linux-kernel - Re: gettimeofday() in 2.6.24

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Message-ID: <48079356.2090307@nortel.com>
Date:	Thu, 17 Apr 2008 12:13:42 -0600
From:	"Chris Friesen" <cfriesen@...tel.com>
To:	Jack Harvard <jack.harvard@...glemail.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: gettimeofday() in 2.6.24

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.

Chris
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