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SubjectRe: gettimeofday() in 2.6.24
On Thu, Apr 17, 2008 at 7:13 PM, Chris Friesen <cfriesen@nortel.com> wrote:
> Jack Harvard wrote:
>
>
> > http://lxr.linux.no/linux+v2.6.24/arch/arm/kernel/time.c#L240
> > 239#ifndef CONFIG_GENERIC_TIME
> > 240void do_gettimeofday(struct timeval *tv)
> > 241{
> > 242 unsigned long flags;
> > 243 unsigned long seq;
> > 244 unsigned long usec, sec;
> > 245
> > 246 do {
> > 247 seq = read_seqbegin_irqsave(&xtime_lock, flags);
> > 248 usec = system_timer->offset();
> > 249 sec = xtime.tv_sec;
> > 250 usec += xtime.tv_nsec / 1000;
> > 251 } while (read_seqretry_irqrestore(&xtime_lock, seq, flags));
> >
>
>
>
> > but I haven't quite figured out how gettimeofday() actually gets time
> > from this added timer, also how xtime is updated?
> >
>
>
> system_timer->offset() uses the added timer to return the number of usecs
> since the last timer tick. It's potentially different for each specific
> type of arm blade, and the function often has "gettimeoffset" in the name.

>
> "xtime" is updated in the core kernel code.

is "xtime" updated by the time tick clock timer, i.e., the timer which
generates interrupts every 1/HZ second to the kernel. Put it in
another way,
does gettimeofday get time in two parts 1) seconds from xtime.tv_sec,
updated by timer0, 2) microseconds from xtime.tv_nsec +
system_timer->offset(), updated by timer0 and timer3.

Do you mean the code here
"http://lxr.linux.no/linux+v2.6.24/kernel/time/timekeeping.c#L45"


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