Re: gettimeofday() in 2.6.24

On Thu, Apr 17, 2008 at 7:13 PM, Chris Friesen <cfriesen@xxxxxxxxxx> 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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