RE: Confused about GPIOTE: pin toggle and interrupt latency

Stian Røed Hafskjold — Wed, 26 Oct 2016 08:51:28 GMT

That's nice! Please click on the accept answer button.

RE: Confused about GPIOTE: pin toggle and interrupt latency

turbog — Wed, 26 Oct 2016 01:47:46 GMT

Thanks!

That solved it.

RE: Confused about GPIOTE: pin toggle and interrupt latency

Stian Røed Hafskjold — Mon, 24 Oct 2016 14:07:01 GMT

Yes, PPI and GPIOTE would be the correct way for this.

You can use three compare registers for this, and set the prescaler to 1 (8MHz):

NRF_TIMER0->PRESCALER = 1;
NRF_TIMER0->CC[0] = 40;
NRF_TIMER0->CC[1] = 100;
NRF_TIMER0->CC[2] = 544;

Use shorts to clear timer on CC[2]. Timer becomes zero right away so it will start to count on 1 next cycle.

NRF_TIMER0->SHORTS = TIMER_SHORTS_COMPARE2_CLEAR_Enabled << TIMER_SHORTS_COMPARE2_CLEAR_Pos;

You can then use CC[2] = 544 to toggle the PIN (as in your T=000, PIN_x = 0), and CC[0] = 40 to toggle the pin again (as in your T=040, PIN_x = 1). Do this with PPI and GPIOTE:

NRF_GPIOTE->CONFIG[0] = (3 << 0) | (PIN1 << 8) | (3 << 16) | (1 << 20); //Task mode, PIN1, Toggle, init: 1
NRF_PPI->CHENSET = 0x3; //enable two channels
NRF_PPI->CH[0].EEP = (uint32_t) &NRF_TIMER0->EVENTS_COMPARE[2];
NRF_PPI->CH[0].TEP = (uint32_t) &NRF_GPIOTE->TASKS_OUT[0];
NRF_PPI->CH[1].EEP = (uint32_t) &NRF_TIMER0->EVENTS_COMPARE[0];
NRF_PPI->CH[1].TEP = (uint32_t) &NRF_GPIOTE->TASKS_OUT[0];

And yes, the time when this happen will be within the 8MHz clock cycle specified in the CC register (T=544/0 and T=40)

Enable interrupt for the CC[1] register:

NVIC_EnableIRQ(TIMER0_IRQn);
NRF_TIMER0->INTENSET = (1 << 17);

Now you can do CPU stuff in the TIMER0_IRQHandler()

void TIMER0_IRQHandler(void){
    if(NRF_TIMER0->EVENTS_COMPARE[1]){
        NRF_TIMER0->EVENTS_COMPARE[1] = 0;
        do_stuff();
    }
}

The CPU would then start executing at T=100 + latency. Since the HF clock and 1.2V peripheral regulator is already running (because of TIMER) the only thing that is started is the 1.7V regulator which takes ~2us to startup (table 32 Power management in the PS). So then T = 100 cycles + 2us.

Clear and start timer after init:

NRF_TIMER0->TASKS_CLEAR = 1;
NRF_TIMER0->TASKS_START = 1;

RE: Confused about GPIOTE: pin toggle and interrupt latency

turbog — Fri, 21 Oct 2016 22:13:00 GMT

Clarify

T=000, PIN_x = 0

T=040, PIN_x = 1

T=100, call a routine

T=543, start over

T=544=0