linux下怎么实现微妙级的定时器？

mozilla

40微妙一次。
是应用程序，不是内核。

kenix

我也想知道,,呵呵

kakuyou

只能通过改内核来实现，这么认为。

风雨纵横

int 24 的功能调用,主板计时器

mozilla

[quote:c75a7d7286="风雨纵横"]int 24 的功能调用,主板计时器[/quote]
不明白

sjinny

使用gettimeofday函数：

$ man gettimeofday

GETTIMEOFDAY(2)            Linux Programmer's Manual           GETTIMEOFDAY(2)

NAME
       gettimeofday, settimeofday - get / set time

SYNOPSIS
       #include <sys/time.h>

       int gettimeofday(struct timeval *tv, struct timezone *tz);
       int settimeofday(const struct timeval *tv , const struct timezone *tz);

DESCRIPTION
       The  functions  gettimeofday  and  settimeofday  can  get and set the time as well as a timezone.  The tv argument is a
       timeval struct, as specified  in <sys/time.h>:

       struct timeval {
               time_t         tv_sec;        /* seconds */
               suseconds_t    tv_usec;  /* microseconds */
       };

       and gives the number of seconds and microseconds since the Epoch (see time(2)).  The tz argument is a timezone :

       struct timezone {
               int  tz_minuteswest; /* minutes W of Greenwich */
               int  tz_dsttime;     /* type of dst correction */
       };

       The use of the timezone struct is obsolete; the tz_dsttime field has never been used under Linux - it has not been  and
       will  not  be supported by libc or glibc.  Each and every occurrence of this field in the kernel source (other than the
       declaration) is a bug. Thus, the following is purely of historic interest.

       The field tz_dsttime contains a symbolic constant (values are given below) that indicates in which  part  of  the  year
       Daylight  Saving  Time is in force. (Note: its value is constant throughout the year - it does not indicate that DST is
       in force, it just selects an algorithm.)  The daylight saving time algorithms defined are as follows :

        DST_NONE     /* not on dst */
        DST_USA      /* USA style dst */
        DST_AUST     /* Australian style dst */
        DST_WET      /* Western European dst */
        DST_MET      /* Middle European dst */
        DST_EET      /* Eastern European dst */
        DST_CAN      /* Canada */
        DST_GB       /* Great Britain and Eire */
        DST_RUM      /* Rumania */
        DST_TUR      /* Turkey */
        DST_AUSTALT  /* Australian style with shift in 1986 */

       Of course it turned out that the period in which Daylight Saving Time is in force cannot be given  by  a  simple  algo-
       rithm,  one per country; indeed, this period is determined by unpredictable political decisions. So this method of rep-
       resenting time zones has been abandoned. Under Linux, in a call to settimeofday the tz_dsttime field should be zero.

       Under Linux there is some peculiar 'warp clock' semantics associated to the settimeofday system call  if  on  the  very
       first  call  (after  booting)  that has a non-NULL tz argument, the tv argument is NULL and the tz_minuteswest field is
       nonzero. In such a case it is assumed that the CMOS clock is on local time, and that it has to be incremented  by  this
       amount to get UTC system time.  No doubt it is a bad idea to use this feature.

       The following macros are defined to operate on a struct timeval :
       #define       timerisset(tvp)\
               ((tvp)->tv_sec || (tvp)->tv_usec)
       #define       timercmp(tvp, uvp, cmp)\
               ((tvp)->tv_sec cmp (uvp)->tv_sec ||\
               (tvp)->tv_sec == (uvp)->tv_sec &&\
               (tvp)->tv_usec cmp (uvp)->tv_usec)
       #define       timerclear(tvp)\
               ((tvp)->tv_sec = (tvp)->tv_usec = 0)

       If either tv or tz is null, the corresponding structure is not set or returned.

       Only the super user may use settimeofday.

RETURN VALUE
       gettimeofday and settimeofday return 0 for success, or -1 for failure (in which case errno is set appropriately).

ERRORS
       EPERM  settimeofday is called by someone other than the superuser.

       EINVAL Timezone (or something else) is invalid.

       EFAULT One of tv or tz pointed outside your accessible address space.

NOTE
       The  prototype  for  settimeofday  and  the defines for timercmp, timerisset, timerclear, timeradd, timersub are (since
       glibc2.2.2) only available if _BSD_SOURCE is defined (either explicitly, or implicitly, by not  defining  _POSIX_SOURCE
       or compiling with the -ansi flag).

       Traditionally, the fields of struct timeval were longs.

CONFORMING TO
       SVr4, BSD 4.3. POSIX 1003.1-2001 describes gettimeofday() but not settimeofday().

SEE ALSO
       date(1), adjtimex(2), time(2), ctime(3), ftime(3)

Linux 2.4                         2003-08-21                   GETTIMEOFDAY(2)

kakuyou

sjinny,你明白定时器timer这个词是什么意思吗？

[code:1]
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/time.h>
#include <memory.h>

static unsigned long tick = 0;

void callback_SIGALRM(int p)
{
    tick ++;
    if(tick %23 == 0)
    fprintf(stdout, "tick value=%ld\n", tick);
}

int main(int argc, const char** argv)
{
    struct itimerval itv;

    if(signal(SIGALRM, callback_SIGALRM) == SIG_ERR) {
        fprintf(stdout, "Faild to register handler of signal.\n");
        return (1);
    }

    memset(&itv, 0, sizeof (struct itimerval));
    itv.it_value.tv_sec = 0;
    itv.it_value.tv_usec = 100;
    itv.it_interval.tv_usec=100;
    setitimer(ITIMER_REAL, &itv, NULL);
    while(1)sleep(3);

    return 0;

}
[/code:1]
上面这个程序每搁100微妙接受到一个signal，积累到23的倍数时打印条信息。

我记得好像linux内核的时间片长度一般是10微秒，40微妙的定时器实在是挺勉强的，
而且，你这是real time要求，我想，最起码你要保证你的进程执行时不发生缺页调
用，同时不能有其他的real time进程。

改内核吧，老大，锻炼的机会来了。