Create accurate microsecond timer without interrupts

[Christoph_I]

Hey guys,

I want to create an accurate timer without interrupts. My timer has to be very accurate because I have to send HIGH and LOW signals for 1us. I have read this post to know that I need high-frequency clock source (HFCLK, 16 MHz), which means better resolution (62.5 ns) and higher power consumption (typ. 5 or 70 uA depending on HFCLK source). But I don't know how to program my code so I followed this post and this post. But I have still some problems with it. I post my code below.

My timer should only replace the unaccurate nrf_delay_us.

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#include <stdint.h>

#include "nrf_delay.h"

#include "app_error.h"

#include "nrf_gpio.h"

#include "nrf_drv_timer.h"

#define OUTPUT_PIN 18

/** @brief Function for Timer 1 initialization.

*/

void TIMEOUT_TIMER1_Init(void)

{

NRF_TIMER1->TASKS_STOP = 1; /**< Stop Timer 1 */

NRF_TIMER1->TASKS_CLEAR = 1; /**< Clear Timer 1 */

NRF_TIMER1->MODE = 0; /**< Mode 0: Timer */

NRF_TIMER1->BITMODE = 3; /**< Bitmode 3: 32 bit (for what?, What happens if I choose 16 bit?) */

NRF_TIMER1->PRESCALER = 4; /**< Prescaler 4: 1us Timer -> f(TIMER) = 16MHz / (2^PRESCALER) = 1MHz -> t(TIMER) = 1us */

NRF_TIMER1->INTENCLR = TIMER_INTENCLR_COMPARE0_Disabled

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#include <stdint.h>

#include "nrf_delay.h"
#include "app_error.h"
#include "nrf_gpio.h"
#include "nrf_drv_timer.h"

#define OUTPUT_PIN  18


/** @brief Function for Timer 1 initialization.
 */
void TIMEOUT_TIMER1_Init(void)
{
    NRF_TIMER1->TASKS_STOP = 1;           /**< Stop Timer 1 */
    NRF_TIMER1->TASKS_CLEAR = 1;          /**< Clear Timer 1 */

    NRF_TIMER1->MODE      = 0;            /**< Mode 0: Timer */
    NRF_TIMER1->BITMODE   = 3;            /**< Bitmode 3: 32 bit (for what?, What happens if I choose 16 bit?) */
    NRF_TIMER1->PRESCALER = 4;            /**< Prescaler 4: 1us Timer -> f(TIMER) = 16MHz / (2^PRESCALER) = 1MHz -> t(TIMER) = 1us */
    NRF_TIMER1->INTENCLR = TIMER_INTENCLR_COMPARE0_Disabled
                            | TIMER_INTENCLR_COMPARE1_Disabled
                            | TIMER_INTENCLR_COMPARE2_Disabled
                            | TIMER_INTENCLR_COMPARE3_Disabled
                            | TIMER_INTENCLR_COMPARE4_Disabled
                            | TIMER_INTENCLR_COMPARE5_Disabled; /**< Disable all interrupts */
}


void TIMEROUT_TIMER1_Start(uint32_t timeout_us)
{
    NRF_TIMER1->TASKS_STOP = 1;
    NRF_TIMER1->TASKS_CLEAR = 1;

    // this line: set TIMER1 to 0 (start value)
    // this line: hand over the time "timeout_us" to TIMER1 (end time)
    // this line: stop TIMER1 if end time ("timeout_us") is reached

    NRF_TIMER1->TASKS_START = 1;
}


void Write_Byte(uint8_t byte)
{
    int walk;

    for (walk = 0; walk < 8; ++walk)
    {
        nrf_gpio_pin_clear(OUTPUT_PIN);    
        if (byte & 0x01)
        {
            TIMEROUT_TIMER1_Start(1);       //instead of nrf_delay_us()                      
            nrf_gpio_pin_set(OUTPUT_PIN);                
            TIMEROUT_TIMER1_Start(60);      //instead of nrf_delay_us()                   
        }
        else
        {
            TIMEROUT_TIMER1_Start(60);       //instead of nrf_delay_us()                      
            nrf_gpio_pin_set(OUTPUT_PIN);                 
            TIMEROUT_TIMER1_Start(1);        //instead of nrf_delay_us()                     
        }
        byte >>= 1;                                       
    }
}


/**
 * @brief Function for application main entry.
 */
int main(void)
{
    uint32_t err_code;
    TIMEOUT_TIMER1_Init;
    
    uint8_t AA = 0xAA;
    nrf_gpio_cfg_output(OUTPUT_PIN);

    while (true)
    {
        Write_Byte(AA);
        nrf_delay_us(20);
    }
}

In line 19: (Init) Why should I use 32 bits and not 16 bits? where is the difference?

In lines 35 - 37: (time function) I hope you can help me here. I don't know how I can hand over my timeout value to my function and to my timer, so that the timer can work with it...

I hope, you can help me.

Thanks in advance,

Christoph