PIT Timer Interrupt < 2.5us

[raghu tumati]

Posted on September 20, 2017 at 19:44

Hi 

I trying to use the PIT to generate an interrupt every 1.7uS to toggle a GPIO and it does not seem to be working well. 

I have a sysclk of 64MHz. Im using PIT1 and setting the LDVAL register with a count. Now the timer seems to be working well for a count of 200000 which corresponds to an intrerupt time of 5uS. 

But any value less than that and the timer is unstable (high value of jitter) 

Going further a value of 1000000 which corresponds to an interrupt time of 1us just does not work. The PIT does not seem to be able to generate an interrupt less than 2.5us. 

I tried chaining the priority of the PIT interrupt to 15 in the file pit_lld.h 

Below is my setting 

#define SPC5_PIT_CH1_IRQ_PRIORITY       INTC_PSR_ENABLE(INTC_PSR_CORE0_15) 

This also did not seem to work. Is there any other setting that I can change to get this to work?

[Tesla DeLorean]

Posted on September 20, 2017 at 23:33

Is it unable to generate interrupts at that rate, or is the processor not able to stack context, and enter/exit an interrupt at such rates.

Figure out where the processors saturation point is. Consider if there are more effective ways for hardware to generate a toggling output signal.

[raghu tumati]

Posted on September 21, 2017 at 00:39

I believe it can generate interrupts at that rate but it is the entering/exiting ISR thats the saturation point. But thats just a guess. The clock is at 64Mz. So thats around 132 cycles for a 2us timer. It should be able to do it. 

Just curios if anyone else in this community has ever had to implement such an exercise? 

[Tesla DeLorean]

Posted on September 21, 2017 at 00:58

Relatively low trafficked forum. When you're up at 500 KHz the exercise is to make the timer to be autonomous, and to recognize that's how to eliminate jitter.

[raghu tumati]

Posted on September 21, 2017 at 01:26

I'm not sure I understand what you mean by autonomous? 

And I can worry about jitter once I can actually get the timer interpret to within a micro second  

[Tesla DeLorean]

Posted on September 21, 2017 at 02:30

>>I'm not sure I understand what you mean by autonomous? 

Let HW do HW work.

>>And I can worry about jitter once I can actually get the timer interpret to within a micro second

Ok, but I think you miss the point.

[Erwan YVIN]

Posted on September 26, 2017 at 10:43

Hello Raghu ,

Could you confirm the device used ?

it is well SPC56P60  ..

Did you try to update SPC560Pxx_RLA PIT Test Application for Discovery ?

   Best Regards

                            Erwan