turning on/off a LED by toggling a GPIO pin using a timer and PPI

[[email protected]]

Hi,

Application: turning on/off a LED by toggling a GPIO pin using a timer and PPI. Important: the on-time of the LED must be very precise, i.e. the jitter must be minimal.

I used the example "gpiote" found in the SDK and changed the toggle frequency in led_blinking_setup() in order to get a LED0 on-time of 20ms. When I measured the on-time of LED0 using a LeCroy waveRunner 64Xi I observed that there is a jitter of up to 70us (!).

My questions:

What is the reason for this high jitter?

Is it possible to reduce the jitter?

Would it be possible to replace the 32 MHz quartz with a more stable oscillator?

Where do I find more electrical specifications of the processor (timing of PLL, IOs, etc)?

Thanks for you help

Felix

[Vidar Berg]

Hi Felix,

The system use the internal oscillator by default (HFINT), which has a typical tolerance of +/- 1.5 % (max. +/- 6%). This probably why you are seeing the jitter.  A solution is to request the HFXO from your application when higher accuracy is needed:

NRF_CLOCK->TASKS_HFCLKSTART  = 1;

while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0;