Timing accuracy of the MPC5674F PIT module

[youngseolee]

I wanna know a timing accuracy of the MPC5674F built-in PIT module.

I downloaded a same SW to two development boards(Both boards have the same design) and measured a 10ms interrupt period generated by the PIT.
(When the PIT interrupt occurs, toggle I/O in the handler and measure the toggled I/O period using an oscilloscope)

For board 1, the interrupt period is measured to be within 0.01% of 10ms. On the other hand, for board 2, the interrupt period is measured to be within 0.02% of 10 ms.
There was a difference of about 0.01% in the PIT interrupt period error of the two boards.

I think that the difference in the PIT interrupt generation period between these two boards is caused by the accuracy of the used oscillator and PIT module (or FMPLL) .
(The oscillator we used has a precision of 0.005%)

We need accurate analysis, and for this we need the accuracy information of PIT module or FMPLL module. Can you let me know?

[youngseolee]

So, what is the timing accuracy of the eMIOS timer (or eTPU)?

i'm curious about the accuracy of the built-in timer & FMPLL of the MPC5674F except for the oscillator accuracy.

[davidtosenovjan · Accepted solution]

A crystal driven PLL is phase and frequency locked on the crystal signal, thus retaining the crystal spec stability and accuracy in PPM. PLL output signal frequency accuracy expressed as +/-PPM deviation to the output target mean frequency is equal to the input target reference mean frequency. This is due to the PLL locking both phase and frequency to the input signal.

eMIOS/eTPU resolution is also given by source accuracy as possible dividers in the way does not change accuracy in ppm.

[youngseolee]

Your answer helped me a lot. thank you.

[davidtosenovjan]

In your case I would see biggest issue with using PIT timer and so necessary ISR handling (may be affected by the core activity, active or pending interrupts and their priorities, XBAR latency and so).

Otherwise an accuracy is mainly given by oscillator accuracy. I would recommend to use eMIOS timer (or eTPU) to remove influence of the core.

[youngseolee]

Spoiler

So, what is the timing accuracy of the eMIOS timer (or eTPU)?

i'm curious about the accuracy of the built-in timer & FMPLL of the MPC5674F except for the oscillator accuracy.