Updating timer capture registers

[T IJ]

Hello DevZone,

Is there a way for hardware to update the timer capture register?

I want to create different frequencies using a single timer. Next to the timer, Bluetooth is active. 

Example, (values are random and not the values I actually need)

CC0 = 20

CC1 = 40, 

CC2 = 125,

CC3 = 189,

CC4 = 323,

CC5 = 6104700 (least common multiple)

I have a short set that on compare 5 the timer will reset.

I have set interrupt enable for every capture register and in the interrupt handler I manually increment every capture register with the value I loaded initially.

The thing is that I do not want to handle this using software, using more timers is not really an option since the frequencies I need to generate will certainly require more timers than there are timers present in the nRF52832.

I've added my code, it might be useful to show what I mean.

Kind regards,

T IJ

Fullscreen main.c Download

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File    : main.c
Purpose : Generic application start

*/

#include "nrf.h"
#include <stdio.h>
#include <stdlib.h>

#define CC1 2000U
#define CC2 4000U
#define CC3 12500U
#define CC4 18900U
#define CC5 32300U
#define CC6 610470000UL

#define TIMER3_HANDLER TIMER3_IRQHandler

void TIMER3_HANDLER(void)
{
    static uint8_t a1 = 0, a2 = 0, a3 = 0, a4 = 0, a5 = 0;
    if (NRF_TIMER3->EVENTS_COMPARE[0] == 1)
    {
        NRF_TIMER3->CC[0] += CC1;

        NRF_TIMER3->EVENTS_COMPARE[0] = 0;
    }

    if (NRF_TIMER3->EVENTS_COMPARE[1] == 1)
    {
        NRF_TIMER3->CC[1] += CC2;
        a2++;
        if (a2 == 2)
            a2 = 0;
        switch (a2)
        {
            case 0:
                NRF_P0->OUTCLR = 1 << 17;
                break;
            case 1:
                NRF_P0->OUTSET = 1 << 17;
                break;
            default:
                break;
        }
        NRF_TIMER3->EVENTS_COMPARE[1] = 0;
    }

    if (NRF_TIMER3->EVENTS_COMPARE[2] == 1)
    {
        NRF_TIMER3->CC[2] += CC3;
        a3++;
        if (a3 == 2)
            a3 = 0;
        switch (a3)
        {
            case 0:
                NRF_P0->OUTCLR = 1 << 18;
                break;
            case 1:
                NRF_P0->OUTSET = 1 << 18;
                break;
            default:
                break;
        }
        NRF_TIMER3->EVENTS_COMPARE[2] = 0;
    }

    if (NRF_TIMER3->EVENTS_COMPARE[3] == 1)
    {
        NRF_TIMER3->CC[3] += CC4;
        a4++;
        if (a4 == 2)
            a4 = 0;
        switch (a4)
        {
            case 0:
                NRF_P0->OUTCLR = 1 << 19;
                break;
            case 1:
                NRF_P0->OUTSET = 1 << 19;
                break;
            default:
                break;
        }
         NRF_TIMER3->EVENTS_COMPARE[3] = 0;
    }

    if (NRF_TIMER3->EVENTS_COMPARE[4] == 1)
    {
        NRF_TIMER3->CC[4] += CC5;
        a5++;
        if (a5 == 2)
            a5 = 0;
        switch (a5)
        {
            case 0:
                NRF_P0->OUTCLR = 1 << 20;
                break;
            case 1:
                NRF_P0->OUTSET = 1 << 20;
                break;
            default:
                break;
        }
         NRF_TIMER3->EVENTS_COMPARE[4] = 0;
    }

    if (NRF_TIMER3->EVENTS_COMPARE[5] == 1)
    {
        NRF_TIMER3->CC[0] = CC1;
        NRF_TIMER3->CC[1] = CC2;
        NRF_TIMER3->CC[2] = CC3;
        NRF_TIMER3->CC[3] = CC4;
        NRF_TIMER3->CC[4] = CC5;
        NRF_TIMER3->EVENTS_COMPARE[5] = 0;
    }
}



/**
 * @brief Function for application main entry.
 */
int main(void)
{
    NRF_P0->DIRSET = (1 << 17) | (1 << 18) | (1 << 19) | (1 << 20);
    NRF_P0->OUT = (1 << 17) | (1 << 18) | (1 << 19) | (1 << 20);
    NRF_TIMER3->TASKS_CLEAR = 1;
    NRF_TIMER3->MODE = TIMER_MODE_MODE_Timer;
    NRF_TIMER3->BITMODE = TIMER_BITMODE_BITMODE_32Bit;
    NRF_TIMER3->PRESCALER = 9;
    NRF_TIMER3->CC[0] = CC1;
    NRF_TIMER3->CC[1] = CC2;
    NRF_TIMER3->CC[2] = CC3;
    NRF_TIMER3->CC[3] = CC4;
    NRF_TIMER3->CC[4] = CC5;
    NRF_TIMER3->CC[5] = CC6;
    NRF_TIMER3->INTENSET = (1 << 16) | (1 << 17) | (1 << 18) | (1 << 20) | (1 << 21);
    NRF_TIMER3->SHORTS = TIMER_SHORTS_COMPARE5_CLEAR_Msk;

    NVIC_SetPriority(TIMER3_IRQn, 2);
    NVIC_EnableIRQ(TIMER3_IRQn);

    NRF_TIMER3->TASKS_START = 1;

    while (1)
    {
        __WFI();
        // Do nothing.
    }
}
/*************************** End of file ****************************/

[Kenneth]

Hello,

There is no way to automatic update the timer compare/capture register no. Have you considered using the PWM instead?

Best regards,
Kenneth

[T IJ]

Hello Kenneth,

I have considered using the PWM module but this does not have the functionality that I need. Two of the timer compares are connected to a GPIO using PPI and the other timer compares are used as triggers for software events.

As far as I can remember the PWM module does not have the flexibility with generating events as the timer does but I could be mistaken.

Kind regards,

T IJ

[Kenneth]

You may consider using the nRF52840, since that has 5 high frequency timers, but other than that I am not aware of any way to update the CC registers automatically, it need to be updated from the MCU.

Best regards,
Kenneth

[T IJ]

I will have a check what the maximum time delay is when using BLE by toggling a pin in main while(1) {}

Upon that I can probably make a workaround.