RE: nordic NRF51822 + PWM + PPI + TIMER1

L.B. — Fri, 22 Mar 2019 11:11:55 GMT

Hello! This solved my answer! And the code you suggested works as expected. Thank you!

Indeed in the datasheet I saw this line:

Only one GPIOTE channel can be assigned to one physical pin. Failing to do so may result in unpredictable
behavior.

but I was unable to quite get it at that time. Now makes sense ...

RE: nordic NRF51822 + PWM + PPI + TIMER1

Vidar Berg — Thu, 21 Mar 2019 14:02:28 GMT

Hello,

It's not possible to assign the same pin to two GPIOTE channels, so that's probably why it's not working. But it should be possible to use the toggle task instead with one channel. Here's a slightly modified version of your code:

void TIMER1_IRQHandler(){
    //NVIC_ClearPendingIRQ(TIMER1_IRQn);
   // NRF_TIMER1->EVENTS_COMPARE[0] = 0;
    //if(NRF_TIMER1->EVENTS_COMPARE[1]){ // No other compare events enabled
        //One PWM period has elapsed
        NRF_TIMER1->EVENTS_COMPARE[1] = 0;
        //NRF_TIMER1->TASKS_CLEAR = 1;
        pwm_triggers++;
    //}
}

void pwm_init(void){
    NRF_GPIOTE->CONFIG[0] = (0x03 | (25 << 8) | (0x3 /*toggle*/ << 16) | (0x01 << 20)); //Make GPIO a task, use pin 25, task sets pin high, init as pin high, 0x111903
//    NRF_GPIOTE->CONFIG[1] = (0x03 | (27 <<8)  | (0x02 << 16) | (0x01  << 20)); //Make GPIO a task, use pin 25, task sets pin low, init as pin low, 0x21903
    
    //NRF_PPI->CHG[0] |= 0x03; // Grouping was not used
    NRF_PPI->CH[0].EEP = (uint32_t)&NRF_TIMER1->EVENTS_COMPARE[0];
    NRF_PPI->CH[0].TEP = (uint32_t)&NRF_GPIOTE->TASKS_OUT[0];
    NRF_PPI->CH[1].EEP = (uint32_t)&NRF_TIMER1->EVENTS_COMPARE[1];
    NRF_PPI->CH[1].TEP = (uint32_t)&NRF_GPIOTE->TASKS_OUT[0];
    NRF_PPI->CHEN |= 0x03;

    //NRF_TIMER1->POWER = 0x01;
    NRF_TIMER1->TASKS_CLEAR = 1;
    NRF_TIMER1->MODE = 0; //Timer mode
    NRF_TIMER1->BITMODE = 0x01; //8-bit
    NRF_TIMER1->PRESCALER = 0; //Prescaler = /1
    NRF_TIMER1->SHORTS = 2; //	Enable COMPARE1_CLEAR to clear timer on CC[1] match 
    NRF_TIMER1->CC[0] = 1; 
    NRF_TIMER1->CC[1] = 20;

    while(NRF_TIMER1->CC[0] != 1){ }
    while(NRF_TIMER1->CC[1] != 20){ }

    NRF_TIMER1->INTENSET = 1 << 17; //Enable interrupt on compare register  1. Event 0 appears to be ignored anyway
    NVIC_SetPriority(TIMER1_IRQn, 3);
    NVIC_ClearPendingIRQ(TIMER1_IRQn);
    NVIC_EnableIRQ(TIMER1_IRQn);
    NRF_TIMER1->TASKS_START = 1;
}

Can you try and see if works?

[quote userid="77810" url="~/f/nordic-q-a/45182/nordic-nrf51822-pwm-ppi-timer1"]With the debugger I see that the interrupt never exits because the COMPARE_EVENT[1] is set whenever COMPARE_EVENT[0] is set, which is not expected.[/quote]

The debugger only halts the CPU while the timers are kept running. So it is impossible to read out compare event 0 before compare event 1 manually.

Just a warning, it starts to become complicated as soon as you want to update the duty cycle on the fly. If that's something you intend to do, you should consider modifying the existing PWM library instead.

Regards,

Vidar