RE: nRF52 wirting GPIOS direct with immediate effect

prpaul — Fri, 24 Feb 2017 13:20:38 GMT

Hi I have solved the problem by implementing the function using a Timer, PPI channels and GPIOTE as you have proposed. Thank you very much. Paul

RE: nRF52 wirting GPIOS direct with immediate effect

Ole Bauck — Tue, 21 Feb 2017 11:27:06 GMT

Hi,

The GPIO peripheral runs off the 16MHz peripheral clock while the CPU runs off the 64MHz CPU clock, so the timing will be determined by this. See here.

If you want exact timing you should consider using PPI and GPIOTE. You should also enable constant latency mode so that CPU wakeup latency and the PPI task response will be constant and kept at a minimum. The drawback of this is that some resources are forced on while in sleep so the current consumption will increase. Enable the constant latency mode like this (not SoftDevice safe):

NRF_POWER->TASK_CONSTLAT = 1;

You may also want to use the crystal clock instead of the internal oscillator as this has much better accuracy. Start the clock like this (not SoftDevice safe):

NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;
NRF_CLOCK->TASKS_HFCLKSTART = 1;
while(NRF_CLOCK->EVENTS_HFCLKSTARTED == 0);

There is some delay when using PPI and GPIOTE, but this should be constant when using constant latency mode.

Ole