Hi. I am trying to control a RC servo with a nRF52810 MCU (in short, a servo needs pulses in range of 1000-2000us once every 20ms to move to specific position. Minimal change in pulse width for servo to move is around 5-10us). At first I configured a 1MHz Timer1 and a CC interrupt to fire at required intervals, and controlled a GPIO in an interrupt. However I noticed that the servo jitters when controlled with this scheme. I've measured the signal with an oscilloscope and saw occasional pulse width changes of ~10us, which causes the servo to jitter. This happens irregularly with couple seconds intervals. My project runs on a small battery, so servo moving when it should be idle will negatively affect battery life.
I am using BLE, so I think the BLE functionality takes over the core from time to time, servicing its own interrupts or disabling interrupts, and this is what causes timing issues. Disabling BLE improved situation, but not much.
Then I decided to move to Timer1+PPI+GPIOTE and forgo timer core interrupts altogether, so that the interrupts will not corrupt my waveform. Surprisingly and unfortunately, this did not remove the problem completely and the jitter still presents itself from time to time, in range of couple microseconds, that still causes servo to jitter.
Since I am using BLE and that works fine, I assume HF crystal is used (switching to it helped in a similar case: RE: Jitter on Timer1+PPI+GPIOTE? ).
Could you advise on what could be the cause of this? Currently I suspect that the whole MCU goes to sleep and wakes up and this affects timer events timing, but I don't have enough knowledge to be sure.
PS The jitter doesn't happen if I use a cheap chinese servo tester instead of an MCU, so the problem is in the MCU, not the servo.
PPS I would like to not use PWM component, as it is taken by other tasks..