7

Good evening, i'm asking your help, to understand how to use a timer in kernel module to achieve periodic task with period less than a microsecond. I was searching on the web and i've found that exists a Timer (ARM side) that is capable of such timing. Has somebody used it and could give me a little hint?

5

Done it! This is the include section

#include <linux/hrtimer.h>
#include <linux/sched.h>

This is the variables block

/****************************************************************************/
/* Timer variables block                                                    */
/****************************************************************************/
static enum hrtimer_restart function_timer(struct hrtimer *);
static struct hrtimer htimer;
static ktime_t kt_periode;

This is the initialization

kt_periode = ktime_set(0, 100); //seconds,nanoseconds
hrtimer_init (& htimer, CLOCK_REALTIME, HRTIMER_MODE_REL);
htimer.function = function_timer;
hrtimer_start(& htimer, kt_periode, HRTIMER_MODE_REL);

This is the procedure to cancel execution of timer

hrtimer_cancel(& htimer);

and this is the callback

static enum hrtimer_restart function_timer(struct hrtimer * unused)
{
        if (gpio_current_state==0){
            gpio_set_value(GPIO_OUTPUT,1);
            gpio_current_state=1;
        }
        else{
            gpio_set_value(GPIO_OUTPUT,0);
            gpio_current_state=0;
        }
        hrtimer_forward_now(& htimer, kt_periode);
        return HRTIMER_RESTART;
}
3

I assume you are looking for timing with greater accuracy than 1 jiffy?

Have you checked out hrtimers?

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