in the microcontroller for going beyond 80khz triggering frequency or something else?

Microcontroller:- S32K344 T-172

Thank you.

[BALRAM1]

Namste @PetrS

Thanks you for your reply and suggestions. 

Here I tried to solve this problem by using Emios_Gpt , Where I am able to trigger the abc() function at higher frequency.

But I am encountering one new problem that is:- When I am triggering Emios_Gpt module at higher frequency the Available BCTU and PIT modules are not receiving the triggers. 

But When EMIOS_Gpt is at lower frequency that time BCTU and PIT Both are working fine. 

Here EMIOS_0 has been used for BCTU and PIT.

EMIOS_1  has been used for EMIOS_Gpt module.

Here I Changed Priority but still there no effect of that.  

Is there some way which I can follow and short it out?

[PetrS]

Hi,

not really sure of your application design. How peripherals are used, where SW or HW triggers are utilized. BCTU can be triggered by HW from eMIOS, so trigger should not be lost. PIT has no input triggers, can be started/stopped by SW. So if you do SW start then same applies for SW latency.

BR, Petr

[BALRAM1]

Namste @PetrS 

Yes I understood your point.

But 

Okay let me try it again.

I am Using Emios_Gpt for triggering one calculation in my algorithm and BCTU is used for triggering another calculation in same algorithm.

Now when I want to run the BCTU call back trigger at 20kHz frequency (50uSec) which I am able to do but when I am Triggering the Emios_Gpt back at 114kHz or Lesser.

but when I am trying to Trigger the call back of Emios_Gpt at Higher frequency then the BCTU is receiving the trigger at lesser frequency.

Same is happening with PIT when I am increasing the frequency of Emios_Gpt more than 80kHz. 

Reason I am not able to understanding that when they are individual peripherals why they are interrupting one another.

Thanks 

petrS

[PetrS · Accepted solution]

Hi,

I think I won’t provide any more input at this point. You have two peripherals, both generating interrupts. Within each interrupt callback, you perform some calculations. I suspect that interrupt priority, latency, and duration are contributing to the issues you're observing.

Try measuring the duration of each interrupt using pin toggling, for example. Also, check the interrupt priorities. If both are set to the same level, keep in mind that eMIOS has a lower IRQ number than BCTU, which gives it a higher priority. Combined with its higher frequency and potentially longer ISR execution time, this could cause the BCTU interrupt to be delayed or even missed.

BR, Petr 

[PetrS]

Hi,

seems this is likely due to CPU or interrupt handling limitations, not the PIT itself. At high frequencies, the CPU may not keep up with the interrupt rate.  At 80 kHz, the interrupt period is $$12.5\mu \text{s. }$$This gives the CPU more time to handle the interrupt. At 400 kHz (2.5 µs), the CPU might be overwhelmed, especially if the ISR is not optimized.

Here are some suggestions:

- Optimize the ISR (keep it short).
- Use hardware triggering (like DMA or timer output) for function, it this is possible.
- Check interrupt priorities.
- Try to set higher code optimization level for project 

BR, Petr