Messages in this thread | | | Date | Fri, 18 Apr 2008 09:54:45 +0100 | From | "Jack Harvard" <> | Subject | Re: gettimeofday() in 2.6.24 |
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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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