[LPC3250] High Resoulution Timer Support

linux kernel 2.6.27.8에서 설정한다.

이 기능은 고분해능 타이머를 사용 할 수 있게 해 준다.

이 타이머는 나노초 단위로 작동한다.

해당하는 함수로는

void hrtimer_init( struct hrtimer *time, clockid_t which_clock, 
                                            enum hrtimer_mode mode );
int hrtimer_start(struct hrtimer *timer, ktime_t time, 
                                       const enum hrtimer_mode mode);
int hrtimer_cancel(struct hrtimer *timer);
int hrtimer_try_to_cancel(struct hrtimer *timer);
int hrtimer_callback_running(struct hrtimer *timer);

예)

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/hrtimer.h>
#include <linux/ktime.h>

MODULE_LICENSE( "GPL" );

#define MS_TO_NS(x)	(x * 1E6L)

static struct hrtimer hr_timer;

enum hrtimer_restart my_hrtimer_callback( struct hrtimer *timer )
{
  printk( "my_hrtimer_callback called (%ld).\n", jiffies );

  return HRTIMER_NORESTART;
}

int init_module( void )
{
  ktime_t ktime;
  unsigned long delay_in_ms = 200L;

  printk("HR Timer module installing\n");

  ktime = ktime_set( 0, MS_TO_NS(delay_in_ms) );

  hrtimer_init( &hr_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL );
  
  hr_timer.function = &my_hrtimer_callback;

  printk( "Starting timer to fire in %ldms (%ld)\n", 
                                         delay_in_ms, jiffies );

  hrtimer_start( &hr_timer, ktime, HRTIMER_MODE_REL );

  return 0;
}

void cleanup_module( void )
{
  int ret;

  ret = hrtimer_cancel( &hr_timer );
  if (ret) printk("The timer was still in use...\n");

  printk("HR Timer module uninstalling\n");

  return;
}